J. Mar. Biol. Ass. India, 48 (I) : 6 - 13, January - June 2006

The of plicatilis species complex (Rotifera: ) from the Southern Kerala (India) with a note on their repro- ductive preferences

P. S Anitha and Rani Mary George Central Marine Fisheries Research Institute, P. B. No. 1603, Ernakulam North P. O., Cochin-682 018, India E. mail: [email protected] Abstract This paper deals with the species of Brackionu.s plicatilis complex (Rotifera: Monogononta) found in a brackishwater lake,Veli-Aakulam, in Southern Kerala. Morphological and reproductive potential studies revealed that these have sigiificant morphological distinction with regard to ecological preferences. The three related rotifers in our study were classified as Brachionu.~plicatilis Miiller, 1786, B. rotundifi)rmi.s Tschugunoff, 1921 and B. murrayi Fadeew, 1925. The fine morphology and morphometric data revealed that taxonomic characters were constant enough to recognize three well-defined morphologies and B. rrlurrayi is redescribed. The reproductive potential studies in relation to ecological parameters showed that the 'r' values of these rotifers were significantly influenced by salinity as well as temperature, and was species specific. In the light of reproductive preferences, the reorganization of three distinct species has been confirmed by this study and this would allow further comparative work in these lines on this economically important species complex. Keywords: Brachionus plicatilis species complex, reproductive preferences

Introduction Among brachionid rotifers, Brachionus plicatilis The occurrence of B. plicatilis in Indian waters was Miiller, 1786 (Monogononta) is probably one of the best- noted by a few numbers of workers (Rao and Mohan, studied taxa because of its suitability as an initial live feed 1984; Shakuntala and Singh, 1993; Gopakumar and for various finfish and shellfish larvae (Lubzens, 1987). Jayaprakash, 2003) whereas the halobiont B. In B. plicatilis, the size and shape of lorica vary greatly rotundiformis (= B. plicatilis 'S' type) has been reported according to the strain (Snell and Canillo, 1984). Because so far only from the estuaries and backwaters of Kerala of the morphological and physiological differences be- (Gopakumar and Jayaprakash, 2003; Molly, 2003). De- tween the strains of this species, several comparative spite this body of evidence the taxonomy of this species studies have been carried out by a number of workers complex has not been established in India. So here, we (Fu et al., 1991a & b; Hagiwara et al., 1995). These present a morphological analysis of three well-defined studies have revealed that B. plicatilis is not a single rotifers belonging to the B. plicatilis complex from Kerala species but a complex of at least two morphologically with a remark on their reproductive rate ('r') to show the recognizable taxa, the so-called 'L' (large) and 'S' (small) ecological preference of these taxa in their natural habitat. types. On the basis of this evidence, Segers (1995) re- Similarly, the maximum lorica size attained by a female examined the existing available names and proposed that rotifer over her life span (from neonate to adult size) was B. plicatilis Miiller, 1786 and B. rotundiformis also recorded for the morphometric data comparison be- Tschugunoff, 1921 were correct names for the 'L' and tween the species. 'S' ty&s respectively. Since then, those names have been Materials and methods applied to several strains from all over the world. How- el&, recent data (Ciros-Perez et al., 2001) from the Spain Fortnightly zooplankton collections were made from waters revealed that the complex is in fact composed of Veli-Aakulam Lake (Lat. 8"25'-S035'N; Long. 7650'- three biological species instead of two and these were 7@58'E) during February 2000 to January 2001 to ex- named as B. plicatilis, B. rotundiformis and B. ibericus amine the morph variations in rotifers. The surface plank- (=B. rotundiforrnis SM type). ton samples were collected by horizontal hauls using

Joltrnal of the Marine Biological Association of India (2006) Taxononzy of three species of rotifers 7

