A NEW CHINESE ISOPOD, ICHTHYOXENUS GEEI.By Pearl L. Boone,Aid, Division of Marine Invertebrates, United States National Museum.The species herein described was found parasitic on the " Tsi-fish "or carp, probably Cyprinus cavpio taken from lakes and canalsaround Soochow, China, by Prof. N. Gist Gee, of Soochow Uni-versity, whose energetic investigations are constantly increasing ourknowledge of this hitherto neglected region.This is the fourth representative of the genus Ichthyoxenus^ agroup whose mode of life is peculiarly interesting. When young,the isopod bores a hole in the body of a fish, just behind the lateralfin, where it lives with its mate, developing so in size that it is im-possible for it to escape through the opening by which it entered.The type species of the genus, Ichthyoxenus jellinghausii Herk-lots,^ described in 1870, was found parasitic on the fish Barbodesmaculatus Bleeker from Java, and in 1908 another host for thisspecies was reported by Maj. P. A. Ouwens,^ namely, the fishNemacheilus fasciatus van Hasselt from the Tji-Seroema nearBatavia.Ichthyoxenus montamts Schioedte and Meinert,* the second repre-sentative of the genus, was described in 1884 as parasitic on PwntiussopJwres in the Himalayan Mountains.In 1913 Richardson described the third species of the genus,Ichthyoxenus japonensiSj* from the following hosts : Acheilognathusrhomheum (Schlegel), Gnathopogon elongata (Schlegel), ^c^?^?P'n?-thiis tabira Jordan and Thompson, A. lanceolatum (Schlegel), A.Gycnostigma (Jordan and Fowler), and A. liwybatunh Jordan andSnyder, from Lake Biwa, Japan.Family CYMOTHOIDAE.Genus ICHTHYOXENUS Herklots, 1870.ICHTHYOXENUS GEEI, new speciea.Plates 40 and 41.Female.?Body subovate, strongly convex, about 23.1 mm. long,greatest width about 11.7 mm. Surface smooth; color (preserved
I Archives Neerlandaises des Sciences, vol. 5, 1870, pp. 128-137, pi. 5, figs. 10-18.'Natuurk. Tijdschr. Nederl.-Indie, vol. 67, 1908, pp. 29-35.'Naturk, Tidsskrift, Kjobenhavn, ser. 3, vol. 14, 1884, pp. 303-309, pi. 11, figs. 10-17.*Proc. U. S. Nat. Mus., vol. 45, No. 1995, pp. 559-562, text-flgs. 1-6,Proceedings U. S. National Museum, Vol. 57?No. 2319.144382?20~Proc.N.M.vol.57 32 497
498 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 67.specimens) creamy yellowish with minute black dots sparsely scat-tered on the body and more densely so on the dorsal surface of thehead. Irregular carinations on the various segments give the dorsalsurface of the body a rugged aspect.Head small, and subtriangulate, convex, 3.1 mm. long, 3.5 mm.wide, frontal margins slightly rounded and posterior margin stronglyrounded. Eyes shining black, subovate, moderately large, 1 mm.long, placed obliquely in the anterolateral angles of the head, andseparated from each other at their nearest point by a distance of 2mm., being distinctly more elongate and different in contour from theeyes of /. japonensis. First antennae short, consisting of 8 articlesand extending slightly beyond the anterior end of the eye. Thesecond antenna consists of 10 articles and extends quite to the pos-terior margin of the head.A comparative diagnosis of the maxillipeds of the present speciesand its closest ally, /. japonensis Richardson,^ seems desirable, es-pecially since the author made no mention of the mouth parts in herdiscussion of japonensis. In geei the maxilliped is relatively quiteshort, its distal margin having the upper two-thirds of both lobesof the first maxilla entirely exposed while in japonensis the space be-tween the anterior lip and the tip of the palp of the maxilliped isquite small and the outer margin of the masticatory lobe is producedbeyond the margin of the epistome and the respective margins alongthe incision bilobating the lower lateral region are greatly roundlyproduced and overlap. Thus in japonensis the maxilliped covers theentire underlying mouth parts except the very tips of the maxillae,which are barely visible, and the distal ends of the palp, which meetabove the epistome. In geei the maxillipeds are much broader in thebasal region, with the bilobation of the masticatory lobe which oc-curs in the upper outer median lateral area marked by a distinct ex-cavation, and the upper part of the lobe is not greatly produced, theinner area being relatively truncate. The palp is well developed andextends quite beyond the anterior margin of the masticatory lobe.The distal joint of the palp is well developed in marked contrast tothat of japonensis, which is rudimentary, almost obsolete. The entirepalp of japonensis is relatively small and overshadowed by the pro-duced masticatory lobe.Thorax roundly ovate, strongly convex, moderately asymmetrical.First segment 3 mm. long in median line, 9 mm. wide, with anteriormargin deeply roundly excavate surrounding the posterior margin ofthe head. The lateral margins have the anterior half produced ante-rolaterally beyond the angles of the head and the posterior half directedalmost straight back ; the posterior margin is also relatively a straight
? Ichthyowenus japonensis Richardson, Proc U. S. Nat. Mus., vol. 45, No. 1995, vol. 45,pp. 561-562, text figs. 4-6.
