re-study of larval stages of amphionides reynaudii ...

JOURNAL OF CRUSTACEAN BIOLOGY, 32(6), 916-930, 2012

RE-STUDY OF LARVAL STAGES OF AMPHIONIDES REYNAUDII (MALACOSTRACA:EUCARIDA) WITH MODERN IMAGING TECHNIQUES

Verena Kutschera 1,∗, Andreas Maas 1, Dieter Waloszek 1, Carolin Haug 2, and Joachim T. Haug 2

1 Biosystematic Documentation, University of Ulm, Helmholtzstr. 20, D-89081 Ulm, Germany2 Zoological Institute and Museum, Department of Cytology and Evolutionary Biology, University of Greifswald,

Soldmannstr. 23, 17487 Greifswald, Germany

A B S T R A C T

Amphionides reynaudii (H. Milne Edwards, 1832) is a rare crustacean species, supposedly the sister taxon to Decapoda sensu stricto.Morphological examination of 33 specimens assigned to A. reynaudii housed in the Museum für Naturkunde Berlin revealed that: 1) thematerial contains different larval stages, and 2) that several of the specimens do not belong to this species. We provide here, for the firsttime, high-quality images of representatives of A. reynaudii. Documentation included white-light microscopy, fluorescence microscopy, andmacrophotography. Subsequently the obtained images were improved applying composite imaging. We identified the different larval stages,but found several discrepancies between our observations and data from the literature. Our findings indicate the presence of additional,previously overlooked larval stages within the series. This re-interpretation is supported by unusually large growth factors between certainstages in older reconstructions of the larval series. Thus, the very gradual developmental pattern of A. reynaudii proves to be even moregradual than originally described. This pattern of development is most likely plesiomorphic. Considering the important phylogeneticposition as supposed sister species to Decapoda sensu stricto, A. reynaudii provides crucial morphological details for reconstructing thecharacter evolution in the decapod lineage, for example, of the maxillipeds.

KEY WORDS: Amphionidacea, ground pattern Decapoda, growth factors, larval series, maxillipeds,morphology

DOI: 10.1163/1937240X-00002092

INTRODUCTION

Amphionides reynaudii (H. Milne Edwards, 1832) is aunique representative of Malacostraca. The French carci-nologist Henri Milne Edwards discovered the first speci-mens in 1832 and described, based on these, the new speciesAmphion reynaudii H. Milne Edwards, 1832. The name,Amphion reynaudii, was changed by Williamson (1973) toAmphionides reynaudii, because Amphion was pre-occupiedby a lepidopteran genus (Hübner, 1818), and Zimmer (1904)described the same species as Amphionides valdiviae Zim-mer, 1904.

Discoveries of A. reynaudii are dominated by larvae(Heegaard, 1969), adult specimens are rarely found. Earlylarval stages (so-called ‘Mysis I-XIII’) live close to the watersurface. ‘Postlarva I-II’ and the adult (= ‘Postlarva III’)live abyssally and are, consequently, more difficult to catch(Heegaard, 1969). Nobody has ever seen an intact completeadult specimen (Fransen, 2010).

Rarity of adult specimens, as well as the pronouncedsexual dimorphism (for discussion see Heegaard, 1969;Williamson, 1973; Fransen, 2010), has limited our under-standing of A. reynaudii. As a result of this, the relationshipof this species to other crustacean taxa has remained un-clear. Milne Edwards (1832, 1837) compared A. reynaudiito phyllosoma larvae of achelate decapods (spiny lobsters,rock lobsters, and slipper lobsters), and stomatopod larvae.

∗ Corresponding author; e-mail: [email protected]

Specimens described by him appear to have been ‘MysisXIII’ larvae, which resemble phyllosomes and certain sto-matopod larvae in their flat and transparent head shield andthe long prominent appendages (Heegaard, 1969; Fransen,2010). Different authors emphasised similarities of A. rey-naudii with Sergestidae (Dendrobranchiata) (Claus, 1876;Willemöes-Suhm, 1876; Koeppel, 1902; Balss, 1938). Boas(1879) stressed similarities between A. reynaudii and Pe-naeoidea (Dendrobranchiata) also referring to larval forms(Heegaard, 1969). A possible relationship between A. rey-naudii and Caridea has also been proposed (Bate, 1888; Kor-schelt and Heider, 1892) as well as a position of A. reynaudiiwithin Polychelida (Ortmann, 1893). Heegaard (1969) andWilliamson (1973) interpreted A. reynaudii as a discretegroup comparable to Euphausiacea, Caridea, and Dendro-branchiata within Eucarida and introduced the taxon nameAmphionidacea. This opinion was shared subsequently byRivera et al. (2004), Felder et al. (2009), and Fransen(2010). Amphionides reynaudii has been proposed as the sis-ter species to Decapoda sensu stricto (Richter and Scholtz,2001; Dixon et al., 2003). Possible synapomorphies are thedorsal fusion of all segments of the head and segments 1-7of thorax I and specialised first thoracopods functioning asmaxillipeds, i.e., transferring food to the maxillae, maxillu-lae, and mandibles.

© The Crustacean Society, 2012. Published by Brill NV, Leiden DOI:10.1163/1937240X-00002092

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KUTSCHERA ET AL.: RE-STUDY OF LARVAL STAGES OF AMPHIONIDES REYNAUDII (MALACOSTRACA: EUCARIDA) WITH MODERN IMAGING TECHNIQUES 917

With this assumed phylogenetic position, A. reynaudii iscrucial for the reconstruction of the evolutionary history ofEucarida and Decapoda. Decapoda is an evolutionarily verysuccessful group and its in-group evolution is characterisedby a drastic adaptive radiation, e.g., the evolutionary changefrom free-swimming shrimp-like forms to short, bottom-living crab-like forms (‘carcinisation’). This success shouldbe coupled to morphological key features, i.e., autapomor-phies that characterise the taxon already in the ground pat-tern. A sound ground-pattern reconstruction for Decapodais thus a requirement for understanding the evolution to-wards, but also within, Decapoda. A detailed knowledge onthe morphology of A. reynaudii is therefore indispensable.

Unfortunately, there is a significant lack of original dataon this species in the literature. No photographs exists, onlyline drawings (see, e.g., Koeppel, 1902; Gurney, 1936, 1942;Heegaard, 1969; Williamson, 1973). Drawings are moresubjective than (untouched) photographs because they areinfluenced by the interpretations of the drawer(s) and somust be treated with cautiousness. This especially holdstrue for composite drawings basing on several specimensinstead of an intact whole mount, as applying to the imagedisplaying an adult specimen of A. reynaudii in Williamson(1973) (Fransen, 2010).

