Small larvae, to 4 mm long, marine.
Antenna with 5 segments on tall pedestal lacking any tooth or spur. Antennal ratio c. 1. Ring organ and well-developed seta basal on 1st antennal segment. Lauterborn organs modest, without pedestals, opposite on apex of somewhat dilate 2nd segment. 3rd and 4th segments subequal. Antennal blade usually as long as 2nd segment, accessory blade fused to base of blade, nearly as long as blade. Style on apex of 2nd segment, as long as Lauterborn organ.
SI seta comb-like, fused at base, SII on large pedestal, distally plumose, SIII short, simple, SIVa present. Labral lamellae well developed. Pecten epipharyngis of 3 distally serrate scales. Premandible with 5 teeth, brush strong; seta premandibularis simple.
Mandible with light brown dorsal tooth, apical tooth and 3 inner teeth. Seta subdentalis long, curved, reaching to base of apical tooth. Seta interna of 4 plumose branches. Pecten mandibularis with several strong lamellae, the outer stronger than remainder, resembling pale outer tooth.
Mentum with triangular median tooth laterally with 1-2 notches, sometimes almost trifid, at least crenulate, 4 pairs of laterals, 1st about same size as median, remainder regularly decreasing in size. Ventromental plates almost in medial contact, subequal in width to mentum, with characteristic coarse striae.
Claws of posterior parapod numerous (c. 60), simple. Anal tubules absent.
The larvae of an undescribed species from southern North America, reared to imago, indicates that the generic concept of Phaenopsectra needs broadening. This larva differs from Phaenopsectra s.str. in having light-brown, not shining-black mentum and mandibles. The dorsal tooth of the mandible is strongly protruding. All 4 median teeth of mentum are about equal in length. The fourth lateral tooth of the mentum is as long as the neighbouring teeth. In addition the imago differs in several respects from Phaenopsectra s.str.
Larvae of Pontomyia are marine, occurring in tidal rock-pools and off-shore to depths of at least 30 m (Bretschko 1981a).
The genus is recorded from the Palaearctic (Japan), Australasia and Neotropics (Belize). There are at least 4 species, of which 2, P. natans and P. pacifica, are known from Japan.