Octocannoides tetranema Xu, Huang & Guo, 2021

Wang, Xuefeng, Lu, Liyi, Zhang, Shenzeng, Lin, Linkun, Xu, Zhenzu, Guo, Donghui & Huang, Jiaqi, 2021, Two new species of hydromedusa (Cnidaria) from the Leizhou Bay, the northern South China Sea, Zoological Systematics 46 (3), pp. 193-199 : 197-198

Octocannoides tetranema Xu, Huang & Guo , sp. nov. ( Figs 5–7 )

Material examined. Holotype (AOB-HL 333), one specimen collected from the Leizhou Bay of the northern South China Sea, S 7 station (20°45'N, 110°35'E), depth 10.4 m, November 2018, coll. Xuefeng Wang and Kun Lin.

Diagnosis. Manubrium broad and long, about 3/4 height of subumbrella cavity; with 8 funnel-shaped radial lobes extending from manubrium wall, 8 oral lips and 8 simple radial canals; 4 marginal tentacles and 24 short club-shaped tentaculae present, all with black pigmented spots in marginal; usually 8–12 elliptic-like gonads present on middle of radial canals, consisting of two lateral halves.

Description. Medusa spherical-like, up to 2 mm height, 3 mm width; dome top round, with very thick jelly, about 1/2 height of bell, thinner toward bell margin; manubrium broad and long, octagon-like in cross section, without gastric peduncle, about 3/4 height of subumbrella cavity; 8 funnel-shaped radial lobes extend from manubrial wall, end connected to radial canals; 8 simple lips present, without short bifurcating; 8 simple radial canals present, with median grooves; 4 marginal tentacles present with base bulbs large, long conical-shaped, without excretory papillae; 24 short club-shaped tentaculae present, without marginal bulbs, all with black pigmented spots in marginal; usually with 8–12 elliptic-like gonads, each consisting of two lateral halves upon middle of radial canal; about 24 closed statocysts present, usually with 1 statocyst located between tentaculae; without ocelli; velum middle broad.

Etymology. The specific name is from the Latin tetranema , meaning four tentacles, referring to the medusa with distinct four tentacles.

Distribution. The northern South China Sea (Leizhou Bay).

Remarks. This new species has 8 simple radial canals, 8 simple lips on mouth, 4 marginal tentacles and 24 short clubshaped tentaculae with black pigmented spots present, and gonads consists of two lateral halves; lacks excretory papillae. These are consistent with the general characters of the family Octocannoididae .

The new species resembles O. ocellata Menon, 1932 , by both manubria without gastric peduncle; having 8 radial canals and 8 simple oral lips; gonads on the middle of radial canals, each consisting of two lateral halves, but can be distinguished from the latter by having 4 marginal tentacles. The genus comprises the following species: O. ocellata Menon, 1932 and O. taeniogonia Xu & Huang, 2004 ( Bouillon et al., 1991; Xu & Huang, 2004b). The new species has elliptical-shaped gonads, located upon the middle of radial canals, which differs from O. taeniogonia . These characteristics are listed in the following keys.

Key to medusa of all known species in genus Octocannoides .

1. Gonads band-liked, S-shaped, along almost whole length of radial canals; with 3 statocysts between tentacles................................... ..................................................................................................................................................... O. taeniogonia Xu & Huang, 2004 Gonads oval or elliptical shaped, upon the middle radial canals.......................................................................................................... 2

2. Umbrella flatter than hemispherical, jelly thick at apex, about 1/5 height of bell; manubrium short and broad, about 1/3 height of subumbrella cavity; radial lobes indistinct; with 8 marginal tentacles and 16–24 club-shaped tentaculae; with 40 statocysts .............. ...................................................................................................................................................................... O. ocellata Menon, 1932 Umbrella near spherical, jelly thick at apex, about 1/2 of bell height; manubrium long and broad, about 3/4 height of subumbrella cavity; with 8 distinct radial lobes; with 4 marginal tentacles and 24 club-shaped tentaculae; with 24 statocysts................................. .......................................................................................................................................... O. tetranema Xu, Huang & Guo , sp. nov.

Funding This work is supported by the Fund of Southern Marine Science and Engineering Guangdong Laboratory (Zhanjiang) (ZJW-2019-06), and Global Climate Change and Ocean Atmosphere Interaction Research: Biological Classification System Research.

Acknowledgements The authors would like to thank Boxin Su and Zhijie Chen for their help in field sampling work. The thanks are also due to the comments and suggestions by two anonymous reviewers and the editor Fuqiang Chen.

Figures

Figures 5–7. Octocannoides tetranema Xu, Guo & Wang, sp. nov. 5–6. Oval views. 7. Lateral view. Scale bars=0.5mm.