plankton net of 32cm mouth diameter with a mesh size newly hatched neonates were measured and removed after of 70pm and immediately preserved in 4% formaldehyde. each observation. These experiments were conducted in Specimens were sorted and examined using a stereo- order to ascertain the identity of these species complex dissecting microscope. All the illustrations given are with ecomorphs, as there is so much confusion to delin- Camera-Lucida drawings made with the aid of a com- eate the species properly. pound microscope. Standard references (Sudzuki, 1987, Results 1995, 1996, 1999; Fu et al., 1991a; Ciros-Perez et al., 2001) were consulted for the identification and classifica- Taxonomic placement: Phylum: ROTIFERA (Cuvier) tion of rotifers. Class: MONOGONONTA Wesenberg-Lund For experimental studies, three morphologically dis- Order: (Hudson & Gosse) tinct females of B. plicatilis were isolated from the Veli- Aakulam waters. They were classified as B. plicarilis, B. Family: Ehrenberg rotrcndiformis and B. mlcrrayi based on the key given by Sudzuki (1999). Each species was cloned from a single Genus: Brachionus Pallas parthenogenetic female and the stock culture was main- Type: Brachionus urceolaris Muller tained in the laboratory by feeding them with Isochrysis galbana @ lmillion cells per ml. The culture temperature Key to the species of plicatilis group and salinity was 28'C and 10 x lo-' respectively for each 1. Lorica ovoid to elliptical; occipital spines saw-teethed; clone. A factorial experimental design was used to inves- broad based; pectoral margin four tigate the effect of temperature and salinity on the repro- lobed...... plicatilis Muller, 1786 ductive potential of these . Females of three spe- cies were first allowed to grow exponentially for six days Lorica, occipital spines and pectoral margin are not in the pre-experimental conditions. Five ovigerous (fe- as above...... 2 males with single egg stage) females from each type were . 2. Lorica vase-shaped; occipital spines small based; isolated and then introduced into lOml test tubes contain- elevated lateral pectoral projections ...... ing 5ml of I. galbana @ 1 million cells per ml at three ...... rotundiformi Tschugunoff, 1921 temperatures (25, 28 & 35°C). 6 salinities and 1000 lux constant light. The salinity levels chosen for B. plicatilis Lorica not as above; inter-medians comparatively and B. murrayi were 0.5 x lo", 5 x10-', 10 x10-', 15 x short; pectoral margin four lobed with lo-', 25 x I@' & 35 x lo-' and those chosen for variations...... murrayi Fadeew, 1925 B. rotundiformis were 2 x 10". 5 XI@" 10 XI@', 15 x Brachionus plicatilis Muller, 1786 (Figs. 2 - 10) 10". 25 x 10" & 35 x 10". The salinity levels were chosen according to the tolerance ranges of the organisms Brachionus plicafilis Miiller, 1786, p. 344, pl. L, studied. After three days, the number of females per tube Fig. 1 was counted, and 'r' value was calculated according to the Brachionus miilleri Ehrenberg, 1838, pl. LXIII, formula: r = (In Nt - In No) / t; where, Nt = number of Fig. V females after 't' days; No = initial number of females, t = duration of experiment (3 days). The size at birth and Brachionus hepatotomus Gosse, 185 1, p. 203 maximum size of a female over her life span was also Material: Several parthenogenetic females from Veli- examined. For this, a large number of egg canying fe- Aakulam Lake males were randomly selected from the acclimatized stock and checked at 15 minutes intervals to collect neonates. Measurements: Total lorica length 171-277pm; maxi- After that, twelve neonates of each type were isolated mum width of lorica 156-225pm; anterior lorica width103- singly into small test tubes containing Iml of I. galbana 156pm; distance from lateral spine to median spine 33.4- @ 1 million cells per ml and at six salinity levels as 68.8pm; median sinus gape 12-22pm; antero-median spine mentioned above. The experiments were carried out at length 20-43pm; antero-intermediate spine length 9-34pm; room temperature based on the best performance of each antero-lateral spine length 15-30pm; maximum width - taxon in the previous reproductive potential trials. The total length ratio 0.81-0.91; anterior width - maximum animals in the test tubes were observed at regular intervals width ratio 0.67-0.69; egg size 98 x 87pm (L x W)

Journal of the Marine Biological Assoriation of India (2006) 8 P. S. Anitha and Rany Mary George

