Biblical Lithographs

OPHELIA, 7: 101-112 (December 1969)

IRRIGATION IN THE SIPUNCULID

PHASCOLION STROl.,fBI (MONT.)

1. HYLLEBERG KRISTENSEN

Kristineberg zoologiska Station, Fiskebackskil, Sweden Present address: Marine Biological Laboratory, DK-3000 Helsing0r, Denmark

ABSTRACT

The species irrigates its habitation by muscular means. The frequency of irrigation waves, the volume of water transported per wave and the capacity of irrigation per gram per hour are calculated from kymograph recordings. Two types of irrigation (continuous and discontinuous) are distinguished. The total irrigation is estimated at 15 ml/g/h at temperatures between 15.0 and 22.2°C.

Generation of over- and under-pressures in P. strombi connected with a vertical capillary is described. The experiments demonstrate that an eventual resistance yielded by the sediment may be overcome by the sipunculid.

A decapitated specimen was studied for thirteen days during which period the irrigation was continuous.

The significance of the irrigation is discussed. The irrigtation was found mainly to serve a respiratory purpose.

INTRODUCTION

Little work has been done on irrigation in sipunculids in contrast to the polychaetes. Observations on Phase a/ion strombi were published by Perez (1925) and Hampson (1964), but the authors only stated that the sipunculid irrigates its habitation.

The present investigation describes the mechanism of irrigation and its capacity, as these are of ecological interest. Several animals are known to cohabit with P.strombi inside its shelter. Descriptions are given by Brumpt (1898), Perez (1924, 1925), Knudsen (1944), Hampson (1964), and Nielsen (1964). Own observations on the fauna will be presented in near future.

P. strombi blocks, as described by Perez (1925, p.75), the aperture of inhabited shells or tubes with sediment cemented together with secreted mucus. A main channel through the cement mass is left for protrusion and retraction of the introvert. In empty gastropod shells used by the sipunculid, a secondary channel may be found near the columella, or in the siphonal channel in shells provided with this structure. Irrigation of the shelter varies according to presence or absence of a secondary aperture as pointed out by Perez (1925, p.76).

102 J. HYLLEBERG KRISTENSEN

The present work was carried out at the Kristineberg Zoological Station, Sweden, and I have received financial support from the Nordic Council for Marine Biology. I express my best thanks for this grant. Furthermore, I give my sincere thanks to the head of the station dr. B. Swedmark for eminent working conditions at the Kristineberg laboratory.

MATERIAL AND METHODS

Phascolion strombi in different types of shelters were dredged in Gas6 Rfinna in the vicinity of the Kristineberg Station. The bottom of the sampling locality consists of silty clay and clay inhabited by an Amphiura community. The depth is 25 to 35 m.

Animals were placed in glass tubes and allowed to establish themselves from five to thirty days. Such animals proved especially valuable as the movements inside the shelter could be studied. In addition animals naturally sheltered in Dentalium or Turritella shells were used. Turritella shells were used with the apex cut off, and shells without secondary apertures in the clay plug were selected, as a secondary aperture makes them unusable due to the technique applied.

The apex end, or its analogue in glass tubes, was connected by a piece of rubber tube with a 75 em capillary bent to a narrow S-form for practical reasons (Fig. I). The capillary was filled with sea water, and while immersed horizontally in a shallow vessel an air bubble was placed in the capillary by a syringe. The sipunculid was then connected with the capillary. The air bubble served as an index of water movements. These movements were followed manually with a two armed indicator on a level writer. The trace was recorded on a smoked kymograph drum. A friction from 0.2 to 4 mm water column (PoiseuilIe's law) has to be overcome within the measured range of irrigation speeds in the horizontal capillary. The friction is insignificant compared with the force of Phascoliol1 (see pp.107-109). The loss of kinetic energy caused by the rubber connection mentioned above is negligible.

Experiments were also made in a system where the components are placed vertically. The capillary was replaced by a 100 cm L-shaped capillary which, after mounting of P.strombi, was put into a 30 cm high jar with sea water.

The capillary surface served as index of water movements produced by the animal. However, in the vertical set-up, physical forces play a role. (Capillary force, friction and hydrostatic pressure influence the movement of the water in the capillary).

