Eucodonium crassonemalis Xu, Guo & Lin, 2019

Wang, Xuefeng, Lin, Kun, Xu, Zhenzu, Guo, Donghui & Huang, Jiaqi, 2019, Some new Hydroidomedusa (Cnidaria) from the northern South China Sea, Zoological Systematics 44 (3), pp. 191-205 : 197

Eucodonium crassonemalis Xu, Guo & Lin , sp. nov. ( Figs 3 , 10 )

Material examined. Holotype (AOB-HL312) and paratypes (AOB-HL313–321), ten specimens 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 nearly spherical-like, slightly higher than wide, with a slight rounded apical projection, lateral wall thin; gastric peduncle short and broad, manubrium large on broad gastric peduncle; oral tube very short, manubrium cylindrical; mouth simple, quadrangular, covered with cnidocysts; medusa buds on interradial sides of manubrium; 4 narrow radial canals and circular canal present; 2 opposite perradial marginal tentacles, short and thick, with ring cnidocysts and 4–5 prominent brown spots at regular intervals; no terminal knob, marginal bulbs spherical-like, inside swelling, no red-brown pigment granules; two other opposite marginal bulbs no present; no ocelli; velum narrow.

Description. Medusa nearly spherical-like, up to 0.6–0.8 mm in height, 0.5–0.7 mm in width, with a slight rounded apical projection, lateral wall thin; gastric peduncle very short and broad, shorter than length of manubrium; manubrium large on broad gastric peduncle, oral tube very short, about 1/3 length of manubrium; manubrium cylindrical, about 1/2 as long as bell cavity; mouth simple, quadrangular, lips inconspicuous, covered cnidocysts; medusa buds on interradial sides of manubrium; 4 narrow radial canals and circular canal present; 2 opposite perradial marginal tentacles short and thick, extending to 1/3 height of umbrella, with ring cnidocysts and 4–5 prominent brown spots on tentacles at regular intervals, and no terminal knob; marginal bulbs spherical-like, inside swelling without red brown pigment granules, and two other opposite marginal bulbs no present; no ocelli; velum narrow.

Distribution. Dapeng Bay of Shenzhen, northern of the South China Sea.

Etymology. The specific name is from Latin crassonemalis , meaning crass-nema, referring to the morphology of the very thick tentacles.

Remarks. The new species can be distinguished from the other species of Eucodonium by: 1) two opposite perradial marginal tentacles, shorter than the bell height; 2) gastric peduncle short and broad, shorter than the length of manubrium; 3) oral tube in conspicuous. This new species is close to E. brevistyle , but differs from the latter by following: 1) two opposite perradial marginal tentacles short and thick, without terminal knob; 2) with 4–5 prominent brown spots in the tentacles at regular intervals.

Key to medusa of all known Eucodonium species.

1. Four perradial marginal bulbs and four tentacles present; tentacles with terminal swelling ...................... E. brownei Hartlaub, 1907 Two perradial marginal bulbs and two tentacles present; tentacles with or without terminal swelling ................................................ 2

2. Two opposite perradial tentacles very long and thin, length up to 3 times bell height, with numerous prominent brown spots at irregular intervals................................................................................................................... E. longitentaculatum Xu, Huang & Wang, 2016 Two opposite perradial tentacles shorter than bell height.....................................................................................................................3

3. Gastric peduncle broad conical, half as long as manubrium; oral tube long, about same length as that of manubrium ......................... ....................................................................................................................................... E. bitentaculatum Xu, Huang & Guo, 2016 Gastric peduncle short and broad, shorter than length of manubrium.................................................................................................. 4

4. Two opposite perradial marginal tentacles short and thin, thread-like, with ring cnidocysts, but no brown spots, with a small terminal swelling ..................................................................................................................................... E. brevistyle Xu, Huang & Lin, 2016 Two opposite perradial marginal tentacles short and thick, with ring cnidocysts, but with 4–5 prominent brown spots at regular intervals, without terminal knob........................................................................................ E. crassonemalis Xu, Guo & Lin , sp. nov.

Figures

Figures 1–6. Hydroidomedusa spp. 1. Nubiella terminaliknoba Xu, Huang & Guo, sp. nov., lateral view. 2. Paranubiella shenzhenensis Xu, Guo & Wang, sp. nov., lateral view. 3. Eucodonium crassonemalis Xu, Guo & Lin, sp. nov., lateral view. 4. Proboscidactyla trifurcata Xu, Huang & Guo, sp. nov., lateral view. 5. Euphysora knides Huang, 1999, lateral view. 6. Monocanna ovale (Mayer, 1900) comb. nov., oral view. Scale bars: 1=0.2mm; 2–3, 5–6=0.5mm; 4=1.0mm.

Figures 7–11. Hydroidomedusa spp., line drawing. 7. Nubiella terminaliknoba Xu, Huang & Guo, sp. nov., lateral view. 8. Ditto, enlargement of marginal tentacle. 9. Paranubiella shenzhenensis Xu, Guo & Wang, sp. nov., lateral view. 10. Eucodonium crassonemalis Xu, Guo & Lin, sp. nov., lateral view. 11. Proboscidactyla trifurcata Xu, Huang & Guo, sp. nov., lateral view. Scale bars: 7=0.2mm; 9–10=0.5mm; 11=1.0mm.