Acasta turriformis Yu & Chan & Achituv & Kolbasov 2017, new species

Acasta turriformis, new species

(Figs. 1–7)

Material examined. Four specimens (holotype and paratypes) in the sponge Lissodendoryx (Lissodendoryx) sp. Topsent, 1892, Gongguan, Green Island, Taitung, Taiwan 22°40′47″N 121°29′29″E, SCUBA diving, depth 9 m. The holotype (dry shell compartments, mouth parts and cirri mounted in glycerol on glass slide) and paratype (shell in EtOH) are deposited in the Zoological Museum of Moscow State University under registration numbers Mg –1230 (holotype) and Mg –1231 (paratype). The other paratypes (ASIZCR000371 and ASIZCR000372) are deposited in the Biodiversity Research Museum, Biodiversity Research Center, Academia Sinica, Taiwan.

Diagnosis. Shell white, elongated in height, with long, narrow slits between wall plates; parietes with long longitudinal ribs internally; carinolatus 2 narrow, basis deep, bowlshaped, with crenated margin; scutum without distinct radial striations, articular ridge prominent, pits of adductor and depressor muscles conspicuous; tergum without long beakshaped apex, spur wide, with end almost quadrate; cirri IV and V with developed curved teeth on anterior rami; basidorsal point of penis absent. Embedded in sponge Lissodendoryx (Lissodendoryx) sp. Topsent, 1892.

Description. (Based on holotype). Shell white, elongated, 9.3–10 mm high, 4.1–4.3 mm rostro-carinal basal diameter; tips of wall plates tinged with pale violet; orifice moderately small, toothed, 2.0– 2.7 mm maximum length, 6 long, narrow slits 2.5–3.0 mm high between proximal halves of wall plates (Fig. 1A, B). Basis deep, bowl-shaped, 4.0– 4.3 mm high, with growth lines concentric, margin crenated, bottom of basis deformed or with 4 radial grooves (Fig. 1A, B, E). Parietes (Fig. 1C, D) with small, dense, granulate, external projections and fine growth lines, basal parts thinner, sheath about 1/3 total length, with horizontal striations, inner lamina beneath sheath with long, distinct longitudinal ribs. Radii and alae with summits oblique, radii ~1/2 length of parietes, with fine, oblique, external striations, alae semitransparent. Carinolatus 2 narrow (Fig. 1A, B, D), paries ~1/5–1/7 width of carinolatus 1.