No. 2319. A NEW CHINESE ISOPOD?BOONE. 499line, in striking contrast to that of japonensis, which is recurvate.The entire segment is distinctly narrower than the second segment,extending only to the inner margin of the latter's epimera. Thesecond, third, and fourth segments are similar and subequal, differingonly in that their lateral parts graduatingly increase posteriorly andtheir respective epimera correspondingly graduatingly decrease pos-teriorly. The fifth, sixth, and seventh segments are similar, eachbeing about two-thirds the length of the preceding segment; all aredecidedly constricted postlaterally, Epimera are present on the lastsix segments; all are roughly triangulate. Those of the second,third, and fourth segments are relatively large, occupying the antero-lateral angle of the margin of their respective segments and beingclosely appressed. The epimera of the fifth, sixth, and seventh seg-ments are proportionately weaker and are almost hidden by the over-lapping of the respective preceding segments due to their greatconstriction. All seven pairs of legs are strongly prehensile, thefirst three being directed forward, tlie last four backward. Thesecond pair are decidedly stronger than any of the others; theseventh pair are uniquely distinctive.In order to emphasize the validity of the present species it hasseemed advisable to present a critical comparative diagnosis of theseventh legs of three adult female specimens, representing, respec-tively, /. geei, I. japcniensis, and /. jdlinghausi% which yields thefollowing results
:
/. geei: Coxopodite rudimentary; basipodite conspicuously con-stricted basally, its gi'eatest width occurring midway the distal end,the outer margin distinctly keeled and deflected, only the distal endapproaching true convexity, the point of union with the ischium isemphasized by a break in the marginal line, the inner side bears adistinct groove near the basal end on either side of which the marginis accentuated and reflected outwards, the distal end is convexly pro-duced, this sculpturing of the entire inner margin dovetails with theflattened inner margin of the ischium, thus greatly enhancing thestrength of the limb. The ischium has the form of an invertedtriangulate pyramid, with each side slightly concavely depressed andthe inferior margin flattened. The merus is nearly half as long asthe ischium, wider than long, the outer margin broadly, roundly pro-duced into a flaring lobe. The inner distal area is only very littleproduced and extends only a trifle along the inner side of the carpusin striking contrast to that of /. japonensis Richardson; the distalmargin of the merus is also differently sculptured, the articulation ofthe carpus with the merus is also different from that of japonensisThe carpus of the present species is approximately as large as themerus of japone7isis, although the specimen of geei is 23.1 mm. long,while japonensis is 14.2 mm. long. In shape the carpus of geei is
500 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 57.quite similar to its merns; its contour and proportions are quite dif-ferent from the carpus of /. ja/ponensis. The propodus of /. geei isreLatively stout, evenly curved, not quite as long as the dactyl, whichforms a strongly curved hook extending upon and overlapping mid-way on the inner side of the carpus. It will be noted that this hookis more strongly pronounced and differently bent from that of any ofthe previously described species of the genus./. japonensis; Coxopodite rudimentary; basipodite slightly widerbasally than distally, the outer side is relatively convex, not con-spicuously keeled; the distal end broadly, roundly shouldered, itspoint of union with the ischium preserving the unbroken marginalline; the inner side bears a distinct groove, which widens near thebasal end; the margins on either side are distinct, slightly pro-duced. The ischium is as long as the basipodite, narrow, sub-cylindric basally, widening distally, roundly thickened along theinner side and with the outer distal portion reduced, flattened.The merus is slightly wider than long, the outer margin evenlyrounded, the inner distal area strongly produced projecting alongnearly seven-eighths of the length of the inner side of the carpus;the distal margin of the merus is strongly deeply excavate, encup-ping the carpus and reenforcing it on the inner side. The carpus isshorter than the merus, subcylindrical, with the inferior margin solittle produced that the " rounded expansion " is visible only at theouter basal area tapering to a hair's breadth at the distal end. Thepropodus is slightly longer than the carpus and only a trifle nar-rower and is evenly recurved. The dactyl is relatively stout basally,but curves somewhat and tapers to a very fine point, which is di-rected toward the distal end of the carpus but barely reaches theextreme tip of the margin of the carpus./. jellinghausii: Coxopodite rudimentary, basipodite but little con-stricted basally and upcurved, relatively convex, distal end pro-nouncedly shouldered, forming a blunt right-angled projection onthe outer distal margin ; the line of union with the ischium is rela-tively straight, the side is convex, in marked contrast to that of geei.The ischium has the form of an inverted truncated triangulate pyra-mid, with the sides not concavely depressed and the margins scarcelyat all produced. The merus is more than half as long as the ischium,slightly longer than wide; the outer margin roundly producedbut with a relatively less flaring lobe than either of its allies. Theproduced inner distal area extends less along the inner side of thecarpus than in geei. The articulation of the carpus with the merusis also distinctive; the carpus is compressed, subpyriform; the pro-podus is a trifle longer than the carpus, is less pronouncedly curvedthan is geei or japort^-nsis. The dactyl is differently inserted basally,
