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

Ise, Yuji, Woo, Sau Pinn, Tan, Shau Hwai & Fujita, Toshihiko, 2019, First record of Hamacantha (Porifera, Demospongiae, Merliida, Hamacanthidae) from Japan, with description of two new species, Zootaxa 4657 (3), pp. 474-482 : 476-478

Hamacantha (Vomerula) mamoi sp. nov.

Figs. 2–3

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 ), 223– 113m depth, collected by R / V ‘Rinkai-maru’, biological dredge, 13 January 2012, in ethanol.

Description of holotype. External morphology ( Fig. 2A ). 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 ). Choano- somal skeleton with ascending bundles of styles ( Fig. 2C ). Diancistras and sigmas distributed in both ectosome and choanosome. Of these, diancistras I mostly attached to style bundles ( Fig. 2D ).

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

Styles (Figs. Fig. 3A, B ), abundant, fusiform, almost straight or slightly curved, sharply pointed at one extremity, blunt end thinner than middle part of the shaft ( Fig. 3B ). Dimensions, 347.5–431.0 (385.3) x 9.7–12.3 (11.2) µm. Diancistras I ( Fig. 3C ), 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 ), 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 ), 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.

Figures

FIGURE 1. Location of sampling sites. Open star indicates sampling site of Hamacantha (Vomerula) mamoi sp. nov., and solid star indicates that of Hamacantha (Vomerula) umisashii sp. nov..

FIGURE 2. Hamacantha (Vomerula) mamoi sp. nov., holotype (NSMT-Po-2438).A, external morphology. B, skeletal arrange- ment of surface of ectosome. C, vertical section shows bundles of styles. D, diancistras I attach on bundle of styles. Scale bars: A, 5 mm; B, C, 200 µm; D, 100 µm.

FIGURE 3. Spicules of Hamacantha (Vomerula) mamoi sp. nov., holotype (NSMT-Po-2438). A, styles. B, magnified view of both extremities of mycalosyle, left: blunt end or base, right: sharply pointed end or apex. C, diancistras I (larger diancistras). D, diancistras II (smaller diancistras). E, sigmas. Scale bars: A, 100 µm; B, E, 20 µm; C, 50 µm; D, 10 µm.