Hydrobiologia 468: 185–192, 2002.© 2002 Kluwer Academic Publishers. Printed in the Netherlands.

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Analysis of the morphology of Spinalona anophtalma Ciros-Perez &Elıas-Gutierrez, 1997 (Aloninae, Anomopoda, Cladocera)

Alexey A. Kotov1,2 & Manuel Elıas-Gutierrez1

1El Colegio de la Frontera Sur, km 2 Carretera Chetumal-Bacalar, Zona Industrial #2,Chetumal, Quintana Roo 77000, MexicoE-mails: akotov@ecosur-qroo.mx eliasgm@ecosur-qroo.mx2A. N. Severtsov Institute of Ecology and Evolution, Leninsky Prospect 33, Moscow 117071, RussiaE-mail: golokot2000@mail.ru

Received 23 July 2001; in revised form 15 October 2001; accepted 19 November 2001

Key words: Spinalona anophtalma, Chydoridae, Anomopoda, Cladocera, limb, redescription, systematics, Mexico

Abstract

Morphology and variability of Spinalona anophtalma Elías-Gutiérrez & Ciros-Pérez, 1997 were re-examined usingmaterial from the original sample from type locality. As a result, some additions were given to the first description,and thoracic limbs were completely redescribed. We revealed and discussed some rare or unique traits of Spinalona,like a peculiar setulation on the labrum, distribution of aesthetascs in the antennular tip, position of the lateral setaon basal segment of endopodite of the second antenna, and the armature of swimming setae, and new structureson thoracic limbs. Although we confirmed previously reported opinion, that Spinalona is the most specific animalamong Alonini, it clearly belongs to this taxon. The genus diagnosis was re-worked according to recent standards.

Abbreviations: acs – accessory seta of limb I; ben – basal endite of limb III; dag – distal armature of gnathobase;den – distal endite of limb III; epp – epipodite; ext – exopodite; fpl – filter plate of limbs IIV; IDL – inner distallobe of limb I; ODL – outer distal lobe of limb I; mxp – maxillar process on limb I; pep – pre-epipodite; sos – softsetae

Introduction

Recently Kotov (2000c) analysed the morphologyof Aloninae Dybowski & Grochowski, 1894 emend.Frey, 1967 (Chydoridae, Anomopoda, Branchiopoda)and subdivided the subfamily into two tribes – Aloninis. str. and Indialonini Kotov, 2000. Spinalona an-ophtalma Ciros-Pérez & Elías-Gutiérrez, 1997 – a solerepresentative of the genus Spinalona – was found tobe the most specific animal among Alonini. A rapid,recent progress in the systematics of the Aloninae(Chiambeng & Dumont, 1999; Dumont & Silva-Briano, 2000; Kotov, 2000a, c; Sinev, 1998, 1999;Sinev & Kotov, 2000) leads to the situation wherewe were able to find small defects in quite detailedprevious descriptions, such as the first description ofthe Spinalona. In addition, different authors frequentlyexplain in a different manner the nature of some struc-

tures, in the first place, on the thoracic limbs. As aresult, Kotov (2000c, Table 1) could not find informa-tion on some important features in the description byCiros-Pérez & Elías-Gutiérrez (1997), like the pres-ence of accessory seta on the first limb or number ofsetae in the IDL of the males. The aim of this article istherefore to elucidate some fine details which we notdescribed in Spinalona, a unique and strange genus,and to elucidate the position of this animal amongAloninae.

Materials and methods

Animals were picked from the original sample, fromwhich the types were previously selected, placed onslides (in a drop of a glycerol-formaldehyde mixture)

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Table 1. Complements of information on limb morphology in Spinalona anophtalma as presented by Ciros-Perez& Elıas-Gutierrez (1997)

Limb Feature Ciros-Perez & Our data

Elıas-Gutierrez, 1997

I Accessory seta Not found Present

Sensillae on endites 1–3 Not found Present

Maxillar process Not described Present

II Seta on exopodite Present Absent, here only a bunch of setules

III Spines on basal endite Not described Described

Sensillae on basal and distal endites Not found Described

IV Soft setae 3 5

V Exopodite setae 3 3–4

‘Filter plate’ 0 1

and studied under an optical microscope in toto. Then,10 adults were dissected for analysis of appendages.

