Poecilochaetus Claparede in Ehlers, 1875

Abe, Hirokazu & Sato-Okoshi, Waka, 2021, Molecular identification and larval morphology of spionid polychaetes (Annelida, Spionidae) from northeastern Japan, ZooKeys 1015, pp. 1-86 : 1

Genus Poecilochaetus Claparede in Ehlers, 1875

Larval diagnosis.

Overall shape long and slender, large in size (> 5 mm) and number of chaetigers (> 30 chaetigers) at metamorphosis. Body transparent, characterized by total absence of pigmentation except pairs of small pigment spot between parapodia or ventro-lateral side of each chaetiger. Two pairs of red or dark red eyes present. Gastrotrochs from chaetiger I onwards in all following chaetigers, gastrotrochs in first and second chaetigers represented by solitary lateral patches of cilia and complete gastrotrochs occur from third chaetiger onwards. Nototrochs absent. Larvae prior to ca. 30-40 chaetiger stages remain in metatrochophore stage, characterized by absence of functional parapodia for swimming and presence of well-developed proto-, telo-, and gastrotrochs for swimming. Metatrochophore have broadened trapezoidal prostomium with tactile cilia in anterior part, broad and low caruncle, provisional larval chaetae, pygidium without anal cirri. Larval stage after metatrochophore stage (often called nectosoma) characterized by reduced trochs, the presence of functional parapodia, and rapid serpentine swimming behavior. In nectosoma stage, caruncle, nuchal lobes, a pair of palps, parapodia, cirriform or digitiform dorsal and ventral postchaetal lobes, and two pairs of anal cirri on pygidium develop gradually ( Thorson 1946; Hannerz 1956; Berkeley and Berkeley 1961; Reddy and Mohan 1982; Plate and Husemann 1994; Magalhães et al. 2015).