with six broad-based saw-toothed spines, nearly equal in Reproductive rate: B. rotundiformis recorded its high- length; pectoral margin rigid, separated into four lobes est 'r' value of 1.83 at the best salinity of 15 x le3and with distinct variations; lorica without posterior spines; at 28°C (Fig. 1). The size at birth and maximum adult size smooth or lightly stippled; foot opening with small of this taxon was recorded as 98 pm and 176 pm respec- subsquare aperture ventrally. tively at the best salinity of 15 x 10-"Table 2). A number of morphs were observed in the plankton Brachionus murrayi Fadeew, 1925 samples as well as in the clones maintained in the labo- (Figs. 17-25) ratory at different culture conditions. The most frequently observed morphs are j miilleri Ehrenberg (Fig. 3), J Brachionus miilleri Murray, 19 13, p. 499-45 1, Figs. hepatotomus Gosse (Fin.- 4a-b),- -f: decemcornis Fadeew 47a-c (Figs. 7-8),J ovalis f. nov. (Figs.9-10). The significant Brachionus miilleri var. murray Fadeew, 1925, diagnostic features of these eco-morphs are given in p. 22, pl. IV, Figs. 4 - 5 Table 1. Brachionus rotundiformis murrayi Sudzuki, 1987, Reproductive rate: The highest 'r' value of 1.47 for B. p. 46, Fig.l.3 plicatilis was recorded at a salinity of 5 x and at temperature of 28°C. Above or below this level, the 'r' Material: Several parthenogenetic females from Veli- values showed a decreasing trend irrespective of tempera- Aakulam. ture (Fig. 1). Similarly, at birth, B. plicatilis females Measurements: Total length of lorica 150-213pm; ranged from 146- 15 1pm and they attained a maximum maximum width of lorica 1 16-144~;anterior lorica width adult size of 257-269pm at a salinity of 5 x lo-' 88-108pm; distance from median to lateral spine 38- (Table 2) 67pm; median sinus gape 22-36pm; antero-median spine Brachionus rotundiformk Tschugunoff, 1 92 1 length 22-36~;antero-intermediate spine length 1 1-18p.m; antero-lateral spine length 13-22pm; maximum width- (Figs.] 1-16) total length ratio 0.67-0.77; anterior width- maximum Brachionus miilleri var. rotundifomis Tschugunoff, width ratio 0.63-0.68; egg size 103 x 89pm (L x W). 1921, p. 120, pl. 1, Fig. 12 Description of the female: Lorica small ovoid to el- Brachionus plicatilis rotundiformis Rodewald, 1937, liptical and not sharply separated into dorsal and ventral p. 239, Fig. 5 plates; occipital spines six in number which are narrow markedly above the broad, inflated base and end in thin, Brachionus rotundiformis estoniana Haberman & acutely pointed tips or small based equilateral, equidistant Sudzuki, 1998, p. 335, Fig. 2 triangular spines; the pectoral margin rigid and scalloped, Brachionus rotundiformis Ciros et al., 2001, p. 1318, shows considerable variations, irregularity of the four Figs.- E-F rounded projections; the occipital spines show consider- able variations especially in the relative length of interme- A few parthenogenetic from diate spines; posterior spines absent; foot opening with a Aakulam. small subsquare aperture ventrally. Measurements: Total length of lorica 125-156pm; maximum width of lorica 87-125pm; antero-width of lorica 5 1-73pm; distance from median to lateral spine 33- 47p; median sinus gape 17-22pm; antero-median spine length 11-22pm; antero-intermediate spine length 9-13~; antero-lateral spine length 9- 13p;maximum width- total length ratio 0.80-0.89; anterior width-maximum width ratio 0.58-0.59., egg size 90 x 65'(L x W). Description of thefemale: Lorica small, more rounded 04 , , , , , , , , , , , , , , , , , , , lo and not sharply separated into dorsal and ventral plates; 1 10 25 5 15 35 1 10 25 occipital margin with small based acutely pointed spines; Salinity (x 10.')1 temperature ( 'c) pectoral margin four-lobed; lateral ones roughly triangu- Fig. 1. Mean 'r' values of Brachionus plicatilis, lar; foot opening with subsquare aperture ventrally and B. rotundiformis and B. nzurrayi reared at different rather ovoid aperture dorsally. salinities at three temperatures

Journal of the Marine Biologiral A.s.soriation of India (2006) Taxonomy of three species of rotijiers

Figs. 2-10: Brachionus plicafilis Miiller, Fig. 2a-b: B. Figs.11-16: Bracllionus rorundlfornlis Tschugunoff, Fig. plicarilis f: typira; Fig. 3: f: miilleri Ehrenberg; Fig.4a- 12c: Enlarged view of pectoral margin showing lateral b: f: heparoromus Gosse; Figs. 5-6: small morphs of elevated lobes; Fig. 14 Shows the vase shaped lorica plirarilis; Figs. 7a-b, 8a-b: f: decemcornis Fadeew; Figs. with irregularity in the occipital spines; a: occipital 9-10: f. ovalis f.nov. a: occipital median spine; b: median spine; b: occipital intermedian spine; c: occipi- occipital intermedian spine; c: occipital lateral spine; d: tal lateral spine; d: pectoral margin; e: egg; f: swollen pectoral margin; e: egg lorica

