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Rapp. P.-v. Réun. Cons. int. Explor. Mer, 178: 593-594. 1981.

ON THE S1NISTRAL FLATFISH LARVAE (SCOPHTHALMIDAE, BOTHIDAE, PISCES) FROM THE WEST ATLANTIC

S. A. Evseenko All-Union Research Institute of Marine Fisheries and Oceanography (VNIRO) Moscow, USSR

Larval flatfish provisory (temporary) features and Lower taxonomic levels, genus or species, have their taxonomic value are presented in this paper. particular identifying features such as pigment Also, relationships between some groups of the pattern. In a number of cases pigment pattern can flatfishes are discussed. characterize a genera group. The material for this paper was provided by According to pigment peculiarities and to other ichthyoplankton sampling carried out in the western provisional features, there are distinguished three part of the Atlantic from South Greenland to genera groups among the Paralichthyinae. These are Venezuela, in the Eastern Atlantic from Great Britain Pseudorhombus, Paralichthys, Tarphops and to Angola, in the Black Sea, in the Eastern Pacific off Hippoglossina group; Citharichthys, Etropus group, Central America, in the Indian Ocean and in the and Syacium and Cyclopsetla group. It is curious, that Arabian Sea. A total of 6500 ichthyoplankton samples the genera of the three groups are united not only by from 5000 stations were studied, from which 27 species provisional features of their larvae, but also by of flatfish larvae were investigated. common features of adult specimens. Provisory and definitive features are used for There are two genera groups among Bothidae, identification of flatfish larvae as well as for larvae of which differ in eye position during larval other groups of fishes. The following eight provisory metamorphosis in relation to the origin of dorsal fin. features can be used to identify flatfish larvae: (1) The first group includes the genera symmetric position of eyes, (2) swim bladder Pseudorhombus, Paralichthys, Tarphops, availability, (3) elongation of cartilaginous posterior Hippoglossina, Syacium, Citharichthys and Etropus process of pelvic bone, (4) elongation of one or several from the Paralichthyinae. During metamorphosis rays of dorsal fin and left ventral fin, (5) development their eye migrates in front of the origin of dorsal fin. of spines on neurocranium (6) development of spines The second group unites the genera Taeniopsetta, on opercular bones, (7) development of spines on Engyophrys, Trichopsetta and possibly Monolene of urohyal, cleithra and posterior process of pelvic bone, the Paralichthyinae, with genera of Bothinae known and (8) pigment peculiarities. to share the feature of having the migrating right eye The presence of a swim bladder in larvae move under the base of dorsal fin. When this is characterizes the whole Bothidae family, its absence happening, the origin of the fin’s base separates from characterizes all Pleuronectidae larvae, while presence the cranium. This pattern is typical for all genera, or absence of swim bladder is not a typical feature to except Cyclopsetta and Bothus. In the latter genera the characterize Scophthalmidae, but only different dorsal fin base is not separated from the cranium groups of genera. during eye migration, rather the eye passes through a Strong development of posterior process of pelvic rupture in the head tissues. bone and availability of one elongated ray in dorsal fin It should be marked that the first group is made up are typical of all the Bothinae and the genera group of by less specialized genera than the second one, which the Paralichthyinae to which Taeniopsetta, unites highly specialized Paralichthyinae and all Engyophrys, Trichopsetta and Monolene belong. The Bothinae, which are even more specialized. fact that these flatfishes have the same above Thus, in the Bothidae family eye position during mentioned shows their close relationship. metamorphosis in relation to the origin of the dorsal 594 S. A. Evseenko

