A new species of Nudibranchia of the genus Aldisa Bergh (Gastropoda, Opisthobranchia) from Thailand

A new species of the nudibranch genus Aldisa Bergh, 1878, Aldisa erwinkoehleri spec. nov., is described from Thailand. The new species is characterized by simple and coalesced tubercles on the notum and a bright colour pattern, with a light blue background, concentric black rings, black rhinophores and yellow areas on the notum. The bursa copulatrix and the receptaculum seminis are joined and the prostatic tract of the vas deferens is not differentiated. A dense network of vessels is visible on the digestive gland. The bright colour pattern of A. erwinkoehleri is convergent with that of some sympatric phyllidiid nudibranchs of the genus Fryeria Gray, 1853.