Brachiopod Larvae from the West Coast of India 61

BRACHIOPOD LARVAE FROM THi~ WEST COAST OF INDIA

BY D. SUDARSAN * (Zoological Survey of India, Calcutta) Received February 27, 1968 (Communicated by Dr. R. Raghu Prasad, F.^.sc.)

ABSTRACT The collection of brachiopod larvae from the Arabian Sea off Karwar was found to consist of three different types belonging to Discinisca sp., Pelagodiscus atlanticus (King) and Lingula sp. The larvae designated as those of Discinisca sp. are very characteristic in having two pairs of long, straight, stiff and brittle spines and are perhaps being described for the first time. Developmental stages of P. atlanticus, younger than so far known, are represented in this collection. The third and the most nume- rous type belongs to a species of Lingula. The probable significance of the time of origin of the peduncle and the attainment of the linear shape in Lingula sp. is discussed. Notes on the breeding seasons of the latter two types are also added.

INTRODUCTION DESPITE the importance of tile study of the developmental stages of braehio- pods from the point of view of the taxonomy of the group as pointed out by RoweU (1960), sufficient attention has not been given to this field of investigation. During a survey tour to the Mysore coast on the western Indian seaboard in January, 1967, a good number of braehiopod larvae were obtained from the plankton samples collected from the Arabian Sea off Kaxwar. This has presented an opportunity to make a systematic study of these larvae. Of the three types of larvae obtained, two are assigned to Pelagodiscus atlanticus (King) and Lingula sp. and the last one which is hitherto un- described perhaps belongs to a species of Discini~ca. Young stages of P. atlanticus not known so far are among the larvae obtained. In view of the

* Present Addrees : OffshoreFishing Station, Government of India, Visakhapatnam-l, Andhra Pradesh. B1 59 60 D. SUDARSAN limited knowledge of the development in the brachiopod genera as a whole and those of the Inarticulata in particular arty additional information on the subject is of special interest.

Reports on the larvae even from the Indian Ocean area as a whole have been very rare and they have been listed by Muir-Wood (1959). Sewell (1912) examined larvae of Lingula sp. collected four miles off the mouth of the Hinze-Basin (Burma). Ashworth (1915) made a detailed study of Lingula and Pelagodiscus larvae, the former from the southern palt 6f the Red Sea and south of Ceylon and the latter off Cape Comorin (India). Helmcke (1940) recorded larvae of Pelagodiscus atlanticus and Lingula from the Vddivia material.

MATERIAL The plankton was collected by horizontal hauls with a ½ metre diameter bolting silk coarse net from three different stations south-west of Karwar. The plan_kton was preserved in sea-water formalin immediately after collection and the larvae sorted out later. The larvae were then cleared in gly- cerine and studied. Due to the fairly long preservation (almost three months) the study of the internal organs presented considerable difficulty. In all, 465 specimens were studied. The details of the plankton hauls and the number of each type obtained are given in Table I.

TABLE I

Number of larvae obtained Date Area of collection New P. Lin- discinid atlan- gula Total larva ticus sp.

16-1-1967 10 miles S.-W. of Karwar* 4 15 186 205 17-1-1967 9 miles S.-W. of Karwar 16 14 221 251 18-1-1567 6 miles S.-W. of Karwar 1 1 7 9

TOTAL .. 21 30 414 465

* Karwar lies on 14° 49' N. and 74° 22' E. Brachiopod Larvae from the West Coast of India 61

OBSERVATIONS

1. A New Discinid Larva Twenty-one specimens of the larvae were examined. It has the general dish-like shape of the discinid larvae. The shell valves, of which the ventral is slightly smaller and relatively flat, are transversely elliptical and translu- cent. The watch-glass-shaped dorsal valve has a medial raised portion towa:d the posterior end. The body of the larva is light yellow in colour at the region of the mantle edge, the rest of it being brownish. The larva (Figs. 1 A and 1 B) is characterised by two pairs of long, straight, stiff, hrittle and fiuely pointed spines directed posterolaterally and attaining a length of about thrice the width of the dorsal shell valve. The length of the specimens along the anterior-posterior axis varied from 253 tz to 311tz and the breadth from 301 t~ to 370/* while the length of the spines from 730 t~ to 1,002 t~.