No. 2319. A NEW GEINESE ISOPOD?BOONE. 601moderately curved, tapering to a fine point, which is reflected ahnoststraight back on the carpus, but does not reach the merus.Male.?The male is similar to the female in general appearance,but is distinctly smaller, the largest full-grown specimen being only14.2 long and 8 mm. wide; the body outline is more elongate ovateand only slightly convex; the telson is not quite so long and is morerounded posteriorly ; the uropoda are relatively larger and are slightlyconspicuous dorsally; and the pleopoda cover almost the entireventral cavity, but not quite extending to its terminal margin.As is the case with many of the parasitic Cymothoidea, the presentspecies is not pronouncedly different in general appearance from itsallies; in fact, a superficial diagnosis would quite probably designateit a form of Ichtliyoxenus japonensis Richardson, but a critical com-parison of the entire series of specimens of the present species with theentire series of /. japonensis Richardson, including the type material,and likewise with the series of /. jelUnghausH Herklots in the UnitedStates National Museum, augmented by careful study of all theliterature on the group Ichthyoxenus^ especially that of /. montanusSchioedte and Meinert, of which no specimens were available, con-sideration of this species being necessarily based on the text andSchiodte's and Meinert's excellent figures of the various phases ofthe species, establish beyond question the fact that /. geei is as dis-tinct specifically as the three previously described members of thegenus.The adult females of /. ffeei are uniformly less asymmetrical incontour than those of /. japonensis; the insertion of the head of geeiis distinctive; the number of ocelli and the shape of the eye ofgeei differs from that of japonerisis; the posterior margin of thefirst thoracic segment of geei is relatively a straight line, while injaponensis this is uniformly recurvate. The proportionately largerand broader telson and the relatively smaller pleopoda and ur?>podaof the female is distinctive of geei, as are the uniquely differentseventh pair of legs. Finally, the differently shaped and proportion-ately much smaller maxillipeds of geei preclude its confusion with theother members of the genus.It is interesting to note that all the so far recorded hosts of themembers of the genus Ichthyoxenus are confined to the fresh-waterfishes of the closely related families Cobitidae and Cyprinidae.Type.?Kn adult fem.ale. Cat. No. 53304, U. S. N. M., and an adultmale paratype, were found parasitic in " Tsi-fish," or carp, probablyGyprinus carpio Linnaeus, taken from lakes and canals around Soo-chow, China. The following additional paratypes?two males, onefemale?and about 40 very young specimens, Cat. No. 53305,U. S. N. M., were likewise collected by Prof. N. Gist Gee, of SoochowUniversity, for v/hom I take great pleasure in naming the species.
502 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 57.LIST OF REFERENCES.Hebklots, J. A. Deux nouveaux genres de crustaces vivant en parasites surdes poissons?epichthys et ichthyoxenos, Archives Neerlandaises des Sciencesexactes et naturelles, vol. 5, 1870, pp. 120-137, pi. 5, La Haye.OuwENS, P. A. Nog iets over Ichthyoxenus jellinglaausii (Herklots), Natuur-kuudig Tijdschrift voor Nederlandsch-Indie, vol. 67, 1908, pp. 29-35, Welte-vreden.RicHAEDsoN, Hakkiet. The Isopod genus Ichthyoxenus Herklots, with descrip-tion of a nevp species from Japan, Proc. U. S. Nat. Mus., vol. 45, No. 1995,pp. 559-562, text-figs. 1-6, 1913, Washington.ScHiOEDTE and Meinekt, Fb. Symbolae and monographian cymothoarum crus-taceorum isopodum familiae. IV. Cymothoidea. Trib. II. Cymothoinae.Trib. III. Livonecinae, Naturhistorisk Tidsskrift, ser. 3, vol. 14, 1884, pp.221-421, pis. 6-18, Kj0benhavn.Webek, Max.^ Die Siisswasser-Crust. des Indischen Archipels, nebst Bemer-kungeu iiber die Siisswasser-Fauna in Allgemeinen, Zool. Ergebnisse, vol. 2,1892, pp. 557-560, pi. 30, fig. 1, Leiden.VViLLiNK, H. D. Tieenk. De " Songkeat " een vischparasiet, Natuui'kundigTijdschrift voor Nederlandsh-Indie, vol. 64, 1905, pp. 156-161, Amsterdam.EXPLANATION OF PLATES.Plate 40.Fig. 1. Ichthyoxenus geei, new species, female, type.2. Ichthyoxenus geei, new species, male, paratype.Plate 41.Fig. 1. Ichthyoxenus geei, seventh leg of female.2. Ichthyoxenus jdponensis Richardson, seventh leg of female.3. Ichthyoexnus jcllinghausii Herklots, seventh leg of female.4. Ichthyoxenus geei, new species, maxilliped.5. Ichthyoxenus japonensis Richardson, maxilliped.
* I have not been able to obtain this paper.
U. S. NATIONAL MUSEUM PROCEEDINGS, VOL. 57 PL. 40
ICHTHYOXENUS GEEI. (1) FEMALE, ( 2j MALE.For explanation of plate see page 502.
U. S. NATIONAL MUSEUM PROCEEDINGS. VOL. 57 PL. 41