Table 1. Diagnostic characteristics of different ecomorphs of B. plicatilis and B. murrayi Specieslforms Diagnosis

f: miilleri Occipital spines broad shaped; pectoral margin obliterated f: 11eparotomu.s Occipital spines with external swellings; pectoral margin not obliterated f: deremrornir Occipital spines without external swellings; median elevated pectorals f: ovalis Lorica roughly spherical in shape; occipital spines scalar in arrangement Brarl~ionus murrayi f: erornis Occipital spines long, short based; pectoral margin obliterated or nearly straight line f. longirornis Occipital spines equilateral, equidistant; scalloped pectoral margin f: divergispinus Occipital spines diverged especially the lateral ones; pectoral margin four lobed

Journal of rhe Mar~rle Biologiral A~~oriationof Indra (2006)

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Discussion The morphological analysis of the plicatilis species complex revealed that three morphologically recognizable species co-existed in the Veli-Aakulam Lake instead of two and they were identified as B. plicatilis, B. rotundiformis and B. nrurrayi based on the key given by Sudzuki (1999). Of these, B. murrayi was originally established as a new variety of B. miilleri (= B. plicatilis r var. murray) by Fadeew (1925) basedon Murray's (1913) 1 collection from S. America. Subsequently, Ahlstrom (1940) 3 and Wiszniewski (1954) grouped this taxon as a variety of B. plicatilis (f:longicornis) in their reviews in rotifers,

t loo- 11111 while Sudzuki (1987) classified it as B. rotundiformis murrayi due to the close morphological resemblance with B. rotundiformis Tschugunoff (1921). According to 2lh - -8 .d 2Ob 0.r~Sudzuki (1987, 1995, 1996), the striking morphological characteristic of the known species B. rotundiformis - 1oo11ni1 ioollln murrayi was the length of the intermediate spine, which %igi is comparatively smaller than the median and lateral oc- cipital spines. Similarly considerable variations in the length of the occipital spines particularly the intermedian was also observed in the rotifers collected from Veli- 00 J Aakulam Lake (Figs. 17-25) but the present taxon has 1 showed some distinct morphological difference especially '1 '1 'on the pectoral margin than that of Tschugunoff's B. rotundiformis. Likewise, the rotifers inhabiting in the

2% Veli-Aakulamlarities with B. waters ibericus exhibited n. sp., some(= B. morphologicalrotundiformis 'SM'simi- y4 loo 11111 type) from Spain waters (Ciros-Perez et al., 2001) and B. rotundiformis 'S' type from Japan (Hagiwara et al., 1995) Figs. 17-25: Braclrionuc murrayi Fadeew, Figs. 19, 20 & but they did not mention any morphological variability in f: & 23: ecornis Fadeew; Figs 17, 18 21: J: longicornis their specimens particularly the pectoral margin, More- Fadeew; Fig. 25: J: divrrgispinus f. nov; Figs. 20b, 21b 23b & 25b: En,arged view of occipital region showing over, according to Serra'et al. (1998) the principal distin- variability in the pectoral margin and the length of the guishing character between B. rotundiformis and B. ibericus spines especially the intermediate; a: occipital median (= B. rotundiformis 'SM' type) was mode of conveying spine; b: occipital intermedian spine; c: occipital lateral the resting eggs. In B. plicatilis and B. rotundiformis, spine; d: pectoral margin; e: egg resting eggs are carried outside the female lorica in the amictic or male eggs, while in B. iberic~isthey are retained within the lorica of the female. However, such females ~h~ morphs represented in the present collection are with resting egg inside the lorica were not observed in our study; because of the above mentioned morphological f: ecornis ~~d~~~,1925 (~i~~.19, 20a-b & 24), J: variability between the present taxon and B. ibericus ~ongicornis~~d~~~, 1925 (~i~~.21-23) and f. (Ciros-Perez et al., 2001) the rotifers that occurred in the divergispinusf, nov. (~i~.2sa-bl. rhe important diagnos- tic features are given in Table 1. brackishwater habitat of Kerala is named as B. murrayi Fadeew, 1925 based on the nomenclature preferences and ReProdrlctive rate: The highest 'r' value of 1.74 was we hope that this would facilitate the future reorganization recorded at the best salinity of 10 x 10" and at 28°C for of this taxon from the Indian waters. this taxon (Fig. 1). Like wise, at birth, B. murrayi females ranged from 146-15 lFm and they attained a The experimental studies on the reproductive potential adult size of 257-269~~at the above-mentioned salinity of these species in relation to ecological parameters re- (Table 2). vealed that all the variables significantly influence the 'r' values of these rotifers. Of these, salinity showed a strong