We present here data on a re-study of A. reynaudii. Weexamined all specimens available in the collection of theMuseum für Naturkunde Berlin. These form an incom-plete series of larval stages (Fig. 1). Different documenta-tion methods have been applied, including macrophotogra-phy, white-light microscopy, and fluorescence microscopy,all combined with composite imaging. Morphological de-tails are described based on this documentation and our find-ings are discussed in comparison with Heegaard’s (1969) de-scription.

MATERIAL AND METHODS

The material is part of the collection of the Museum fürNaturkunde Berlin and consists of 33 specimens assignedto A. reynaudii. Different larval stages are represented inthe material, and their identification based on data providedby Heegaard (1969) (but see below). Several specimensare damaged; a clear identification of the larval stage wasimpossible in those cases (specimen numbers: 26789-20;26789-22). A few other specimens probably do not belong tothe species A. reynaudii (specimen numbers: 12480; 17587-01; 17587-03; 17587-05). Information from the originallabels of each specimen is given in Table 1.

Most of the specimens were studied under a fluorescencemicroscope (Zeiss Axioskop 2 or Zeiss Observer Z1 withspinning disk, both equipped with an Axiocam), taking ad-vantage of the autofluorescence exhibited by many malacos-tracans (Michels, 2007; C. Haug et al., 2011; J. Haug et al.,2011). Mainly ultraviolet (UV) light (358 nm) was used todocument the outer morphology. Some specimens exhibited

only weak autofluorescence under UV light; this was mostlikely caused by storage in formalin. These specimens weredocumented with blue light (470 nm). Under blue light in-ner structures showed stronger autofluorescence and fluores-cence of outer structures caused scattered light. Yet the re-sults were of comparable quality to those obtained using UVlight. Some specimens were documented with white-lightmicroscopy (Zeiss Axioskop with a DCM 510 ocular cam-era), with transmitted and/or reflected polarised light, or viamacrophotography with a digital camera (Canon EOS 450D,with a EFS 60 mm objective lens) on a light table.

All micrographs were produced following the protocolgiven by J. Haug et al. (2011) for composite imaging: singleimages with a low depth of focus were fused into one sharpimage applying the freely available software CombineZP.These images were connected to each other in X- and Y-axis, until one entire specimen was completed in a singlesharp image. These images were further processed in AdobePhotoshop CS 3 by histogram optimisation and removing thesurrounding dirt particles.

Larval stages were assigned to stages identified by Hee-gaard (1969). However, we applied a more neutral termino-logy concerning the larval stages (see Discussion). The stageterms of Heegaard (1969) are additionally given in brack-ets and quotation marks. Heegaard’s terminology for the de-scription of morphological structures was not adopted. Weused, instead, the terminology proposed as a standard systemfor Crustacea s. l. and Arthropoda in general as put forwardby Walossek (1993, 1999) and his collaborators (J. Haug etal., 2009, 2010a, 2010b, in press; Maas et al., 2009). Abbre-viations are given in Table 2.

RESULTS

The different larval stages (Table 3) are treated successively,as they appear during ontogeny. Only morphological charac-ters important for this paper are considered in the summaris-ing table (Table 4); for a detailed description of larval stages(those known at that time) see the comprehensive work byHeegaard (1969). The assignment of the specimens, eitherto a larval stage (if possible) is given in Table 3. The charac-terisation of each stage was based mostly on body size anddevelopment of appendages, including the shape of uropodsand the tail fan. Table 4 provides also information on somemeasured parameters.

The material (Fig. 1) does not include the complete larvalseries of A. reynaudii according to the staging system ofHeegaard (1969). The earliest stage available is a ‘MysisIV’ stage (here stage 1); all prior stages are missing in ourmaterial, for details of ‘Mysis I-III’ see Heegaard (1969:14ff). Nothing is known about the embryology and thehatchling of A. reynaudii.

Fig. 1. Images of all specimens of Amphionides reynaudii from the Museum für Naturkunde, Berlin, to the same scale with respective repository numberin lateral view. All images fluorescence micrographs, except for 2025 being an inverted macro photograph and 12480, 17587-03, 17587-05 taken withwhite-light microscopy. All specimens except 12480, 17587-01, 17587-03, 17587-05 (classified as ‘Putative representatives’) represent various stages of thespecies A. reynaudii.

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Table 1. Specimen number and text on the respective label indicatinglocality and mostly date.

Number Label

2025 Südsee, Godeffroy12480 Straße von Malacca; Heinroth s. Mencke(?) 190113253 Atl. Ozean bei Cap Palmas 3. IV 1906

Dr Graet. S.M.S. Planol17587-01/02 Dtsch. Südpol. Exp. 1903; 13. X 1903 3000 m17587-03 Dtsch. Südpol. Exp. 1903;

10. III 1903 Vert 3000 m17587-04 Dtsch. Südpol. Exp. 1903; 3. IX17587-05/06 Dtsch. Südpol. Exp. 1903; 26. VIII 0317587-07 Dtsch. Südpol. Exp. 1903; Amphion17587-08 Dtsch. Südpol. Exp. 1903;

SPE 1200m Vert 11. X 190126789-01-22 Dana 3565 IV 7°45.55 I35 22W w. 100

M.S. 150 19. IX 1928 19.40 h

General Remarks

All larval stages described here have several characters incommon.

Eyes.—The eyes are always stalked and possess ommatidia,each with four crystalline cone cells (Figs. 2B, G, L; 3E, L;4B, I).

Uropods.—The uropods always form a tail fan together withthe telson (Figs. 2E, J, P; 3C, J, O; 4G, K, O; 5G).

Stage 1 (= ‘Mysis IV’; Fig. 2A-E; Table 4)

Material.—Two specimens, 26789-01, 26789-08 (Fig. 1;Table 3).

Measurements.—BL 6.1-6.2 mm; CtsL 2.2-2.3 mm (Ta-ble 4).

Description.—Cephalothoracic shield lentiform in lateral as-pect (Fig. 2A); oval in dorsal view with margins beingwaisted half way up (Fig. 2D); dorsally attached to thora-comeres 1-4 (Fig. 2A). Eyes large, taking almost one sixth ofwhole body length (Fig. 2A). Thoracopods 1 arising medio-ventrally from antero-posterior middle of cephalothoracicshield close to mouth (Fig. 2A; Table 4); with coxa, basipod,endopod, and exopod. Thoracopods 2 and 3 fully developed;

Table 2. Morphological abbreviations and their respective meanings.