Experiments in the horizontal system were carried out with stagnant water, while the longer lasting experiments in the vertical system were performed with running sea-water. Salinities ranged between 31 and 34%0'

The vertical distance recorded on the smoked paper was a measure of the pumping activity of P. strombi, 1 cm equalling 0.01 ml sea water. (The volume of the bore was estimated by measuring the length of the water column after the filling of the capi1lary with a known quantity of sea-water).

IRRIGATION IN PHASCOLION STROMBI [03

FIG. I. Horizontal set up used for manual registration of irrigation in Phascolion strombi

Over-flow technique was used in two experiments. The conclusions on irrigation in P.strombi are based on 20 recordings (355

min.) in the horizontal system and 70 recordings (3500 min.) in the vertical system.

RESULTS

The mechanism of irrigation

Examination of animals in glass tubes demonstrated that P.strombi belongs to the type of worms in which the irrigation is produced by muscular means (Fig. 2). Piston-like swellings similar to peristaltic and antiperistaltic waves of the intestine travel along the trunk.

The analogy with peristalsis of the gut is especially obvious when water is transported from the posterior end of the trunk and forwards. When water is transported in the opposite direction it is usually possible to distinguish a depression on the right side and one on the left side; the latter is the first to reach the posterior end of the trunk (Fig. 2). The result is in both directions a transport of a finite volume of water, and no qualitative difference is seen on kymograph recordigs.

Anima[s in tubes open at both ends principally move the water over the body from the posterior end and forwards. The aperture for protrusion of the introvert functions as exhalant aperture while the apex opening is the inhalant aperture.

104

..

CLAY PLUG

J. HYLLEBERG KRISTENSEN

CURRENT CURRENT

" d " l't -" . . ") I

GLASS TUBE

=t:g: ..... .

=It ..

ANUS TRUNK

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FIG . 2. Mechanism of irrigation in Phaseo/ion strombi observed in a glass tube. The animal was transferred from a TlIrifel/a shell with secondary (inhalant) opening in the clay plug. The small arrows indicate movements of coelomic fluid caused by muscular activity in .connexion with

irrigation.

However, the current may be reversed by the animal. This occurs spontaneously, or it is induced by foreign particles like lndia ink or carmine powder in the water. Similarly a current from the anterior to the posterior end will be reversed if suspended matter comes in contact with the front part of the trunk.

Irrigation of Turritella and other gastropod shells was similar to the type just described if the shell had a damaged apex, or if it had been drilled by naticids. (See also Perez, 1925, p. 76). 1 f the Turritella shell is undamaged, the main orifice will function as an exhalant aperture and the secondary opening close to the columella is the inhalant aperture. In gastropods with siphonal canal the inhalant aperture will be found in this canal.

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~ 0.10 (!)

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0.00

IRRIGATION IN PHASCOLION STROMB!