Journal of the Marine Biological Association of India (2006) Taxonomy of three species of rotifers 11

Table 2. Mean (k SD) values ji)r the size at birth, size at fir.st egg production and rnaxinlurn size attained by B. plicatilis, B. rotundiformis and B. murrayi over their lifespan at different salinities at room tenlperature (28-30°C).

Salinity Neonate Size at first egg . Maximum size Life span (x lo-') OW production (pm) (pm) (days)

35 145.6450.84 186.1 1k0.48 257.10k9.62 3.89k0.18

Brachionus rotundiformis

Brachionus murrayi

influence on the 'r' values of these rotifer populations. B. timum salinity in which their 'r' is high. The size at birth plicarilis, B. rot~tndiformisand B. murrayi recorded their and maximum adult size attained by the female of B. highest 'r' values at their optimum salinities of 5 x lo4, plicatilis, B. rotundiformis and B. murrayi were 151- 15 x and 10 x10-' respectively, and above or below 265pm, 98-173pm and 137-225pm (laboratory clones) at these levels their 'r' values decreased irrespective of the the best salinities of 5 x 15 x 10-Qnd 10 x lW3 temperature (Fig. I). Thus the present study is in a good respectively and this suggests that each individual rotifer agreement with the findings of Miracle and Serra (1989) had a specific size range, which is directly correlated with and Serra et al. (1998) who concluded that the direct the genotype of the respective taxon. effect of salinity on 'r' values depended on the species Therefore, the morphology and reproductive potential and genotype. The influence of salinity on rotifers is studies of theplicatilis species complex that inhabited the directly correlated with their osmo-regulatory capacity Veli-Aakulam Lake revealed that there are three morpho- which in turn is strongly dependent on their genotype. logically and ecologically recognizable taxa co-existing in Thus the genotype of each species is adapted to an op- this estuary instead of two. Further, based on the iden-

Journal of the Marine Biological A.s.sociation of India (2006) 12 P. S. Anitha and Rany Mary George

