Echiodon atopus Anderson, 2005, new species

Echiodon atopus, new species

(Figs. 1-2)

Holotype: USNM 380406 (male, 176 mm TL), north of Inaccessible Island; RVIB NATHANIEL B. PALMER sta. 91/OT 60; 37° 16.1'S, 12° 42.2'W to 37° 16.6'S, 12° 43.1'W; 10 m otter trawl; 0- 139 m; 19:49- 20:06 hr; 9 July 2004.

Diagnosis. A species of Echiodon as defined by Markle and Olney (1990), with the following combination of characters: PCV 38; D30 46; A30 46; ARDO 7; P1 18; posterior swim bladder tunic ridges ventral.

Description. Meristics: PCV 38; D30 46; A30 46; P1 18; ARDO 7; DRAO 0; MAO 7; MDO 8; VAO 6; VDO 8; VPB 6; IO 8; SO 5; LT 3; MD 5; POP 2; ST 2; branchiostegal rays 7. Proportions as percent HL: body depth 48.8; bony interorbital width 13.7; eye diameter 20.3; head depth 48.8; head width 34.3; lower jaw length 52.0; upper-jaw length 46.4; prepectoral length 96.4; preanal length 118.1; predorsal length 129.3; pectoral-fin length 65.2; snout length 17.0; distance snout to anus 111.8.

Head elongate-ovoid; eye circular, entering dorsal profile of head when viewed laterally. Cephalic pores small, rounded, difficult to observe, pored lateral line mediolateral, extending posteriorly to anterior quarter of tail; pores becoming more widely spaced posteriad. No sensory papillae on head or along seismosensory canals. First gill arch with three elongate, tooth pads on upper limb, three slender, developed rakers and four rounded, toothed pads on lower limb. Posterior portion of maxilla unsheathed. Dorsal portion of gill opening extending forward about 3/4 eye diameter. Branchiostegal membrane free of isthmus, joined on vertical about 1 1/2 eye diameters posterior to rear margin of eye. Single enlarged caniniform tooth near symphysis in premaxilla, dentary with two. Vomer with three smaller canines in a row surrounded by 25 tiny denticles. Palatine teeth in four irregular rows anteriorly blending into single, posterior row. Outer flap of upper lip at symphysis with single, furcate, ventrally-directed lobe fused to a broad, inner flange with a larger, conical lobe on either side. Dorsal-fin origin one eye diameter posterior to vertical through anal-fin origin. Posterior swim bladder constricted, with ventral tunic ridges as illustrated for E. dentatus (Cuvier) by Markle and Olney (1990, fig. 35).

Fresh coloration silvery blue, with fine, scattered melanophores. These are denser on dorsum than ventrally, except on tail, and form chevron patterns outlining myomeres on body posteriorly to middle of tail. Abdomen and eye dark blue. Peritoneum, stomach, lining of orobranchial chamber, including tongue and gill bars, black.

Etymology. From the Greek atopos, (out of place) in reference to my original expectation that the specimen was Echiodon cryomargarites and its subsequent identification.

Comparisons. Markle and Olney’s (1990) zoogeographic analysis of Echiodon revealed three distributional patterns that they hypothesized resulted from species radiation of an outer-shelf Indo-West Pacific ancestor. These are: 1) North Atlantic; 2) austral; and 3) a largely boreal temperate/subtropical group that includes the austral E. cryomargarites. Echiodon atopus is close to the austral E. neotes Markle and Olney 1990 and E. rendahli (Whitley) and seems to fit in that clade, although its larvae are unknown (Williams and Machida 1992). It differs from E. neotes in its significantly higher D30 count (38 in E. neotes vs 46 in E. atopus), more precaudal vertebrae (35 in E. neotes vs 38), ventral swim bladder tunic ridges (vs. lateral ridges in E. neotes) and lack of the larval vexillum, although the latter character is difficult to evaluate in the one known specimen of E. neotes. Echiodon atopus differs from E. rendahli in its A30 count (37-38 in E. rendahli vs 46 in E. atopus), greater number of anal-fin rays anterior to the dorsal-fin origin (0-4 in E. rendahli vs 7) and greater number of precaudal vertebrae (31-35 in E. rendahli vs 38). Finally, E. atopus differs from all other congeners in its equal D30 and A30 counts, although, owing to variability in fin-ray anatomy in ophidiiform fishes, this should not be expected to endure as a diagnostic character for the species when more specimens are found.