Monocanna ovale Wang & Lin & Xu & Guo & Huang 2019, comb. nov.

Monocanna ovale (Mayer, 1900) comb. nov. (Figs 6, 14–15)

Multioralis ovalis Mayer, 1900: 54–55, pl. 30, figs. 129–130.

Gastroblasta ovalis: Mayer, 1910: 281, pl. 35, figs. 7–8.

Gastroblasta ovale: Bouillon et al., 2006: 417; Xu et al., 2012: 310, fig. 3. 48; Xu et al., 2014: 717, fig. 616a–b.

Phialidium ovale: Kramp, 1961: 171; Xu & Huang, 1983: 101–102, pl. 1, figs. 1–2; Li & Chen, 1991: 90.

Clytia ovalis: Guo et al., 2008: 231; Tang & Gao, 2008: 319.

Material examined. 3 specimens (AOB-HL328–330) collected from Dapeng Bay, northern of the South China Sea, station V 4 (22°35 ˊ N, 114°19 ˊ E), depth 13.5 m, 26 August 2018, coll. Zike Zhao, Guanjie Min and Shihao Deng.

Diagnosis. The species is different from others by following: umbrella elliptical in outline; a straight canal along major axis of bell; with 2 to 4 manubria along a straight canal; no centripetal canal; two small gonads near ends of canal; 12–25 short marginal tentacles; marginal statocysts slightly more numerous than tentacles, with one concretion.

Description. Umbrella 2.4–4.0 mm in width, flat, elliptical or hemispherical; with a slender circular canal, and a straight canal along major axis of bell; with 2–4 manubria, 2 equally developed large manubria on either side of center of subumbrella, upon straight canal, and 2 small manubria upon same canal centrifugally away from larger manubria; without centripetal canal; 2 small gonads upon near ends of canal; with 12 to 25 short, simple, coiled marginal tentacles with well-developed basal bulbs; statocysts slightly more numerous than tentacles, usually 1, but occasionally 2, being found between each successive pair of tentacles, each with one concretion; velum simple and quite broad.

Distribution. Haichang on the Jiulong River Estuary of Fujian (Xu & Huang, 1983); Dapeng Bay of Shenzhen and Beibu Gulf (Guo et al., 2008) of the northern South China Sea; Nansha Island (Li & Chen, 1991) of the southern South China Sea; Tortugas, Florida on the east coast of North America (Mayer, 1900); Brazil (Kramp, 1961).

Remarks. This species was reported by Mayer (1900) as Multioralis ovalis from Tortugas, Florida, USA. Then, it was redescribed in detail (Mayer,1910), and transferred from the genus Multioralis to the genus Gastroblasta by having 2 or more radial canal and more than one manubrium. Kramp (1961) indicated that ovale could not be placed in the genus Gastroblasta, because its medusa had not centripetal canals and with numerous statocysts, and regarded it as an abnormal species of Phialidium (a junior synonym of Clytia). However, the change was not well accepted and the species was reported under Gastroblasta, Phialidium and by different scholars.

Although only 10 specimens were obtained from the Dapeng Bay, their good preservation provides enough morphological evidences to us. A redescription of Monocanna ovale (Mayer, 1900) comb. nov. is done here as the type species of the genus Monocanna Xu, Guo &Wang, gen. nov.

Funding The work is supported by the Special Fund for Agro-scientific Research in the Public Interest (201403008), Foundation for Distinguished Young Teachers in Higher Education of Guangdong, China (YQ2014002), the National Natural Science Foundation of China (41876180), Global Climate Change and Ocean Atmosphere Interaction Research: the Marine Biological Sample Museum Upgrade and Expansion (GASI-01-02-04) and Biological Classification System Research.

Acknowledgements The authors would like to thank Mr. Weidi Yang and Mr. Dingxun Wu, from Xiamen University, for their help in digital image processing. We also thank the Associate Editor, Fuqiang Chen, and anonymous referees for their valuable comments and suggestions.