In the present article, we used a system of enu-meration of setae on the limbs proposed by Kotov(2000a, b, c): all marginal setae of (1) exopodites,(2) inner limb portions (‘endopodites’), and (3) distalarmature of gnathobases numbered from distalmost tobasalmost elements without attempts to determine ho-mologies between different limbs. Setae of the innerportion of limb I are marked by letters, a–h.

Results

Spinalona anophtalma Ciros-Pérez & Elías-Gutiér-rez, 1997Ciros-Pérez & Elías-Gutiérrez, 1997: 19–28, Figures1–41.

Type material: see Ciros-Pérez & Elías-Gutiérrez(1997).

Type locality: Los Baños temporary lagoon nearAtlacomulco town, the State of Mexico (19◦ 39′ 59"N; 99◦ 51′ 16" W, at 2507 m above sea level).

Material examined: 16 ephippial and 4 partheno-genetic females from the type locality.

Amended genus diagnosisFemale. Body somewhat elongated, with regularlycurved dorsal margin and distinct postero-dorsalangle, moderately compressed laterally, without dorsalkeel on head or rest of body (Fig. 1). Head relativelylarge, head shield in plane view broad and relat-ively short, with posterior margin rounded, somewhatelongated, rostrum blunt. Three major head pores,

each major pore a cavity with a small pore on the bot-tom. Lateral pores located in a slight depression, abouttwice the inter-pore distance (Fig. 3). Labral keel well-developed, with slightly expressed or not expressedapex, and with keel margin thickened to form a spe-cial rim (Fig. 4). Body of labrum with a pair lateralprojections in the middle (Fig. 2), distally on it (nearlabral plate) a row (more basally) and a group (moredistally) of setules on each side (Fig. 5). Compoundeye and ocellus absent. Valves with series of longitud-inal, weak furrows (Fig. 1); ventral margin of valvedepressed in the middle. Setules between marginalsetae completely absent.

Postabdomen (Fig. 7) relatively short and high,ventral margin straight, with three rows of long hair-like setae. Preanal margin straight or slightly convex,postanal margin short, convex, tapering from projectedpostanal angle toward claw, with a deep depressionin distal portion, forming a peduncle for the claw.On preanal margin five-six clusters of small marginaldenticles, plus 3–4 groups of setules in anal region.Lateral surface with 10–11 series of long, fine setules,plus other rows of smaller setules in proximal halfof anal region. Postabdominal seta short, althoughexceeds preanal part of postabdomen, with distal seg-ment slightly shorter than basal one and setulatedwith long, dense setules. Postabdominal claw large(Fig. 8), about half the postabdominal length, with along (about half length of claw), stout basal spine; abunch of about 7–8 long needle-like setules near basalspine, overlying it. A row of small denticles on ventralside of claw, distally.

Bases of antennules compressed each other, al-though not in touch (Fig. 2). Antennules elongated in

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Figures 1–14. Spinalona anophtalma, females from Los Baños temporary lagoon near Atlacomulco town, State of Mexico, Mexico, collectedin 28.01.1994 by Ciros-Perez & Elıas-Gutierrez. Figure 1. Ephippial female in lateral view; Figure 2. Its head in ventral view; Figure 3.Head pores; Figure 4. Labral keel in anterior view; Figure 5. Labrum in lateral view; Figure 6. Postero-ventral portion of valve in innerview; Figures 7–8. Postabdomen and postabdominal claw in lateral view; Figures 9–10. Antennule in anterion and distal view; Figures 11–12.Second antenna and its exopod; Figures 13–14. lateral swimming seta in lateral view and crossing section. All scale bars denote 100 µm.

