Hamacantha ( Vomerula ) mamoi, Ise & Woo & Tan & Fujita, 2019

Hamacantha ( Vomerula) mamoi sp. nov.

Figs. 2–3 View FIGURE 2 View FIGURE 3

Materials examined. Holotype NSMT–Po–2438. Off Jogashima , Kanagawa, Sagami Bay, Japan, 35º7.484′N – 139º33.212′E to 35º7.504′N – 139º33.625′E ( Fig. 1 View FIGURE 1 ), 223– 113m depth, collected by R / V ‘Rinkai-maru’, biological dredge, 13 January 2012, in ethanol. GoogleMaps

Description of holotype. External morphology ( Fig. 2A View FIGURE 2 ). Evenly encrusting sponge, attached on sandstone, about 5 x 5 cm and 1mm thick. Surface seems smooth, oscula not visible. Color in life not recorded, grey in etha- nol.

Skeleton. Ectosomal skeleton a thick tangential reticulation of polyspicular tracts of styles ( Fig. 2B View FIGURE 2 ). Choano- somal skeleton with ascending bundles of styles ( Fig. 2C View FIGURE 2 ). Diancistras and sigmas distributed in both ectosome and choanosome. Of these, diancistras I mostly attached to style bundles ( Fig. 2D View FIGURE 2 ).

Spicules. Skeleton consists of styles as megascleres, two types of diancistras and sigmas as microscleres ( Fig. 3 View FIGURE 3 ).

Styles (Figs. Fig. 3A, B View FIGURE 3 ), abundant, fusiform, almost straight or slightly curved, sharply pointed at one extremity, blunt end thinner than middle part of the shaft ( Fig. 3B View FIGURE 3 ). Dimensions, 347.5–431.0 (385.3) x 9.7–12.3 (11.2) µm. Diancistras I ( Fig. 3C View FIGURE 3 ), common, shaft slightly contorted, surface smooth, thin fimbriae (fringe/edge) along entire surface of the bended inner shaft, except around notch and sometimes at mid point, 139.5–163.0 (153.5) x 14.9–17.9 (16.5) µm in shaft width. Diancistras II ( Fig. 3D View FIGURE 3 ), rare, shaft contorted, fimbriae along entire surface of the bended inner shaft, except in the middle, 28.1–36.3 (33.5) x 1.7–2.5 (1.9) µm in shaft width. Sigmas ( Fig. 3E View FIGURE 3 ), common, elongated, 51.4–63.7 (55.9) x 1.5–2.6 (1.9) µm in shaft width.

Etymology. Specific epithet ( mamoi ) refers to a nickname “Mamo” of Mr. Mamoru Sekifuji, the captain of R / V ‘Rinkai-maru’, who operated the sample collection of the present species.

Origin of Japanese name. New Japanese vernacular name: Mamo-kaimen is proposed herein. “Kaimen” is sponge in Japanese.

Remarks. The possession of stylote megascleres and diancistra microscleres properly attributes our specimen to the subgenus Vomerula . Up to now, a total of twelve species of Hamacantha ( Vomerula) have been recorded globally ( Van Soest et al., 2018). Three species, H. ( V.) acerata Lévi, 1993 , H. ( V.) carteri Topsent, 1904 and H. ( V.) esperioides Ridley & Dendy, 1886 are comparable to H. ( V.) mamoi sp. nov. by their spicule composition: styles as megascleres, two types of diancistras, and one type of sigmas as microscleres.

The smaller category of diancistras of H. ( V.) acerata was treated as “sigmancistra” by Leví (1993). However, it has fimbriae (knife-like edges) at both the apices and on the inner bended shaft (see Lévi, 1993: Fig. 13A), and thus it should be considered as a diancistra. H. ( V.) acerata has larger diancistras ( 190–200 µm vs 139.5–163.0 µm, 42–45 vs 28.1–36.3 µm), and much smaller sigmas ( 18 µm vs 51.4–63.7 µm) than those of H. ( V.) mamoi sp. nov.

Hamacantha ( V.) carteri has much larger styles ( 700–800 µm vs 347.5–431.0µm in length) and much smaller sigmas ( 20 µm vs 51.4–63.7 µm in length) ( Hajdu, 1994) than those of H. ( V.) mamoi sp. nov. Smaller “diancistras” of the two types of diancistras in H. ( V.) carteri seems to lack fimbriae on the inner side of the shaft ( Hajdu, 1994), and thus might be regarded as cyrtancistra-like diancistras, which is also different from the authentic diancistras of H. ( V.) mamoi sp. nov.

Hamacanta ( V.) esperioides also has much larger styles ( 700 µm vs 347.5–431.0 µm in length), much smaller sigmas ( 38µm vs 51.4–63.7µm in length), and relatively larger diancistras I ( 177µm vs 139.5–163.0µm in length) than those of H. ( V.) mamoi sp. nov.

The three species are also geographically distant from H. ( V.) mamoi sp. nov.: there is one record of H. ( V.) acerata from deep-water New Caledonia ( Lévi, 1993), H. ( V.) carteri from Azores ( Topsent, 1904), and H. ( V.) esperioides from both sides of the Atlantic ( Ridley & Dendy, 1886, 1887; Lévi, 1963; Uriz, 1987, 1988, Hajdu, 2002).

Comparison with H. ( V.) umisachii sp. nov. will be carried below.