Indian Journal of Marine Sciences Vol. 2, June 1973,pp. 32-37

Structure & Early Development of an Opisthobranch Mollusc, militaris (Alder & Hancock)

K. VIRABHADRA RAO & L. KRISHNA KUMARI National Institute of Oceanography, Panaji, Goa

Received 5 January 1973

The external and internal morphology, the spawn and early development of C. militaris, obtained locally, have been described. It is a facilinid having elongated oral tentacles, smooth rhtnopnores, tentacular anterior angles of the foot and clusters of each with a varying number of oblique rows. The presence of oral and salivary glands, paired jaw plates with cutting edges, uniseriate raduta with teeth having a prominent pointed median cusp and seven lateral cusps On each side, and a c1eioproctic anus opening at about the middle in the second cluster of cerata Onthe right side are the main features of the alimentary system. The mollusc feeds on the hydroid, Gar1lia franciscana (Torrey). The nervous, circulatory and renal systems are typically eolidacean in character. The statocysts have each, numerous statoliths. An enlarged convoluted gonoduct into a seminal ampulla, a distinctly separate lobed prostate gland proximally cormected to the vas deferens and an unarmed conical penis are prc rnfnerrt among the reproductive organs. The mucoatbumtnous glands, the vaginal duct and the spermatneca are normal in character as in most nudtbranchs, The spawn string is a fiat spiral with two rather irregular linear series of eggs and its attachment to substratum leaves gaps where the string forms loops remaining free. The larva is blind when hatched and the shell is smooth On the surface, spirally ovate and bears an .

HE eolidacean mollusc, formerly known as fully stretched and dragging behind a fairly Eolis militarisl, has been redescribed by Burn elongated tapering tail (Figs. 1, 7 and 8). The T and Narayanan- as Caloria militaris based measurements of parts given in the following account on certain facelinid characters, as the presence of are referable to the largest of the in tentacular processes in the anterior region of the the collection. foot, smooth , cerata in oblique rows The head bears a pair of oral tentacles (Fig. 8, o.t). and a cleioproctic anus. These authors have also and a pair of rhinophores (rh). The former are about given a complete synonymy of the species 0·7 em long, stout at the base, but tapering towards from the available literature. Apart from this the free ends and the latter about 0·5 em in length recently established taxonomic status, very little are smooth on the surface and a little shorter. As is known about its morphology and life-history. in other eolids, a pair of pigmented dots below the During the course of investigation on certain marine skin at the bases represents the eyes. molluscs the occurrence of this little known species The foot (ft) is long, about 0·5 em in width in the rock pools near Baga (Goa) was noted. Sub- and broader than the dorsum. Anteriorly it bears sequently, more samples were collected from two short flattish tentacular processes (Lft), one on Ribander and Old Goa near Panaji from the test- each side. A slender transverse groove separates panels suspended in shallow waters for observations the rest of the foot from these processes. The mouth on the settlement and growth of the sedentary or- is slit-like and placed between two labial thickenings ganisms. These molluscs have always been found at the bases of the oral tentacles (Fig. 2). The foot associated with colonies of hydroids, Garvia fran- excluding the tail is about 3 em long and the latter ciscana (Torrey), upon which they were feeding. about 0·9 em long. Dissections were made under the stereoscopic The cerata are very slender, the larger ones among microscope to study its structure. Stained serial them measuring about a centimetre in length when sections of the whole animals fixed in Bouin's fluid they are fully e~panded. They are in 9 paired enabled presentation of details of its . clusters, each cluster having a varying number of When they were kept for observations, they depo- oblique rows. In the first 3 clusters, the cerata are sited spawn which facilitated tracing their early in 5-7 oblique rows and in the posterior ones the developmental stages. number of rows gradually diminishes from 4 to 2. The number of cerata in each of the oblique rows Results also differs, depending on their location on the dorsum. Those in the anteriormost oblique rows of External Features each cluster are fewer in number and smaller in size. The animals ranged from 2 to 4·1 em in length In the oblique rows of the posterior clusters they when fully expanded. They were graceful in are invariably small. The cerata are traversed by appearance, creeping with the expanded foot amidst digestive gland diverticula, which are unbranched hydroids, with tentacles, rhinophores and cerata but bear minute dark grey lobules. Terminally the