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Figures 15–27. First maxilla and thoracic limbs of Spinalona anophtalma from Los Baños lagoon, Mexico. Figure 15. First maxilla; Figures16–19. Anterior view of limb I, its IDL, setae 1 and d; Figures 20–21. Posterior view of limb II and distal armature of its gnathobase; Figures22–23, Posterior view of limb III and its inner portion; Figures 24–25, Limb IV and its inner portion; Figures 26–27, Limb V. All scale barsdenote 100 µm.

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lateral plane, reaching tip of rostrum, and greatly com-pressed in transversal body plane, bases of aesthetascsnot forming a circle, but distributing along elongateddistal antennular surface (Figs 9 and 10). Aesthetascsprojected behind tip of rostrum, two among nine aes-thetascs larger than the rest. Four transversal rows ofsetules at lateral margin of antennule, plus row ofsetules in lateral portion of distal antennular surface.One–two rows of analogous setules on anterior surfacetoo. Antennal formula: setae 0-0-3/1-1-3; spines 1-0-1/0-0-1. Each of two proximal exopod segments ofantenna with a series of 8–12 long needle-like strongsetae inserted distally. Both apical and lateral swim-ming setae with densely setulated basal segments,and tri-laterally armed distal segments. Basal lateralswimming seta arising not from the distal end of theendopodite segment, but from its medium portion.

All epipodites of the limbs are globular, withoutany projections. Limb I with external accessory seta(Fig. 16, as), ODL with one very long seta, IDL withthree setae of different size, no hook-like among them(Fig. 17). Two setae on both endites I and II. Anteriorseta on e3 relatively large, with two sensillae at base,small elements on endites 2 and 1 also (Fig. 16). Max-illar process I with one short seta (Fig. 15). ExopoditeII without setae (Fig. 20). Differences in setulation ofall scrappers of limb II is minimal. Filter plate II with5 setae, nearest to endopodite shorter than others. Ex-opodites III and IV small. Exopodite III with 4 setae.5 soft setae on limb III, stout spines are expressed nearstiff setae (Figs 22 and 23). Filter plate III with 3 longand 2 short setae (Fig. 22). Six soft setae on exopodof limb IV, filter plate IV with only 2 setae. ExopoditeV with 3 (sometimes 4) setae. ‘Filter plate’ V with asingle seta only. Limb VI absent.

Ephippial female. Only part of valves modified andto form ephippium, demarcation line obscure. Dorsalportion of valve wall strongly chitinized. No outwardexpansion of valves in the region of ephippium, nodorsal keel. A single egg within ephippium. Valvesurface of ephippial female over the egg locule finelypunctuate. Pigmentation over the dorsal and ephippialregion brown-yellowish (Fig. 1).

Mature male. Relatively lower than partheno-genetic female. Postabdomen with slightly projectedpreanal and postanal angles, and gonopores opennear claw bases. Marginal (postanal) denticles smal-ler, postabdominal claws somewhat shorter, but basalspines relatively longer, slightly curved. Antennulewith twelve aesthetascs and an accessory, subterminalfinger-like male seta. Limb I with all IDL setae smal-

ler than in female; long copulatory hook, attenuateddistally, with two transverse ridges at the tip; largemale seta, longer than IDL setae, its distal part some-what broad and flattened, with almost parallel edges,tapering at distal fourth.

Some fine details of morphology, our additions tothe first descriptionHabitus of ephippial female: Dorsal portion of valvewall chitinized (Fig. 1).

Major head pores organized quite specifically(Fig. 3): each pore is a cavity with small pore onthe bottom. This is visible on SEM photograph ofCiros-Pérez & Elías-Gutiérrez (1997) on Fig. 12.

Labrum with well-expressed labral keel (Figures2, 4 and 5), but its apex is not distinct in all females(Fig. 5). Keel margin thickened as special rim (Fig. 4).Body of labrum very thick in ventral view, with a pairlateral projections in the middle (Fig. 2). Distally (nearlabral plate) a row (more basally) and a group (moredistally) of setules on each side.