Abbreviation Meaning Abbreviation Meaning

a1 antennula hp hepatopancreasa2 antenna la labrumba basipod pl pleomereBL total body length pp pleopodco coxa ro rostrumcts cephalothoracic te telson

shieldCtsL length of th thoracomere

cephalothoracicshield

en endopod tp thoracopodest eye stalk up uropodex exopod

both arising ventrally from lateral margin of cephalotho-racic shield; both with coxa, basipod, endopod, and exopod(Fig. 2A; Table 4). Thoracopods 4 partly developed (Fig. 2C;Table 4), with coxa, basipod, endopod, and exopod but notyet having complete size of fully developed thoracopods(compared to stage 2, see below). Pleon with 6 pleomeres;pleomere 6 longer than pleomeres 1-5 together; pleopods 1-5 not developed (Table 4). Uropods (= pleopods 6) devel-oped; comprising basipod, endopod, and exopod, the latterbeing 2.3 times as long as the endopod (Fig. 2E; Table 4).Telson oval in dorsal view with cut-off anterior margin; lat-eral sides parallel to each other; 1.2 times as long as uropods(Fig. 2E; Table 4).

Stage 2 (= ‘Mysis V’; Fig. 2F-J; Table 4)

Material.—Four specimens, 26789-04, 26789-05, 26789-06,26789-09 (Fig. 1; Table 3).


Description.—Cephalothoracic shield flattened in dorso-ventral axis (Fig. 2F) compared to stage 1 (Fig. 2A); dor-sally attached to thoracomeres 1-5 (Fig. 2F); anterior fourthrounded in dorsal view with two lateral spiky outgrowthspointing anteriorly (Fig. 2I, white arrowheads); lateral mar-gins parallel, slightly converging posteriorly (Fig. 2I). Tho-racopods 1 close to mouth (Fig. 2F), enclosing mouth areaposteriorly opposite to labrum (Fig. 2H; Table 4).

Stage 3 (= ‘Mysis VI’; Fig. 2K-O; Table 4)

Material.—Three specimens, 17587-06; 26789-10; 26789-11 (Fig. 1; Table 3).


Description.—Cephalothoracic shield flattened in dorso-ventral axis (Fig. 2K) and posteriorly narrower in dorsalview (Fig. 2N) compared to stage 2 (Fig. 2F); dorsally at-tached to thoracomeres 1-5 (Fig. 2K); with lateral spiky out-growth (Fig. 2O). Thoracopods 1 close to mouth (Fig. 2M;Table 4).

Stage 4 (= ‘Mysis VIII’; Fig. 3A-C; Table 4)

Material.—Three specimens, 17587-04; 26789-02; 26789-07 (Fig. 1; Table 3).


Description.—Cephalothoracic shield (Fig. 3A) dorsallyattached to thoracomeres 1-6; with apparent hepatopancreas(= midgut glands, midgut diverticula) starting to develop,visible as dotted tubes within the shield (Fig. 3B; whitearrowheads). Thoracopods 1 close to mouth (Fig. 3A;Table 4).

Stage 5 (Fig. 3D-J; Table 4)

Material.—Seven specimens: 17587-02, 17587-07, 26789-12, 26789-14, 26789-16, 26789-18, 26789-21 (Fig. 1; Ta-ble 3).

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Table 3. Assignment of specimens. Most specimens could be assigned to a particular larval state, except for two, indicated by ‘Larval state ?’. Others aredoubted to represent Amphionides reynaudii (Milne Edwards, 1832) implied by ‘Amphionides reynaudii ?’.

Larval state Specimen/s Larval state Specimen/s

Stage 1 (= Mysis IV) 26789-01; 26789-08 Stage 7 (= Mysis XI) 13253Stage 2 (= Mysis V) 26789-04; 26789-05; 26789-06; 26789-09 Stage 8 (= Mysis XII) 26789-19Stage 3 (= Mysis VI) 17587-06; 26789-10; 26789-11 Stage 9 (= Mysis XIII) 17587-08Stage 4 (= Mysis VIII) 17587-04; 26789-02; 26789-07 Stage 10 (Postlarva I) 2025Stage 5 (= between Mysis IX and X) 17587-02; 17587-07; 26789-12; Larval state ? 26789-20; 26789-22

26789-14; 26789-16; 26789-18; 26789-21Stage 6 (= Mysis X) 26789-03; 26789-13; 26789-15; 26789-17 Amphionides reynaudii ? 12480; 17587-01;

17587-03; 17587-05


Description.—Cephalothoracic shield flattened in dorso-ventral axis (Fig. 3D); slightly oval from dorsal with parallellateral margins tapering posteriorly (Fig. 3G); dorsallyattached to thoracomeres 1-7 (Fig. 3D); two lateral lobeslatero-posterior at cephalothoracic shield (Fig. 3I; whitearrowheads). Hepatopancreas further developed (Fig. 3H)compared to stage 4 (Fig. 3B). Individual ommatidia ofeyes rectangular in cross section in proximal growth zone(Fig. 3E; white arrowhead); otherwise round in cross section(Fig. 3E). Thoracopods 1 close to mouth (Fig. 3D, F;Table 4). Thoracopods 7 partly developed (Fig. 3D; Table 4;see below).

Remarks.—All specimen at this developmental level couldnot be clearly assigned to any larval stage given by Heegaard(1969), but appear to lie between ‘Mysis IX’ and ‘MysisX’ stage. The specimens possess thoracopods 7, whichare partly developed, i.e., the whole appendage has notyet reached its full size but is already differentiated intocoxa, basipod, endopod, and exopod (Fig. 3D). The ‘MysisIX’ stage as described by Heegaard (1969) should havethoracopods 7 developed only as small buds with no visibledifferentiation into coxa, basipod, endopod, or exopod (seehis Fig. 65). The ‘Mysis X’ stage of Heegaard (1969)possesses thoracopods 7 (see his Figs. 70 and 79), whichare much more advanced than in the specimens on thesame developmental stage in our material (Fig. 3D). Othercharacters, e.g., the telson shape, are consistent with the‘Mysis IX’ stage of Heegaard (1969), although stage 5specimens are slightly further developed (see Discussionbelow).

Stage 6 (= ‘Mysis X’; Fig. 3K-O; Table 4)

Material.—Four specimens: 26789-03, 26789-13, 26789-15,26789-17 (Fig. 1; Table 3).

Measurements.—BL 13.0-15.5 mm; CtsL 7-9 mm (Table 4).

Description.—Cephalothoracic shield dorsally attached tothoracomeres 1-7 (Fig. 3K). Thoracopods 1 close to mouth(Fig. 3K, M; Table 4). Initial gill at base of thoracopods4 (Fig. 3K; white arrowhead). Initial pleopods 1-5 presentlatero-ventrally at pleon as undifferentiated, rudimentaryappendages (Fig. 3N; Table 4).

Stage 7 (= ‘Mysis XI’; Fig. 4A-G; Table 4)

Material.—One specimen, 13253 (Fig. 1; Table 3).

