N. Pengo described in 1879 a new genus and species of polyphemid Cladocera from the Sea of Asov under the name of Corniger maeoticus.

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1 Crustaceana, 12 (1-3), pp , 1967 ON THE TAXONOMY OF THE GENUS CORNIGERIUS (CLADOCERA, POLYPHEMIDAE) PH. D. MORDUKHAI-BOLTOVSKOI Institute of Inland Water Biology of the Academy of Sciences of the U.S.S.R., Borok, distr. Nekouz, U.S.S.R. N. Pengo described in 1879 a new genus and species of polyphemid Cladocera from the Sea of Asov under the name of Corniger maeoticus. Although the very appropriate generic name Corniger the genus is distinguished from the rest of the family by horn-like diverging processes on the head has been used several times in the literature on Cladocera, it cannot be maintained since it is preoccupied by Corniger Agassiz (1831) for a genus of fish and by Corniger Bohm (1879) for a genus of Pycnogonida. Much to my regret I have to propose a new name to replace Corniger Pengo, 1879, and I suggest Cornigerius nom. nov. I am much indebted to Dr. J. H. Stock for this indication and for aid in the choice of a new name. Zernov (1901) confirmed the existence of the species C. maeoticus, and described briefly two more species of the genus, namely C. horribilis and C. bi-cornis. A new polyphemid obviously close to C. maeoticus was described by G. O. Sars (1902) from the Caspian Sea but referred by him to the genus Evadne under the name E. hircus. Sars denied the independence of the genus Corniger and named Pengo's species Evadne cornigera. Meissner (1908), emphasizing the close resemblance of the two forms, reduced the Caspian E. hircus to the status of a "local variety" of the species from the Sea of Asov and named it E. maeotica (Pengo) var. hircus (G. O. Sars), while Corniger horribilis described by Zernov was considered by him not to be a distinct species but merely a form of E. maeotica. Later on Behning (1938) reestablished the genus Corniger but in a different scope. As the most distinctive character of this genus Behning considered the strongly developed and diverging caudal claws. In his opinion the processes on the head "horns", though present in the majority of the species of this genus, may be absent, as in the new species described by him as Corniger glabriceps. Behning intended to give a detailed description of this genus and all its species in his revision of the whole group of the Caspian polyphemids. This revision was not published, but the conclusion may be drawn from his papers on other topics (Behning 1938, 1941) that he suggested five species, namely Corniger maeoticus (with some forms), C. glabriceps, C. auritus (mentioned but not described by him), C. lacustris and a fifth one

2 (unknown). C. lacustris was described by Spandl (1923, 1924) under the name Evadne lacustris. In my review of the Caspian fauna (Mordukhai- Boltovskoi, 1960) I included in the list of Caspian species neither Corniger auritus (since it is a nomen nudum) nor C. bicornis (since this species, very unsatisfactorily described in 1901 by Zernov, was not found thereafter during sixty years). I also refrained from the restoration of the genus Corniger and thus listed only Evadne maeoticus (in the Pontoasov basin), E. m. hircus, and E. glabriceps (in the Caspian Sea). However, the more detailed study of the pontocaspian polyphemids led me to the conclusion that the genus Corniger is to be restored, but rather in the sense of Pengo than that of Behning. A common character of all species of this genus is in my view the presence of appendages on the head ("horns"). Therefore Corniger glabriceps should not be included in this genus (it belongs probably to the genus Podonevadne). On the other hand Corniger bicornis Zernov, found by me in the Caspian Sea, is a good species of the present genus. In this paper the diagnosis of the genus Cornigerius is given, as well as the description of all four species belonging to it, one of which is new. C. maeoticus and C. bicornis are redescribed in more detail than by previous authors. Cornigerius nom. nov. (pro Corniger Pengo, 1879, preocc.) Type species: Corniger maeoticus Pengo, Diagnosis. Head on the frontal surface 1 ) with two appendages developed to various degrees, from a small spine-like projection to long horn-like processes bent on the end. Depression behind head also variable and sometimes hardly noticeable. Shell more or less elongate, elliptical or tapering to end but never quite round. The caudal claws are always very well-developed, and diverging. The armament of the exopodites fits generally the setal formula , i.e., as in the majority of Caspian podonids, and the structure of the legs closely resembles that in Podonevadne camptonyx Sars. However, in one species (C. bicornis) this formula is variable, the lesser seta of the exopodite of the second and third pair being underdeveloped, sometimes lacking. At present four species are known; three of these are endemic in the Pontocaspian basin. 1 ) On the figures the front side is situated above, the hinder part below, as usual in the representation of podonids (= polyphemids without caudal appendage; see Mordukhai- Boltovskoi, 1965), i.e., in a swimming position. The distance from the lower edge of the head to the top of the shell (which covers only the brood pouch and heart and may be named the incubatory chamber), called the length by many authors, is properly the height and does not coincide with the morphological length, i.e., the distance from the frontal edge of the head to the hind edge of the postabdomen or caudal claws.