Valves without setules between marginal setae(Fig. 6). A row of numerous setules at some distancefrom posterior valve margin. These setulae of differentlength, which was not marked in the first description.

Postabdominal seta short, although exceedspreanal part of postabdomen. Distal segment some-what shorter than basal one and setulated with long,dense setules (Fig. 7).

Postabdominal claw with setules along dorsal andventral side reaching the same distance from the clawbase (Fig. 8).

Antennule elongated in lateral plane (Fig. 9),reaching tip of rostrum, and greatly compressed intransversal body plane, bases of aesthetascs not form-ing a circle, but distributing along elongated distalantennular surface (Fig. 10). Four transversal rows ofsetules at lateral margin, plus row of setules in lat-eral portion of distal antennular surface. One-two rowsof analogous setules on anterior surface too. Basesof antennules compressed each other, although not intouch (Fig. 2).

Second antenna with apical spines and spine frombasal exopod segment normally longer than segments,from which those arising (Fig. 12), but in smallerpart of animals all these are shorter than segments(Fig. 11). Basal lateral swimming seta arising not fromthe distal end of the endopodite segment, but from itsmedium portion. Both apical and lateral swimmingsetae with numerous setules on distal segments, andtri-laterally armed distal segments (Figs 13 and 14).

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Maxilla I as a hillock with two longer and oneshorter setulated setae (Fig. 15).

Full redescription of thoracic limbsLimb I (Figs 16–19): epipodite small, globular. A del-icate, slender accessory setae (Fig. 16: as) denselyarmed with fine setules on external limb face. ODLwith a sole, long, bisegmented seta, its distal segmentarmed with short, relatively robust setules. IDL ofsimilar size with ODL, with three robust, bisegmentedsetae of different size. Two of them long, their distalsegments armed with fine setules. Third seta short,seems to be naked.

Endite III with three thick bisegmented setae (1, a–c), seta c particularly long, all armed with short hairs.Seta 1 stout, with short setules distally, two sensillaeof different size near its base (Fig. 18). Endite II withtwo long setae of unequal size (d–e), both setulatedat their distal and basal part, but setules in the middlepart are particularly robust (Fig. 19). A small elementat border with endite III (Fig. 16), this is a sensillum orremainder of seta 2 of other Aloninae (Kotov, 2000a,c), here and below all these elements, probably, re-ceptors, are marked by thick arrows. Endite I with tworelatively long, thin, bisegmented setae (f–g), a smallelement also at border with endite II, this is a sensil-lum or remainder of seta 3 of other Aloninae (Kotov,2000a, c) or other chydorid-like Anomopoda (Kotov,2000b). Two ejector hooks of equal size anteriorlyon outer portion of limb corm. Also here a series ofbunches of short and long setules. Low, naked maxillarprocess with single, very short, unilaterally setulatedseta on inner side of limb base.

Limb II (Figs 20 and 21): exopodite reduced to asmall lobe with rows of setules, without setae. Eightscrapers (Fig. 20: 1–8) with length regularly decreas-ing in inner direction, armed similarly by fine setules,only on scraper 5 these setules somewhat thicker.Minute hillocks near scrapers 1 and 5; relatively smalllobes near scrapers 2–4. Gnathobase with promin-ent basal-ventral angle, supplied with bunch of longsetules. Distal armature of gnathobase with four ele-ments, one a bottle-shaped sensillum (Fig. 21: 1),located far from the others. Filter plate with five setae,distalmost one shorter than the others.

