Diagnosis: characterized by the combination of the following characters: 7 pairs of gill pouches, 3/3 multicusps, 12–15 prebranchial slime pores (modally 14), 78–86 total slime pores, slime pores without narrow white rim, preocular length 4.8–5.8% TL, and body colour brown to dark brown; differs from all other congeners except E. caribbeaus, E. menezesi, E. strahani, E. cirrhatus, and E. goliath by having 7 pairs of gill pouches and 3/3 multicusps; Eptatretus caribbeaus, E. menezesi, and E. strahani are not found in New Zealand; differs from E. caribbeaus by the number of anterior unicusps (10–11 versus 11–13), posterior unicusps (8–10 versus 10–11), and body colour (brown to dark brown versus light tan); differs from E. menezesi by the tail slime pores (11–14 versus 14–18), total slime pores (78–86 versus 86–94), and ventral finfold colour (brown versus whitish margin); it differs from E. strahani by having visible (versus absent) eyespots, rounded (versus slit-like) 1st few branchial apertures, vestigial (versus welldeveloped) ventral finfold (0.17–0.64%TL versus 1.12–1.16%TL), rounded (versus angled) ventral caudal fin profile, and shallower tail depth (8.1–10.6%TL versus 10.9–12.7%TL); differentiation from E. cirrhatus by the prebranchial slime pores (12–15, modally 14 versus 15– 18, modally 16), its more robust appearance (body depth 8.9–12.0% TL versus 5.9–11.2% TL, often <8.6% TL), and body colour (brown to dark brown versus dark brown to purple-brown); some, and often most, slime pores of E. cirrhatus have a narrow white rim, whereas slime pores in E. cryptus sp. nov. are the same colour as the rest of the body; care must be taken not to interpret residual slime or internal structure of the slime pore for the presence of a white rim; Eptatretus cryptus differs from E. goliath by the trunk slime pores (46–54 versus 56–60) and total slime pores (78–86 versus 89–95); the following character can also help in dissociating E. cryptus from E. goliath: preocular length (>4.8 versus 3.7–5.2% TL) and prebranchial length (>20.3 versus 18.3–20.9% TL) (Ref. 115309).
Description: meristics: 3/3 multicusp pattern; anterior unicusps, 10 (10–11); posterior unicusps, 9 (8–10); left-side cusps, 25 (24–27); prebranchial pores, 14 (12–15); branchial pores, 7 (6–8); trunk pores, 47 (46–54); tail pores, 13 (11–14); total pores, 81 (78–86); 7 pairs of gill pouches associated with 7 pairs of gill apertures; morphometrics, as percentage of TL: preocular length, 5.2% (4.8–6.0%); prebranchial length, 21.5% (20.3–23.6%); branchial length, 6.8% (6.1–8.1%); trunk length, 54.0% (52.4–56.9%); tail length, 17.6% (15.6– 18.5%); greatest body depth including ventral finfold, 10.0% (8.9–12.0%); greatest body depth excluding ventral finfold, 9.8% (8.5–11.5%); depth at pharyngocutaneous duct, 7.7% (7.4–9.8%); depth at cloaca, 8.4% (7.5–9.2%), tail depth, 9.8% (8.1–10.6%); body subcylindrical, slightly deeper than wide at prebranchial and branchial regions, laterally compressed at trunk and strongly compressed at tail; rostrum bluntly rounded; 2 minute bilaterally symmetrical nasal-sinus papillae in the dorsal surface of the nasal sinus (sometimes not observable); eyespots usually well defined, circular in shape and paler than surrounding skin; 3 pairs of barbels on head, 1st 2 subequal in size, 1.4–1.6% TL (0.9–1.6% TL), 3rd one longer, 1.7% TL (1.5–2.1% TL) and adjacent to oral cavity; ventral finfold small, 1.1 mm (1.0–4.9 mm), its origin difficult to assess but located within anterior 51% (50–59%) of body length, extending to cloaca; no ventrolateral branchial finfolds; caudal finfold rounded, thick, its ventral outline nearly straight, beginning immediately posterior to edge of cloaca, extending around tail to dorsal surface, ending about over cloaca; gill aperture well-spaced and linearly arranged; last branchial duct confluent with pharyngocutaneous duct on left side, forming a larger aperture; posterior tip of dental muscle reaches 5th (3rd to 5th) gill pouches (counting from head), with length 22.8% TL (18.9– 23.9% TL); ventral aorta branches at 7th gill pouch (Ref. 115309).
Colour: body uniformly brown to dark brown, without contrasting narrow white rims around the slime pores; branchial apertures and pharyngocutaneous duct openings white; barbels brown with white tips; some specimens bearing pale to white blotching or healed white scarring (Ref. 115309).