Abstract
Two undescribed species of polychaetes in Mediomastus (Annelida: Capitellidae) were collected from intertidal to shallow habitats in Tokyo Bay, Japan. These are M. duobalteus sp. n. and M. hanedaensis sp. n. Mediomastus duobalteus sp. n. is distinguishable from all congeners by the following characters: 1) segments 3, 4, 8–11 stainable with methyl green, 2) thoracic capillary chaetae unilimbate, 3) abdominal capillary chaetae absent, 4) paddle-like chaetae in the thorax absent, and 5) abdominal hooded hooks not flared. Mediomastus hanedaensis sp. n. is similar to M. warrenae Green, 2002, but differs from the latter in the shapes of the thoracic capillary chaetae and the abdominal hooded hooks, and the staining pattern with methyl green. In addition, a key to all Mediomastus species is provided.
Highlights
Capitellids in the genus Mediomastus Hartman, 1944 are benthic polychaete worms that occur in marine and brackish water
Mediomastus is distinguishable from other genera in Capitellidae by the following characters: 1) peristomium without chaetae, 2) thorax with 10–12 segments, 3) segments 2–5 with capillary chaetae in both
In Japan, species in the genus have been reported from eight localities (Fig. 1, references therein), but only two of these records were identified to species: M. californiensis from Sagami Bay (Imajima 2006) and M. opertaculeus from Hokkaido (Abashiri, Monbetsu, Rishiri Island, and Oshoro) (Tomioka et al 2013, 2014)
Summary
Capitellids in the genus Mediomastus Hartman, 1944 are benthic polychaete worms that occur in marine and brackish water. Rami, and 4) remaining thoracic and abdominal segments with hooded hooks (Hartman 1944, Warren et al 1994, Green 2002). In Japan, species in the genus have been reported from eight localities (Fig. 1, references therein), but only two of these records were identified to species: M. californiensis from Sagami Bay (Imajima 2006) and M. opertaculeus from Hokkaido (Abashiri, Monbetsu, Rishiri Island, and Oshoro) (Tomioka et al 2013, 2014).
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