Limb III (Figs 22 and 23): large ovoid epipodite.Exopodite flat, relatively small. Distally on it, foursetae of different size (Fig. 22: 1–4), no lateral setaepresent. Distal endite armed with three bisegmentedsetae with length decreasing basad (Fig. 23: 1–3).Setae 1 & 2 stout, with short setules distally. Seta

3 with somewhat inflated basal part, distal part withlong hairs. Relatively large sensillae near seta 2 and3. Basal endite of similar size with distal endite. Theanteriormost position on limb occupied by a row of 3robust spines and one hillock, these elements regularlydistributed. A row of marginal elements consists ofone distalmost sensilla bottle-shaped and four setae.Each of this setae (4–7 in Fig. 23) with inflated base,and thin basal part, setulated with long hairs. Posteri-orly, five soft setae of equal size, armed with rare,delicate hairs (Fig. 22). Gnathobase unclearly demarc-ated from basal endite, distal armature with 4 elements(Fig. 23: 1–4), one of them (1) a thick, bottle-shapedsensillum of middle size, located far from the others.Five setae in filter plate, 2 distal members short, withinflated basal part, similar to soft setae.

Limb IV (Figs 24 and 25): pre-epipodite relativelylarge, setulated; epipodite small, ovoid. Exopodite nottoo large, with 4 setae distally (Fig. 24: 1–4) and 2setae laterally (5–6). Marginally on inner limb face, arow of 4 setae (Fig. 25: 1–4). Seta 1 longest, stout,seems to be naked. Each of setae 2–4 with stronglyinflated basal part, and elongated distal part, armedwith fine setules. Setae 3 and 4 slightly smaller than2. Small elements (sensillae?) near base of setae 2 and3. Posteriorly, two groups of soft setae: 3 more distaland shorter, 2 more basal and longer. Distal armatureof gnathobase with 4 elements (Fig. 25: 1–4): ele-ment 1 a truncate cone sensilla of middle size, seta2 large, thick, bisegemented, unilaterally setulated inbasal segment and bilaterally asymetrical setulated indistal segment. Element 3 similar to a hook, and 4 likea short spine. Filter plate with 2 setae of similar size.

Limb V (Figs 26 and 27): Pre-epipodite small, setu-lated; epipodite biloobed. Exopodite small, with only3 setae (Fig. 26: 1–3). In a single female there were 4setae on exopodite V in both limbs (Fig. 27). Innerlimb portion with protruding flap-like distal projec-tion, fringed by long setules. Two submarginal setaeon inner face of limb, distal member (1) protrud-ing sligthly behind distal endopodite projection or notprotruding at all. Gnathobase slightly expressed top,usually single. Bifurcated in the female with 4 setae inthe exopodite. A single seta in ‘filter plate’.

Discussion

We agree with Ciros-Pérez & Elías-Gutiérrez (1997)about the absence of the eye and the ocellus. Addi-tionally, shape and armature of the postabdomen are

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generic-specific traits of Spinalona. Here a series ofnew features were described, but some small defectswere found in the first description of the thoracic limbs(Table 1). Some of these features, as well as some oth-ers, not discussed by Ciros-Pérez & Elías-Gutiérrez(1997), are rare or unique traits of Spinalona, an-damong the Alonini also (the tribe Indialonini is notconsidered here).

Rows of setules on distal portion of the lab-rum body were revealed in Spinalona. These werenot found previously in other Aloninae (Frey, 1991;Kotov, 2000a, c), but a similar pattern of setulationwas described for many species of the Ilyocryptidae(Kotov, 1999a, Kotov & Dumont, 2000). More dis-ordered setulation of distal part of the labrum bodywas found in some Macrothricidae (Kotov, 1999b).Dumont & Silva-Briano (2000) pointed out the im-portance of labrum features for the Aloninae system-atics, while in the past these features were used epis-odically in the taxonomy of chydorids, predominantlyLeydigia (Smirnov, 1971).

In many Aloninae, there are small setules betweenthe marginal setae (Kotov, 2000a, c; Sinev & Kotov,2000), while in Spinalona these are completely re-duced. Unfortunately, this part was not described wellby the majority of previous authors, and we can not af-firm that this is a unique feature for this representativeof the Aloninae.