32 RAO & KUMAR I: STRUCTURE & EARLY DEVELOPMENT OF C. MILITARIS 7 O.5mm

3

E E to

Figs. 7 and 8 - Caloria militaris [Fig. 7; Right lateral aspect of the anterior part of the . Fig. 8; Anterior dorsal aspect of the animal with cerata fully expanded]

oral tentacle on its anterior face. The lines of the tentacles of the opposite sides meet in a small tri- Figs. 1 to. 6 - .Caloria militaris [Fig. 1 ; Dorsal aspect of the angular patch of the same hue on the upper surface animal. Fig. 2; Enlarged ventral view of the head. FIg. 3; of the head. There is also a similar deep orange Cerata. Figs. 4 and 5; Jaw plates. FIg. 6; Two. VIews of streak on the posterior face of each of the oral ten- the radular teeth. AbbreviatiQns used III FIgs. 1 to. 18; al.gl, albumin gland; am.hgl, ampulla of ~ermaphrQdite gland;.an, tacles. The tips of the oral tentacles are lemon- anus; au, auricle; b.g, buccal ganglia: ce, cerata ; cru , cnido- yellow or pale white, but sub-terminally an orange- sac; c.plg, cerebropleural ganglion: dgl.d? diverticula of the red colouration spreads over the surface to about digestive gland; d.kd, diverticulum of kidney: eX.Q, excre- the middle of their lengths. The rhinophores are tor y organ : eX.QP, excretory open in g ; ey, eye;. ft, foot ; ge.Q, genital orifice: hgl, hermaphrodite gland; mt, intestine: also deep orange-red except distally where they are j.pl, jaw plates; It.I, left digestive gland lobe ; !.ft, lateral lemon-yellow. The head region between the rhino- prolongations of foot; mu.gl, mucQalbummQus gland; oe, phores bears yet another patch of red colouration. oesophagus: QP, operculurn ; o.t, oral tentacles; p.c, pericar- Two, rather indistinct streaks of the same colour, dium; p.g, pedal ganglion: p.pr, pericardia! prominence : pr.g, prostate gland; rd.s, radular sac; rh, rhinophores: rh.g, one in front and one behind in the dorso-median rhinophoral ganglion : r.p.f, renQpericardial passage; rt.I, aspect are continuous with this coloured patch bet- right digestive gland lobe; sgl, salivary gland; sh, sheJl; spt, ween the rhinophores. In some, it was noticed sperrnatheca ; st, stomach: st.c, statocyst; ve, velum] that the anterior streak joined the triangular patch of the same colour already described, situated bet- ween the oral tentacles. Very prominent are the diverticulum leads by a narrow channel into a two lateral streaks of orange-red, one on either side spindle-shaped, which opens to the exterior below the level of the ceratal groups. They extend at the tip of the cerata (Figs. 1, 3, 7 and 8, ce). in front to the oral tentacles and behind the last The genital orifice is situated laterally to the right paired group of cerata, they run dorsolaterally to side of the body at about the posterior end of the almost the tip of the tail. The terminal region of first cluster of cerata (Fig. 7, ge.o). The anus the tail is lemon-yellow. is cleioproctic being amongst the right side cluster The cerata for the most part of their length are of cerata of the posterior part of the digestive gland generally dark grey because of the diverticula (an). Its location is dorsolateral in about the middle of the digestive gland of the same colouration of the second cluster of cerata of the right side. extending into them. In some freshly obtained The nephroproct or the renal (ex.op) is close specimens the cerata had a rusty or reddish brown in front of the anus. colouration. The epithelium of the cerata is almost Colouration - The major part of the dorsum, the colourless except for a faint yellowish orange tinge lateral aspects of the body and the entire foot are distally to some distance towards the base. In colourless or pale white. The outer edges of the fresh individuals, occasionally it was noticed that tentacular processes of the foot are for the most part this yellowish tinge was replaced by a pale pinkish deep orange, but lemon-yellow or pale white at their hue. The apices of the cerata are pale white free ends. There is a deep orange-red line along the or light yellow. From the base of the cerata to