T E~

FIG. 1 A-D. A &B. Larvae of Disciniscasp. C. Principal chaetao enlarged (not to ~,ale) to show the spines. D. A portion of the long spine enlarged (not to ~cale) to show the spinules. 62 D. SUDARSAN

All the larvae are in the 4 pair cirri (p.e.) stage with one to three posteriorly directed chaetae. In the smaller larvae only one pair of ~he latter is seen. This is the first pair of principal chaetae with fine spines along its inner edge. In the older larvae (Fig. 1 B) which are larger, the second and third (of which the former is slender) pairs of chaetae make their appearance. These do not bear any spines. The long spines originate from a fold just to the side of the main body on either side. These spines appear to be movable, along the lateral plane, as they are found at different angles to the body of the animal. They may, besides acting as a floatation mechanism, function as rudders during the movement of the larvae. The long spines carry rows of extremely minute and pointed spinules as shown in Fig. 1 D. These spinules are visible only under very high magnification and are present from a short distance from the outside edge of the shell to almost the tip. The frontal tentacle is quite prominent and a little behind on the ventral side is the epistome and the mouth. There are two otocysts one on either side of the stomach. The only other larva with long spines or setae ever recorded was the single specimen described by Simroth (1897). This larva had one bundle of extraordinarily fine, hair-like and simple setae on either side of the gastric pouch. The right bundle had four and the left three setae. These, however, were not of equal length, the second being the longest and the fourth (third on the left side) being the shortest. The longest seta was six times as long as the gross diameter of the shell. Simroth's (l.c.) specimen further differs from the present form in having just three pairs of cirri all of which were nearly of the same thickness and length in contrast to the general rule in other known brachiopod larvae where the length of the cirri increases from anterior to posterior. A discussion on this aspect is made at a later stage in the paper. On the basis of the geneIal shape and structure of the larva it is assigned to the family Discinidae. Only one discinid, i.e., Discinisca indica Dall is known from the west coast of India (Dall, 1921). This larva described here may belong to the same or allied species of the genus Discinisea.

2. Pelagodiseus atlanticus (King) Thirty larvae of Pelagodiscus atlanticus were found in the collection. The larvae exhibited marked differences in the characters, at first suggesting that they may belong to two or three different types but on .a closer examina- tion ot the features coupled with a morphometric study, it was apparent that Brachiopod Larvae from the West Coast of India 63 the variations are due to the fact that the larval characters like ehaetae were still under formation. The largest specimens (Fig. 2 D) correspond remark- ably with the excellent description of the larvae of P. atlanticus given by Ashworth (1915). The following observations deal with the growth of the larva, the order of development of the chaetae and the stage at which the peduncle makes its appearance. As in the case of Lingula there appears to be a tendency for the transfor- mation of the shape of the shell from the broad to the linear form. in the younger larvae the body is considerably broader than long. From this stage onward differential growth in favour of a linear shape appears to set in and ultimately the larvae may attain the linear form before settling down. This trend is evident when the morphometric measurements presented in Table II are studied. TABLE II Showing the morphometric measurements of the larvae of P. atlanticus

S1. Breadth Length Formation of No. in O.D.* in O.D.* characters

1 39 34.0 2 39 34.0 3 40 34" 5 Bulbous expansion of first principal ehaetae 4 40 34.5 5 43 38.0 Rudiments of peduncle and third pair of principal chaetae 6 43 38.0 7 43 38.5 8 43 38,5 9 43 38.5 10 43 39.0 11 43 39.0 12 43 39.5 Rudiments of fourth pair of principal chaetae 13 43 39-5 14 43 39.5 15 43 40.0 16 43 40.0 17 43.5 40.5) 18 44 41.0 /-/ Fifth pair of principal chaetae and laterally direc- 19 44 41.5 I ted slender chaetae 20 45 42.5 j

* O.D. (one Ocular Division) = 9.727 p, 64 D. SUDARSAN

In the smaller larvae only three pairs of chaetae, i.e., the first and second principal and one pair of slender chaetae are present. All of these are directed posteriorly. There is no bulbous expansion of the first pair of principal ehaetae near the proximal end, but the minute spines are clearly seen. In slightly larger larvae, the first pair of principal chaetae have developed the bulbous expansion and the rudiments of the third pair of principal chaetae and the peduncle are visible. In still larger forms the fourth pair of principal ehaetae make their appearance and the third pair and the peduncular base are more prominent. The fifth pair of chaetae and the laterally directed slender chaetae are seen only in the largest specimens in the collection.

