Pachycara caribbaeum, Anderson, M. Eric, Somerville, Russell & Copley, Jonathan T., 2016

Anderson, M. Eric, Somerville, Russell & Copley, Jonathan T., 2016, A new species of Pachycara Zugmayer, 1911 (Teleostei: Zoarcidae) from deep-sea chemosynthetic environments in the Caribbean Sea, Zootaxa 4066 (1), pp. 71-77 : 72-76

Pachycara caribbaeum sp. nov.

( Figs. 2–4 , Table 1 )

Holotype. BMNH 2015.9.10.1 (immature male, 199 mm SL), Von Damm Vent Field, Mid-Cayman Spreading Centre, 18°22.503' N, 81°47.858' W, collected by suction sampler from ROV Isis , dive 198, depth 2313 m, water temperature 4.4ºC, RRS James Cook cruise JC82, 10 February 2013.

Paratypes. MCZ 171014 (immature male, 117 mm SL), Von Damm Vent Field, Mid-Cayman Spreading Centre, 18°22.62' N, 81°47.89' W, collected by suction sampler from ROV Hercules, dive H1295, depth 2309 m, water temperature 4.4°C, EV Nautilus cruise NA034, 26 August 2013. MCZ 171085 (immature female, 197 mm SL), same data as preceding specimen.

Diagnosis. A species of Pachycara as defined by Anderson (1989, 1994) with the following combination of characters: vertebrae 31–33 + 76–79 = 107–112; pectoral fin rays 12–14; pelvic fin rays 2; single mediolateral branch of the lateral line system; scales present on nape and cheeks.

Description. Head ovoid, deeper than wide in larger specimens than smallest, snout gently sloping in all. Scales cycloid, relatively sparsely distributed in these juveniles, absent on fins and pectoral base and axil; scales present in nape to about one eye diameter posterior to eye in smallest specimen, to interorbital area in others. Eye small, rounded, entering dorsal profile of head in larger of the three fish. Gill slit moderate, reaching ventrally to lower edge of pectoral base or just below it. Opercular lobe at dorsal margin of gill slit slightly rounded posteriorly, extending forward about one eye diameter except on right side of MCZ 171085 where it does not extend forward.

Pectoral-fin origin slightly below body midline, insertion on abdomen; posterior margin of fin wedge-shaped, with rays 4–6 from dorsalmost the longest; ventralmost rays not noticeably thickened, no ray tips exserted. Right pectoral fin of holotype appears deformed, shorter than the left (32.1 vs. 45.8 % HL; Fig. 3A ), with the tips of the dorsalmost rays missing ( Fig. 3 B).

Mouth very slightly subterminal and oblique, upper jaw extending posteriorly to middle of eye. Epidermal prickles absent on head. Nostril tube not reaching forward to upper lip. Oral valve reaching just posterior to anterior edge of vomer. Jaw teeth small, conical; premaxilla with single row of teeth in smallest, two or three anterior rows blending into single posterior row in larger specimens; dentary with three rows of teeth anteriorly blending into single posterior row in all. Vomerine teeth few in these juveniles. Palatine teeth in single row, also relatively few.

Cephalic lateralis system with no variation in pore counts. Two postorbital pores (one and four of Anderson 1994). Suborbital pores 6 + 0 on both sides of all. Eight preoperculomandibular pores. Two anterior supraorbital (nasal) pores, one set anteromesial to nostril tube, the other dorsoposteriorly. Interorbital and occipital pores absent. Body lateral line system with single, mediolateral branch originating just posterior to postorbital pore 4, running to tail tip. No trace of ventral or dorsolateral neuromasts.

Dorsal-fin origin associated with vertebrae 7–8, with no free pterygiophores ( Fig. 4 ). Anal fin origin associated with vertebrae 30–31 (ultimate precaudal), with 3–5 pterygiophores inserted anterior to haemal spine of first caudal vertebra. Last dorsal ray associated with fourth preural vertebra, last anal ray associated with second preural vertebra. Caudal fin with two epural, four upper hypural and four lower hypural rays. Gill rakers short, those on upper limb (epibranchial) acute, lower rakers (ceratobranchial and hypobranchial) blunt, roughly triangular. Pseudobranchial filaments short and slender. Branchiostegal rays 4 + 2.

