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A new genus Proeumicrotremus gen. nov. is established for the Soldatov’s lumpsucker Eumicrotremus soldatovi. The new genus differs from Eumicrotremus in a number of plesiomorphies in the structure and location of the external body armour, as well as in body proportions and a greater maximum length. Proeumicrotremus occupies an intermediate position between generalized genera and Eumicrotremus in the Cyclopteridae family system.

Phylogenetic morphological, and molecular analysis of lumpsuckers of the family Cyclopteridae is carried out. The cladograms reveal the validity of three subfamilies within the family Cyclopteridae: Cyclopterinae, Aptocyclinae, and Eumicrotrematominae. Five valid genera (Cyclopterus, Aptocyclus, Cyclopsis, Lethotremus, and Eumicrotremus) are revealed, and the genus Cyclopterus is accepted as the most generalized within the family Cyclopteridae. The genus Lethotremus is separated from the species of the genus Eumicrotremus, and, thus, the generic status of the former genus is restored. The taxonomic position of E. soldatovi is discussed. Based on the presence of a large number of monotypic genera among generalized clades of lumpsuckers, they could represent the remains of the former widely distributed fauna with a weak development or absence of external armament. The forms of the genus Eumicrotremus with a good armament represent a comparatively young group of weakly differentiated species. Several heterochronies of the paedomorphic and peramorphic types are revealed in the evolution of the family Cyclopteridae.

The variability of morphometric characteristics, the structure of the seismosensory system and the external skeleton in females and nonspawning and spawning males of the spotted lumpsucker Eumicrotremus pacificus were studied. Females differed from males in their greater anteanal distance and stability of the structure of the external skeleton throughout the adult period of life. Spawning males are characterized by a significant change in a number of plastic characters and the structure of their external skeleton, apparently related to the features of the spawning biology of the Eumicrotremus species. No noticeable variability was revealed in the structure of the axial skeleton, the skeleton of unpaired fins, and the seismosensory system of the head of E. pacificus. Using the characters of external morphology and the external skeleton of females and nonspawning males in the systematics of the lumpfishes was confirmed as valid.

In the collection of the Zoological Institute, Russian Academy of Sciences (ZIN), a female of the spiny lumpfish SL 25.1 mm from the Pacific waters of the southeastern tip of Paramushir Island was found that morphologically corresponds to the original description of E. gyrinops. The individual has gonads of the III–IV stage of maturity. The data of its morphological analysis and comparison with data on morphology and distribution of E. gyrinops, E. brashnikowi, and E. asperrimus are given.

The species status is justified for the Okhotsk lumpsucker Eumicrotremus ochotonensis based on the morphological characters. The differences from the closely related species E. derjugini inhabiting the Arctic Ocean are given. Two species were redescribed basing on type series, their diagnoses were clarified, and the lectotypes were designated. Intraspecific variability is discussed using new materials from the Barents, Kara, Laptev, and Okhotsk seas. The two species differ markedly in a complex of morphological features (shape of the submerged dorsal fin, proportions of the body, number and location of bony plaques) and characteristics of biology (spawning season). The modern disjunction of the ranges of E. ochotonensis and E. derjugini covers the Bering, East Siberian, and Chukchi seas. Sequence analysis of the cytochrome oxidase (COI) gene fragment of mtDNA revealed differences in the haplotypic diversity of the two species. Weak genetic divergence between species indicates a relatively recent isolation of E. derjugini and confirms its status of the evolutionary young species.

A new species multituberculate lumpsucker Eumicrotremus multituberculatus from the western part of the Aleutian Islands of the Bering Sea is described. The absence of tubes of the anterior nostrils and the presence of very short tubes of the posterior nostrils, numerous and very small conical bone plaques on the head and the trunk (15–17 in the circumpectoral row) without the central large spine on the plaque top distinguish the new species from other species of the genus Eumicrotremus. The new species is also differed by the terminal shape of mouth, equal length of jaws and smaller size of eye from the close species E. asperrimus and E. phrynoides. The sizes of pre-spawning females of E. multituberculatus are much less, than those of E. asperrimus. E. multituberculatus also differs from E. phrynoides by the presence of three to four rows of bone plaques on the throat and the presence of bone plaques on the rays of the first dorsal fin, and from E. asperrimus—by a dark peritoneum.