Measurements.—The posterior body end, including partsof pleomere 5 with pleopods 5, pleomere 6 with uropods,and telson, is disrupted. Therefore the body length cannotbe given precisely. BL minimum 17 mm; CtsL 10 mm(Table 4).

Description.—Cephalothoracic shield dorsally attached tothoracomeres 1-7 (Fig. 4A). Thoracopods 1 close to mouth(Fig. 4D; Table 4). Feather-shaped gills at outer base ofthoracopods 3 and 4 (Fig. 4C; white arrowheads). Pleopods1-5 further developed (Fig. 4E; Table 4) compared to stage 6(Fig. 3N); pleopods 2-5 with basipod, endopod and exopod(Fig. 4E).

Stage 8 (= ‘Mysis XII’; Fig. 4H-K; Table 4)

Material.—One specimen, 26789-19 (Fig. 1; Table 3).

Measurement.—Cephalothoracic shield damaged; antero-dorsal parts of shield, mouthparts, and thoracopods 1 aremissing. Therefore, description abandoned and neither lengthmeasurements could be given precisely nor images of moutharea and thoracopod presented. BL 21 mm; CtsL minimum13 mm (Table 4).

Remark.—Specimen 26789-19, although damaged (Fig.4H), is assigned here to stage 8. The specimen should havepossessed seven fully developed thoracopods, a character of‘Mysis XII’. This interpretation is consistent with the size ofthe specimen (Table 4) and shape of its pleopods (Fig. 4J).

Stage 9 (= ‘Mysis XIII’; Fig. 4L-O; Table 4)

Material.—One specimen, 17587-08 (Fig. 1; Table 3).

Measurements.—Cephalothoracic shield damaged; eyes,mouthparts, and thoracopods 1 are missing. Therefore nei-ther length measurements can be precisely given nor im-ages of eyes, mouth area, and thoracopods 1 are presented.Left uropod missing. BL minimum 24 mm; CtsL minimum11.5 mm (Table 4).

Description.—Thoracopod 8 developed; with coxa, basipod,and ramus built of 4 annuli (Fig. 4M). Pleopod 1 withexopod and endopod (Fig. 4N; white arrowhead).

Remarks.—Specimen 17587-08 (Fig. 4L) is interpreted asstage 9, although the cephalothoracic shield is damaged and

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many anterior parts, such as the eyes, the mouthparts andthoracopods 1 are missing. Specimen 17587-08 should havehad eight thoracopods, a character of ‘Mysis XIII’ stage.The main argument for this interpretation is the overall size.A difficulty is the developmental state of the pleopods in thisspecimen, which are in fact smaller than those of the stage 8specimen (but see Discussion).

Stage 10 (= ‘Postlarva I’; Fig. 5A-G; Table 4)

Material.—One specimen, 2025 (Fig. 1; Table 3).

Measurements.—BL 31.5 mm; CtsL 13.5 mm (Table 4).

Description.—Eyes without luminescence organ in stalk(Fig. 5C). Thoracopods 1 close to mouth (Fig. 5D; Table 4).Pleopods 1 with appendix interna (process of the petasma)(Fig. 5F; white arrowhead).

Undetermined Fragments of Larvae

Two specimens, 26789-20 and 26789-22 (Fig. 1), are soseverely damaged that it was not possible for us to identifytheir larval stage with certainty, but they can be assigned toA. reynaudii.

Specimen 26789-20 (Fig. 1) is damaged; its cephalotho-racic shield is dorsally disrupted resulting in the absenceof the left maxilla, all thoracopods, and the pleon. Yet, thisspecimen undoubtedly is an A. reynaudii based on the shapeof the shield, the shape of antennae, and appearance of theeyes. Additionally, the fluorescence properties of the spec-imen are very similar to those of other specimens of A.reynaudii. Considering size, shape of the antennal scale,and shape of the anterior cephalothoracic shield, specimen26789-20 is most likely corresponding to stage 2 (‘MysisV’) or stage 3 (‘Mysis VI’).

Specimen 26789-22 consists only of a central part of thecephalothoracic shield including four pairs of laterally at-tached thoracopods (or at least their bases) on each side(Fig. 1). The anterior and posterior margins of the shield arenot identifiable. The shape of the cephalothoracic shield andthoracopods (Fig. 1) suggests that this specimen representsA. reynaudii. This is supported by the fluorescence proper-ties of the specimen, which are similar to those exhibited byother specimens. Assuming that thoracopod 1 was present inthis specimen, it possessed 5 pairs of thoracopods originally,which would make it at least a stage 4 specimen (‘MysisVII’). But the size of the fragment suggests it even being afurther developed stage (Fig. 1).

Putative Representatives of Amphionides reynaudii

Four specimens (12480; 17587-01; 17587-03; 17587-05;Fig. 1) do not belong to the species A. reynaudii although

labelled as such. This conclusion is based on morphologicaldetails and fluorescence properties of the specimens all incomparison with true A. reynaudii.

DISCUSSION

We found discrepancies between Heegaard’s (1969) descrip-tion and our reconstructed larval series. These discrepan-cies concern especially the development of the thoracopodsand the attachment of thoracic segments to the cephalotho-racic shield, which will be discussed below. Terminologicalproblems concerning the larval stages and thoracopods 1 as‘maxillipeds’ were also encountered, and these are taken intoaccount in the following.

First Thoracopods

The first thoracopods of A. reynaudii insert medio-ventrallyposteriorly to the mouth and cover the mouthparts in all in-vestigated larval stages with preserved first thoracopods (Ta-ble 4). We assume that stages within the larval series of A.reynaudii, which are not present in our material, should havefirst thoracopods in a similar position (Heegaard, 1969). Thisposition of the first thoracopods close to the mouth in A.reynaudii indicates that the first thoracopods are function-ing in transferring food-particles to the (other) mouthparts.This conclusion is supported by the specialised morphologyof the first thoracopod having a broad and flattened basi-pod (Figs. 3F, M; 4D; 5D). This differs significantly fromthe morphology of the second thoracopods. The first thora-copods insert medio-ventrally and have broad bases whereasthe second thoracopods insert laterally at the shield mar-gin and are entirely stenopodous. The shape and location ofthe first thoracopods in A. reynaudii allow the functional-morphological interpretation that they help in food macera-tion, i.e., the term ‘maxilliped’ can be applied here.

However, the term ‘maxilliped’ bears certain problems.There are no concrete criteria for the use of this term (theexceptions appear to be the third maxillipeds in Decapodaidentifiable by a ‘crista dentata’). Presence of a maxillipedis therefore not seen as a strict phylogenetic character.Use of the term in A. reynaudii is thus restricted to afunctional meaning, not necessarily implying a homology tothe first maxilliped in Decapoda. A precise comparison ofthe morphology of the sixth appendage in different eucaridgroups will be necessary to shed more light on this issue.

