Small to large; large larvae often red with haemoglobin, maybe reddish-brown flecked, or yellowish-white; smaller larvae greenish yellow, perhaps red flecked, or yellowish-white, rarely completely white; anterior side of procercus mostly brown; some claws of posterior parapod, in a series of genera, darker than remainder, Eye usually with an elongate or kidney-shaped spot, exceptionally with 2 spots (Guttipelopia). Large species with rather long, slender, sometimes almost rectangular head; cephalic index ratio of width: length 0.45-1.00.
Clypeus covering entire head; anterior 1/2 strongly broadened, reaching lateral margin of head, posteriorly rounded, anteriorly more or less straight, level with anterior margin of head. Median suture more or less distinctly developed or absent. Submentum ending in straight line anteriorly, or concave or alternatively with angular median indentation. Dorsally, in intermediate zone between clypeus and labrum, on either side 3 simple or feathered setae.
Always well developed and similar in structure, capable of complete retraction into head. Four segmented, except for Anatopynia which is 5 segmented. Antennal ratio varying from about 2.5 to 16. Basal segment long to very long, up to 18x as long as basal width, with a ring organ and with distal end straight or oblique so that flagellum is mesally directed; segment 2 always several times longer than segment 3; last segment no longer than 3rd. Style situated on segment 2, rarely extending beyond flagellum (Clinotanypus and Coelotanypus); basal part may be cylindrical and more strongly chitinized than the somewhat broadened distal part. Lauterborn organs two usually small, insignificant, weakly chitinized pegs, sometimes more strongly sclerotized tuning fork-like process located opposite at margin of segment 2 between style and segment 3. Blade usually as long as or slightly shorter than flagellum, basally as thick as antennal segment 2 (longer and thicker in Clinotanypus and Coelotanypus, longer in Djalmabatista); height of basal ring, from which accessory blade arises, ranges from 1/2 to almost 5x width. Accessory blade more or less equal in length with blade.
Sensory organs ventrally placed except frontal in Clinotanypus and Coelotanypus, consisting of a group of 7 setae and pegs on each side, in part with bladder-like bases or, if not bladder-like, then mostly rod-shaped and standing on elongate, membranous sockets and ventral margin of labrum bordered by hair-like fringes (Pentaneurini).
More or less strongly curved and tapered towards apex, with dark apical tooth occupying about 1/3 to 1/4 mandible length. Usually with mola, resembling large basal tooth, into which seta subdentalis is inserted; immediately distal to this lies a variably developed inner tooth; molar dilation sometimes absent (e.g in Anatopynia, with 2 approximated inner teeth); inner teeth absent in non-Pentaneurini genera; additional inner, dorsal or ventral teeth. Pecten mandibularis present only in Clinotanypus and Coelotanypus. Three dorsoventral to ventrolateral setae and a sensillum minusculum in a row on outer margin or ventral side of mandible; in Pentaneurini ventrolateral seta is mostly a short peg and sensillum minusculum lies proximal to seta 3, in other taxa the sensillum minusculum is located between setae 2 and 3. Seta interna usually present, with 4-8 branches, some or most of which are plumose or serrate.
Highly variable, with 3-29, usually 8-12 teeth. Ventromentum may be delimited from the lateral regions (dorsomentum) and connected with ventromental plates. Ventromental plates range from nearly indistinguishable to very elongate - laterally and/or posteriorly; with or without setal beard.
Palp large, basal segment, with ring organ, usually simple, occasionally subdivided into several segments; with 7 partly multisegmented sensory organs, peg-like and rod-like sensillae; b-seta 2 or 3 segmented. Lacinia bilobed, bush-like beset with filaments. Stipes with 2 simple or feathered setae, a further seta at base of maxilla usually seated on tall base.
With or without (Pentaneurini) fringe of swim setae. With 2 pairs of anal tubules (sometimes 3 in Tanypus); anal tubules may be situated at anal opening, sometimes longer than posterior parapods (Pentaneurini) or short and situated at base of posterior parapods. Supraanal setae and setae of posterior parapod sometimes unusually large and coloured. Procercus generally 3-4x, occasionally up to 6x as long as wide, with 7 to about 25 anal setae; anterodorsal and posteroventral setae simple or feathered, small or large. Claws of posterior parapods variable in size, form, and colour; larger claws usually with small, fine points on inner and/or outer margin and ending apically in short hooklet, seldom produced into fine point; smaller claws sometimes specifically variable in form, colour and border of points on inner margin.