The second specimen of Eumicrotremus brashnikowi was found in collection materials of ZIN RAS. The species was placed in the genus Eumicrotremus on the basis of the following diagnostic characters: bone plaques spread all over head and body, including caudal peduncle; two pores in the infraorbital canal of the seismosensory system; pores of the seismosensory system are situated on the ends of long skin tubules on the chin and the lower part of a gill cover. The validity of E. brashnikowi is confirmed by the presence of bone plaques in the form of flat plates covered with very thin and short bone spines forming the rosette. The similar structure of bone plaques was not revealed in juveniles and adult specimens of other species of the genus Eumicrotremus. The redescription of E. brashnikowi is carried out. The considerable similarity of the external skeleton structure of E. brashnikowi and E. phrynoidesis is confirmed. The synonymy of E. phrynoidesis and E. asperrimus is not supported.

A juvenile specimen of the papillose lumpsucker Georgimarinus barbatus (Lindberg et Legeza, 1955) is first described and collated with juveniles of species of the close related genus Eumicrotremus.

The species status of a rare species Eumicrotremus eggvinii from the family Cyclopteridae has been revalidated. Some authors considered its specimens as males of close species E. spinosus. In the Zoological Institute collection, males of E. spinosus that are morphologically similar with females of this species have been found. This is evidence of absence of sexual dimorphism in E. spinosus. In new samplings from waters of the Franz Josef Land archipelago (Barents Sea), a specimen of E. eggvinii was found and described. The opinion of some authors that individuals of E. eggvinii represent males of E. spinosus is refuted. A new finding widens the species area to the northeastern limits of the Barents Sea. The number and character of distribution of bone plaques remain reliable taxonomic characters.

The juvenile specimen of Cyclopteropsis jordani from the Kara Sea was first found and described. According to the trapezoid form of the first dorsal fin, the largest length of its median rays, slightly lateral compression of the body and the number of rays in the dorsal, anal and pectoral fins, the juvenile is classified as Cyclopteropsis jordani. From one-size juvenile of Eumicrotremus derjugini it is distinguished by the complete absence of bone plaques.

New genus of cyclopterids, Georgimarinus gen. nov., is established for Eumicrotremus barbatus (Lindberg et Legeza, 1955). The new genus is characterized by the next unique apomorphies: teeth in the outer row at symphysis of premaxillae fuse with premaxillae, teeth at symphysis of dentary fuse among themselves and with dentary, forming the regular cutting edge; there are numerous barbs on the head and body; the bony plaques located in centers of connective tissue tubercles leaving the edges free.

The structure of skeleton of Bathylutichthys balushkini was studied and comparative analysis of it with representatives of other families of the suborder Cottoidei was performed. It was found that Bathylutichthyidae are characterized by the presence of a great number of original characters supporting its family status. They include: absence of mesethmoideum; bony canals of seismosensory system on frontale, pteroticum, and parietale and their strong reduction on infraorbitale; and absence of pterosphenoideum, intercalare, pharyngobranchiale 2, and basihyale. At the same time, Bathylutichthyidae retain a considerable number of generalized specific features: location of parietalia laterally to supraoccipitale and absence of their joint between themselves, presence of mesoptergoideum and basibranchialia 2 and 3. Cladistic analysis based on osteological characters and characters of the seismosensory system of 11 families of Cottoidei demonstrates that Bathylutichthyidae are combined into one group with families Rhamphocottidae, Agonidae, Psychrolutidae, Cyclopteridae, and Liparidae occupying an intermediate position between Psychrolutidae and the two last families. The cladogram obtained does not support the point of view of existence in the suborder Cottoidei of an independent superfamily Cyclopteroidea, including families Liparidae and Cyclopteridae.

The redescription of Eumicrotremus andriashevi Perminov, 1936, and designation of the new subspecies Eumicrotremus andriashevi aculeatus Voskoboinikova et Nazarkin ssp. n. (Litke Strait, Bering Sea) have been performed. E. andriashevi aculeatus differs from the nominative subspecies by the presence of larger and higher bone plaques that form the “cheeks” and make the external view of the fish “disheveled” and by the larger body height and smaller snout length, as well as by the shape of the infraorbitals and mesethmoideum.

