Psednos

Stein, David L., 2012, A Review of the Snailfishes (Liparidae, Scorpaeniformes) of New Zealand, Including Descriptions of a New Genus and Sixteen New Species, Zootaxa 3588, pp. 1-54 : 50-52

Psednos sp.

Material examined. NMNZ P.025760, ripe male,> 83 mm SL, TL unknown, 38°59.50' S, 167°22.60' E, Challenger Plateau, R/V James Cook, Stn. JCO 8902/014, 13 March 1989, 936– 950 m. Poor condition (broken, flattened, and skinned).

Description. Counts: V>39, D>32, A>27, P 15?, radials unknown, pc 7, pores unknown. Ratios (all in % HL): orbit ~ 26, uj 54.5, lj 54.0, preD 152.0, preA 142.9, mabd 164.6, pabd 107.1.

Head short, moderately deep; dorsal profile rising steeply and evenly at an angle of about 50° to moderate occipital hump, gradually tapering posteriorly. Snout and symphysis of upper jaw slightly included, tip of mandible most anterior point of body. Snout short, low, about on horizontal through mid pupil or orbit. Nostril single, not tubular, directly anterior to orbit above middle of eye. Eye probably small; orbit below dorsal profile of head. Mouth oblique, its angle about 50°, oral cleft short, reaching to below anterior margin of orbit; posterior of upper jaw below middle of orbit. Teeth lanceolate canines; a deep symphyseal notch present in premaxillae. Upper jaw teeth in about 30 oblique rows of up to 8–9 teeth each, forming a narrow band, its width gradually increasing anteriorly. Mandibular teeth in about 27 oblique rows of up to about 5 teeth each, forming a narrower band than in upper jaw except near symphysis, where it widens more abruptly than in upper jaw. Teeth similar to those in upper jaw, but generally larger and longer, especially innermost teeth; a narrow but distinct gap present at symphysis. Angle of retroarticular about 90°. Gill opening above pectoral and possibly extending ventrally in front of 6–7 rays. Opercle a broad, straight sword-like blade extending almost vertically down, its tip reaching to base of sixth pectoral fin ray. Pore formula unknown.

Pectoral fin dorsalmost ray about on horizontal between mouth and orbit. Pectoral fin rays 7–8+3?+5? Lengths of upper and lower lobes and notch depths unknown, rudimentary rays absent. Fin rays of upper and lower lobes distinctly more closely spaced than those in notch. Pectoral girdle not examined.

Trunk anteriorly deep, tapering evenly and rapidly to tail, curvature of occipital hump posteriorly weak, hump sloping evenly into trunk; highest and deepest point of body almost directly above gill opening. Number of vertebrae probably>50, posterior part of tail missing; 39 vertebrae (12+>27) present. Anterior vertebrae forming only a moderate dorsal curve. Neural spines 1–4 thicker, spines 5 and 6 are forked; the remainder are single and slender. Dorsal fin origin between vertebrae 7–8, anal fin origin between vertebrae 12–13. Anus position unknown. Abdomen about equal to HL. Pyloric caeca thin walled, digitate, long.

Color of body unknown, completely skinned; head whitish; mouth dusky blackish, tongue brown dotted; branchial cavity brown dotted on pale background. Peritoneum dark brown, visible through body wall; stomach dusky brownish, caeca pale. Intestine brownish near stomach, but distally white except for black ring at anus.

Distribution. Known from a single specimen collected above the Challenger Plateau northeast of New Zealand at 936– 950 m.

Comparisons. This specimen is in poor enough condition that, although it does not seem to be the same as any of the other species, it does not merit description because too many characters are unknown. The few undamaged characters indicate that it differs from the others in having an almost vertical opercle, a deep notch at the premaxillary symphysis, brown intestine, unusually long predorsal length (152 vs <140% HL), and short preanal fin length (143 vs>157% HL and longer than 130% HL).

Species Authority NMNZ Number Distribution Depth (m) Aetheliparis taurocanis new genus, new species P.04515 Near Moa Seamount 731–869 Until recently, only two snailfish species were known from New Zealand waters: Careproctus novaezelandiae and Notoliparis kermadecensis . Specimens from the NMNZ show that there are many more. Because there has been no systematic survey of the deeper waters of the New Zealand Exclusive Economic Zone (EEZ) slope and continental rise ( Gordon et al. 2010), these waters remain poorly explored and I expect more liparid species to be discovered from this region in the future. Although our knowledge of the liparid fauna of New Zealand is incomplete, enough is now known to permit some speculation regarding their distributions and origins.