Thoracopods 2-7 and Growth Factors

The first larval stage Heegaard (1969) described is a ‘prom-ysis.’ This stage was not represented in our material or inthe material he examined. Nevertheless, Heegaard included

Fig. 2. Fluorescence micrographs of larval stages 1 (A-E), 2 (F-J), and 3 (K-P) of Amphionides reynaudii. A-D, taken with 470 nm; B-C, 488 nm; E-P, 358 nm. A-E, specimen 26789-01; F, H, I, specimen 26789-04; G, J, specimen 26789-06; K-L, N, P, specimen 26789-10; O, specimen 26789-11. A,overview in lateral aspect, thoracopod 1 is functional maxilliped close to mouth, thoracopod 4 partly developed; B, stalked eye, individual ommatidia withfour crystalline cone cells (bright dots); C, partly developed thoracopod 4 with coxa, basipod, endopod, and exopod; D, overview in dorsal aspect, left eyemissing; E, tail fan in dorsal view constituted by oval telson and uropod; F, overview in lateral aspect, thoracopod 4 fully developed, thoracopod 5 starts todevelop indicated by hump emphasised by white arrowhead; G, stalked eye, single ommatidia round in cross section; H, mouth in ventral view displayinglabrum and thoracopod 1 concealing maxillae and mandibles; I, overview in dorsal aspect, white arrowhead indicating lateral outgrowth of cephalothoracicshield; J, tail fan in dorsal view with telson and uropods; K, overview in lateral aspect, thoracopod 5 is partly developed, image mirrored; L, stalked eye,individual ommatidia with four crystalline cone cells (bright dots); M, mouth in lateral view enclosed by labrum and thoracopod 1; N, overview in dorsalaspect; left eye missing; O, overview in ventral aspect; P, tail fan in dorsal view, exopod of uropod with lateral spine emphasised by white arrowhead.

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ally

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all

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=no

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part

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plet

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fully

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lope

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age;

post

.=po

ster

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erio

rly;

vent

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ly.

Com

bina

tions

ofnu

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dle

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.

L.s

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age

1St

age

2St

age

3St

age

4St

age

5St

age

6St

age

7St

age

8St

age

9St

age

10H

.s.

Mys

isIV

Mys

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Mys

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ysis

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I–

Mys

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Post

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aI

BL

(mm

)6.

1-6.

26.

2-6.

77.

1-7.

99.

0-9.

19.

4-1.

613

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5.5

a.l.

1721

a.l.

2431

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Cts

L(m

m)

2.2-

2.3

2.7-

2.8

3.0-

3.2

3.8-

4.2

5.0-

5.2

7.0-

9.0

10a.

l.13

a.l.

11.5

13.5

tp1

f.d.

;ari

sing

med

.-ve

nt.

near

bym

o;(2

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f.d.

;ari

sing

med

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nt.

near

bym

o(2

F,H

)

f.d.

;ari

sing

med

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nt.

near

bym

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f.d.

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med

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nt.

near

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o(3

A)

f.d.

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med

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nt.

near

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o(3

D,

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sing

med

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near

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o(3

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f.d.

;ari

sing

med

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nt.

near

bym

o(4

D)

??

f.d.

;ari

sing

med

.-ve

nt.

near

bym

o(5

A,

D)

tp2

f.d.

;lat

.-ve

nt.

atta

ched

toct

s(2

A)

f.d.

;lat

.-ve

nt.

atta

ched

toct

s(2

F)

f.d.

;lat

.-ve

nt.

atta

ched

toct

s(2

K)

f.d.

;lat

.-ve

nt.

atta

ched

toct

s(3

A)

f.d.

;lat

.-ve

nt.

atta

ched

toct

s(3

D)

f.d.

;lat

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nt.

atta

ched

toct

s(3

K)

f.d.

;lat

.-ve

nt.

atta

ched

toct

s(4

A)

f.d.

;lat

.-ve

nt.

atta

ched

toct

s(4

H)

f.d.

;lat

.-ve

nt.

atta

ched

toct

s(4

L)

f.d.

;lat

.-ve

nt.

atta

ched

toct

s(5

A,B

)

tp3

f.d.

;ins

ert

lat.-

vent

.atc

ts(2

A)

f.d.

;ins

ert

lat.-

vent

.atc

ts(2

F)

f.d.

;ins

ert

lat.-

vent

.atc

ts(2

K)

f.d.

;ins

ert

lat.-

vent

.atc

ts(3

A)

f.d.

;ins

ert

lat.-

vent

.atc

ts(3

D)

f.d.

;ins

ert

lat.-

vent

.atc

ts(3

K)

f.d.

;ins

ert

lat.-

vent

.atc

ts(4

A)

f.d.

;ins

ert

lat.-

vent

.atc

ts(4

H)

f.d.

;ins

ert

lat.-

vent

.atc

ts(4

L)

f.d.

;ins

ert

lat.-

vent

.atc

ts(5

A,B

)

tp4

p.d.

;ins

ert

lat.-

vent

.atc

ts(2

C)

f.d.

;ins

ert

lat.-

vent

.atc

ts(2

F)

f.d.

;ins

ert

lat.-

vent

.atc

ts(2

K)

f.d.

;ins

ert

lat.-

vent

.atc

ts(3

A)

f.d.

;ins

ert

lat.-

vent

.atc

ts(3

D)

f.d.

;ins

ert

lat.-

vent

.atc

ts(3

K)

f.d.

;ins

ert

lat.-

vent

.atc

ts(4

A)

f.d.

;ins

ert

lat.-

vent

.atc

ts(4

H)

f.d.

;ins

ert

lat.-

vent

.atc

ts(4

L)

f.d.

;ins

ert

lat.-

vent

.atc

ts(5

A,B

)

tp5

n.d.

i.d.(

2F;w

hite

arro

whe

ad)

p.d.

;ins

ert

lat.-

vent

.atc

ts(2

K)

f.d.

;ins

ert

lat.-

vent

.atc

ts(3

A)

f.d.

;ins

ert

lat.-

vent

.atc

ts(3

D)

f.d.

;ins

ert

lat.-

vent

.atc

ts(3

K)

f.d.

;ins

ert

lat.-

vent

.atc

ts(4

A)

f.d.

;ins

ert

lat.-

vent

.atc

ts(4

H)

f.d.

;ins

ert

lat.-

vent

.atc

ts(4

L)

f.d.

;ins

ert

lat.-

vent

.atc

ts(5

A,B

)

tp6

n.d.

n.d.

n.d.

p.d.

