Thalenessa , Baird, char, emend. Mcintosh, 1885, p. 139 [Not Baird, 1868, p. 34.]
Euthalenessa (nomen mutatum) Darboux, 1900, p. 114. Type species, herein designated: Thalenessa digitata Mcintosh , 1885. Gender: feminine.
Haswellia Darboux , 1900, p. 116. Type-species, by monotypy and original designation: Thalenessa microceras Haswell , 1883; = E. festiva (Grabe, 1875). Gender: feminine.
Remarks.- Euthalenessa Darboux was established for the following three species from the Challenger Expedition described by Mcintosh (1885) under the genus Thalenessa , Baird, char, emend.: T. digitata , T. fimbriata , and T. oculata . The latter name is preoccupied by Euthalenessa oculata (Peters, 1854). Knox (1960) considered Mcintosh's three species synonymous and referred T. fimbriata and T. oculata Mcintosh to Euthalenessa digitata (Mcintosh) . The latter species is herein selected as the type-species of Euthalenessa Darboux.
Thalenessa microceras Haswell , the type-species of Haswelia Darboux, is herein referred to Euthalenessa festiva (Grube) . See page 12.
Diagnosis.-Body elongate, with numerous segments. Prostomium and tentacular segment (I) fused and withdrawn into few anterior segments; 3 small antennae widi ceratophores emerging from anterior border of prostomium and fused to dorsal sides of tentacular parapodia; 2 pairs of large eyes; pair of long tapering palps emerging ventral to tentacular parapodia. Tentacular parapodia (I) directed anteriorly, with single aciculum, pair of short tentacular cirri, and convex inner tentacular bract or ridge; setae usually few or lacking. With bulbous facial tubercle. Elytra on segments 2, 4, 5, 7... 27, then on every segment. Elytra smooth, with lateral fringes of branched papillae. Single pair of dorsal cirri on segment3. Cirriform branchiae beginning on setigers 4-7. Large cup-shaped ctenidia, 3 per parapodium. Notopodia and neuropodia with well-developed bracts; notopodial bracts with stylodes throughout body. Neuropodia of anterior segments greatly modified, with petal-like stylodes and enlarged anterior bracts enclosing long slender compound neurosetae with multiarticled blades. Notosetae spinous capillaries. Neurosetae compound falcigers with bidentate tips. Ventral cirri short, tapered, Pharynx widi 11 pairs of papillae, 2 pairs of jaws, and subdistai V-shaped muscular ridges.
