Synsyllidia Uchida, 2004: 32 (nomen nudum, without type species fixation); Ruta et al. 2006: 101.

Diagnosis. Prostomium rectangular, with two antennae and bi-articulated palps. Without facial tubercle. Proboscis with distal ring of papillae, without jaws. Three apodous tentacular segments bearing six pairs of cirri with distinct cirrophores. Neuropodia subconical, without extra lobes. Each neuropodium with single acicular simple chaeta and several compound heterogomph falcigers. Some anterior segments without simple chaetae.

Type species. Synsyllidia alternata sp. nov., fixed by original designation.

Gender. Feminine.

Etymology. The genus is named after the resemblance to Syllidia Quatrefages, 1865.

Remarks. Seven known genera of hesionids have six pairs of tentacular cirri and papillae on the outer rim of the proboscis: Microphthalmus Mecznikow, 1865, Micropodarke Okuda, 1938; Neopodarke Hartman, 1965; Heteropodarke Hartmann-Schröder, 1962; Parahesione Pettibone, 1956; Nereimyra Blainville, 1828; and Syllidia. The last two have horny jaws or horny ridges in proboscis, while palps are simple in Microphthalmus, Heteropodarke, and Parahesione. Neopodarke has clearly uniramous parapodia, without notopodial acicula. Synsyllidia is closely related to Micropodarke. Both genera have two antennae, two bi-articulated palps, six pairs of articulated tentacular cirri, and sub-biramous parapodia. However, Synsyllidia possesses simple subconical parapodia, and acicular chaetae, whereas Micropodarke has conspicuous parapodial lobes and lacks acicular chaetae.