The development of bony skeleton is studied in the ontogeny of lumpfish Cyclopterus lumpus. In general, the sequence of appearance of the bony elements is similar to that in other teleost fishes with the exclusion of the absence of the basihyal anlage and the presence of only cartilaginous basibranchials in all examined larvae and juveniles. Bony elements of the ventral sucking disc appear very early (together with the parasphenoid, maxilla, opercle, and cleithrum), and they are characterized by rapid development. The intercalar is observed in the neurocranium of the larvae. In late larvae and in juveniles, the anlage of the medial extrascapular fused with the parietal and the lateral extrascapular attached to the pterotic are registered. C. lumpus differs from Cyclopsis tentacularis and the species of the genus Eumicrotremus in the presence of the cutting in the upper margin of the ceratohyal instead of the berycoid opening. The larvae and juveniles of C. lumpus and C. tentacularis are characterized by the presence of a reduced spiny ray at the origin of the second dorsal fin, most likely, representing a plesiomorphy of the Cyclopteridae. In the larvae of C. lumpus and C. tentacularis of a similar size, the degree of development of skeletal elements is the same, which suggests a similar developmental rate of their skeletal elements.

The external morphology, osteology, and distribution of a rare fish species Psychrolutes pustulosus (Scorpaeniformes: Psychrolutidae) is examined based on an extensive material for the first time. P. pustulosus shows an extreme degree of reduction of the skeleton among the Psychrolutidae. The comparative morpho� logical analysis confirms the placement of this species in the genus Psychrolutes rather than in Gilbertidia. The new data show that P. pustulosus is widespread in the Sea of Okhotsk. The occurrence of this species in the Sea of Japan (Tatar Strait, Peter the Great Bay) is recorded for the first time. Reports on the findings of P. pustulosus in the Bering Sea are erroneous.

Comparative-osteological investigation of all species of the genus Zoarces is made: Z. fedorovi, Z. andriashevi, Z. elongatus, Z. viviparus, Z. americanus, and Z. gillii. In the skeleton of hyoid arch in species of Zoarces, Lycozoarces, and Lycodes, paired bony elements are found, not described previously, identified as parurohyalia which may be synapomorphy of Zoarcidae. Differences between the Zoarces species are revealed by 56 external morphological and osteological characters. Cladistic analysis yielded one tree 135, Ci 0.57, Ri 0.54 long. Cladistic analysis confirms validity of a recently described species Z. fedorovi, which turned out to be the most generalized in the genus Zoarces, as well as the validity of Z. elongatus. The species Z. americanus and Z. gillii occupy a terminal position preventing their isolation to independent genera as was previously supposed, as this would lead to paraphyly of the genus Zoarces.

The development of pigmentation of the Fedorov eelpout (Zoarces fedorovi) from hatching out of egg integuments to delivery is studied. In Z. fedorovi, the adult coloration develops immediately, without larval coloration, obviously, due to viviparity. Comparative analysis of the sequence of anlage and morphogenesis of elements of the cartilaginous skeleton and the bony skeleton demonstrated that the sequence of anlage of cartilaginous and bony regions of the skeleton of Z. fedorovi principally correspond to the sequence in Z. viviparus and in other perciform fishes. Morphogenesis of the bones of ethmoidal and interorbital regions of the skull, of the axial skeleton, and of the skeleton of the caudal fin is highly similar in eelpouts and other fishes of the suborder Zoarcoidei, differing from that in the generalized perciform fishes. At the same time, the larvae of Z. fedorovi in comparison with Z. vivparus are characterized by a higher rate of development of the skeleton. Advanced structural traits in structure of the skeleton of larvae of Z. viviparus in comparison with Z. fedorovi are pointed out. Differences in size at which anlage of bony elements occurs, as well as in the formation of particular bony elements seem to indicate to a rather prolonged divergence of these species.

