Abstract
A new species of harpacticoid copepod, Dactylopusioides malleus sp. nov., belonging to the family Thalestridae is described from central Japan. The species is obligately endophagous in dictyotalean brown algae (Dictyota dichotoma (Hudson) J.V. Lamouroux, Dictyota maxima Zanardini and Dictyopteris undulata Holmes). The species nests by burrowing into the algal tissue during the copepod naupliar stages, while copepodids and adults reside in a dome-shaped, transparent capsule made of mucus and formed on the algal tissue. In laboratory experiments, the new species progressed through its complete life cycle (i.e. from egg to adult) while feeding only on unialgal dictyotalean tissues; this confirmed the obligate relationship with the host. The new species shares the following morphological characters with other species of Dactylopusioides: 1) antennary exopod 1-segmented; 2) first segment of P1 endopod in female elongated with a long seta on the inner proximal margin; 3) baseoendopod and exopod of P5 in female with five setae. It differs from other species in the following ways: 1) antennary exopod with six setae; 2) a stout hammer-shaped inner spine on the basis of P1 in male; 3) terminal short seta on third segment of P2 endopod in male is plumose.References
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