;ins

ert

lat.-

vent

.atc

ts(3

A)

f.d.

;ins

ert

lat.-

vent

.atc

ts(3

D)

f.d.

;ins

ert

lat.-

vent

.atc

ts(3

K)

f.d.

;ins

ert

lat.-

vent

.atc

ts(4

A)

f.d.

;ins

ert

lat.-

vent

.atc

ts(4

H)

f.d.

;ins

ert

lat.-

vent

.atc

ts(4

L)

f.d.

;ins

ert

lat.-

vent

.atc

ts(5

A,B

)

tp7

n.d.

n.d.

n.d.

n.d.

p.d.

;ins

ert

lat.-

vent

.atc

ts(3

D)

f.d.

;ins

ert

lat.-

vent

.atc

ts(3

K)

f.d.

;ins

ert

lat.-

vent

.atc

ts(4

A)

f.d.

;ins

ert

lat.-

vent

.atc

ts(4

H)

f.d.

;ins

ert

lat.-

vent

.atc

ts(4

L)

f.d.

;ins

ert

lat.-

vent

.atc

ts(5

A,B

)

tp8

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

n.d.

f.d.

;ins

ert

lat.-

vent

.atc

ts(4

L,M

)

f.d.

;ins

ert

lat.-

vent

.atc

ts(5

A,B

,E)

pp1

n.d.

n.d.

n.d.

n.d.

n.d.

i.d.(

3N)

p.d.

(4E

)p.

d.(4

J)f.

d.(4

N)

f.d.

(5A

,B,F

)

pp2-

5n.

d.n.

d.n.

d.n.

d.n.

d.i.d

.(3N

)p.

d.(4

E)

f.d.

(4J)

f.d.

(4N

)f.

d.(5

A,B

)

pp6/

upf.

d.;e

x=

2.3

×en

(2E

)f.

d.;e

x=

1.7

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(2J)

f.d.

;ex

=1.

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P);e

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ine

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row

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en(4

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ine

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en(5

G);

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ine

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tesl

ight

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)

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)

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this stage in his larval series of A. reynaudii, based on a de-scription by Gurney (1942), and interpreted it as the hatch-ing stage. Apart from this scarce information nothing isknown about the earliest development of A. reynaudii. In thedescription and assignment of the subsequent larval stagesHeegaard (1969) is very precise concerning particularly theearly stages (his ‘Mysis I’-‘Mysis IX’). He distinguishes thevarious stages by the progressive formation of the respectivemost posterior appendages during development. This pro-gressive formation is demonstrated in Fig. 6; for example,stage 2 (‘Mysis V’) exhibits thoracopods 5, which are devel-oped as small buds (Fig. 2F; Table 4). These buds becomepartly developed by stage 3 (‘Mysis VI’; Fig. 2K). Full sizeof thoracopods 5 is reached in the ‘Mysis VII’ stage of Hee-gaard (1969), which was not represented in the material athand.

The larval development of Crustacea is generally de-scribed as a sequence of morphologically distinct stages(cf. Walossek, 1993; Anger, 2001), and these stages areseparated by moults (Gurney, 1942; Williamson, 1969).Step-wise acquisition of features, as demonstrated for tho-racopods 5, can well be used to distinguish the instarsprecisely. Our findings demonstrate that the developmentalpattern of A. reynaudii is very gradual, even more gradualthan described by Heegaard (1969). We found three differ-ent, gradual morphological states concerning thoracopods 7(Fig. 6): Heegaard’s (1969) ‘Mysis IX’ has small bud-shapedthoracopods 7 (see his Fig. 65), stage 5 specimens exhibitpartly developed thoracopods 7 (Fig. 3D; Table 4), and ‘My-sis X’ possesses fully developed thoracopods 7 (Heegaard,1969, his Figs. 70, 79). These three states document the mor-phological change of thoracopods 7 and indicate three dis-tinct larval stages, corresponding to moults. Stage 5 couldnot be arranged in Heegaard’s (1969) staging system. Weconclude that stage 5 is a larval stage between ‘Mysis IX’and ‘Mysis X’ that was not present in Heegaard’s (1969)material.

The interpretation that Heegaard (1969) missed this larvalstage is supported by the growth factors from one stage toanother (Fig. 6; see Heegaard, 1969; his table I). The growthfactors of ‘Mysis II-IX’ range between 1.04 and 1.14 fromone stage to the next (Fig. 6), values that are congruentwith Brooks’ Law (Fowler, 1909) stating that growth factorsduring early development should approximately be constant.From ‘Mysis IX’ to ‘Mysis X’ we determined a factor of1.38, which is comparably high. We calculated a growthfactor of 1.10 from ‘Mysis IX’ to stage 5 and 1.23 from stage5 to stage 6 (‘Mysis X’), which are more plausible valueswhen compared to those of the earlier stages.

In summary, both morphological changes of the sevenththoracopod as well as growth factors between the moultssupport the presence of a developmental stage betweenHeegaard’s (1969) ‘Mysis IX’ and ‘Mysis X’.

Other high growth factors are found from ‘Mysis I’ to‘Mysis II’ (1.38), from stage 6 (‘Mysis X’) to stage 7 (‘MysisXI’) (1.32) and from stage 7 (‘Mysis XI’) to stage 8 (‘MysisXII’) (1.35) (Fig. 6; see also Heegaard, 1969, his table I).As mentioned above, such values are suspicious and point tomissing stages (Fig. 6; hypothetical stages between ‘Mysis I’

and ‘Mysis II’; stage 6 and 7, and stage 7 and 8). A largersample size should be able to fill these supposed gaps.

Eighth Thoracopod

Another inconsistency is the developmental fate of thora-copods 8. In stage 9 (= ‘Mysis XIII’) they are underdevel-oped appendages compared to thoracopods 2-7. Prior stepsof its development, e.g., a ‘small bud’ or a ‘partly developed’state, like they occur in other thoracopods (see above; Fig. 6)cannot be found, as the younger stages have no thoracopods8. The thoracopods 8 could also pass through a successionlike the anterior thoracopods (Fig. 6; hypothetical stages be-tween stage 6 and 7 and stage 7 and 8). These additionalstages are also indicated by the growth factors (see above).

The adult of A. reynaudii (‘Postlarva III’) and the preced-ing stage (‘Postlarva II’) lack thoracopods 8, which conse-quently must have become reduced. A similar situation canbe found in Euphausiidae, which have the exopod of thethoracopods 8 reduced (Maas and Waloszek, 2001). Con-trasting to the development of the anterior thoracopods 1-7,the development and reduction of the exopod of the thora-copods 8 proceeds differently, i.e., less successively (Maasand Waloszek, 2001). This example emphasises, that the tho-racopod 8 can develop differently, in terms of gradation, toall other thoracopods.