33 INDIAN J. MAR. SCI .• VOL. 2. JUNE 1973 about five-sixths of its length there is a conspi- cuous opaque white streak. Such whitish streaks are conspicuousin individuals kept in the laboratory for long time. when the cerata contract consider- ably. J.pl Integument and Internal Organs rd.S~~~, The integument of the foot or the pedal epithe- sgl lium reveals columnar ciliated cells interspersed by I.ft rather cuboid nonciliated unicellular mucous gland O~ cells opening to the exterior. In the subepithelial connective tissue also there are mucous glands which are multicellular. opening out to the exterior through the pedal epithelium. Such multicellular mucous glands are numerous in the subepithelial tissue of the anterolateral angles of the foot. Below this pedal epithelium is the basement membrane followed by loose connective tissue. through which traverse circular and oblique muscle strands. The connective tissue has numerous blood spaces cons- tituting the general haemocoel. The general body wall covering the dorsum. the rhinophores. the oral 1mm tentacles and the cerata has the epidermal layer with spt ft rather cuboid cells with sparsely distributed mucous gland cells. The epidermisis ciliated over the cerata Figs. 9 to 12 - Transverse sections of Caloria militaris and the tentacles. It has also the scattered pigment [Fig. 9: TS of head region through jaw plates and . granules. The subepithelial layer here has the same Fig. 10: TS through oesophageal region. Fig. 11: TS through structure as that of the foot. the region of heart and anterior genitalia. Fig. 12. 1'S through posterior region] In general arrangement the digestive organs of Caloria correspond to those of the other facilinids. The slit-like mouth leads into a narrow short oral "hindwards to be continued by the rectum which tube into which open numerous small buccal glands. opens to the exterior by the anus. The nematocysts The oral tube has a chitinous lining. The pharyn- liberated from the hydroid food remain unexploded geal bulb is large and highly muscular. containing in the alimentary canal and are lodged in the cnido- within a pair of serrated jaw plates about 1·1 mm blast cells lining the epithelium of the at in the long axis (Figs. 4, 5 and 9. j.pl). They are the tip of the cerata (Fig. 10, cni), The heart hinged together dorsally, and their serrated free consisting of an anterior ventricle and a posterior cutting edges protrude into the oral tube. The ser- auricle is enclosed in a fairly spacious pericardium, rations are in a single series of about 20 in each jaw the position of which is externally indicated by a plate. In most specimens the jaws were straw- roundish median bulging behind the first pair of yellow but in some reddish in colour. The radula cerata clusters (Fig. 7, p.pr; Fig. 11. p.c). Three is uniseriate with 19 horseshoe-shaped teeth. each prominent veins collecting blood from various organs having a prominent sharp-pointed median cusp open into the auricle. From the ventricle an aorta and 7 comparatively much shorter lateral cusps on runs forwards supplying blood to the organs. The either side (Fig. 6). In a few, the number of teeth kidney or the renal organ is saccular, lying behind was from 17 up to 21 and the minimum number of the pericardium and giving of an anterior diverti- lateral cusps was 5. A short and narrow oesophagus culum (Fig. 11, d.kd), which runs forwards to the (Fig. 10. oe) leads into a fairly large stomach. the right of the pericardium. The diverticulum com- inner wall of which is thrown into a number of longi- municates with the pericardium by a short reno- tudinal folds which are prominently seen in serial pericardial passage (Fig. 11, r.p.f) lined by cells transverse sections. The lining epithelium of the bearing much elongated cilia; anteriorly it also opens folds bears darkly staining gland cells. A pair of to the exterior by the nephroproct. large salivary glands (Fig. 10, sgl) lies resting over The central nervous system (Fig. 13) consists the wall of the digestive tract with their narrow mainly of a pair of large cerebropleural ganglia elongated ducts opening dorsolaterally into the (c.pl.g) and a pair of comparatively smaller pedal pharyngeal bulb. ganglia (p.g). A pair of rhinophoral ganglia (rh.g) The stomach posteriorly receives the right and is borne by slender peduncles arising from the left anterior diverticula and a median posterior di- anterodorsal aspect of the cerebropleural ganglia. verticulum of the digestive gland (also known as A pair of buccal ganglia (b.g) is situated over the the midgut-gland). Branches of the two main an- pharyngeal bulb ventrally to the root of the oeSo- terior diverticula enter the cerata of the first cluster phagus. Connectives between the ganglia of the of the corresponding side. The main posterior same side and commissures between those of the diverticulum runs mid-dorsally to almost the pos- opposite side are as in other eolids'', Innervated terior end of the body giving off lateral branches, dorsolaterally from the cerebropleural ganglia are the subdivisions of which enter the cerata of all the the paired eyes (Fig. 13,ey), each with a roundish clusters behind the first pair (Figs. 11 and 12. dgl.d). crystalline lens and a dark pigmented retinal cup. The intestine arising from the stomach at the junc- Ventrally on either side, at the junction of the cere- tion of the right anterior diverticulum and the bropleural ganglion with the pedal ganglion and posterior diverticulum turns to the right and proceeds receiving nerve fibres from the former, there is an