FB. 2 A-D. Different larval stages of Pelagodiscus atlanticus. D. Only a few slender chaetae are shown.

The fact that the larvae of Pelagodiscus as well as of other discinids have nearly always been found to be in the 4 p.o. stage with the exception of a single specimen with five pairs obtained by Yamada (1956) and the one with three pairs described by Simroth (1897), has always been and still remains a puzzle. Ashworth suggests that the attachment of these larvae takes place at about the 4 p.e. stage or not long after that. Though all the larvae in the Brachiopod Larvae from the West Coast of India 65

collection being reported upon in this paper are also in the 4 p.c. stage it should be pointed out that they represent earlier stages than reported previously. Just as Simroth felt to be the case in his larva of Diseinisea sp. with 3 pairs of cirri, there may be a prolonged larval phase in the present case also during which no more cirri are formed. The larval growth may only be in size with the chaetae increasing in number to facilitate floatation during this prolonged larval phase. The same may be the case in Diseinisea sp. described earlier in this paper. Miiller (1861) suggested that the younger stages may be retained in the shell of the parent. Ashworth, however, does not agree with this contention but says that the younger stages live on or at the bottom. With the existing knowledge about these larvae it is not possible either to support or reject these two views. Breeding.--Reeords of the larvae of this cosmopolitan species have been made from different parts of the oceans during different seasons of the year. Ashworth obtained his specimens off Cape Comorin during October 1914. The present material, it may be recalled, was obtained in mid January. On the west coast of India this species appears to be spawning during the post- monsoon period with a considerably protracted spawning season.

3. Lingula sp. This is the most abundant type in the collection, there being 414 specimens varying from the youngest stage with the fourth pair of cirri under formation to the oldest where seven pairs have fully formed. The larvae exactly resemble the larvae of Lingula anatina of Yatsu (1902) in almost all the details but differ from those of Sewell (1912) and Ashworth (1915) in the stage at which the peduncle makes its appearance and the larva attains a linear shape. In the present lot the peduncular rudiment is seen at the 6 or 7 p.c. stage just as in the case of Lingula anatina (Yatsu, 1902). In Sewell's specimens taken in December the peduncle begins to develop at the 9 p.o. stage, but in the larva obtained in February only at the 14 p.o. stage. In Ashworth's material it makes its appearance at the 11 p.o. stage. The change over to the linear shape of the shell takes place at 7 or 8, 9 (and 14 in the February specimen) and 11 p.o. stages in the larvae of Yatsu, Sewell and Ashworth respectively. In the Karwar material the largest specimens (7 p.c. stage) aie nearly as long as broad. From a critical examina- tion it can easily be seen that there is a correlation between the formation of the peduncle and the attainment of the linear shape which follows the 66 D. SUDARSAN former. It is probable that the difference in the stages at which these pheno- mena occur varies ill the different species of Lingula and is of stystematic significance. The youngest larva (174t,/308t~)in the Karwar collection (Fig. 3A) is smaller than the youngest (protegulum stage) planktonic larva obtained by Yatsu; but from the developmental point of view, it is slightly more advanced in that it has the fourtb pair of cirri under formation.

i,--, O Jr I'~ +: B

FIG. 3 A-B. Larvae of Lingula sp. B.E., Bulbous expansion; C, Cirri; CH, Chaetae; E, Epistome; H, Hinge; M, Mouth; M.E., Mantle edge; O.C., Otocyst; O.M., Oeclusor muscle; P, Peduncle; P.D., Dorsal protegulum; P.V., Ventral protegulum; S, Spine; S. Ch., Slender chaetae; S.M., Shell margin; Sp., Sl~inule; T, Tentacle.

Breeding.--Sewell, based on his material from Burma, inferred that Lingula has two breeding seasons, one in summer and the other in winter. Awati and Kshirsagar (1957) who studied Lingula from the northern part of the west coast of India observed that the breeding season of this genus is restricted to July-August and indicated that 'the spawning may be induced by the unusual admixture of the freshwater brought down by the neigh- bouring streams and thus causing abnormal conditions'. Further they added that no female specimens have fully developed ova during the winter months. While the data at hand are not adequate to connect the present larvae to any particular species it is most likely that they belong to a species other than the one studied by Awati and Kshirsagar. The genus Lingula does breed during the winter months also on the west coast of India. Ramamurthy (1965) recorded brachiopod larvae in the Karwar plankton from January to ffuly 1955 indicating that they as a group have a protracted spawning season, Brachiopod Larvae from the West Coast of India 67

Ashworth has pointed out that in the Red Sea Lingula may have succession of spawnings from March to September.