1

introvert induced .activity

I

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discontinuous irrigation

~~~.-

absence 01 irrigation

2 3 4 5 10 15 20

TIME

continuous irrigation

25

105

min

FIG. 3. Copy of trace on a smoked drum in horizontal set-up demonstrating two types of irrigation in Phascolion sfrombi. Between the continuous and the discontinuous irrigation is a section without irrigation. Water is moved from the anterior to the posterior end of the trunk. Individual naturally sheltered in shell of Dentalium entalis. Temperature 22 c C. Weight of individual 0.11 g.

The present designations "inhalant" and "exhalant aperture" are in contrast to those used by Perez (1925, p. 75). According to my observations, it is the secondary orifice which mainly functions as inhalant aperture. Also Hampson (1964, p.127) mentions that suspended particles pass into the siphonal canal of Nassarius shells inhabited by P. strombi.

Capacity of irrigation and frequency of waves

By use of the vertical set-up it was possible to observe the activities of P. strombi for a long period without disturbance of the animal. However, physical forces were significant as previously mentioned and it was difficult to measure the capacity of irrigation.

In the horizontal set-up, the frequency of irrigation waves per unit of time and the volume of the water transported per wave were easily recorded, but the time at disposal for observations was limited.

In one experiment out of twenty the water movements were observed for 83 minutes. Usually, the period was much shorter. After 3-15 minutes the bubble used as index of water movements was at one end of the capillary, and it was necessary to interrupt the observation and introduce another bubble into the capillary.


An extract of a record from the horizontal set-up is shown in Fig.3. Two types of irrigation are distinguished in the example. In the discontinuous irrigation, movements of the introvert will move water in the habitation. Protrusions will induce water to be drawn into the shelter while retractions causes ejection of water. These introvert induced movements are supplemented by peristaltic waves of irrigation. In the continuous irrigation water is drawn rhythmically through the habitation. The current was always in one direction during an observed period of continuous irrigation, but recordings were obtained, where forward irrigation was succeeded by discontinuous irrigation, and this again by continuous irrigation in the opposite direction.

The introvert is often, though not always, withdrawn during continuous irrigation.

The results of measurements of continuous irrigation on the smoked paper are summarized in Table 1. The irrigation ranges from 15 to 54 ml/g/h when water is moved forward from the posterior end. In the opposite direction irrigation ranges from 11 to 55 ml/g/h. The experimental temperatures were between 15.0 and 22.2 c C. An effect of temperature on the rhythm and on the capacity of irrigation is not evident from the present recordings. It was noted that irrigation varied significantly in the same individual at the same temperature, even when the recordings were made with an interval of a few minutes.

Irrigation calculated at temperatures from 15.0 to 19.0°C was 29.4 ml/g/h, and between 19.1 and 22.2°C, it was 31.0 ml/g/h, both directions taken into consideration.

Continuous irrigation has been observed for 153 minutes in twenty experiments. Discontinuous irrigation or an absence of irrigation has been observed for 203 minutes in the same experiments. In view of this finding, the total irrigation must be reduced to about half when calculated from the continuous irrigation. A value of 15 ml/g/h at 15.0-22.2°C is thus considered representative for irrigation of Dentalium-type shelters for longer periods. Similar figures, 14.1 and 14.6 ml/g/h, were found in two experiments by use of over-flow technique during periods of 90 and 250 minutes, respectively (16 ° C).

Table 1 shows that only in two experiments were frequencies of peristaltic waves found to be higher than 10 waves per minute. The highest frequency was recorded in an individual which also showed the lowest frequency (2.7 waves per minute). Maximum and minimum values were recorded at about the same temperature. In the other experiments, frequencies were found to range from 4.5 to 8.0 waves per minute at tempeartures between 15.0 and 22.2°C.

A quantitative difference is evident when irrigation in the two directions is compared (Table 1). The frequency of peristaltic waves and the resulting irrigation was greater from the posterior end and forward compared with the opposite direction. An exception was the smallest individual weighing 0.09 g. The forward direction represents the inhalant current in the natural position of the shelter on

I RRIGATION IN PHASCOLION STROMBl 107