The structure of the skeleton of Cyclopsis tentacularis, an endemic species from the northern part of the Sea of Okhotsk, is studied for the first time. Generally, it corresponds to that in other representatives of Cyclopteridae. The differences in structure of Cyclopsis and of other investigated cyclopterids are both plesiomorphic and apomorphic. The plesiomorphic ones are comprised of sutural articulation of pteroticum and prooticum, spiny ray in the beginning of D2, berycoid opening in ceratohyale, bony pharyngobranchiale 2, emergination in the anterior margin of scapula, and postcoracoid opening in coracoideum. The apomorphic ones are separation of parietalia, absence of bony basibranchialia, presence of emargination in the posterior margin of supracleithrum, and reduction of several last epipleural ribs. The presence of numerous plesiomorphies does not confirm Ueno’s viewpoint (Ueno, 1970) on the advanced position of Cyclopsis in the family Cyclopteridae. Final conclusions on the position of Cycloposis in the system of cyclopteridae and of the system of this family itself may be made only after proper investigation of the external morphology and osteology of all genera of Cyclopteridae.

A revision of the genus Genioliparis Andriashev et Neelov, 1976 with a description of a new species G. kafanovi sp. n. (holotype ZIN no. 54079), the Ross Sea, depth of 987–1727 m) was made. The genus Odontoliparis Stein, 1978 was reduced to the synonymy of Genioliparis. A hypothesis was suggested of the origin of the genus Genioliparis, which was previously considered an endemic of the Southern Ocean, in the northern Pacific and of its dispersal together with other genera of liparids (Paraliparis and Careproctus) to the southern hemisphere along the periphery of deep waters of the American continents. A key to identification of the species of the genus was compiled.

The external morphology and development of skeletal elements is investigated in larvae and fry of one of the most generalized representatives of the suborder Gobioidei—the Amur sleeper Perccottus glenii. It is characterized by an indirect type of development accompanied by the expressed metamorphosis, according to Balon's classification (1985). Fry of P. glenii are capable of an active mode of life and exogenous feeding almost immediately after hatching which favors a wide distribution of this species. Morphogenesis of previ- ously revealed diagnostic characters of Gobioidei is investigated. New apomorphies are found also indicating to a high separation level of P. glenii from representatives of other suborders of Perciformes. At the same time, it is found that some developmental traits of P. glenii are characteristic of generalized Perciforems. Some advanced characters acquired in parallel with representatives from the group of suborders Blennioidei s. l. also indirectly indicate that P. glenii and, generally, Gobioidei belong to Perciformes. Analysis of special traits of development of the skeleton of P. glenii supports the ideas of Regan (1911) on the origin of Gobioidei from generalized Percoidei. With consideration of advanced characters, general for Gobioidei and the suborders Trachinoidei, Notothenioidei, Zoarcoidei, and Blennioidei of the group Blennioidei s. l., it is assumed that Gobioidei and Blennioidei s. l. stem from the same group or from the related groups of Percoidei.

The authors describe, for the first time, juveniles of four species of Antarctic notothenioid fishes of the families Artedidraconidae and Bathydraconidae: Artedidraco orianae Regan, 1914; Dolloidraco longedorsalis Roule, 1913; Akarotaxis nudiceps (Waite, 1916); and Bathydraco macrolepis Boul., 1907. The probable features of larval pigmentation of Histiodraco velifer (Regan, 1914) are given. A comparison is made of juvenile and adult pigmentation.

Antarctic fish from the suborder Nototheniidae (the order Perciformes) have been evolving under the conditions of a long-term temperature decrease from +15 to ‐1.9 ° C. At present, representatives of the generalized families Bovichtidae, Pseudaphritidae, Eleginopsidae, Nototheniidae, and Harpagiferidae mostly inhabit the Antarctic low-latitude and temperate waters. Species of the Trematominae subfamily of Nototheniidae, as well as species of the Artedidraconidae, Bathydraconidae, and Channichthyidae families, had spread to the coastal waters of the Antarctic high latitudes covered with ice. The original concept of Nototheniidae cold compensation through a significant increase in their metabolic rate compared to low-temperature metabolism of low- and temperate-latitude fishes was not confirmed [1]. Nevertheless, in Nototheniidae, a series of intracellular and molecular adaptive mechanisms proved to compensate the effect of low temperatures on physiological processes [2‐6 etc.]. These mechanisms are the most pronounced in the members of the advanced families Artedidraconidae, Bathydraconidae, and Channichthyidae, which is the result of Nototheniidae evolution during resettling from the mild temperature of temperate waters to the Antarctic region.