GENERAL REMARKS

Information on the Brachiopoda, occurring along the coasts of India, is extremely inadequate. Apart from the scanty references to their occurrence as a group no systematic account is available. The only work of real value from India is the monographic treatment of Lingula (anatina ?) by Awati and Kshirsagar (1957). DaU (1921) described Discinisca indica from Bombay and Ceylon. Besides, Qureschi and Hashmi (1963) recorded four species of Lingula from Karachi. To understand the real significance of the difference in the larval features and their usefulness in the taxonomy of the group, more knowledge about the adults occurring in the Indian waters is essential. The availability of the different types of larvae off Karawar indicates the richness of the brachiopod fauna along the Mysore coast and an inten- sive survey of the benthos of this area will probably throw much light on the group.

SUMMARY Three different types of brachiopod larvae belonging to the class Inarti- culata obtained from the Arabian Sea off Karwar on the west coast of India are dealt with. Of these, the one characterised by two pairs of long, straight, stiff and brittle spines has not been described hitherto and this is provisionally assigned to the genus Discinisca. Younger stages of Pelagodiscus atlanticus (King) which have not been known earlier are also described. The third type belongs to a species of Lingula. Notes on the breeding seasons of the latter two forms and comments on the significance of the time of origin of the peduncle and the attainment of the linear shape in the last type are added.

ACKNOWLEDGEMENTS

I wish to express my thanks to Dr. A. P. Kapur, Director, Zoological Survey of India, for the facilities provided for carrying out this work and to Dr. B. S. Chauhan and Dr. A. K. Dutta for their interest and encourage- ment. My thanks are also due to Dr. A. N. P. Ummerkutty under whose leadership the survey was conducted.

REFERENCES

Ashworth~ J. H, .. "On the larvae of Lingula and Pelagodiscus (Discinisca)~" Trans. R. Soc. Edinb., 1915, 51, 45-69. 68 D. SUDARSAN

Awati, P. R. and Kshirsagar, "'Lingula from the western coast of India," Zool. gem. Univ. G.R. Bombay, 1957, No. 4. Dall, W. H. .. "Annotated list of the recent Braohiopoda in the collections of the U.S. National Museum," Prec. U.S. ham. Mus., 1921, ST, 261-377. Helmcke, 1. G. .. "Die I/a'achiopoden tier Deutschen Tiefsce Expedition," Wiss. Ergeb. dr. Tiefsee. Exped. Valdivia, Jena, 1899-99, 1940, 24, 217-316. Muir-Wood, H.M. .. "Report on the Brachiopoda of the John Murray Expedition," John Murray Expedition Scientific Reports, 1959, 10, 283-317. Miillcr, F. .. "Die Brachiopodonlarve yon 'Santa Catharina'," Arch. Natur- gesch., 1861, 27, Bd. 1, 53-56. * Quroschi, F. and Hashmi, S. S. "Taxonomic 'study of Brachiopoda of Karachi coast," Agri- culture Pakist., 1963, 14, 329--37. Ramamurthy, S. .. "Studies on the plankton of the North Kanara coast in rela- tion to the pelagic fishery," J. Mar. biol. Ass. India, 1965, 7, 127-49. Rowell, A. J. .. "Some early stages in the development of the Brachiopod Crania anomala (Miiller)," Ann. Mag. nat. Hist., 1960, 3 (13), 35-52. Sewoll, R.-B. S. .. "Note on the development of the larva of Lingula," Rec. Indian Mus., 1912, 7, 88-90. Simroth, H. .. "Die l?xachiopoden dcr plankton Expedition," Ergebnis~e du plankton Expedition, 1897, Bd. 2, 1-I7. Yamada, M. .. "Notes on discinid larvae from Osyoro west coast of Hokkaido," Annotnes Zool. Jap., 1956, 29, 165-67. Yatsu, N. • . "On the development of Lingula anatina," J. Coll. sci. imp. univ. Tokyo, 1902, 17, Art. 4, 1-112. * Not referred to in original.