Cottunculus tubulosus, Ingvar Byrkjedal & Alexei M. Orlov, 2007

Ingvar Byrkjedal & Alexei M. Orlov, 2007, A new species of Cottunculus (Teleostei: Psychrolutidae) from the Mid Atlantic Ridge., Zootaxa 1580, pp. 63-68 : 65-68

Cottunculus tubulosus sp.n.

(Figs. 2-3)

Holotype. male, NORTH ATLANTIC, 51°45'N - 29°33'W, 17 July 2004, 1950-1872 m depth, soft bottom , R/V G.O.Sars, super station 56, local station 378 , bottom trawl. ZMUB 16361 .

Diagnosis. The species differs from other species of Cottunculus by having very prominent tubes externally visible along all of the lateral line, and dense single and double prickles, readily apparent to the unaided eye, covering the body. The head is fairly slender and head tubercles are well developed, as are the infraorbital (non-paired) and preopercular spines. The peduncle is short and relatively deep.

Description. SL 47, 0 mm, fresh weight 3.7g. Other measurements are given in Table 1 and meristic characters in Table 2. General shape fairly slender and elongated for a Cottunculus , with a marked convex nuchal area and a short caudal peduncle no longer than its depth (Fig. 2 and 3). From above the snout has a convex outline, and regularly sectioned bony tubes stand out clearly all along the lateral line, extending on to the caudal fin. Snout and interorbital areas concave, the latter displaying prominent orbital rims.

Cranial spines well developed. Following the numbering of Nelson & Nakamura (1980), and Nelson (1982), spine 1 not apparent, while the most prominent spines are 6>3>5>4>2. Spines of pair number 2 (interorbital spines) are least spaced, followed by 3<6<4<5. There are two distinct tabular spines. Opercular with 5-6 fan-spread ridges, lowermost of which ending in 3 minor spines. Suborbital, mandibular and preopercular pores large and separated by single (non-paired) bony spines which point obliquely outwards-downwards. A single large median chin pore present. A pore present midlaterally on the operculum posterior to a single spine. Nasal spines present but small. Anterior pair of nostrils with long tubular openings, posterior pair without tubular openings. Lateral line pores situated on the posterior end of the lateral line bony tubes, but with no tubular opening.

Lower jaw protrudes clearly beyond upper jaw. Dentary and vomerine teeth small and numerous in dense irregular rows. Small, yet clearly visible, single and double spinules cover the body from posterior part of nape and backwards, extending on to about basal one third of the dorsal fin. Smaller and more scattered spinules on head; nuchal region bald.

Dorsal fin originates well posterior to the nuchal region. Anal fin originates slightly posterior to the perpendicular from the dorsal fin origin. About 1/3 of the free part of pelvic fins pass beyond anus. Three pelvic fin soft rays present, the first ray shortest and the second ray longest. Number of vertebrae 28, anterior eight precaudal. The first dorsal fin ray above vertebra # 12. Urogenital papilla well developed, but not reaching anal fin origin.

Uniform brownish grey colour with no indication of banded pattern, becoming slightly paler on the underside of the head, along the subopercular rim, along the lower part of the pectoral fins, and ventrally from the urogenital papilla, the latter being whitish. Small black dots scattered over the ventral area. Colours still intact after several months in preservation fluid.

Etymology. The specific epithet tubulosus (from the Latin tubus, meaning “pipe”) refers to the prominent bony tubes of the lateral line.

Discussion

According to Nelson (1989) the genus Cottunculus is diagnostisized by the following combination of characters: spines present on at least some of the cranial archs, teeth present on head of vomer, cirri absent or weak, a rigid interorbital area, and parietal spines fixed to the cranium. These characters are found in C. tubulosus .

Cottunculus tubulosus differs from all congeners except C. spinosus in the following characters: prominent spines present between dentary pores; lateral line tubes prominent and clearly visible; low number of dorsal fin-rays; low number of pectoral fin rays; a relatively long predorsal length; and a relatively shallow caudal peduncle. It differs from that species in having clearly visible dense dermal prickles; lateral line tubes not gradually smaller toward the tail; clearly fewer lateral line pores; and in the relative size of cranial spines. While the exact number of lateral line pores in C. spinosus is not known, the number judged from Gilchrist’s (1906) illustration obviously far exceeds 14, possibly reaching as high as 24.

The new species can be separated from the other known congeners by the arrangement of cranial spines alone. C. tubulosus differ from C. konstantinovi , C. microps , and C. sadko (Nelson 1982, personal observation contra Myagkov 1991) by the presence of a well-developed spine on arch 5, and from C. granulosus , C. spinosus , C. thomsonii , and C. nudus (Gilchrist 1906, Nelson & Nakamura 1980, Nelson 1989) by a small knob instead of spine on arch 4. The ridge on cranial arch 2 in C. tubulosus is also different from the prominent spine of C. spinosus in this head region. The new species differs from C. granulosus , C. thomsonii and C. nudus in having single, not double, suborbital spines, and from C. microps , C. sadko , and C. konstantinovi in having prominent preopercular spines (Nelson & Nakamura 1980, Nelson 1989).

Among the Atlantic species of Cottunculus , C. thomsonii is found from temperate to tropical waters, whereas the others are either Southern Hemisphere species ( C. spinosus , C. granulosus ) or belong to boreal and arctic waters ( C. microps , C. sadko , C. konstantinovi ; Fedorov & Nelson 1986, Scott & Scott 1988, Nielsen & Bertelsen 1992). Thus, C. thomsonii is the species of Cottunculus whose range gets closest to the locality of C. tubulosus , but C. thomsonii is found on the continental shelves and slopes, and on the Faroe-Iceland ridge, not on the Mid Atlantic Ridge. Also the South Atlantic C. granulosus and C. spinosus are found on the shelves. Thus, C. tubulosus is the only species of Cottunculus reported from the Mid Atlantic Ridge. Although C. thomsonii has been found at almost 1500 m depth (Scott & Scott (1988), only C. spinosus has been reported from a depth similar to C. tubulosus (1460-2180 m, Nelson 2003), the other species primarily found between 200 and 1000 m deep (Nelson & Nakamura 1980, Fedorov & Nelson 1986, Nelson 1989, Nielsen & Bertelsen 1992).

The station at which the specimen was caught had a soft bottom, a usual bottom habitat of psychrolutids (Fedorov & Nelson 1986). From the bottom trawl catch the demersal and benthopelagic fish fauna at the station consisted of at least 43 species representing 23 families of which Gonostomatidae (2 species), Moridae (1 species), Macrouridae (5 species), Alepocephalidae (6 species), Halosauridae (1 species), Melamphaidae (3 species), and Bathylagidae (1 species) made up 80% of the individuals.