Presence of four transversal rows of setules at themargin of antennule seems to be common for theAloninae (see pictures of Alonso, 1996), althoughwe are not sure that this is a synapomorphy. Incontrast, the characteristic transversal flattening ofantennule leads to re-distribution of aesthetascs. Asa result, they do not distribute in a circle. This kindof arrangement is not characteristic for the majorityof the Anomopoda. The same transformation of theantennule was found previously in another alonine,Nicsmirnovius camerounensis Chiambeng & Dumont(1999) although one of aesthetascs in the latter is lar-ger and located far from the others. In the bosminidBosminopsis, the aesthetascs do not distribute in acircle also, while in Bosmina their arrangement isquite typical for anomopods (Kotov, 1997).

Insertion of the lateral seta in the middle of thebasal segment of the second antenna is a specific, ad-vanced feature, not frequent in all Anomopoda, inclus-ive the Aloninae (see pictures of Silva-Briano, 1998).Tri-lateral armature of swimming seta in Spinalona isanalogous to that in Eurycercus (Kotov, 2000b), butwe are not sure about its evolutionary significance.

Ciros-Pérez & Elías-Gutiérrez (1997: 27) poin-ted on two main peculiarities of the Spinalona limbs:presence of only 4 setae on exopodite III and threeon exopodite V. In fact, these traits are rare, but notunique for Aloninae, because there are 3–5 setae onexopodite III in Leydigia (Kotov, 2000c, Table 1), andexactly four seta in L. australis (see Sars, 1885), andthree setae on exopodite V in Notoalona freyi (see Ra-japaksa & Fernando, 1987). Rare for Alonini are alsothe 5 setae in filter plate II, and only 1 seta in ‘filterplate’ V.

Really unique traits of Spinalona are associatedwith the inner portion of limbs III and IV. In allanomopods here, there are two rows of setae (Smirnov,1971). According to Kotov (1998, 2000c), the row ofmarginal scrapers is continued in the distal armatureof gnathobase, and the more medially and posteri-orly located row of soft setae continued basally in thefilter plate of gnathobase. The marginal row in Spin-alona is organized quite typically for Alonini. Butthe second row is special in this genus, as comparedwith other alonine genera. In the majority of Aloninithere are 4 (or less) soft setae here, a tendency to areduction of this number is characteristic for limb IV.In Spinalona there are 5 soft setae both on limb IIIand IV. To our mind, the seta, which is the distal-most member of filter plate in the majority of Alonini,was included to the row of soft seta in Spinalona asa basalmost member. Partially, this is an explanationof small number of setae in the filter plates III–IVin Spinalona. Also, five setae in the filter plate IIIis a rare feature for the Alonini, and only 2 setae inthe filter plate IV is unique. Numerous soft setae onlimbs III-IV occur in different Macrothricidae (Silva-Briano, 1998; Dumont & Silva-Briano, 1998; Kotov,1999b). We consider that the above described struc-ture of limbs III–IV in Spinalona is not primitive, butresults from a secondary modification. Another caseof a deep secondary modification of the alonine limbswithin a local clade was revealed by Kotov (2000a) forKozhowia-Parakozhowia.

Although we confirm here the previously reportedopinion (Ciros-Pérez & Elías-Gutiérrez, 1997; Kotov,2000c), that Spinalona is the most specific animalamong Alonini, there is no reason to create a spe-cial supra-generic taxon for this genus, as was donefor Indialona (Kotov, 2000c). It seems that all tri-pored alonine genera are closely related, but it shouldbe considered that recent attempts to analyze phylo-genetic relationships within chydorid-like anomopods(i.e. Olesen, 1996) are very preliminary, because of

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a lack of data for many representatives of Aloninae.Moreover, the phylogeny of all Branchiopoda is stillcontroversial and under discussion (i.e. Olesen, 2000;Fryer, 2001).

Acknowledgements

We thank Prof. N. N. Smirnov for his valuable con-sultations and Prof. H. J. Dumont for criticism andlinguistic corrections of earlier draft. A. A. Kotovthanks the Consejo Nacional de Ciencia y Tecnolo-gía (CONACYT) for supporting his stay in Mexico,through the Catedras Patrimoniales program.

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