Decamastus Hartman, 1963

Genus Decamastus Hartman, 1963 View in CoL

Type species: Decamastus gracilis Hartman, 1963 .

Diagnosis: (amended afer Hernández-Alcántara et al. 2019). Prostomium conical or rounded, palpode present or absent; eyespots present or absent; nuchal organs absent. Achaetous segment absent. First chaetiger uniramous or biramous. Ten thoracic chaetigers with capillary chaetae in both rami or last one or two thoracic chaetigers with hooded hooks in neuropodia. Abdominal segments with hooded hooks in both rami. Branchiae present or absent; when present, digitate filaments on both noto- and neuropodia from middle-abdominal chaetigers. Lateral organs not observed. Pygidium simple, without appendages.

Remarks: Te genus description originally recognized only species with 10 thoracic chaetigers with capillaries. Black (2000) amended the description to include specimens with hooded hooks in the last few thoracic neuropodia. Specimens from the Edmond vent field most closely fit the definition of Decamastus by having 10 thoracic chaetigers with capillaries on chaetigers 1–9 and transitional chaetiger 10, abdominal chaetigers with hooded hooks, and a biramous first chaetiger. Te vent specimens have digitate branchiae rising from middle abdominal chaetigers, which is a unique characteristic for the genus and should be included in the genus definition. Two monotypic genera, Pseudoleiocapitella Harmelin, 1964 and Pseudonotomastus Warren & Parker, 1994 , have 10 thoracic chaetigers with capillary chaetae only. Pseudoleiocapitella can be distinguished from Decamastus by the presence of capillaries in the first two abdominal chaetigers. Pseudonotomastus differs from Decamastus by the presence of an achaetous chaetiger. Neonotomastus Fauchald, 1972 was also erected with 10 thoracic chaetigers with capillaries only. However, García-Garza and León-González (2011) found 11 thoracic chaetigers with capillaries when re-examining the type materials. Neonotomastus is also distinct from Decamastus by the presence of capillaries in the first two abdominal chaetigers.