Pogonophryne neyelovi, a new species of Antarctic short-barbeled plunderfish (Perciformes, Notothenioidei, Artedidraconidae) from the deep Ross Sea

Abstract This paper continues descriptions of new deep-water Antarctic barbeled plunderfishes of the poorly known and the most speciose notothenioid genus Pogonophryne. It is based on a comprehensive collection obtained by the authors in 2009–2010 during an Antarctic toothfish (Dissostichus mawsoni) fishing trip. A new species, the hopbeard plunderfish Pogonophryne neyelovi, the twenty-second species of the genus, is described. The new species belongs to dorsally-spotted short-barbeled species forming the “Pogonophryne mentella” group. Pogonophryne neyelovi sp. n. is characterized by the following combination of characters: a very short and small mental barbel with an ovaloid and short terminal expansion covered by flattened scale-like processes that are mostly bluntly palmate; a moderately protruding lower jaw; a high second dorsal fin almost uniformly black and lacking a sharply elevated anterior lobe; pectoral fins striped anteriorly and uniformly light posteriorly; the anal and pelvic fins light; the dorsal surface of the head and the area anterior to the first dorsal fin covered with large, irregular dark brown blotches and spots; the ventral surface of the head, breast and belly without sharp dark markings. The new species is compared to the closest species Pogonophryne brevibarbata, Pogonophryne tronio, and Pogonophryne ventrimaculata. English vernacular names are proposed for all species of the genus.


Keywords
Southern Ocean, deep-water fishes, taxonomy, mental barbel, biology, reproduction introduction Antarctic barbeled plunderfishes of the genus Pogonophryne (Perciformes: Notothenioidei: Artedidraconidae), the most speciose among notothenioid fish with a circum-Antarctic distribution, inhabit inshore and bathyal bottom zones of the Southern Ocean. Pogonophryne is one of the most taxonomically complex notothenioid genera (Eakin et al. 2001;Shandikov et al. 2013). Identification of Pogonophryne species is furher complicated by the deficiency of molecular-genetic data, known to date for only half (11) of the species (Eakin et al. 2009), and by the poor knowledge of intra-and interspecific variation due to the lack of material so far available for a comparative study. Among 21 species currently recognized within the genus Pogonophryne (Shandikov et al. 2013), whose limits are yet to be determined, 12 species (about 57%) belong to the most species-rich "P. mentella" group of dorsally spotted species defined by Balushkin and Eakin (1998). Three new deep-water fishes belonging to the short-barbeled and medium-barbeled species of this group were recently described from the marginal seas of continental Antarctica (Eakin et al. 2008;Balushkin et al. 2010;Shandikov et al. 2013) − spotless nape plunderfish P. bellingshausenensis Eakin, Eastman & Matallanas, 2008, shortbeard plunderfish P. brevibarbata Balushkin, Petrov & Prutko, 2010 and turquoise plunderfish P. tronio Shandikov, Eakin & Usachev, 2013. One more, the forth short-barbeled species − spotbelly plunderfish P. ventrimaculata Eakin, 1987, is known only from the shelf waters of East Antarctica.
In addition to the currently recognized species of Pogonophryne, including the new species P. neyelovi, seven previously unknown forms from the deep Ross and Amundsen seas that may represent formally undescribed species were considered by Shandikov (2013) as Pogonophryne species A to G in his brief review of the genus.
In this paper we continue descriptions of new species of the genus Pogonophryne collected as by-catch of Antarctic toothfish, Dissostichus mawsoni Norman, 1937 (Nototheniidae), by the first author as a CCAMLR (Commission for the Conservation of Antarctic Marine Living Resources) international scientific observer from Ukraine during the austral summer 2009-2010 fishing cruise of longliner F/V Tronio (Grupo Regal, Celeiro, Lugo, Spain) to the Ross and Amundsen seas. The twenty-second currently recognized species of the genus, the hopbeard plunderfish P. neyelovi sp. n., is described herein from the deep Ross Sea.

Materials and methods
Description of coloration was taken from fresh and formalin-preserved (10%) specimens, counts and measurements were taken from the formalin-preserved holotype following Shandikov et al. (2013) with digital callipers to the nearest 0.1 mm. Stage of gonad maturity (SGM, stages I to VI) was identified following Shandikov and Faleeva (1992) by visual examination with stereo-binocular microscope. Hepatosomatic index and gonadosomatic index (GSI) were calculated using body weight without swallowed bait.
Additional morphological data obtained by the authors from direct field observations and laboratory examination of specimens of most of the other species of the genus Pogonophryne were also used for the comparison, except for two species: finespotted plunderfish P. permitini Andriashev, 1967 andlongbeard plunderfish P. mentella Andriashev, 1967, that were compared based on the original descriptions by Andriashev (1967

Diagnosis.