34 RAO & KUMARI: STRUCTURE & EARLY DEVELOPMENT OF C. MlLITARIS

the genital orifice close behind the opening of the penial pouch. Associated with these organs is a narrow duct, the vaginal passage leading from the oviduct into a tiny sac, the spermatheca (spt), which opens into fertilization chamber. When two indi- viduals copulate, the transference of the sperms is mutual. The everted penis of one enters the oviduct of the other; the ampulla of the hermaphrodite duct by its contraction drives the sperms through the vaginal passage into the spermatheca where they are stored for a time after the copulating individuals separate. Later when the eggs enter the fertili- zation chamber, the sperms received from another individual and stored in the spermatheca also reach the place and fertilization takes place. The ferti- lized eggs enter the mucoalbuminous gland where they are surrounded by albumin and enclosed in membranous capsules; generally each capsule has one egg and very rarely two eggs. Finally in the act of spawning, they leave through the oviduct and the genital orifice with a copious amount of mucus.

Oviposition and Early Development When the animals were kept under observation in the laboratory, copulation and deposition of spawn took place only during the night-time. The thread- 18 like spawn with two linear sereies of eggs enclosed in mucus was deposited in a flat spiral having 2t to ft 4 coils (Fig. 15). In those examined the diameter Op of the entire spawn varied from 4 to 11 mm. The largest of the spawn string had a length of 9 em with ~"~~~t#.lt .1 a width of about 0·5 mm .. The spawn string was not attached to the substratum by its entire length, but only at spaces of short intervals with the result that the string between successive places of attachment formed loops remaining free. The 100.,.u eggs were yolk-laden and pale yellow, the almost spherical yolky part measuring about 80 [.L and the enclosing capsule from 135 to 165 [.L in its long axis (Fig. 16). The formation of the polar bodies, the Figs. 13 to 18 - Caloria militaris [Fig. 13: Dorsal aspect of the central nervous svstem. Fig. 14: Ventral view of nervous l st, 2nd, and 3rd spiral cleavages took place in rapid system showing the' statocyst. Fig. 15: Spawn deposited succession as observed in F avorinus argentimaculatus': on oyster shell. Fig. 16: Enlarged VIEW of spawn string. and the blastula stage appeared at the end of 12 hr Figs. 17 and 18: Two views 01 the veliger larva] after oviposition. Gastrulation by epiboly was com- pleted by 36 hr and this was followed by the closure of the blastopore and the appearance of shell gland, oval statocyst (Fig. 14, st.c) with a large number primordia of the velar lobes and the foot. The embryo of nearly 50 statoliths. exhibited slow movement within the capsule with From about the hind region of the stomach to the the help of cilia of the last two structures. In 50 very posterior end, the body space is occupied ~y to 60 hr, the early veliger stage was reached, having the reproductive organs. The hermaphrodite a cup-shaped shell, small velar lobes, foot, midgut, follicles (Figs. 11 and 12, hgl) of which there is a stomodaeum, proctodaeum, the right and left diges- large number are packed compact, pressed close to tive gland lobes and a pair of statocysts. one another, each follicle showing a large central The fully developed veliger (Figs. 17 and 18) male acinus and several small peripheral female formed at about 80 hr after spawning had a acini. Small ductules from the follicles join in a measurement of 170 [.L in its long axis. The spiral median hermaphrodite duct which distally enlarges shell (sh) was ovate and provided with an operculum into a twisted, elongate saccular ampulla (Fig. 11, (op) to close the aperture when the soft parts were am.hgl), dividing into the male and female portions drawn in. Thevelarlobes (ve) were large and rounded in a complex mass of anterior genital organs. In bearing powerful, stout, long cilia beating rhythmi- the former there is a slender long vas deferens, which cally bringing about the characteristic jerking move- is proximally connected with a small much lobed ments. Ventral to the velar lobes was the tongue- prostate gland (Fig. 11, pr.g) and distally lead~ into shaped foot (ft) bearing delicate cilia and placed a muscular, conical, protrusible unarmed penis ~n- over the operculum. The mouth opening between closed in a penial pouch opening into the gen~tal the velar lobes and the foot was found lead- orifice. The latter, viz. the female portion, consists ing into the narrow oesophagus which communicated mainly of a small fertilization chamber, a large, with an enlarged stomach (st), the inner wall lobed mucoalbuminous gland (Fig. 11, mu.gl) and of which was ciliated. It was followed by a narrow a short wide oviduct, the last of which opens into intestine (int) running forwards and opening dorso-