3 Key to the species of the genus Cornigerius 1. Head with one strong process (the "trunk") directed forwards and ramifying in two smaller processes (the "horns")...2 Head with two processes either immediately on its frontal surface or on the rounded prominence of its frontal surface Horns usually very large and curved. Caudal claws very long, strongly diverging (usually more than at right angle), smooth, often curved......c. maeoticus (Pengo) Horns very small, not curved. Caudal claws slightly diverging, covered with tiny spinules......c. lacustris (Spandl) 3. The frontal processes are very small, like spines or knobs, and set widely apart. Caudal claws strongly diverging. Setal formula of exopodite always C. arvidi n. sp. The frontal processes may be developed in various degrees, their bases being close together and situated on the prominence of the head. Caudal claws comparatively slightly diverging. Setal formula of exopodite variable...с. bicornis (Zernov) Cornigerius maeoticus (Pengo, 1879) Corniger maeoticus Pengo, 1879; Zernov, Evadne maeotica, Sars, 1902; Meissner, 1908; Behning, 1941; Mordukhai-Boltovskoi, Female. The head bears on its frontal surface one strong thick process the "trunk", dividing into two "horns". Caudal claws always very long, strongly diverging, usually curved on the top. Shell more or less elongated, elliptical or pointed on the top. Armament of exopodites fits the formula According to their structure and armament the legs are similar to those of Podonevadne camptonyx, differing in having somewhat greater armament of the exopodite of the first pair (a bundle of hairs on the hind edge), the endopodites of the first to third pairs and the maxillar appendages (groups of setae and hairs on the sides). Moreover, the smaller of the apical setae of the first endopodal segment of the first leg and of the last endopodal segment of second and third legs is longer and does not differ markedly from the rest of the setae, and the smallest seta on the exopodite of the third leg is also longer than in P. camptonyx. The maxillar appendages of the second and third legs bear two dentiform spines each, the distal one being the shorter in the second and the longer in the third leg, and a conical sensitive seta (sensilla) on the lateral edge (figs. 9-11). The legs of the fourth pair, like in other podonids, are small, their exopodite is reduced to a minute nrominence bearing a seta. One or two large latent eggs (winter-eggs covered with a hard thick shell) develop in the brood pouch of gamogenetic females; the ephippia are not produced as in all polyphemids. Male. Differs from the female, as in all polyphemids, in having two copulative appendages (penes), hooks on the distal segment of the first leg, and a larger

4 head (due to the better developed eye). Moreover, the processes on the head and caudal claws are noticeably shorter than in the female. С. maeoticus has a subspecies in the Caspian and another in Pontoasov basins, both subspecies forming a similar deviating form (aberratio). Key to the subspecies and forms of Cornigerius maeoticus (Pengo), based on the females 1. Horns of the head long, strongly diverging, curved at the top, separated by a rounded interspace...2 Horns of the head short, nearly straight, separated by an angular interspace... C. maeoticus abb. horribilis (Zernov) 2. Shell oviform, rounded on top. Pontoasov basin... C. maeoticus maeoticus (Pengo) Shell tapering towards the top, usually pointed. Caspian Sea...C. maeoticus hircus (Sars) Cornigerius maeoticus maeoticus (Pengo) Corniger maeoticus Pengo, 1879; Behning, Evadne cornigera Sars, Evadne maeotica Meissner, 1908; Mordukhai-Boltovskoi, Female. Horns on the head usually strongly chitinized and often coloured brown (as well as the top part of the trunk), always pointed, curved at the ends and strongly diverging, divided by an arcuate interspace. They vary in form, being often curved and bearing on the end