Cephalothoracic Shield and Fusion of Thoracic Segments

Another difference between Heegaard’s (1969) descriptionand our observations is the status of inclusion of thoracicsegments into the cephalothoracic shield. According toHeegaard, ‘Mysis’ stages I, II, III, V, VI, VIII, X-XIII,and ‘Postlarva I’ possess cephalothoracic shields comprisingall head segments plus the developed segments of thoraxI (four in ‘Mysis II’ and III; five in ‘Mysis V’ andVI; six in ‘Mysis VIII’; seven in ‘Mysis X’, XI, andXII; eight in ‘Mysis XIII’ and ‘Postlarva I’). By contrastto ‘Mysis II’ and III, ‘Mysis IV’ should have includedonly thoracomeres 1-3 into the cephalothoracic shield;the fourth thoracic segment should have been free again(Heegaard, 1969: 19ff). Heegaard (1969) explains this withthe larger growth of the thorax than the shield itself, but thisexplanation is insufficient. Likewise, a secondary reductionof the number of segments involved in the shield duringontogeny appears highly unlikely. Stage 1 (= ‘Mysis IV’)clearly has all developed thoracomeres (1-4) included intothe cephalothoracic shield (Fig. 2A). Hence, Heegaard’s(1969) observations are considered to be erroneous. Weassess a secondary constriction of the cephalothoracic shieldresulting in free segments as impossible.

Our restudy could not reveal, if the eighth thoracicsegment is dorsally attached to the cephalothoracic shieldor not. The one specimen [17587-08; stage 9 (‘Mysis XIII’)]having an eighth thoracic segment, is so damaged that a cleardiagnose of fusion of segments to the shield is impossible.In stage 10 (‘Postlarva I’) we were not able to clearlyidentify remains of an eight thoracomere not being fusedto the cephalothoracic shield as found in Euphausiacea andDecapoda. However, a secondary reduction of the entiresegment from stage 9 to stage 10 seems unlikely.

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Fig. 4. Images of larval stages 7 (A-G), 8 (H-K), and 9 (L-O) of Amphionides reynaudii. A-E, G-O, fluorescence micrographs; F, white-light microscopicimage. A-C, E, N, taken with 470 nm; D, G-M, O, taken with 358 nm. A-G, specimen 13253; H-K, 26789-19; L-O, 17587-08. A, overview in lateralaspect, cephalothoracic shield unnaturally flexed dorsally, posterior body end disrupted; B, stalked eye; C, gills at base of thoracopods 3 and 4 beneathcephalothoracic shield accentuated by white arrowheads; D, mouth in ventral view displaying labrum and thoracopod 1; E, pleopods 1-5; pleopods 2-5 withbasipod, endopod, and exopod; F, overview in ventral aspect; G, tail fan in dorsal view, uropodal exopods with lateral spines emphasised by white arrowheads,telson triangular in dorsal view; H, overview in lateral aspect, cephalothoracic shield lacking anterior dorsal parts and mouthparts; I, stalked eye; J, lateralview onto pleopods 1-5, pleopod 1 only with basipod and exopod, 2-5 composed of basipod, endopod, and exopod; K, tail fan from ventral, uropodal exopodwith lateral spines emphasised by white arrowheads, telson triangular in dorsal view; L, overview in lateral aspect, cephalothoracic shield damaged, eyes andmouthparts missing, thoracopod 8 developed; M, thoracopod 8 in lateral view; N, pleopods 1-5 in ventro-lateral view, pleopod 1 with endopod emphasisedby white arrowhead; O, tail fan in dorsal view, right uropod missing, uropodal exopod with lateral spine emphasised by white arrowhead.

Fig. 3. Images of larval stages 4 (A-C), 5 (D-J), and 6 (K-O) of Amphionides reynaudii. A-B & D-O, fluorescence micrographs; C, white-light microscopicimage. A, B, H, J, taken with 470 nm; D-G, I, taken with 358 nm. A, specimen 26789-07; B, 26789-02; C, 17587-04; D-G, I, 26789-16; H & J, 17587-02;K, M-O, 26789-15; L, 26789-17. A, overview in lateral aspect; thoracopod 5 fully developed, thoracopod 6 partly developed; B, anterior head region indorsal view, hepatopancreas partly developed, discernable as dotted tubes within the shield; C, overview in ventral aspect, posterior body end disrupted;D, overview in ventral aspect, thoracopod 6 fully developed, thoracopod 7 partly developed; E, stalked eye, ommatidia in growth zone rectangular in crosssection emphasised by white arrowhead; F, mouth in ventral view displaying labrum and thoracopod 1 concealing maxillae and mandibles; G, overview indorsal aspect; area surrounded by rectangle magnified in I; H, anterior head region in dorsal view with hepatopancreas; I, magnification of rectangular area ofG, dorso-posterior margin of cephalothoracic shield with two lateral lobes accentuated by white arrowheads; J, tail fan in ventral view, uropodal exopod withlateral spines highlighted by white arrowheads; K, overview in lateral aspect, initial gill close to thoracopod 4 emphasised by white arrowhead, thoracopod 7fully developed; L, stalked eye built of ommatidia; M, mouth in ventral view displaying labrum and thoracopod 1; N, pleomeres 1-5 in lateral view, pleopods1-5 start to develop visible as small appendages; O, tail fan in dorsal aspects; uropodal exopods with lateral spines emphasised by white arrowheads, telsontriangular in dorsal view.

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Fig. 5. Images of stage 10 of Amphionides reynaudii, all display specimen 2025. A, macro-photography image; B-G, fluorescence micrographs. B, D-E, G,taken with 358 nm; C, F, taken with 470 nm. A, overview in lateral aspect emphasising translucency and fragility of specimen; B, overview in latero-ventralaspect; visible are all appendages except for mouthparts; C, eye stalk without luminescence organ; D, mouth in ventral view, mouthparts overlapped bythoracopod 1; E, thoracopod 8 in posterior view; F, pleopod 1 in median view, endopod with appendix interna emphasised by white arrowhead; G, tail fan indorsal aspect, exopod with lateral spines emphasised by white arrowhead.

Sexual Dimorphism

According to Williamson (1973) and Fransen (2010), stage8 (‘Mysis XII’) and stage 9 (‘Mysis XIII’) are not succes-sive stages but male and female representing the same on-togenetic stage. Males at this developmental level have in-ter alia an eighth thoracopod and a biramous first pleopod.This holds true for specimen 17587-08 (Fig. 4L, N; whitearrowhead). Contrasting, females should have no eighth tho-racopods and a uniramous first pleopod (Williamson, 1973;Fransen, 2010). These conditions are found in specimen26789-19 (Fig. 4H, J). In this context, our stages 8 and 9have to be interpreted to be male and female rather than twoconsecutive stages. However, our reconstruction of the on-togenetic sequence (Fig. 6) refers to Heegaard (1969) and isnot combining stages 8 and 9.