A new species of the genus Pogonophryne distinguished from other species of the "P. mentella" group by the following combination of characters. Short and tiny mental barbel, light-brownish dorsally, reaching anterior edge of orbit over snout with mouth closed; its length about 9% SL (Table 1). Very short poorly developed ovaloid terminal expansion composed of bicolored, white and brownish, scale-like and mostly bluntly palmate processes; its length less than 1/3 of barbel length. Lower jaw  (1-2)+0+(8-10)=9-10 1+0+(7+8)=8-9 6-10 Gill rakers, posterior row 0+1+8=9 0+1+7=8 (0-1)+(0-1)+(6-8)=7-9 (0-1)+(0+1)+(6-7)=7-8 moderately protruding with weakly visible anterior teeth on symphysis and hidden dorsum of tongue when mouth closed. Second dorsal fin high in male (its height about 25% SL), lacking any prominent anterior elevated lobe, with longest rays (1 st to 7 th ) very soft, sinuous distally and branched from about mid-length; fin almost entirely black in coloration with bluish insertions in anterior one third and dark basally with light upper margin posteriorly. Dorsal surface of head and area anterior to first dorsal fin covered by dark-brown irregular spots, vermiculations and markings; belly, breast and lower surface of head brown or brownish in general, without distinct dark spots. Mandibular oral valve light. Pectoral fin vertically dark-striped in its anterior part and uniformly lightish in posterior part. Description of holotype. For all measurements and counts see Table 1. Body robust and tadpole-like from dorsal and ventral views. Head depth (maximum body depth) 20% SL. First dorsal fin with two soft spines, comparatively low, length of its base very short. Second dorsal fin with 27 rays and very high, its dorsal profile not concave and without a prominent elevated anterior lobe. Longest second dorsal fin rays (1 st to 7 th ) very soft, sinuous distally and branched from about mid-length. Anal fin with 18 fleshy rays. Left and right pectoral fins with 20 rays. Pelvic fin not long, fleshy and notably wide (almost as wide as long). Posterior margin of caudal fin sharply rounded.
Eye filling orbit, snout rounded in dorsal view. Lower jaw moderately protruding (distance between tip of lower jaw and tip of upper jaw 1.9% SL or 4.8% of head length) with weakly visible anterior teeth on symphysis and hidden top of tongue when mouth closed. Posttemporal ridges not prominent. Both oral valves anteriorly possess sparsely distributed short and simple papillae; inner margins of both lips fringed.
Mental barbel (Fig. 2b) small and short, its length about 9% of head length, somewhat rounded distally, reaching anterior edge of orbit in backward extended mode over snout with mouth closed. Barbel base about 21% as wide as long. Proximal part of stem covered by sparsely distributed short papillae; median part of stem covered by sparsely distributed elongated papillae; distal part of stem covered by densely distributed flattened and acute-angled processes. Terminal expansion short, ovaloid and barely wider than stalk (width about 3.2 mm or 12% of barbel length, depth about 2.8 mm or 10% of barbel length), composed of scale-like, mostly bluntly palmate (resembling cat's paw) processes; bifurcated, truncate and serrated processes also occur.
Teeth on both jaws sharp and conical, slightly curved inwards, somewhat enlarged on tips of jaws in posterior rows, somewhat larger on upper jaw; up to five irregular rows at symphyses of lower and upper jaws.
Radiograph. Total vertebrae 38: 16 abdominal and 22 caudal. Coloration. In live specimen general ground coloration of upper and lateral surfaces of head, upper jaw, back and lateral trunk sandy-pale. Bases of pectoral fins uniformly dark-brown. Abdominal surface of body lacking evident dark spots or markings: belly generally dark brown with some lighter indistinct areas and longitudinal zigzag-like striations, Breast lighter than belly, lower surface of head light. Dorsal and lateral surface of head anterior to first dorsal fin, back and lateral parts of trunk covered by dark-brown, specific irregular (not rounded) markings − vermiculations and spots, markings covering up to 50% of upper surface of head anterior to first dorsal fin. Spotted skin extends over dorsal parts of eyes. Nostrils unpigmented. Upper jaw mostly spotted, posterior tips of maxillaries and angle of mouth uniformly white. Mandibular oral valve whitish to somewhat light brownish, maxillar oral valve whitish. Fringes on inner margins of both lips and oral cavity overall whitish. Mental barbel indistinctly bicolored dorsally: with brownish stem and bicolored, whitish and brownish, scale-like processes on terminal expansion, ventral surface of stem lighter.