tification key given by Sudzuki (1999) they are classified Haberman, I. and M. Sudzuki. 1998. Some notes on as B. plicatilis, B. rotundifomis and B. murrayi. The Brachionus rotundifornlis (Tschugunoff) in Lake observations recorded here will provide significant tips to Palaeostomi. Hydrobiologia, 388: 333-340. differentiate similar species when biological species are Hagiwara, A,, T. Kotani, T. W. Snell, M. Assava-Aree and recognized on ecological, physiological and molecular K. Hirayama.1995. Morphology, reproduction, ge- data. Further, for these reasons, this study contributes to netics and mating behaviour of small tropical marine establish a reference base for further comparative works Brachionus strains (Rotifera). J. Exp. Mar. Biol. Erol., and elucidates the actual species identity of those related 194: 25-37. B. plicatilis-like rotifers from Indian waters. Lubzens, E. 1987. Raising rotifers for use in aquaculture. Hydrobiologia, 147: 245-255. Acknowledgements Miracle, M. R. and M. Serra. 1989. Salinity and tempera- The first author acknowledges the Indian Council of ture influence in rotifer life history characteristics. Agricultural Research for the award of Senior Research ibid, 1861187: 81-102. Fellowship for canying out this study in partial fulfilment Molly, V. 2003. The rotifer, Brarllionus rotundiformis of Doctor of Philosophy in Fish and Fishery Science Tschugunoff isolated from Cochin Backwater, Kerala. (Mariculture) of CIFE, Mumbai. We are grateful to Prof. J. Mar. Biol. Ass. India, 45: 9-19. (Dr.) Mohan Joseph Modayil, Director, CMFRI, Cochin, Shri. Prabhakaran Nair, Dr. P. P. Pillai and Dr. A. P. Miiller, 0. F. 1786. Anintalcula infusoria ,fluvitilia et marina, Lipton for providing required facilities. quae d~fexitsyitematire descript et ad vivum delineari curvit, Copenhagen, LeipziL 367 pp. References Murray, J. 1913. South American Rotifera. Part 11. J. Roy. Ahlstrom, E. H. 1940. A revision of the Rotatorian genera Microsco. Soci., 5: 341-362. Brarl~ionusand Platyias with descriptions of one new Rao, R. K. and P. Chandramohan. 1984. Brackishwater species and two new varieties. Bull. Ant. Mus. Nut. Rotifera from Visakhapatnam harbor, India. J. Mar. Hist., 77: 148-1 84. Sci., 13: 92-93. Ciros-Perez, P., A. Gomez and M. Serra. 2001. On the Rodewald, R. 1937. Radertierfauna Rumaniens 11. Neue taxonomy of three sympatric sibling species of und bemerkenswerte Radertiere aus Rumanien. Zool. Bracl~ionusplicatilis (Rotifera) complex from Spain, Anz., 118: 235-248. with the description of Brachionus ibericus n. sp. J. Plank. Res., 23 (12): 1311-1323. Segers, H. 1995. Nomenclatural consequences of some recent studies on Brachionus ulicatilis (Rotifera: Ehrenberg, C. G., 1838. Die lnfusionsthierchen als Brachionidae). Hydrobiologia, 31 31314: 121-122. vollkommene Organismen. In: Ein Blick in das tiefere organisrhe Leben der Natur. Folio, Leipzig, pp.1- Serra, M., A. Gomez and M. J. Carmona. 1998. Ecological 1 12. [in German] genetics of Brachionus sympatric sibling species. ibid, 3871388: 373-384. Fadeew, N. N. 1925. Sur la connaissance de la fauna de lacsdu Transcucasie. Raboty sev. Kavkazskoj. Gidiobio. Shakuntala Pandey and U.N.Singh. 1993. The rotifer fauna Stancil., 1: 17-25. [in Russian] of Champaran, north Bihar (India) Brachionus-2. Further contributions to the family Brachionidae. Proc. Fu. Y., K. Hirayama and Y. Natsukari. 1991a. Morpho- Acad. Environ. Biol., 2: 143-147. logical difference between the two type strains of the rotifer Brachionlcs plicatilis 0. F. Muller. J. Exp. Mar. Snell, T. W. and K. Carrillo. 1984. Body size variation Bio. Erol., 151: 29-41. among strains of the rotifer Brachionus plicatilis. Aquaculture, 37: 359-367. , -. 1991b. Genetic diver- gence between 'S' and 'L' types strains of rotifer Sudzuki, M. 1987. lntraspecific variability of Brackionus Braclrionus plicatilis 0. F. Muller. ibid, 151: 43-56. plicatilis. ibid, 147: 45-47. Gopakumar, G. and V. Jayaprakash. 2003. Community 1995. Taxonomy of Brachionus pliratilis structure and succession of brackishwater rotifers in and its related groups 1. Discussion and Consider- relation to ecological parameters. J. Mar. Biol. Ass. ations on the papers before 1925. Obum Ronso Nilzon India, 45: 20-30. Daigaku. Omiya, 40: 1-21. Gosse, P. H., 1851. A catalogue of Rotifera found in 1996. Taxonomy of Brarhionus pliratilis Britain, with descriptions of five new genera and and its related groups 2. Discussion and Consider- thirty-two new species. Ann. Mag. Nut. Hist. Ser., 2 ations on the papers during 1926-1952. ibid, 42: 1- (8): 197-203. 22.

Journal of the Marine Biological Association of India (200 Taxor~ornyof three species of rotifers 13

1999. An approarll to tile identifiration of Wiszniewski, J. 1954. Mateiaux relatifs a la nomenclature rl~econrrnon rotifer.~.Sanseido Publishing Co. Ltd., et a la bibliographic des Rotiferes. Polaskie. Arch. Tokyo, 150pp. Hydrobiologia, 2 (15) 2: 7-250. Tschugunoff, H. L. 1921. A study of the plankton of the arctic regions of the Caspian Sea. Report of tlle Volga Biologic.al Station, No. 6, p. 11 1-364. [in Russian with English abstract] Accepted: 20 May 2006

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