TA B LE l. Continous irrigation in Phascolion stromhi. Animals in glass tubes (g. t.), Turritella shells (T.),. or Dentalium shells (D). Experiments at room temperatures in

stagnant sea water. Sediment present (+) or Jacking (-).

Type of shelter

g.t. g.t. g.t. g.t. g.t. D. D. g.t. g.t. D. T. D. D. D.

T. g.t. T. D. D. D.

Sediment I I

Temp. cc I

Liv~ weight I Frequen~y I Volu~e per m g waves/mm wave m ml

Irrigation from the posterior to the anterior end of the trunk

15.5 0.14 4.7 0.020 15.5 0.14 3.6 0.015 15.5 0.14 2.7 0.0\3 16.0 0.14 10.5 0.009 16.0 0.14 14.1 0.009

+ 17.5 0.11 7.5 0.007 1- 18.0 0.11 4.5 0.012

19.0 0.38 4.8 0.027 ·1 19.5 0.38 4.8 0.036 ..j.. 21.0 0.11 5.4 0.013

21.0 0.17 7.6 0.018 -,. 21.5 0.11 8.0 0.010 -i 21.5 0.11 6.2 0.008 , 22.2 0.11 5.6 0.009

Irrigation from the anterior to the posterior end of the trunk

15.0 0.15 6.0 0.008 15.5 0.14 4.5 0.012

T 19.5 0.13 5.5 0.007 -1"" 21.2 0.09 6.9 0.012

22.0 0.11 6.4 0.004 22.0 0.11 5.0 0.004

Irrigation ml/g/hour

40 23 15 41 54 29 30 21 27 38 48 44 27 28

18 23 18 55 14 II

the sea bottom. The water is drawn in at the posterior end and seeps away in front of the animal.

Table 1 shows that the volume of water transported per wave increases with increasing weight of the individuals.

It could be expected that a greater number of waves per unit of time would tend to reduce the volume of water transported per wave. However, such correlation is not demonstrable from the data.

Generation of o ver- and under-pressures

It was commonly seen on recordings in the vertical system that water was rhythmically pressed from the anterior end of the trunk and backwards against an opposite directed force exerted by the column of water in the capillary. The animal produces in this wayan increasing pressure on the trunk. The maximum pressure produced and withstood by P.strombi ranged from 80 to 130 mm sea

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J. HYLLEBERG KRISTENSEN

generation of overpressure

_. --\ .. ,F,:,;:,,·· -..... "~~"M·" \ underpressure

i

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FIG. 4. Copy of trace on a smoked drum in vertical set-up, demonstrating a very rhythmical generation of an over-plessure by transport of water from the anterior to the posterior end of the trunk. The underpressure is produced by water transport in the opposite direction. Individual naturally sheltered in Turritella shell without secondary aperture in the clay plug. Temperature J 6 0 C. Weight of individual 0.30 g.

0.00 I--L--L--L-L......JL......JL......J'---l'---l--'--'--'--'--'-1 2 3 4 5 6 7 8 9 10 11 12 min

TIME

water at 16°C, 33%0 S (weight of animals 0.1 to 0.3 g). This over-pressure was calculated from the O-point of the capillary.

Generation of an over-pressure (Fig.4) involves two contributions from P. strombi: (1) a finite volume of water is transported backwards by a peristaltic wave, and (2) at the same time a part of the body wall must be pressed against the wall of the habitation in order to withstand the pressure of the increasing water column in the capillary.

Co-ordination of the two contributions (compare with Fig.2) results in an increase in pressure on the trunk.

A decrease in pressure involves the same two contributions. The decrease is never produced by a simple ooze away of water. If the animal relaxes completely, the pressure yielded by the falling water on the posterior end of the trunk would tend to press the animal out of the shelter. When the column of water has reached the O-point of the capillary, the animal must pump the water out of the shell against the opposed capillary force. The water is transported from the posterior end and forwards by peristaltic waves. In this way a still increasing under-pressure is produced and withstood but the ability to prevent water from seeping into the shell decreases with increasing under-pressure as seen from Fig. 4. This figure also shows that when an under-pressure is formed the volume of water transported per wave is similar to the volume let out above the O-point, indicating that a

IRRIGATION IN PHASCOLlON STROMEl 109

decrease in pressure is not generated by simple seeping, but involves transport of a finite volume per wave. The time used to let out the water and produce an underpressure is similar to the time used to let in the water and generate an over-pressure.

Generation of over- and under-pressures in P. strombi must be seen in relation to circumstances in nature. When the shelter is dragged through the sediment by the animal, the inhalant orifice may be completely buried in the bottom material. Irrigation under these conditions will call for a pressure which will overcome resitance against movement of water.

A comparison of the traces of rise and fall in Fig.4 shows a difference in transport of water from the front to the rear and vice versa. The animal used in this experiment lived in a Turritella shell with a perforated apex. Before the experiment started, it was controlled that the holes in the apex were used in irrigation under natural conditions. The falling part of the trace reflects the inhalant current, and the rise reflects the situation when irrigation has been reversed as previously described.

