Genus Streblospio Webster, 1879 Emended

Type species: Streblospio benedicti Webster, 1879. By monotypy

Synonym: Hekaterobranchus Buchanan, 1890, p. 175.

Type-species: Hekaterobranchus shrubsoli Buchanan, 1890

Diagnosis. Prostomium oval, fusiform or conical; anteriorly rounded with one or several papillae scattered on the anterior surface (except S. japonica), and posteriorly tapered extending to anterior margin of chaetiger 1; 2–4 pairs of eyes, or eyes absent; presence or absence of a papilla on the dorsum of chaetiger 1, between branchiae; peristomium fused with first chaetiger; peristomium moderately developed, expanded laterally, partially enveloping prostomium (some species with anterior peristomium more developed than others) and extending around base of palps, forming short lateral wings; one pair of short palps, extending to chaetigers 3–10; palps with frontal cilia, latero-frontal cirri and lateral cilia, palp sheaths absent; one pair of branchiae on chaetiger 1, with or without distal digitiform appendage; branchiae extending to chaetigers 4–11; chaetiger 1 without notopodial postchaetal lamellae, and capillary notochaetae few or absent; entire or bilobed membranous dorsal collar or pouch across the dorsum of chaetiger 2; anterior margin of pouch hooded and open anteriorly, posterior edge of pouch may extend to chaetiger 3; notopodial and neuropodial postchaetal lamellae small, oval, rounded, subtriangular or flap-like on anterior chaetigers, and digitiform or highly reduced or absent on posterior chaetigers; prechaetal notopodial and neuropodial lamellae absent throughout the body; dorsal crests present or absent; all notopodial chaetae capillary; neuropodial chaetae include capillaries; multidentate hooded hooks first appear on chaetigers 6–10; sabre chaetae from chaetigers 2–7; notopodial hooks absent; pygidium simple or lobed, with or without ventral lappets; papillae scattered throughout the body or absent.

Remarks. This diagnosis is based on the original descriptions of all species in the genus. The main changes from previous diagnoses concern the presence of one or more papillae scattered on the anterior surface of the prostomium; dorsal crests that are found from the mid body to the end; cuticle covered by numerous papillae scattered throughout the body; and the absence of prechaetal notopodial and neuropodial lamellae.