Evolution of Larval Types in Decapoda s. l.

One of the putative representatives of A. reynaudii is veryinteresting and worth mentioning: Most of the morpholo-gical characters found in specimen 17587-03 (Fig. 7) fit per-fectly to those present in a ‘Mysis II’ stage referring to Hee-gaard (1969), e.g., three developed thoracopods and the lackof uropods. With a size of 14.3 mm the specimen is ap-proximately three times as large as a ‘Mysis II’ stage of A.reynaudii. Specimen 17587-03 exhibits a prominent dorsalbump on the third pleomeric segment (Fig. 7; white arrow-head), which is not found in a ‘Mysis II’ stage (Heegaard,1969, his Fig. 14). The bump on the dorsal side of the thirdpleomere (Fig. 7; white arrowhead) reminds of similar struc-tures in larvae of Crangonidae (see Gurney, 1942: Fig. 74A;Williamson, 1960: Fig. 9), which additionally have a simi-

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Fig. 6. Scheme of development of thoracopods in Amphionides reynaudii. tp = thoracopod. Grey numbers in upper line give growth factors adapted fromHeegaard (1969; his Table I) occurring between his stages, exception are growth factors in black being calculated on inclusion of our stage 5 with anarithmetic averaged body length of 10.5 mm.

lar size. This is why we assume specimen 17587-03 to be acrangonid larva. Especially interesting is the fact that cran-gonid larvae resemble early larval stages of A. reynaudii, andcan be especially differentiated by size. This partly explainsthe interpretations of Korschelt and Heider (1892) and Bate(1888) who pointed out a possible relationship between A.

Fig. 7. White-light micrograph of putative representative of Amphionidesreynaudii most likely being a crangonid larva. Overview in lateral aspect,third pleomere with bump indicated by white arrowhead, telson tilted to itsventral side.

reynaudii and Caridea. Indeed, the question arises whetherthese similarities represent shared ancestral features (sym-plesiomorphies), or adaptations to a specific ecological niche(convergencies). A comparative approach over a wider sys-tematic range involving different developmental stages willbe necessary for answering this question. Such developmen-tal patterns can provide important phylogenetic and evolu-tionary information, as demonstrated by studies of for ex-ample Rehbachiella kinnekullensis Müller, 1983 (Walossek,1993) or stem derivatives of Eucrustacea from the Cambrian(J. Haug et al., 2009; 2010b). A detailed knowledge of alllarval stages of A. reynaudii is crucial for understanding theevolution of Decapoda s. l.

Therefore, reinvestigation of the complete larval seriesof A. reynaudii is required. Renaming of all stages shouldbe considered. We used a neutral staging system referringonly to ‘stage’. This was done because the terms appliedby Heegaard (1969) are problematic. For instance, Anger(2001: 20) suggested avoiding the term ‘Postlarva’ as it isinconsistent and imprecise (but see Felder et al., 1985). Hesuggested the use of Kaestner’s (1980) ‘decapodid’ conceptinstead. Yet the system proposed by Williamson (1969) isstricter and more stringent than Kaestner’s and is preferred.Williamson’s concept tries to establish a terminology foreuphausiacean and decapod larvae and should thus beapplicable to A. reynaudii, but this application is currently

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hampered by the probable incompleteness of the series.These gaps of knowledge need to be filled, because onlyexact knowledge of the morphology of each semaphorontof A. reynaudii can allow correct phylogenetic conclusions,also impacting the ground pattern of Decapoda s. str.

CONCLUSIONS AND OUTLOOK

Our re-investigation of A. reynaudii provided new insightsinto the morphology and ontogeny of this unusual malacos-tracan species:

1) The extremely gradual development of the thoracic ap-pendages is most likely plesiomorphic. A compara-ble pattern is also found in Euphausiacea (Maas andWaloszek, 2001), the next outgroup to supposed A. rey-naudii + Decapoda sensu stricto.

2) The incorporation of thoracic segments 1-7 into theshield appears to be continuous during ontogeny, as faras it can be deduced from the available material. Nosecondary exclusion of segments from the shield, whichhad already been incorporated into it in earlier stages,could be observed, in contrast to Heegaard’s (1969)descriptions.

3) We cannot evaluate the phylogenetic significance of thefirst thoracopods and their function as maxillipeds, whichmight be another autapomorphy of Decapoda sensu lato.The first thoracopods of A. reynaudii have a specialisedmorphology and are involved in transferring food parti-cles to the mouthparts. The first thoracopods in Decapodaalso accomplish this function. Yet, because of termino-logical confusion concerning the term ‘maxilliped’ thephylogenetic validity of this character must remain un-clear until a more thorough comparison.

With the re-investigation of ten stages of the larval se-ries of A. reynaudii we contribute high-resolution images ofrepresentatives of this species. However, the complete on-togenetic sequence needs to be reinvestigated. The compre-hensive Danish material was analysed in detail by Heegaard(1969). We documented the whole material from the Mu-seum für Naturkunde Berlin. By continuing the work onmaterial reared in museums, all existing stages of A. rey-naudii might be discovered and explored. With a reinvesti-gation of the total larval sequence, the inconsistencies wefound in the series may be solved, e.g., eventually miss-ing states or inadequate description of characters like thecephalothoracic shield. Knowledge on the complete larvalseries of A. reynaudii will also contribute to a reconstructionof evolution of larval types of Decapoda s. l.

ACKNOWLEDGEMENTS

Thanks are due to the Museum für Naturkunde, Berlin, namely to thecurator for Crustacea and Protozoa, Ch. Oliver Coleman, for giving usthe opportunity to investigate the material. We are also grateful to StefanLiebau, Ulm, for providing access to the Zeiss Axioskop 2, and to NilsJohnsson and Thomas Gronemeyer, Ulm, for access to the Zeiss Observer.We also like to thank all programmers involved in realisation of the freelyavailable software, such as CombineZP and OpenOffice. CH and JTH arevery grateful to their host Derek E. G. Briggs, Yale University and YalePeabody Museum, New Haven, for his support. JTH is currently kindlyfunded by the Alexander von Humboldt-Foundation with a Feodor Lynenfellowship for postdoctoral researchers. We also want two thank Jody

Martin and one anonymous reviewer for their helpful comments on themanuscript.

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RECEIVED: 13 March 2012.ACCEPTED: 28 May 2012.

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