Dorsal spines (total): 2-2; Dorsal soft rays (total): 7-7; Anal spines: 0-0; Anal soft rays: 11-12; Vertebrae: 43-44. Diagnosis: Gogo atratus is distinguished from congeners in having a longer snout, 54.8-56.4% of head length vs. 47.1-54.3%; and faintly mottled dark gray colouration vs. uniform brown, highly mottled dark gray and cream, or mottled brownish-gray (Ref. 75790). It further differs from Gogo ornatus in having a larger eye in specimens larger than 110 mm standard length, eye diameter 13.0-14.3% of head length vs. 9.2-12.5% (Ref. 75790). It differs from G. brevibarbis in having unicuspid teeth vs. bicuspid, and a smaller eye, eye diameter 13.0-14.3% of head length vs. 19.5% (Ref. 75790). It differs from G. arcuatus in having a narrower head, head width 17.8-18.9% of standard length vs. 20.8-21.0% and interorbital distance 28.9-30.5% of head length vs. 34.8-35.1%; smaller eye, eye diameter 13.0-14.3% of head length vs. 17.7-18.6%; shorter dorsal spine, 17.7-20.6% of standard length vs. 21.2-21.8%; shorter pectoral spine, 16.5-18.9% of standard length vs. 19.9-20.2%; and a straight dorsoposterior margin of the dorsal fin vs. concave (Ref. 75790).
Description: Body cylindrical, becoming more laterally compressed toward caudal peduncle (Ref. 75790). Dorsal profile mildly convex from dorsal-spine base to anterior orbital margin, nearly straight anterior of orbit; ventral margin of frontal over orbit with pronounced brow ridge; dorsal profile horizontal from dorsal-fin origin to middle of adipose-fin base, then sloping gently ventrally to end of caudal peduncle; ventral profile almost horizontal to anal-fin base, sloping gently dorsally to end of caudal peduncle (Ref. 75790). Head moderately depressed; dorsal profile slightly convex, ventral profile almost straight (Ref. 75790). Bony elements of dorsal surface of head covered with thick skin, although granular surface of neurocranium faintly visible in inter- and postorbital region; supraoccipital spine short and broad, with gently converging sides and blunt tip; in contact with anterior nuchal plate (Ref. 75790). Eye ovoid, horizontal axis longest, with free margin; located entirely in dorsal half of head (Ref. 75790). Gill openings wide, extending from ventral to posttemporal region to isthmus at vertical through anterior orbital margin; gill membranes broadly fused to each other and attached to isthmus, save for narrow flap along posterior margin at isthmus; gently notched at ventral midline (Ref. 75790). Snout strongly produced, with rounded profile in lateral view; mouth inferior; oral teeth small and unicuspid, arrayed in irregular rows on all tooth-bearing surfaces; premaxillary tooth band broad and crescentic, coalescing in middle, and of equal width throughout; premaxillary teeth conical; palatal teeth absent; dentary tooth band in two semicrescentic patches separated at midline; much narrower than premaxillary ttoth band at symphysis; dentary teeth recurved (Ref. 75790). Barbels in three pairs; maxillary barbel short, thick, and flattened, extending to midway between its base and base of pectoral spine; maxillary barbel with membranous extension along posterior edge; extension flaring posteriorly along proximal half of barbel; inner mandibular-barbel origin proximate to midline; barbel narrow and flat; extending to vertical through anterior orbital margin; outer mandibular barbel originating at about same level as inner mandibular barbel; narrow and flat, extending to vertical through posterior orbital margin (Ref. 75790). Dorsal fin with spinelet, spine, and 7 rays; dorsal-fin origin anterior to mid-body, at about two-fifths of body length; dorsal-fin margin straight, first branched fin ray longer than other rays; dorsal-fin spine long, straight, and slender; adpressed spine not reaching origin of adipose fin; anterior and posterior margins of spine not serrated; anterior nuchal plate rectangular, closely sutured to supraoccipital process; median nuchal plate with truncate anterior tip (Ref. 75790). Pectoral fin with stout spine, sharply pointed at tip; with 9 rays; anterior-spine margin with 24-27 shallow medially-directed serrations along entire length; posterior-spine margin with 11-14 strong, retrorse serrations along middle of spine; pectoral fin triangular, with straight anterior and posterior margins; humeral process short and slender, with concave dorsal edge; extending to vertical through posterior tip of anterior nuchal plate (Ref. 75790). Pelvic-fin origin at vertical through midpoint between posterior margin of dorsal-fin base and adipose-fin origin, with i,5 rays and slightly convex margin; tip of adpressed fin not reaching anal-fin origin; anus and urogenital openings located at vertical through midpoint of adpressed pelvic fin (Ref. 75790). Adipose fin with convex margin along entire length; deeply-incised posteriorly; length of adipose-fin base approximately twice length of anal-fin base (Ref. 75790). Anal-fin origin located at vertical through posterior half of adipose fin; anal fin with iv,7-8 rays and straight posterior margin (Ref. 75790). Caudal peduncle deep; caudal fin moderately forked, with i,6,7,i principal rays; dorsal and ventral caudal lobes broad, pointed distally; dorsal lobe longer than ventral; procurrent rays extending only slightly anterior to fin base (Ref. 75790). Skin smooth; lateral line complete; canal running along lateral myoseptum, with pores emanating from short ventrally- and dorsally-directed oblique branches (Ref. 75790).
Colouration: Ground colouration in ethanol mottled dark gray on dorsal and lateral surfaces of head and body, fading to light gray on ventral surfaces; adipose fin, and fin rays and membranes of median fins, mottled dark gray; paired fins mottled dark gray dorsally, light gray ventrally; maxillary barbels gray dorsally, light gray or cream ventrally (Ref. 75790). Colour in life similar, but with more strongly mottled pattern consisting of gray, dark gray, and cream patches on dorsal and lateral surfaces of head and body (Ref. 75790).