Benthodytes marianensis, a new species of abyssal elasipodid sea cucumbers (Elasipodida: Psychropotidae) from the Mariana Trench area

摘要

Benthodytes marianensis sp. nov., is described from the Mariana Trench at the depth of 5567 m. This is the thirteenth species in Benthodytes Theel, 1882. The new species has a broad brim around the body, dark violet skin, 9 pairs of large dorsal papillae with other papillae of equal or smaller size situated elsewhere, forming two zigzag rows, and some minute papillae scattered around the anterior region. Body wall ossicles are rods, crosses with three or four arms and central apophyses, and crosses of an unusual type. Crosses with four arms and central bipartite, tripartite and tetrapartite apophyses and peculiar cross-shaped ossicles with high apophyses ending in two horizontal arms are present in the dorsum. Large rod-shaped ossicles with bipartite apophyses and crosses with three or four arms and rudimentary apophyses are present on the ventrum. B. marianensis is morphologically most similar to B. incerta, but it is distinguished from B. incerta by the number and arrangement of dorsal large papillae, the broad brim and details of ossicle morphology. The phylogenetic analyses based on (16S, COI) and nuclear genes (H3) all confirm the morphological identification.