Metamorphosed females of D. platynogaster are distinguished from those of all other genera of the family in having an unusually deep caudal peduncle (21.6–23.8% SL); a blunt snout and short, highly convex frontals resulting in an extremely short head (29.7–30.5% SL); and remarkably few teeth in the jaws (20–32 in the upper jaw, 20–31 in the lower jaw).

Metamorphosed females of D. platynogaster are further unique in having the following combination of character states: Vomerine teeth are present. The sphenotic spines are well developed (their length 2.9–3.6% SL) and directed dorsolaterally. The lower jaw bears a stout symphysial spine. The hyomandibular has a double head. The quadrate spine is well developed (its length 2.5–5.0% SL), but the articular spine is less than one-half the length of the quadrate spine. The posterior margin of the opercle is deeply notched. The subopercle is long and narrow, its dorsal end tapering to a point (the posterior margin without indentation), its ventral end oval in shape (without an anterior spine or projection). The caudal-fin rays are without internal pigmentation. The illicium is considerably longer than the length of the esca bulb. The pterygiophore of the illicium emerges on the snout from between the frontal bones, its anterior end exposed, its posterior end concealed beneath the skin. The first ray of dorsal fin is well developed. There are 6 dorsal-fin rays and 4 anal-fin rays . The pectoral-fin lobe is short and broad (its length 6.6–8.9% SL), shorter than the longest rays of the pectoral fin (16.3–19.9% SL). There are 15–16 pectoral-fin rays. The skin is smooth and apparently naked, without dermal spinules (but specimens are unavailable for clearing and staining). Darkly pigmented skin of the caudal peduncle extends well past the base of the caudal fin (only three known specimens, 134–175 mm; material unavailable for internal osteological examination).