FAUNA OF THE CHILKA LAKE. CRUSTACEA COPEPOD~.. By R. B. SEYI\-10UR SEWELL, 1\1.A .• F.A.S.B., F.Z.S., F.t.S., A1ajor, 1.111.5., Surgeon· Naturalist to the j\;larine Survey 0/ India and Superintendent, Zoological Survey 0/ I nJta. (Plat~s xLlv-- LIX.) CONTENTS. Page. Page. Introduction 773 Saph irella indica, sp. n07. .. 800 List of species 778 Oorycaeus (Onyclwcorycaeus) giesbrecht~ p([l'ucalanus crassil'ostris Dahl 780 F. Dahl 8uS Acrocalanus inermis Sewell ... 781 Ergasilus sp. 803 Isias tropica, sp. nov. .;. 782 Longipedia coronata Claus 804 Pselcclodiaptomus serricaudatus (T. Scott) 785 Longipedia 'J'osea Sars 806 Pseudodiaptomusltickmani Sewell 786 Oanuella furcigera Sars 807 Pseudodiaptomus lobipes, Gurney 736 Ectinosoma normani T. and A. Scott 808 808 Pseudodiaptomus bingham~ Sewell 786 Ectinosoma melaniceps Boeck Pseuclodiaptomus annandalei Sewell 787 1J,iicrosetella norvegwa (Boeck) 809 Pseuclodiaptomus tollinger'/, Sewell 787 H arpacticus littoralis Sars 810 Diaptomus blanci de Guerne and Richard 788 H arpact1,'cus grac~lis CIa us var. or~entaUs. 811 Diapto1nus cinctus Gurney ... 788 nov. Harpacticella lacustris, sp. nov. 813 Diaptomus contort1 1s Gurney 788 Parategastes sphaericus (Claus) va,r. Diapto1nus pulcher Gurney '" 7-88 similis, nov. 815 Diaptomus stri"gilipes Gurlley 788 I dyaea furcata (Baird) 8]7 Labirlocera }Javo Giesbrecht ... 789 I dyaea ens1,fera (Fischer) var. indica, nov. 817 Acartia sp1:nirauda Giesbrecht 789 Dactylopusia brevicornis (Claus) ... 819 Acartia centrura Giesbrecht ... 790 Amphiascus scotti, nom. nov. [=Dacty- Acartia southwelli Be\\' ell 790 lopus propinquus T. Scott] •.. 819 Acartia chilkaensis Sewell 790 Stenhel1,a inopinata (A. Scott) 823 Acartiella major Sewell 791 1Jlesoch'J'a nana Brady 824 Acartiella minor Sewell 791 .llesoclzra sp. 826 Oithona nana Giesbrecht 791 J./itocra spinipes Boeck var. onentalzs, Oitlbona bl'evicornis Giesbrecht 792 nov. 827 Cyclopina intermedia, sp. nov. 792 Nitocra tllpica Boeck var. lacHstfis, nov. 828 U,ljclopina longiJurca, sp. nov. 79-1 Nitocra yahiai (Blanchard and Richard) 029 Hal/cyclops m'1gniceps (Lilljeborg) 796 Laoplwnte chatlwmensis S:1rs 830 Hali;~yclop8 tenuispina, sp. nov. 796 Laophollte quinquespinosa, sp. nov. 832 e!J( lops bicolo)' Surs 797 Cleta secunda, sp. nov. 835 Cyrlops buxtoni Gurney 798 Euterpina acutifrons (Dana) 836 11esocyclops obsoletas (Koch) 798 Bibliography 836 llesof)yclops oithonoides S:Lrs 799 Ljst of Sttttions 842 CRUSTACEA COPEPODA. By R. B. SEYMOUR SE'VELL. INTRODUCTION. The collection of Copepoda obtained in the Chilka Lake is one of great interest, partly by reason of the various species that occur and partly also from the very marked changes t.hat take place in the local conditions from season to season and from year to year. As Annandale and I(emp have pointed out in the introduction to this volume, the lake communicates on the one hand with the l\lahanaddi river and on the other, in any Donnal year, with the open waters of the Bay of Bengal. At the northern end tributaries of the Mahanaddi pour their Hood-waters into the lake during the rainy season from June to August, "\Yhereas during the dry winter months the level of the lake, owing to the great amount of evaporation that takes place, tends to fall below sea-level and in consequence we get an inflowing current of sea-,vater through the entr.ance chal,lnel. Each of these influxes in turn will carry with it a representati"e collection of its planktonic forms. We should, therefore, expect to find at different seasons of the year and in different parts of the lake great variation in the composition and relative numbers of the inhabitants. It has further been shown [Sewell and Annandale, 1922] that the degree of salinity of the lake water may vary very considerably from year to year and this again must have a profound influence oli the general character of the planktonic fauna (loc. cit., p. 696). In several instances species are represented in the collection by either single or only very few specimens, and not uncomnlonly the only locality in which these were obtained wa:s ill or near the entrance channel. When once the infiowing· Cllrrent of sea-water has become established any littoral-haunting form is liable to be swept in by it through the channel, and it tow-netting or other collection made in this area.at the- crucial moment will reveal its presence in the l~ke ; and the greater the influx, the larger ,yill be the number of such species that are like!y to occur. The sanle of cours~ equally applies to purely fresh­ water forms that may be washed out of the Mahanaddi river system by the nlonsoon floods J and since these processes alternate with· the changing seasons one ·would expect to find a corresponding change in the type of fauna present. The present collection includes in all sixty-nine samples-tow-nettings, weed-wash­ ings, etc.