Sibogita geometrica Maas, 1905 New

Zhenzu Xu, Jiaqi Huang, Mao Lin, Donghui Guo & Chunguang Wang, 2016, Taxonomic notes on Hydroidomedusae (Cnidaria) from South China Sea II: Family Bythotiaridae (Anthomedusae), Zoological Systematics 41 (2), pp. 149-157 : 155-156

Sibogita geometrica Maas, 1905 New record to China ( Figs 14–16 )

Sibogita geometrica Maas, 1905: 17 , pl. 3, figs. 16–18; Mayer, 1910: 186, fig. 99; Kramp, 1965: 49; Kramp, 1968: 57, fig. 151a–b; Schuchert, 2009: 455, fig. 8.

Sibogita geometrica occidentalis Kramp, 1959: 28 , 129, pl. 2, figs. 2–3, text-figs. 4–5.

Calycopsis geometrica Bigelow, 1919: 290 , pl. 40, figs. 5–7, pl. 41, fig. 2.

Material examined. One specimen, Beibu Gulf of South China Sea, station J62 (18°28’N, 108°34’E), depth 25m, 31 July 2006, coll. Donghui Guo.

Description. Umbrella bell-shaped, 4.5 mm in height, 3.5 mm in width, with round dome, apex very thick, manubrium short small, about 1/3 length of subumbrellar cavity; mouth simple, circular; gonads in eight adradial rows, about four transverse folds in each row; with 4 primary radial canals, which somewhat irregularly branched, as seen from the figure they arise from the corners of the manubrium in four unequal groups; most of them bifurcated once or twice at various levels, some of them immediately before reaching the circular canal, occasional anastomoses occur; a few of them proceed undivided to the circular canal; no centripetal canals; altogether 9 canals join the circular canal; radial canals widening containing dark pigment granules; with 9 fully developed tentacles, without basal swellings, and no accumulations of pigment granules, but their basal part adnate to exumbrella, sunk into a narrow furrow between two marginal lobes; everyone of the fully developed tentacles placed opposite a radiating canal, and between two successive tentacles without small tentacles or wart-like protuberances; each tentacles with a terminal knob of cnidocysts, and no ocelli; velum narrow.

Biology. The species is a quite rare oceanic species. Bleeker & Van der Spoel (1988) proposed a diel vertical migration as all night samples were taken above depth 200 m and all day samples were taken bellow. Our specimen was found at 25 meters from the Beibu Gulf, northern South China Sea.

Distribution. Malayan Archipelago and tropical Indian Ocean ( Maas, 1905; Bigelow, 1919), Bay of Biscay, Azores and mid-Atlantic ( Kramp, 1959; Bleeker & Van der Spoel, 1988), Benguela current off South Africa ( Pagès et al., 1992), northern South China Sea.

Remarks. Our specimen has little different with Maas (1905). In original description, the single specimen has 32 canals and only 16 tentacles. In our specimen, there were 9 canals join the circular canal, and 9 fully developed tentacles, each of which placed opposite a radiating canals. On the other hand, the 4 primary radial canals somewhat irregularly branched. Thus, our specimen represents an intermediate form during its development. Although Bigelow (1919) observed the presence of pigment spot or ocelli at the base of the tentacles of the Philippine specimens, no such structures were observed in Maas’s specimen and ours.

Kramp (1959) proposed that the Atlantic population slight differs from the Pacific one and then introduced the former as the subspecies Sibogita geometrica occidentalis . The differences to the nominate subspecies were given as a smaller bell-size, fewer gonadal folds, and radial canals dividing already close to the centre. After checking more specimens from the Pacific, Kramp (1965) synonymized the subspecies occidentalis with the nominal Pacific species. Some other authors (e.g. Winkler, 1982; Blecker & Van der Spoel, 1988) also confirmed this. Both forms are occurring in the Atlantic and the Pacific and they are treated as intermediate forms ( Schuchert, 2009).

Funding This study was supported by Global Climate Change and Ocean Atmosphere Interaction Research (GASI- 01-02- 02-03, GASI- 01-02-04,GASI- 01-02-02-01), the Marine Biological Sample Museum of the Chinese Offshore Investigation and Assessment, and the National Basic Research Program of China (2011CB403604).

Figures

Figures 14 – 16. Sibogita geometrica Maas, 1905. 14. Medusa from Pacific, side view, bell 38 mm in height, modified after Maas (1905) and Mayer (1910). 15. Medusa from Atlantic, aboral view, showing branching pattern of radial canals, after Winkler (1982). 16. Medusa from northern of South China Sea, side view, bell 4.5 mm in height. Scale bars: 15 = 3.0 mm, 16 = 2.0 mm.