Scaridelphys deplanata gen. et sp. nov.

(Fig. 442)

Typematerial. Holotype ♀ (intact, MNHN-IU-2014- 21467) from Didemnum parau Monniot C & Monniot F., 1987 (MNHN-IT-2008-3200 = MNHNA2/DID.C/533), CRRFOCDN 8855-K, Baluan, Papua New Guinea (02°32.27 Ń, 147°17.97 É), depth 7 m, 22 June 2003.

Etymology. The specific name is derived from the Latin deplanat (=flattened), referring tothe dorsoventrally depressed body.

Description of female. Body (Fig. 442A) dorsoventrally flattened, flatworm-shaped. Bodylength 4.42 mm; greatest body width 770 μm across cephalosome. Body surfaces covered with ornamentation of minute papillae, densely on dorsal surface and sparsely on ventral surface. Cephalosome (Fig. 442B) nearly quadrate, with truncate frontal margin. Cephalosome and 4 pedigerous somites discernible by 4 faint dorsal suture lines: lengths of cephalosome and pedigerous somites approximately 0.81, 0.41, 0.27, 1.2, and 1.6 mm, respectively. Last metasomite graduallynarrowingposteriorly. Freeurosome (Fig. 442C) small, 177×208 μm, articulated from trunk on ventral surface, but without any trace of articulation on dorsal surface, weaklybilobeddistally,withshallowposteromedial (anal) incision. Caudal rami and caudal setae absent.

Rostrum absent. Antennule (Fig. 442D) represented by small anterolateral prominence (Fig. 442B) tipped with about 5 small setae. Antenna absent. Labrum (Fig. 442E) longerthan wide, broadening distally, with slightly convex distal margin. Mouth visible beneath labrum (Fig. 442E). One small, vestigial lobe (Fig. 442E, F) tipped with several papillae, probably representing mandible, present on each side of base of labrum. Other mouthparts absent. Legs absent.

Male. Unknown.

Remarks. This species is treated as congeneric with Scaridelphys papillata gen. et sp. nov. on the grounds that both retain the antennules, the labrum, and one pair of vestigial mouthparts, but lack antennae and any vestiges of other mouthparts. The pair of vestigial appendages is tentatively interpreted here as the mandibles, mainly on the basis of its position lateral to the base of the labrum. There are several differences between these two species: the body iscylindricalin the typespecies butflattened in S. deplanata gen. et sp. nov., the cephalosome is snake-head-shaped in the type species and but quadrate in S. deplanata gen. et sp. nov., the antennule is spherical in S. papillata gen. et sp. nov. but represented by a small lobe in S. deplanata gen. et sp. nov., the labrum tapers distally in S. papillata gen. et sp. nov. but broadens distally in S. deplanata gen. et sp. nov., and the rear margin of the abdomen is bilobed with a deep posteromedian incision in S. papillata gen. et sp. nov. but is weakly bilobed with a shallow posteromedian incision in S. deplanata gen. et sp. nov.