5 several minute denticles (figs. 1-4). Occasionally anomalies occur, e.g., underdevelopment of one horn. The shell is evenly rounded, comparatively short, and as long as wide at the base. Adult parthenogenetic females measure between 0.55 and 1.1 mm; being usually 0.7 to 8 mm. The parthenogenetic female has been described in detail by Pengo (1879), though he figured it in an unnatural position. Gamogenetic females, i.e. those bearing the one or two latent eggs, do not differ from the parthenogenetic females in their appearance. They occur rather rarely and as single specimens. Male. The males differ from the females, in addition to the above mentioned characters, in the shape of the shell, tapering towards, though rounded at the top. Males are somewhat smaller than females, measuring 0.6 to 0.7 mm. They were found first in August 1963 in the Sea of Asov. Distribution. Sea of Asov, mainly in slightly brackish (oligo- and meiomeso-haline) waters (Gulf of Taganrog and northeastern part of the open sea); Dnje-pro- Bug liman and limans in the Danube delta. It occurs also in quite fresh waters and in the Danube River; during the last years it appeared in the Kachovskoie reservoir of the Dnjepr and near Zimlianskoje on the Don (Mordukhai- Boltovskoi, 1964).

6 Cornigerius maeoticus hircus (Sars) Evadne hircus Sars, 1902, Corniger maeoticus hircus Behning, Evadne maeotica hircus Mordukhai-Boltovskoi, Female. Shell more or less triangular, tapering to the end and usually pointed, 1.5 to 2 times longer than broad at the base. Pointed top of the shell often slightly bent and directed somewhat forward. In the structure of the head appendages and the legs it does not differ noticeably from C. m. maeoticus (figs. 5-11). The adult parthenogenetic females measure between 0.7 and 1.3 mm, i.e. somewhat more than the above-mentioned subspecies, but this is on account of the more elongated shell only. Gamogenetic females occur rarely. I found them in the autumn only, my material consists of single specimens with one or two winter eggs. Male. The male differs from the female as in the typical subspecies. The shell is pointed as in the female but its top is always directed upwards (Mordukhai- Boltovskoi, in press). They are rare, and until now have been found only in the central Caspian Sea: one specimen in

7 May 1963 and many in only one of the samples taken in September Distribution. Caspian Sea. Throughout the whole sea, including the freshened northern part. Cornigerius maeoticus aberratio horribilis (Zernov) Corniger horribilis Zernov, Evadne maeotica Meissner, Corniger maeoticus horribilis Behning, Female. The female differs from the typical form of both subspecies in the armament of the head only. The horns are markedly shorter than in the typical form, they are separated from each other by an angle, which is often less than 90 degrees. The horns are straight or nearly straight and have sometimes blunt tips and a rugged or wrinkled surface (figs ). This form was undoubtedly found first by Pengo, who mentioned the existence, besides the typical С maeoticus, of specimens with "short, straight and as if twisted horns". Zernov (1901) found them anew and described them as a distinct new species under the name Corniger horribilis. However, Meissner (1908) denied the independence of this species. Indeed, specimens occur in the Sea of Azov with horns to a certain extent transitional to the horns of typical form. Otherwise, no marked difference exists between the two forms either in the shape of the shell or in other characters including the dimensions ( mm). This form occurs in the Sea of Asov as well as in the Caspian Sea and may be ranked not more than a variety or, at best, an aberration. Cornigerius lacustris (Spandl) Evadne lacustris Spandl, 1923, 1924; Mordukhai-Boltovskoi, Corniger lacuslris Behning, Female. The long conical process of the head, the "trunk", bears two short horns, which are rather markedly set off from it. Shell tapering to the top and usually pointed, more rarely rounded. Caudal claws strong and long, but slightly curved and diverging, covered in distal part with numerous minute spinules (figs , from Spandl). Females measure mm; the male is still unknown. Distribution. This species was found in June 1914 by Spandl in a mountain freshwater lake, Lake Goldjik, in Turkey. Remarks. Judging from the description of Spandl, which is somewhat insufficient although based on numerous specimens, C. lacustris differs distinctly from C. maeoticus. However, the author suggested the possibility that they may represent extremes of a single variable species. Unfortunately С. lacustris has not been studied thoroughly. So far its single known locality is lake Goldjik in the basin of the Euphrates. This is also the single known occurrence outside the Ponto-Aral-Caspian basin of a polyphemid, which undoubtedly belongs to the Caspian complex.