35 INDIAN J. MAR. SCI., VOL. 2. JUNE 1973 laterally to the right of the median line by the anus clusters, foot with much produced anterior angles, into the space. The two digestive gland denticulate jaw plates and uniseriate radula. It lobes, i.e. the larger left lobe (It.I) and the smaller has scarlet lines one on each side of the body, run- right lobe (rt.1), communicated with the stomach. ning lengthwise, similar lines on the oral tentacles Situated on the right side, close to the anus was an and a distinct patch of the same colour dorso- excretory organ (ex.o) or the kidney opening into the medianally between the oral tentacles. The cerata mantle space, the corresponding one of the left side are numerous, in 6 paired clusters, moderately stout also opening in a similar manner into the mantle and of reddish brown colour with bright yellow tips. space. There was a pair of statocysts (st.c), each It is not known whether the type species had the containing a single statolith, at about the base of penial armature. the velar lobes, one on either side. The retractor Specimens from the Gulf of Mannar, viz. Pamban muscles of the velar lobes and the foot were present and Shingle Island, have been stated to be whitish as in other species of opisthobranch larvae. The with red lateral lines and dark blue cerata faintly were not liberated from the capsules tinged red below the apices-". The arrangement till about 90 to 100 hr after spawning. The larvae of the cerata in them is in 6 paired clusters. were blind without the pigmented eyes characteristic Those reported from the Gulf of Kutch- have the of those of some of the aeolid species. The veliger same general colour pattern as in the type species larvae remained alive in the finger bowls for about from the Lawson's Bay. However, the cerata 4 days without any further development. clusters are in 6 to 7 paired groups with brick-red colouration having the digestive gland light black Discussion and the tips yellowish. Some points of taxonomic interest deserve special Specimens from Goa reported here have shown mention here. Caloria belongs to the family Faci- the cerata groups in a maximum number of 9 pairs. linidae under the cleioproctic, eolidacean The orange-red colour lines along the sides of the molluscs of the subclass of the body and other markings conform in a general way class . The facelinid characters have to those reported in the type species. The speci- been briefly stated in the introductory account of mens from this region and those from the Gulf of this paper. In some of the members, the penis is Kutch have revealed no penial armature. In the armed as in the F acelina. The system of present report cerata have been observed to be of classification which is generally accepted and moderate length in preserved material or in those followed here is that of Odhner+ with slight modifi- kept alive under laboratory conditions for some time. cation suggested by Taylor and Soh16 and adapted In fresh specimens they have often been observed to by Hyman", However, Miller" is against acceptance be linear and very much elongate; the general coloura- of the subdivisions under Eolidacea on the basis of tion of the cerata has been found to be variable as shifting anal positions into Pleuroprocta (with anus reported in detail in the preceding account. It may in its primitive lateral position), Acleiprocta (anus be concluded that there are no distinctive features dorsally between the right and left anterior diverti- demarcating specimens from different localities; cula of the digestive glands) and Cleioprocta (anus the general arrangement of the cerata and the colour laterally on the right side between the digestive pattern fundamentally remain the same, although gland branches of the posterior diverticulum enter- individual variations occur in a wide range. ing the clusters of the cerata). It is not doubted In the alimentary system, the special features in that shifting anal positions in the members indicate this species are the numerous buccal glands pouring certain evolutionary trends in the Eolidacea, but their secretions into the oral tube, the long salivary he finds that such grouping cuts through instead glands leading by their slender ducts opening on the of separating some of the families which exhibit more roof of the buccal cavity, the denticulate jaws, the than one type of anal positions. uniseriate radula and the cleioproctic anus. With The species named Eolis militaris was founded reference to their type species, the only difference by Alder and Hancock! on an examination of a few between Caloria Trinchese and Bergh is specimens collected from Lawson's Bay, Waltair, in the shape of the jaws, dorsally indented in the on the east coast of India. Burn and Narayanan" former and rounded in the latter, a distinction which have shown that Learchis indica of Bergh" first ob- is not considered significant enough for their separa- tained from Amboina in Molluccas and later reported tion at generic level". The position of the cleio- under the same name from Japan and Hawaii!" is proctic anus in C. militaris in the middle of the second synonymous with E. militaris Alder & Hancock', cluster of cerata of the right side is characteristic They have also pointed out that the generic name of the family Facilinidae as contrasted with the Learchis Bergh being preoccupied by Caloria of position of the same either immediately behind the Trinchese 1888, it is necessary to rename the species second cluster of cerata or farther posteriorly on E. militaris Alder & Hancock (= Learchis indica the right side as obtained in the family Eolidiidae". Bergh) as Caloria militaris (Alder & Hancock). The central nervous system with the main The other synonyms of this species are Hervia ganglia, the associated sensory structures, viz. the militarisll-14 occurring on the Indian coasts: Aeolidia eyes and statocysts, the organs of blood circulation dangeri and H ervia dangeri15,l6 from New Caledonia; and those of renal secretion are in this species and Learchis howensisl7 from the Lord Howe Island. typical of the other eolid members. It may thus be seen that the species is widely distri- In the manner of arrangement of the reproductive buted in the Indian and the Pacific . organs the present species shows some special The type species from Lawson's Bay! is charac- features. Apart from the absence of the penial terized by the presence of long, stout and terminally armature reported by Burn and Narayanan-, these tapering oral tentacles, smooth but slightly centrally organs, so far as the authors are aware, have not swollen rhinophores, branchial papillae in paired been described earlier and hence an attempt is made

