Mastobranchus Eisig, 1887

Silva, Camila Fernanda Da & Amaral, Antonia Cecilia Zacagnini, 2022, Capitellidae (Annelida) from the Brazilian Continental Margin (SW Atlantic): new occurrences of three genera and description of new species, Zootaxa 5104 (1), pp. 89-110 : 92

Genus Mastobranchus Eisig, 1887 , amended

Type species: Mastobranchus trinchesii Eisig, 1887: 831–835 , pl. 1, fig. 3, pl. 24–26, figs 9–11, 13–16, pl. 34, figs 24–26.

Type locality: Gulf of Naples , Italy .

Generic diagnosis. (amended after Magalhães & Blake 2020). Prostomium conical, palpode present; eyespots may be present in multiple spots; nuchal organs present. Peristomium clearly distinct from prostomium; achaetous segment may be present. First chaetiger uniramous or biramous. Eleven thoracic chaetigers. Chaetigers 1 to 9 with only capillaries; chaetigers 10 and 11 with only capillaries or capillaries in noto- and hooks in neuropodia. Thorax clearly demarcated from abdomen. Variable number of abdominal segments with mixed capillaries and hooks in notopodia (> 9); neuropodial abdominal segments with only hooded hooks. Poorly developed neuropodial lobes. Branchiae may be present; when present, retractile, bifurcated, digitate, or palmate. A pair of genital pores from chaetiger 7 up to chaetiger 14. Lateral organs present on thorax and abdomen. Pygidium adorned with four caudal cirri.

Remarks. The genus Mastobranchus is peculiar among capitellids because it includes species having mixed capillaries and hooded hooks on notopodia of abdominal chaetigers. It was originally introduced by Eisig (1887) with the description of M. trinchesii from the Gulf of Naples, Italy, a species having 11 thoracic chaetigers bearing only capillaries, palpode, chaetiger 1 with both noto- and neuropodia, and abdominal chaetigers with capillaries and hooded hooks on notopodia and hooks on neuropodia. In 1921 and 1936, Mastobranchus indicus Southern, 1921 and M. dollfusi Fauvel, 1936 were described, respectively; however, M. dollfusi was transferred to the genus Leiocapitella by Bellan (1964). Ewing (1984) revised the genus and both species, M. dollfusi and M. indicus , were considered incertae sedis because the chaetal formula did not fit that of Mastobranchus ; additionally, he also described a new species from the Gulf of Mexico, Pacific Ocean, M. variabilis . Green (2002) amended the generic definition to include the presence of an achaetous segment between the peristomium and chaetiger 1 in Mastobranchus near loii , and later, Tomioka et al. (2017) described the new species M. uru , from Japan. So, there are until now four valid species, Mastobranchus trinchesii Eisig, 1887 , Mastobranchus loii Gallardo, 1968 , Mastobranchus variabilis Ewing, 1984 , and Mastobranchus uru Tomioka, Yoshida & Kajihara, 2017 . In this paper, we amend the generic diagnosis to correct the number of thoracic chaetiger from “nine or 11” to 11, because the type-material of Mastobranchus loii could be analyzed and redescribed. The original description and further papers did not mention that the holotype was a specimen regenerating its anterior end, that is why the lower number of thoracic chaetigers, but all other features fit the genus diagnosis. Another change on the diagnosis is the number of abdominal chaetigers bearing capillaries and hooded hooks, from “two or more” to “higher than nine” (nine in Mastobranchus loii ). Two abdominal chaetigers with capillaries was a feature of M. indicus , however, this species is currently considered as incertae sedis sensu Ewing (1984).