Existence of a unique New Zealand liparid fauna is to be expected based on the common distribution pattern for these taxonomically and ecologically diverse fishes. As has been discussed elsewhere ( Stein et al. 2001; Andriashev, 2003; Stein 2012; and others) liparids are easily isolated and numerous new species are often found in previously poorly known regions. New Zealand and its associated waters is such a region ( Gordon et al. 2010). The New Zealand species are from depth zones including mesopelagic (118–1340 m: Psednos and Aetheliparis ), slope and continental rise (802–2821 m, most species at less than 2000 m: Careproctus , Osteodiscus , and Paraliparis ), and hadal (6660–7261 m: Notoliparis ).

The relationships of the New Zealand liparids to species elsewhere are unknown. Among the New Zealand Paraliparis species, each has a character suite that differs from all the Australian species with the same number of radials. For instance see P. exilis , which differs from all seven of the Australian species having four radials in having a shallower body depth, narrower interorbital space, shorter gill opening, and a longer upper pectoral fin lobe. This suggests that within New Zealand waters, species are more similar (and more difficult to distinguish from each other) than to those elsewhere. The pectoral girdle structure of Paraliparis exilis with its notched radials suggests a possible affinity to the many Antarctic species with similar pectoral girdles, but discussions of relationships can only be speculation until more specimens are collected and analyzed.

Southeastern Australia also has a diverse liparid fauna ( Stein et al. 2001) that includes both benthic and pelagic species, but clarification of the relationships between that fauna and the New Zealand species requires many more specimens. However, C paxtoni Stein, Chernova, & Andriashev 2001 , the sole known Australian species of the genus, has similarities to both C. novaezelandiae and C. narilobus in having a pectoral girdle of 3+1 radials, notched scapula, R1, R2, and R3, many pectoral fin rays (34–35 vs 37–38), trilobed teeth (as in C. novaezelandiae ) and two suprabranchial pores and a high vertebral count of 58–59 (as in C. narilobus ).

The new Psednos species from New Zealand do not appear to form a single group as do those of Australia ( Stein et al. 2001). Chernova and Stein (2002) defined three species groups of Psednos : an “ Australia group” (V 56 –58, radials 3 [2+0+1], notched; a “micrurus group” with V 40 –44, a coronal pore and no postorbital pore; and a “christinae group” with V 46 –47, no coronal pore and a postorbital pore. Five of the new New Zealand species (all except P. microstomus , V 49; P. struthersi , V 53; and possibly P. longiventris , V>45) could be in the Australia group (>56 vertebrae); the three exceptions with low numbers of vertebrae appear to fit in none of the groups. It is noteworthy that P. longiventris has four, rather than three, radials, although this could be an anomaly. All other species that have been examined have 3 radials, either 1+1+1 or 2+0+1 pattern.

New Zealand’s distance from other land masses, EEZ bathymetry and deep water (CANZ 2008), complex ocean current system and associated temperature regimes ( Stevens and Chiswell 2009) isolate its liparids from Australia and Antarctica. It is an unusual characteristic of the New Zealand liparid fauna that there are so many pelagic species (e.g., Aetheliparis and Psednos , at least nine species) versus the 11 or more benthic or epibenthic species. This may be the result of the geographic isolation of the region, an artifact of the paucity of samples, or a combination of both. Typically, benthic or epibenthic snailfishes have geographically and bathymetrically limited distributions (Chernova et al. 2004), probably because they lack pelagic larvae, have low fecundities, and may have some form of parental care or reproductive parasitism ( Stein 1980). The liparid fauna of southeast Australia is more typical in its domination by benthic or epibenthic species. It has three Psednos , one Careproctus , and 26 Paraliparis species, with only the Psednos holopelagic in habit.

Pelagic liparids such as Psednos may not be similarly limited. Perhaps because New Zealand is relatively small and widely separated from other land masses by deep water, it is more likely to be colonized by pelagic, rather than benthic liparid species. The Psednos species reported here occur all around New Zealand and were collected in several different water masses and currents. Most specimens were caught on or around the Chatham Ridge (possibly reflecting sampling effort rather than distribution). The factors explaining their diversity are unknown, and without (at a minimum) many more specimens to demonstrate their distributions, unknowable. The answer lies, as in other mesopelagic fishes, in determining what isolating factors lead to speciation ( Norris, 2000). That is a question to be answered by future studies.