Continuous irrigation (i. e. rise and fall of the recording), discontinuous irrigation and an absence of irrigation were observed both in the vertical and in the horizontal set-up.

Extirpation of the introvert

In order to investigate the influence of the introvert on the irrigation, an animal (0.15 g) in a Dentalium shell was decapitated and observed for thirteen days in the vertical system.

The protruded introvert was seized in the middle region with a pair of tweezers and the tip of the introvert cut off. The remaining part of the introvert was evidently too damaged to allow the normal regeneration from the wound described by Schleip (1934). Three days later the introvert was autotomized along a predestined line on the transition between trunk and introvert.

In the decapitated animal an unusually high pressure maximum was sustained on the first day after decapitation. It ranged between 200 and 250 mm sea-water (16°C, 33%0 S). No regular rhythm was found in the irrigation, but water movements were never interrupted. The frequency of peristaltic waves was about 180 per hour and did not change significantly during the observed period of the regeneration. Rhythmical pressure maxima were produced three to four times every hour from the eighth day after decapitation (Fig. 5). Between two pressure maxima was a horizontal part, usually with rise and faIL This rhythm was maintained for the next five days. Then the experiment was terminated.

Fig.5 shows that when an over-pressure is produced it is difficult for the decapitated animal to prevent water from oozing away at the end of a peristaltic wave. At a low over-pressure the loss is about 20 % and at the maximum it is about 50 %. This loss together with the decreasing volume transported per wave results in an S-form of the rise of the curve.


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0.10

0.01

0.05 r \

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~~ of capillary

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TIME

FIG. 5. Two pressure maxima from a recording of a Phascolion in a Denfalillm shell in vertical set-up made on the tenth day after decapitation of the animal. It demonstrates very rhythmical irrigation.

Temperature 16°C. Weight of individual 0.15 g.

Under-pressures were not generated during the time of observation. This is interpreted as a behaviour to prevent rupture of the membrane sealing the wound after decapitation. Generation of an under-pressure requires peristaltic waves towards the anterior end, resulting in an increasing pressure in the anterior region of the body. When an over-pressure is generated the anterior region can be kept contracted and the coelomic pressure increased instead to the rear.

Observations on several decapitated individuals kept in various sediments indicate that oxygen requirements and movements of the coelomic fluid are very considerable during regeneration. The rhythmic irrigation is maintained after removal of the brain, suggesting that irrigation is governed by local circuits or by a rhythm in the nerve cord of the trunk. This would be in agreement with decapitation experiments in polychactes (Wells, 1951).

DISCUSSION

The Significance and pattern of irrigation

Lindroth (1941, p.486) pointed out that irrigation in polychaetes serves a variety of purposes, e. g. respiration, taste, feeding, digging, and defaecation. Irrigation in Phascolion strombi is not necessary for the feeding, as the tentacles are used to pick up food particles from the sediment. Neither is irrigation requisite for a taste

IRRIGATION IN PHASCOLlON STROMBI 111

function. According to Akesson (1958, p. 179), the nuchal organ at the dorsal base of the tentacles is most probably a chemoreceptory organ. The introvert is used in digging as well as dragging of the shelter, but these functions do not depend on irrigation. On the other hand, feeding, digging and dragging always cause displacement of water in the habitation, resulting in what I have termed discontinuous irrigation, which evidently has a certain respiratory significance. However, measure.ments of oxygen concentrations of the inhalant and exhalant currents are needed to estimate the exact relations of the two types of irrigation to respiration. The significance of irrigation for defaecation and removal of excretory products is unknown.

A relation of irrigation to respiration is indicated by nitrogen bubbling experiments (vertical set-up), as the pattern of irrigation is altered when the oxygen tension is lowered. On one occasion bubbling was continued for six hours. During the first hour of bubbling irrigation was increased and continuous. Next, irrigation gradually decreased and became intermittent. Pauses with no other activity than occasional protrusions of the introvert alternated with short-lasting bursts of irrigation at the end of three hours. This intermittent irrigation was continued for the rest of the period.