fin depends on the extent of specialization of a neurocranium and opercular bones. particular genus and its deviation from the initial The larvae of only two species of Microstomus have form, which has an eye moving across the head profile, spines on acoustic capsules. judging by observations of primitive Bothidae. Spines on acoustic capsules are typical only of M. When early period of bothid development is studied achne and M. pacificus larvae on their family, which one’s attention is drawn to the extraordinary likeness emphasizes peculiarity of flounders of Microstomus of Taeniopsetta, Engyophrys, and Trichopsetta larvae genus. and such representatives of the subfamily Bothinae as Should we refer to the data concerning fish larvae of Crossorhombus, Psettina, and Engyprosopon. In my other orders, we would find that many Perciformes previous papers (Yevseyenko, 1976; Evseenko, 1977) I larvae have spines on bones of gill cover and already discussed possible reasons of likeness between neurocranium. They are developed best on larvae of Engyophyrys and above-mentioned flatfishes and the primitive family Serranidae and some other made an assumption that this genus must be very close Perciformes. Spines are likely to have a protective to the Bothinae and not to the Paralichthyinae, to function and to increase buoyancy. which it was referred by Norman (1934). Head spines of the most of the mentioned flatfishes Quite recently it has been shown that the genera are small and it is hard to assume that they have any Taeniopsetta, Engyophrys, Trichopsetta and special function. Then the question arises, what caused Monolene are closer to the Bothinae and not to the these spines in Pleuronectoidei ontogenesis. Paralichthyinae, both according to the features of In my opinion, the appearance of spines on bones of adult specimens (Hensley, 1977) and those of larvae gill cover and neurocranium in ontogenesis of (Futch, 1977; quoted from Hensley, 1977). So, the Pleuronectoidei may be regarded as recapitulation of position of these genera in Norman’s system of the ancestral features, which have some phylogenetic family Bothidae has to be revised. meaning and indicate the origin of flatfishes from To conclude, it would be of interest to examine Percoid ancestors. other provisory larval features such as availability of At least, there should be mentioned an spines on neurocranium and gill cover bones. extraordinary likeness in the position of head spines of The least specialized Pleuronectoidei and some deep Psetta (Pleuronectoidei) and Achirus (Soleoidei) water species of this suborder possess the common larvae, which are found, according to my data and feature of spines on the gill cover bones, based on my those of Futch et al. (1972) on preopercule, observations and a review of the literature. interopercule, posttemporale, and supraorbital For example, Brachypleura novaezeelandiae larvae section of neurocranium. If my explanation of the from the family Citharidae, which, according to appearance of spines on flatfish larvae is right, the Hubbs (1945) are an intermediate link between similarity of representatives of the two suborders in Psettodes and other flatfishes, have regularly the early life history may be regarded as one of the positioned spines on their preoperculars. criteria for monophyletic origin of Pleuronectiformes. Scophthalmidae larvae, which are the closest to the Citharidae (Hubbs, 1945), have spines on preoperculars, with the most developed ones REFERENCES belonging to larvae of the primitive genera Psetta and Evseenko, S. A. 1977. Larval Engyophrys senlus Ginsburg, 1933 Scophthalmus. (Pisces. Bothidae) from the American Mediterranean Sea. FAO In the family Bothidae only Paralichthyinae larvae Fish. Rep., No. 200: 171-185. have spines on opercular bones, and not all of them, Futch, C. R. 1977. Larvae of Trichopsetta ventralis (Pisces, but only the least specialized ones. Bothidae) with comments on intergeneric relationships within the In the family Pleuronectidae the larvae of Bothidae. Bull. Mar. Sei., 27: 740-757. Atheresthes, the most primitive representative of this Futch, C. R., Topp, R. W., and Houde, E. D. 1972. Developmental group of flatfishes, have preopercular spines. Besides osteology of the lined sole, Achirus lineatus (Pisces, Soleidae). Contr. Mar. Sei. 16: 33-58. that, small irregularly placed preopercular spines are Hensley, D. 1977. Larval Engyophrys senta (Bothidae) with found on larvae of Glyptocephalus zachicus, Gl. cyno- comments on intermuscular bones in flatfishes. Bull. Mar. Sei., glossus, and Tanakius kitaharae. 27(4): 681-703. Further, only the larvae of those species and genera, Hubbs, C. L. 1945. Phylogenetic position of the Citharidae, a family which are characterized by availability of opercular of flatfishes. Mus. Zool., Univ. Michigan, Miscel. Publ., No. 63: spines, have spines on sphenoticum and spines which 38 pp. form a supraorbital collar. It should be noted that the Norman, J. R. 1934. A systematic monograph of the flatfishes more primitive features are found in adult flatfishes of (Heterosomata). Vol. 1. Psettodidae. Bothidae, Pleuronectidae. Brit. Mus. (Hat. Hist.): viii+ 459 pp. the familites of Scophthalmidae, Bothidae, and Yevseyenko, S. A. 1976. Larval Engyophrys senlus Ginsburg Pleuronectidae and the larvae of these species have the (Pisces, Bothidae) of the American Mediterranean. Progr. Mar. most pronounced development of spines on Res. Carib. Adjac. Reg., C1CAR-II Symp., abstract.