Soft spines in first dorsal fin whitish, fin-fold blackish basally and light-bluish distally. Second dorsal fin generally black in anterior third with partly bluish fin-fold sectors along first to third and sixth-seventh rays, and dark basally with light upper margin posteriorly. Anal and pelvic fins light, somewhat pinkish (fleshy), without the contrasting (dark-light) vertical bicolored pigmentation typical of most congeners. Pectoral fins with about six to seven narrow dark vertical stripes anteriorly, distal third of fins light. Caudal fin with creamy-pinkish (fleshy) ground coloration, dark very basally and in median superior part more evident in three upper branched rays, with about six indistinct dark vertical stripes medially.
Gill chamber light, somewhat light-brownish. Peritoneum creamy white, with very sparsely distributed black dots.
In formalin-preserved specimen general features of pigmentation remain unchanged except for bluish and pinkish coloration on fins being faded.
Variability. The second dorsal fin in the adult male is considerably higher than in the female (24.8% SL vs. 18.9% SL in female, Table 1), this may be due sexual dimorphism. In the female the point of primary branching of the anterior longest rays in the second dorsal fin is located somewhat above the mid-point of the rays (vs. midpoint of rays in male). General body and fin coloration is similar in both sexes. Wide, very fleshy and uniformly light pinkish pelvic fins, as well as fleshy anal-fin rays and uniformly light pinkish coloration of the anal fin and ground coloration of the caudal fin, may be considered as nuptial or age-related changes in post-spawning adults, both male and female. Similar nuptial or age-related changes in adult fish were recently found in P. tronio by Shandikov et al. (2013). Immature subadult or juvenile individuals probably possess vertically bicolored (dark and whitish) anal and pelvic fins, and the pelvic fins are narrowed as can be seen in the smaller unpreserved specimen 305 mm TL (Fig. 4).
Distribution. P. neyelovi is a deep-water benthic species known from three captures in the Ross Sea at depths of 700-1,390 m.
Mode of life. Like other morphologically close deep-water congeners (Shandikov et al. 2013) P. neyelovi might be considered predatory in its feeding behavior. It probably also feeds by necrophagy. Three known specimens of P. neyelovi were captured by hooks baited with large pieces (about 4×3×2 cm) of giant Peruvian squid, Dosidicus gigas. In the holotype, the liver is large, filling about 35% of the abdominal cavity length and creamy in coloration; hepatosomatic index reaches 2.0. Spawning probably took place within one month prior to the capture, around December -January. The testes are paired, well developed and folded, reaching about 68 mm in length, 14 mm in width and 6.5 mm in depth. GSI was about 0.6, and SGM apparently corresponds to early post-spawning stage VI or VI−II. Etymology. The new species is named after Alexey V. Neyelov who contributed significantly to the knowledge of Antarctic fishes, and to whom the first author is sincerely thankful for the valuable help during his PhD studies in Zoological Institute, Russian Academy of Scienses, St Petersburg, Russia. Vernacular names proposed for P. neyelovi: hopbeard plunderfish -in English and хмельовуса бородатка [khmelyovusa borodatka] -in Ukrainian.

Comparative remarks
Pogonophryne neyelovi sp. n. belongs to plunderfishes of the "P. mentella" group that is characterized by the following characters: 1. the body and the head are covered with conspicuous dark markings; the spots are usually present on the top of the head, the nape and the back anterior to the first dorsal fin, spots on the top of the head varying in size and shape, mostly large, rounded, irregular or vermiculated, and usually sparsely distributed covering less than half the surface; 2. the anterior margin of the orbit is rounded, the eye entirely filling the orbit anteriorly; 3. the mental barbel is slender, tiny or stout and considerably varying in length (8-30% SL), its terminal expansion (inconspicuous or prominent) being present; 4. the inerorbital distance is wide (over 6% SL); 5. ridges on the top of the head are not well developed; 6. the snout slopes gradually (45° or less from the horizontal) in the lateral view; 7. the tip of the lower jaw is pointed or rounded and considerably varying with regard to its projecting beyond the upper jaw.
Pogonophryne neyelovi sp. n. belongs to the four species of the "short-barbeled subgroup" of the "P. mentella" group characterized by the mental barbel not exceeding 13% SL. This subgroup also includes one shallow-water species, P. ventrimaculata, known from the Weddell Sea and the Cosmonauts Sea, and two recently described deep-water species, P. brevibarbata and P. tronio that are sympatric with P. neyelovi and captured from the same locality in the deep Ross Sea.