Fresh colouration of holotype ( Figs. 2 and 3A ) and paratype MCZ 171085 uniformly pinkish white, edges of unpaired fins translucent, abdomen bluish black, eye blue. In preservative all specimens dull whitish, orobranchial chamber pale.

Etymology. The specific name recognises the first records of the genus at deep-sea chemosynthetic environments in the Caribbean Sea.

Distribution. Known from two bathyal collections at chemosynthetic environments in the Caribbean at the hydrothermally active Von Damm Vent Field on the Mid-Cayman Spreading Centre (depth ca. 2300 m). Tentatively referred specimen. MCZ 171653 (sex undetermined, 56.5 mm SL), methane seep near Tobago, 11˚14.302’N, 59˚20.681’W, suction sampler from ROV Hercules, dive H1392, 1049 m, temperature 5.3˚C, EV Nautilus cruise NA054, 5 October 2014.

Figures

FIGURE 2. Photographic lateral view of Pachycara caribbaeum sp. nov. holotype in fresh condition (scale bar 50 mm; image by Adrian Glover, BMNH).

FIGURE 3. A) Photographic ventral view of head and pectoral region of Pachycara caribbaeum sp. nov. holotype in fresh condition (scale bar 20 mm; image by Adrian Glover, BMNH); B) microCT ventral view of holotype head and pectoral region (image by Daniel Sykes, BMNH).

FIGURE 4. MicroCT lateral view of Pachycara caribbaeum sp. nov. holotype (scale bar 10 mm; image by Daniel Sykes, BMNH).

Tables

TABLE 1. Comparison of meristic and morphometric characters among specimens of Pachycara caribbaeum sp. nov. Holotype measurements of left pectoral fin given, with right pectoral fin values in parentheses. MCZ 171653 is tentatively referred to P. caribbaeum.

Counts Vertebrae	Holotype 199 mm SL 33 + 79 = 112	Paratype range (n = 2) 117 –197 mm SL 31–32 + 76–78 = 107–110	MCZ 171653 56.5 mm SL 28 + 72 = 100
Dorsal fin rays Anal fin rays Caudal fin rays	104 78 10	99–101 77–82 10	- - 10
Pectoral fin rays Pelvic fin rays Vomerine teeth	14 8	12 2 3–6	- Absent -
Palatine teeth Gill rakers Branchiostegal rays	6 6	4–5 2 + 11 6	- - 6
Pseudobranchial filaments % SL Head length	4 17.9	4–5 17.0–17.4	- 19.5
Head width Head depth Pectoral fin length	8.9 8.8 7.6 (5.3)	7.5–9.1 8.8–9.4 9.2–11.0	6.6 9.4 8.7
Predorsal length Preanal length Body depth	22.8 42.7 9.2	21.3–22.1 43.9–45.0 7.8–9.1	24.1 - 8.0
Gill slit length Caudal fin length % HL	5.3 2.8	5.5–6.9 1.7–2.5	6.2 2.7
Head width Head depth Upper jaw length	53.9 53.0 42.2	43.9–52.7 50.7–55.8 41.8–47.3	33.6 48.2 37.3
Pectoral fin length Caudal fin length Snout length	45.8 (32.1) 11.8 24.2	54.3–63.5 9.9–14.9 18.8–26.4	44.6 13.6 24.6
Eye diameter Gill slit length Bony interorbital width	14.2 32.1 11.8	15.2–22.7 31.5–40.8 8.3–10.8	15.5 31.8 9.1
Fleshy interorbital width Interpupillary width Pectoral base/length ratio	15.7 29.5 57.0 (73.6)	9.9–13.2 24.3–25.1 42.6–50.0	- - 36.7