8 Cornigerius arvidi n. sp. Holotype. A parthenogenetic female in the collection of the Zoological Institute of the Academy of Sciences of the USSR, No Locality: Central Caspian Sea between Makhach Kala and Sagindik, depth 46 m, 28 August Paratypes. Several parthenogenetic females from the same sample and from other samples, taken in the Central Caspian in 1958, deposited in the same collection as paratypes, No Description of female. Head large and widened at both sides. Lateral areas of the head prominent, resembling angular knobs, usually bearing small spiniform processes, sometimes unequal in size. Though the spiniform processes are often lacking, the angular knobs are always present and readily visible when the animals are viewed from the back (figs ). At its base the shell is swollen, it strongly tapers toward the top, and is nearly always pointed; in females with developed embryos it becomes more bulging though it preserves essentially the same shape. Caudal claws very long, curved and strongly diverging, mostly to opposite sides (figs. 21, 22). Legs built very similar to those of C. maeoticus. Armament of exopodites showing setal formula Maxillar appendages of second and third legs less hairy, but dentiform spines on their tops larger than in С. maeoticus (figs ). Parthenogenetic females measure 0.65 to 0.70 mm; gamogenetic females and male are still unknown. Distribution. Central and southern Caspian Sea. Discovered first in samples taken in 1913, collected again between 1940 and Remarks. This species is named in honour of Prof. Arvid Behning, outstanding carcinologist, who greatly advanced our knowledge of the fauna of the Caspian basin.

9 While giving a brief characterization of the genus Corniger, Behning (1938) wrote: "The majority of species [of this genus] bear processes on the upper surface of the head, from little spinules (C. auritus) to branched horns (C. hitcus)". Perhaps Behning implied under the name C. auritus the above species. However, the lack of figures and of any satisfactory description in Behning's paper prevents the identification with these names 2 ). Corniger bicornis Zernov, Cornigerius bicornis (Zernov) Female. The appendages on the head are represented by two horns, issuing separately from the frontal surface or, more often, from a rounded bulge or low knob. A distinct "trunk" never exists. The shape and size of these horns, as shown in figs , are extremely variable, ranging from slightly obtuse knobs to rather long pointed processes sometimes unequal in length.