Pogonophryne neyelovi sp. n. clearly differs from P. ventrimaculata, P. brevibarbata and P tronio in having a very short (less than 1/3 of mental barbel length) and poorly developed ovaloid terminal expansion composed of bicolored, light and brownish, scale-like mostly bluntly palmate processes with transverse overall orientation (Figs 1d,  2b, 3d, 4d). In P. ventrimaculata (Fig. 2d) the terminal expansion is well developed, bushy, stout and long (1/2 to 2/3 of mental barbel length), composed of light, mostly slender and tapered processes. In P. brevibarbata it is tubiform and less developed than in P. ventrimaculata but still long (more than 1/2 of mental barbel length), composed of light slender processes united mainly in longitudinally or obliquely oriented folds and rosettes (Fig. 2c). In contrast, in P. tronio (Fig. 2a) the terminal expansion of the mental barbel is weakly developed, tapering and short (of about the same length as in P. neyelovi sp. n.).
With regard to the shape of the dorsal fin, a short digression should be given here. There can be distinguished four types of the shape of the second dorsal fin in males of Pogonophryne (Fig. 5). Type 1 ("P. tronio type", Fig. 5a): the fin is low (its height is up to 20% SL), slightly raised anteriorly, with a straight (not evidently concave) dorsal profile and without an anterior lobe; this type is known in six species (P. macropogon, P. lanceobarbata, P. cerebropogon, P. squamibarbata (?), P. bellingshausenensis, and P. tronio). Type 2 ("P. brevibarbata type", Fig. 5b): the fin is moderately high (its height is about 21-23% SL), definitely raised in its anterior part, with a concave or ladder-shaped dorsal profile, and commonly with a more or less prominent anterior lobe; this type is known in three species (P. ventrimaculata, P. eakini, P. brevibarbata) and four undescribed forms (Pogonophryne sp. C, D, E and F) (Shandikov 2013). Type 3 ("P. neyelovi type", Fig.  5c): the fin is high (its height is about 25% SL), greatly raised in its anterior part, with an almost straight (not clearly concave) and gradually raised dorsal profile and without a prominent anterior lobe; this type is known in only one species, P. neyelovi sp. n. Type 4 ("P. barsukovi type"): the fin is very high (its height is 25-35% SL), considerably raised in the anterior part, with a clearly concave or ladder-shaped dorsal profile and a prominent anterior lobe; this type is found in five species (P. scotti Regan, 1914, P. marmorata Norman, 1938, P. barsukovi Andriashev, 1967, P. immaculata Eakin, 1981, P. stewarti Eakin, Eastman & Near, 2009 and in one undescribed form (Pogonophryne sp. B) (Shandikov 2013). We could not classified the following seven species and one undescribed form as they have been known only by juveniles or females: P. permitini, P. mentella, P. albipinna Eakin, 1981, P. platypogon Eakin, 1988, P. dewitti Eakin, 1988, P. fusca, P. orangiensis and Pogonophryne sp. A in Shandikov (2013. Thus, as shown above, the shape of the second dorsal fin in the new species is rather peculiar (type 3, Fig. 5c) and possesses sinuous anterior rays that begin branching at about the mid-point of its length (vs. straight rays that begin branching at about the upper one forth of the ray in three other species in comparison). In contrast to males of P. brevibarbata and P. ventrimaculata (type 2, Fig. 5b) the male P. neyelovi has neither a concave dorsal profile nor a prominent anterior elevated lobe in the second dorsal fin. In contrast to males of P. tronio (type 1, Fig. 5a) it shows a significant difference in height of the anterior and posterior parts of the second dorsal fin (height of the posterior part of the second dorsal fin is 57% of maximum height of the second dorsal fin vs. 81-91% in P. tronio).
The new species also differs from P. ventrimaculata in lacking evident dark sharp spots and markings on the bases of the pectoral fins, the ventral parts of the head, breast and belly and in lacking any evident oblique dark striations on the second dorsal fin as well as in having uniformly pale pinkish anal and pelvic fins in adult individuals (vs. dark-light vertically bicolored or striped ones). It can be further distinguished from the latter in having more numerous total vertebrae (38 vs. 36-37). The new species has probably a deeper bathymetric distribution (700-1,390 m vs. 247-423 m).
The new species is morphologically closer to sympatric P. tronio but it differs form the latter, besides the characters mentioned above, in having a more prominent lower jaw (teeth on the symphysis of the lower jaw are seen with the mouth closed vs. completely unseen in P. tronio) and by the peculiarities of the coloration: in having an almost black second dorsal fin in the male (similar to P. brevibarbata) rather than a sharply striped or mottled fin as in P. tronio. In addition it may be noted that a recently post-spawning P. neyelovi possesses remarkably fleshy and wide pelvic fins (up to 91% as wide as long) being similar in this regard to both sexes in post-spawning P. tronio (81)(82)(83)(84)(85)(86)(87)(88)(89)(90). Although the taxonomic validity of this character (probably nuptial) is still unclear in Pogonophryne, it was not so prominent in adult specimens of the other species with narrower pelvic fins (e.g. 52-60% as wide as long in P. brevibarbata; Shandikov et al. 2013).