Structure & Early Development of an Opisthobranch Mollusc, Caloria
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Indian Journal of Marine Sciences Vol. 2, June 1973,pp. 32-37 Structure & Early Development of an Opisthobranch Mollusc, Caloria 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 cerata 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 veliger larva is blind when hatched and the shell is smooth On the surface, spirally ovate and bears an operculum. 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 animals in tentacular processes in the anterior region of the the collection. foot, smooth rhinophores, 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 rhinophore 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 anatomy. 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 animal. 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, cnidosac 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 aperture (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.