Wells (1950, p.138) described irrigation in the polychaete Arenicola marina which resembles the intermittent type observed in P. strombi during oxygen deficiency. He found that intermittent irrigation with short bursts of irrigation is useful, as Arenicola marina during tidal exposure may detect when favourable conditions return. A testing function of the shortlasting bursts is possbile in P. strombi, too, but it seems more likely that the bursts of irrigation are related to removal of waste products from the shelter. Exploration of the surroundings can more easily be made by occasional protrusions of the introvert.

An irrigation in P.strombi of 15 ml per g per hour at 15 to 22°C looks rather small. Unfortunately, it is impossible from the present knowledge to estimate the amount of oxygen taken up through the trunk, introvert and tentacles, respectively. In addition the oxygen consumption is unknown. The oxygen capacity of the coelomic fluid is estimated at 0.008 ml oxygen per g, by use of the data from Sipunculus nudus (Florkin, 1933, p.705). Florkin finds that the oxygen content of the coelomic fluid is 1.6 % by volume of the coelomic fluid, which makes 50 % of the total animal volume. The oxygen content of 15 rnI aereated deep sea-water at 15°C is about 0.087 ml oxygen. The oxygen store of the coelomic fluid could theoretically be renewed every five minutes if all oxygen is taken up from the irrigated water, but this is undoubtedly not the case. Polychaetes take up 50 to 60 ;.; of the oxygen in the irrigated water (Dales, 1960, p. 81).

Most probably there is only oxygen enough in the irrigated water for a local su pply of the body wall. It must be taken into consideration that besides P. strombi, the micro flora and fauna of the clay plug, about 30 entoprocts and 10 other small cohabiting animals in the shelter, take up their oxygen from the water.


In large sipunculid species of some genera (e. g. Sipunculus) I coelomic canals of the integument make the contact between oxygen and coelomic fluid easier. Such canals are not found in P.strombi. The oxygen must pass through the relatively thick body wall to come in contact with the erythrocytes, the number of which is low. Franzen & Fange (1962) estimated the cell volume in sipunculids to a little higher than 3 % of the coelomic fluid. Florkin (1933) mentioned 7 % for Sipunculus nudus.

A steep oxygen dissociation curve (Florkin, 1932, p.833), and an absence of a Bohr effect (Florkin, 1932), together with a low concentration of erythrocytes and a minimal vascularization, indicate that sipunculids in general have small demands on oxygen. Information given by Theel (1875, p.7) and own observations support this for Phascolion strombi. A small irrigation is on this background not surprising.

REFERENCES

AKESSON, B. J 958. A study of the nervous system of the Sipunculoideae. Dissertation Lund. (U nders. over Oresund. 38) 249 pp.

BRUMPT, E. 1897. Quelques faits relatifs a l'histoire du Phascolion strombi. Archs Zool. expo gen. 3. Ser., 5: 483-496.

DALES, R. P. 1963. Annelids. Hutchinson Univ. Lib., London, 200 pp. FLORKIN, M. 1932. La courbe de dissociation de l'oxyhemerythrine dans Ie liquide coelomique

du Siponcle. C. r. hebd. Seanc. Acad. Sci., Paris, 195: 832-833. - 1933. Le pouvoir oxyphorique du liquide coelomique et des hematies de Sipllnculus nudus.

C. r. Seanc. Soc. Biol., 112: 705-706. FRANZEN, A. & R. FANGE. 1962. Observations on hemerythrin-containing coelomocytes in in

vertebrates. Report from the third Scandinavian conference on cell research, pp. 31-32. Danish Science Press, Copenhagen.

HAMPSON, G. R. 1964. Redescription of a commensal pelecypod, Roche/ortia ellenala, with notes on ecology. Nautilus, 77: 125-129.

KNUDSEN, J. 1944. A gephyrean, a polychaete and a bivalve living together (commensalistically) in the Indo-Malayan Seas. Vidensk. Meddr dansk naturh. Foren., 108 : 15-24.

LINDROTH, A. 1941. Atmungsventilation der Polychaten. Z. vergl. Physiol., 28: 485-532. NIELSEN, C. 1964. Studies on Danish entoprocta. Ophelia, 1: 1-76. PEREZ, C. 1924. Le complexe ethologique de la Turritelle et du Phascolion strombi. Bull. Soc. zoo1.

Fr., 49 : 341-343. - 1925. Sur Ie complexe ethologique du Phaseolion strombi. Ibid ., 50: 74-76. SCHLEIP, W. 1934. Die Regeneration des Riissels von Phascolioll strombi Mont. (Sipunculidae).

Z. wiss. Zoo!., 145: 462-469. THEEL, H . 1875. Recherches sur Ie Phascolion strombi (Mont.), K. svenska VetenskAkad. Handl.,

14: 1-32. WELLS, G. P. 1950. Spontaneous activity cycles in polychaete worms. Symp. Soc. expo Bio1., 4:

127-142. - 1951. On the behaviour of Sabella. Proc. R. Soc., B, 138: 278-299.

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