36 RAO & KUMARI: STRUCTURE & EARLY DEVELOPMENT OF C. MILITARIS to give a detailed account of them. The main her- ment. They are also thankful to Dr V. D. Rama- maphrodite duct or the gonoduct enlarges into a murthy and Shri S. K. Onkar for some of the convoluted spacious ampulla which serves as the specimens collected. seminal vesicle and the prostrate is a distinct much lobed gland connected to the proximal part of the References vas deferens. In contrast to these structures in 1. ALDER, J. & HANCOCK, A., Trans. zool. Soc. Lond., 5 Cuthona (= Cratena) adyarensis the seminal vesicle (1866), 144. is a fusiform appendage to the main hermaphrodite 2. BURN, R. & NARAYANAN, K. R., J. malac, Soc. Aust., duct and the prostrate is only a much enlarged 2 (1970), 83. 3. RAO, K. VIRABHADRA, J.zool. Soc. India, 3 (1952), 229. glandular part of the vas deferens continued by 4. RAO, K. VIRABHADRA, Proceedings, Symposium on Mol- the ejaculatory duct leading to the armed penis", lusca, Vol. 3 (Marine Biological Association of India), The spawn in the form of a fiat spiral is charac- 1969, 1009. 5. ODHNER, N. H., K. norske. Vidensk. Selsk., SM., 1 (1939), teristic of most of the eolidacean species of nudi- . 1. branch molluscs but its special feature lies in its 6. TAYLOR, D. & SOHL, N., Malacologia, 1 (1962}, l. attachment to the substratum at intervals, forming 7. HYMAN, L. H., The , Vol. 6 (McGraw-Hill free loops in the in-between spaces. The early Book Co. Inc., New York), 1967, 503. development followsthe same lines as in most other 8. MILLER, M. C., Zool. J. Linn. Soc., 50 (1971), 311. opisthobranch molluscs, but the veligers when 9. BERGH, R., Revue suisse Zool., 4 (1896), 386. 10. BABA, K., Pubis Seto mar. bioi. Lab., 16 (1969), 399. hatched are blind and their rather short ovoid shells 11. FARRAN, G., Report to the Govt of Ceylon on the are smooth on the surface without any . oyster fisheries of the Gulf of Manaar, 3 (1905), 331. 12. O'DONOGHUE, C., Proc. malac, Soc. Lond., 20 (1932), Acknowledgement 141. 13. SATYAMURTHI, S. T., Bull Madras Govt. Mus. N.S. The authors express their gratitude to the Council (Nat. Hist.), I (1952), 250. of Scientific & Industrial Research, New Delhi, for 14. NARAYANAN, K. R., Proceedings, Symposium on , the sanction of grant-in-aid which enabled them to Vol. 1 (Ma.rine Biological Association of India), 1969, <:arry out the present investigation. They express 211. 15. RISBEC, J., Faune Colon., tr.. 2 (1928), 252. their deep indebtedness to Dr N. K. Panikkar, 16. RISBEC, J., Faune u«. Ir-, 15 (1953), 136. Director, for providing facilities and for encourage- t 7. BURN, R., J. malac, Soc. A usl., 10 (t 966), 25.

37