-of which, however, tl\relve contained no Oopepoda. The rem.ainder revealed the presence in the collection of fifty-seven specie~. In view Qf the comparaf1ively little systematic work that has been carried out on the Cope'!loda of Indian waters, it was only to be expected that a number of new species and varieties would be dIscovered. In 3. [ 773 ] 774 Jlemoirs of the Indian lJluseu11L [VOL. V, previous paper (Sewell, 1919) 1 have described five forms that had up till then been unknown, nanlely:- PSl?lldodiaptom us ((}ij/(l ildalei, Acartia chilkaensis, PSl?lulofliapto}}w8 tollillgeri, Acartiella major, and Acnrtiella ul1'nor. In the following pages I give descriptions of seven further species which appear to me to be new; V~Z.:- Isias t (opica, sp, nov" Cyclopina longiJurca, sp. nov., Halicyclops tenuispina, sp, nov" [lw'1JacticeUa lacusli'is, sp. nov., CyclopiJltl iJltennedia, sp, noy" Laoplwnte quinquespinosa, sp. nov., Clda secunda, sp. 110Y., ;lud in addition I have described what I believe to be varieties of five other species: Harpacticus gmcilis Claus, val'. orientalis, I dyaea ensifera (Fischer), var. ind'iea, nov. nov. Nitocf(t slJ'i'nipes Boeck, val'. orierdalis, nov. Pa)'({.tegastes sphacrieus (Claus), val', and Nilocra typica Boeck, var. lacustris, nov. simdis, noy, The types of these species and varieties have been deposited in the Indian Museum. A detailed analysis of t.he contents of the different samples sho,vs that the permanent lake-dwellers, upon ,vhose presence in any given series of samples one can rely with any (legree of certainty, are cOlnparatively few. Indeed out of all the species now recorded fronl the lake t.he only ones that have any claim to be regarded as permanent inhabitants, <1,S opposed to fortuitous visitors~ are but fourteen in number, namely :- P(lmcalarlus crassirostris Dahl, Acadia chilk(lensis ~ewell, Pseudodiaptorn/us a:nncouZ(ilei Sewell, Ac((.rtiella major 8'ewell, Psewlodiaptm'tlu8 binghami Sewoll, ACCllfti€lla tni-Hor Sewell, PseudodiiJptomus hidanani Sewell, OiJhonct IIla1W Gietlbrt:lCht, Labidocera pa1.'O Giesbreoht, Oithona brevicorn-is -Giesbrecht, dearh'a cenirw'(, Giesbrecht, P(lrl'(lttegastes sphaefJ'icus (Claus) var. si'milia, nov., <1.ud pOH~ibly Amphiru.:cus scofti, nom. nov, [=Da(J/.'I1.()pus propirtlJuus T. Scott]. ~Iany of these species are already well known to be inhabitants of brackish ·water. ParrtcalanU8 crassirostn's Dahl, for instance, has been found in the estuarine \vaters of the Congo and ...~nlazon Rivers and I have previously recorded Acrocalc~nu8 i·nennis and Pseudo­ diaptomHs hick'ma!Jbi frOlll t.he Rangoon river estuary, in water whose specific gravity "ras as lo\y as 1002 at 27·6°c.1 The genera PseudodiaptoTltU8 and Aca·rtiella as a whole seem to prefer brackish water as their habitat, hut it is interesting to ~nd that such typical nlarine Bpecies as Labidocera pa co Giestrecht, Acaltia centrura Giestrecht, Parctlegastes sphael'icus (Claus) anll the two species of Oitlwua have been able to persist, though in some cases with a eel'tain degree of modification of structure, under the very variable conditions of salinity tha t occur in the lake. 'Vith the onset of the monsoon rains a great change occurs in the lake. Owing to the inrush of river 'water at the nort.h end the normal inhabitants of the lake are slrept towards 1 Througuout thi~ pa pt'r the specific gravity of disti1l€"d water is tak~n as = 1000, 1924.J Fatuw of tlu' Cllilka L(llt'(~: Crustacea ·Copepoda. 775 the southern end and lllilUY are undoubtedly carried out to Hea by the outfiowing current, but at the extreule :.;outh end of the lake in l~alnhha Bay and to a certain extent in the deeper waters of the body of the la.ke t.he change in density of the water is not flO great as in other parts and here the pct)llanent inhahitant~ call survive until the subsidence of the flood water~ again ena.hlp~ t helH to populate the lake as a whole. During this inrush of river l\~ater large lluluher:; of purel~~ fre~h-\Vater inhabitants are swept into the lake and the character of the ('opepo(l fauna (,haugeH to a Inarked extent. \Ve now find present numbers of such specic8 as :- PsetfdodiaplvtHul'I lobip{'.'i (lunlPY, Diaptomw< strigilipe,'i Gurne.y, IJWptomus blalt~i deGlleI'lW a.nd Richard, ('yclop,'" iJiru/ur Bars, J)i('ptomtls ('ittctll~ Gurney, ('ydOjJ8 fJllJ:toJli Gurney, Diaptomulf ("unlQdu8 UunH'Y, ~Ue8ocydops obsolclux (Koch) and nia-ptolllus pulclu:,., GUl"lll'y, Jleso('ycio}Js oithouoides Sarr;o Similarly during the winter lnonths there iH an influx of sea-water that raises the density of the It.Lke us a whole. In contSequence of thiH al1 the ahove species once again disappear and we now get a number of trtle marine fonus that are being steadily carried into the lake hy the inflowing current fron} the Bay of Bengal.