10 The shell is always more or less elongated, tapering to the top, but also very variable in shape. The external appearance of the animal therefore is very changeable, varying from comparatively large specimens with a nearly oviform body and a very low head to considerably smaller ones with a shortened nearly triangular shell and an elevated head. The caudal claws are strongly developed but as a rule slightly curved and not much diverging (at an angle of less than 90 degrees), by which the species under description differs from the rest of the Cornigerius species. Another important difference of С. bicornis consists in the partial reduction of the exopodite setae of the second and third legs. A part of my individuals has the usual expodite armament of , but in many others a seta, namely the lesser one, is undeveloped and very thin or lacking on the third and sometimes also on the second leg, the exopodite armament then fitting the formulae or even (figs ), i.e., like Podonevadne trigona. Sometimes specimens occur in which there is a different setal formula on the right and left legs. Thus the exopodite armament in this species is unstable, С. bicornis occupying in this respect a particular position in the family Polyphemidae, where the setal formula is usually considered a good distinctive specific character. Parthenogenetic females measure 0.5 to 0.7 mm; gamogenetic females and males are unknown. Distribution. Caspian Sea and Sea of Asov. Remarks. C. bicornis was found first by Zernov (1901) in the Sea of Asov in May In his description Zernov limited himself to the indication of two horns, issuing directly from the head (not from a common trunk as in the rest of Cornigerius species). Zernov added that he saw this species twice only and could not study its structure in detail. So far no indications of this species have been published after the appearance of Zernov's paper. In looking through the plankton samples taken in the Caspian Sea in May 1913, I unexpectedly discovered in rather great numbers a polyphemid corresponding to the above given description. The resemblance in the situation of head processes and in the body shape with Zernov's description, in spite of the incompleteness of the latter, puts beyond doubt the identity of this form with Cornigerius bicornis (Zernov). Later on the species was found (in two specimens only) by L. Butorina in samples taken in the Central Caspian in May ) In my preliminary review (Mordukhai-Boltovskoi, 1964) I listed С. auritus Behning with the notation that it was not described. Later on it turned out that in one more species of Corniger, namely С. bicornis (described below) the processes on the head are also often reduced to little knobs. So it is difficult to determine which species was named by Behning C. auritus and it would be best to ignore this nomen dubium.

11 Judging by the fact that in summer and autumn samples from the Caspian and Asov Seas C. bicornis was never found, the assumption arises that this species is one of the very few polyphemids connected with the spring season. CONCLUSIONS All the species and subspecies of the genus Cornigerius have a common character, viz., appendages on the head, distinguishing them from the rest of polyphemids (excepting Caspievadne, which has in addition, however, two large processes on the shell). However, with respect to the structure of the legs and the caudal claws the species of Cornigerius are not quite uniform and may be divided into two groups: (1) C. maeoticus (with all its forms) and C. arvidi, in which the exopodite armament formula is and which have strongly diverging caudal claws, and (2) C. bicornis and C. lacustris, in which the caudal claws do not strongly diverge; in the first species of the second group

12 the exopodite armament is unstable, in the second the setal formula is A more detailed study of the latter is very desirable and would help to clear up the relationship of Cornigerius with other polyphemids. ZUSAMMENFASSUNG REFERENCES BEHNING A.L., О zimnem zooplanktone Kaspiiskogo moria. Trudy po kompleksn. Izucheniu Kasp. moria, 5: [in Russian]., Cladocera Kawkaza. Vysokogorn. biolog. stancia Gruzii: i-vii, [in Russian]. MEISSNER V., Mikroskopische Wassertiere des Aralsees und der einmiindenden Fliisse. Wissen. Ergebn. Aralsee- Exped., 8: 1-102, pls [in Russian]. MORDUKHAI-BOLTOVSKOI PH.D., I960. Kaspiiskaia fauna w Azovsko- Chernomorskom basseine: (Moskwa, Akad. Nauk). [in Russian]., Polyphemidae of the Pontocaspian Basin. Hydrobiologia, 25 (1-2): , in press. On the males and gamogenetic females of Caspian Polyphemids. Crustaceana., in press. О Kaspiiskih Polyphemidae w wodohranilishchah Dona i Dniepra. [in Russian]. PENGO N., О nowom rakoobraznom iz sem. Polyphemidae. Trudy Obshch. Ispytat. Prirody Harkow. Univ., 13: 9-20, pi. 1. [in Russian]. SARS G.O., On the Polyphemidae of the Caspian Sea. Ann. Mus. zool. Ac. Sc. St.-Petersb., 7: , Notes on the Crustacean fauna of the Caspian Sea. Festschrift fur Prof. N. Knipowitsch: SPANDL H., Zur Kenntnis der Siisswassermikrofauna Vorderasiens. Ann. nat. Mus. Wien, 36: , Hydrobiologisches aus Armenien. Verh. intern. Verein. LimnoL, 1: ZERNOV S.A., Resultaty zoologich excursii po Azovskomu morju V Ann. Mus. zool. Acad. Sci. St.- Petersb., 6 (4): [in Russian]. Received for publication 8 September 1964.