Proboscidactyla trifurcata Xu, Huang & Guo, 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 : 198-199

Proboscidactyla trifurcata Xu, Huang & Guo , sp. nov. ( Figs 4 , 11 )

Material examined. Holotype (AOB-HL322) and Paratype (AOB-HL323–325), four specimens collected from the 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 almost hemispherical, exumbrella with scattered cnidocyst clusters; manubrium quadrangular, short, with 4 radial gastric lobes; mouth with a sinuous margin; 4 primary radial canals, each branching 3 secondary radial canals, most secondary radial canals bifurcating, about 24 terminal branches and tentacles as many; gonads on the manubrium and lateral wall of manubrium lobes.

Description. Umbrella nearly hemispherical, 2.5–3.0 mm in width and 2.0– 2.2 mm in height; jelly thick at apex, but thinner toward bell margin; exumbrella with scattered cnidocyst clusters; 4 primary radial canals, each branching two times, giving rise to additional branches bearing 24 terminal branches; 3 secondary radial canals arise from each primary one, secondary radial canals very long, each arise bifurcation after a short distance in tertiary canals, and finally almost all bifurcate canals joining solid endodermal marginal exumbrellar core; without ring canal; manubrium short, quadrangular, with large base, extending along to radial gastric lobes, generally with 4 gastric lobes in perradial position of manubrium; mouth with 4 lips often poorly marked, being masked by sinuous margin; gonads situated at base of manubrium wall, extending along lateral wall of radial gastric lobes, slightly onto proximal part of primary radial canals; marginal tentacles up to 24, each situated at end of a radial canal branch, hollow, rather short, stiff, each without adaxial cnidocyst cushion; one cnidocyst exumbrella cluster between each pair of tentacles.

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

Etymology. The specific name is from the Latin trifucata, meaning tri-furcate, referring to each primary radial canal branching 3 secondary radial canals.

Remarks. By marginal structure characters, the medusa is placed under the genus Proboscidactyla , Proboscidactylidae . The genus current comprises seven valid species, i.e. P. abyssicola Uchida, 1947 , P. circumsabella Hand, 1954 , P. flavicirrata Brandt, 1835 , P. menoni Pagès, Bouillon & Gili, 1991 , P. mutabilis (Browne, 1902) , P. ornata (McCrady, 1859) , P. stellata ( Forbes, 1846) , and five species in doubt: P. brooki ( Mayer, 1910) and P.furcata (Haeckel, 1879) = P. stellata ( Forbes, 1846) , P. occidentalis (Fewkes, 1889) and P. pacifica (Maas, 1909) = P. flavicirrata Brandt, 1835 , P. conica Menon, 1932 = P. ornata (McCrady, 1859) ( Bouillon et al., 2006) .

The members of the genus Proboscidactyla can be distinguished by following characters: the number of radial canals, their branching and the position of the gonads as well as the present of medusa buds or not. The new medusa differs from other valid species by having 4 primary radial canals with terminal branches, with 4 radial gastric lobes, without medusa buds, gonads on manubrium wall and lateral wall of manubrium lobes. It is also similar to P. menoni Pagès, Bouillon & Gili, 1991 by having gonad at base of the manubrium wall, extending along lateral wall of gastric lobes, but differs from the latter by: 1) the new medusa has the manubrium with 4 radial gastric lobes, while P. menoni has the manubrium with 8 to 16 radial gastric lobes; 2) the new medusa has each primary radial canal branching 3 secondary radial canals, while P. menoni has each primary radial canal branching 2 secondary radial canals; 3) P. trifurcata Xu, Huang & Guo , sp. nov. has the gonads extending onto proximal part of primary radial canals, while P. menoni has the gonads extending to the secondary branches of radial canals; 4) the new medusa has 24 terminal branches and tentacles as many, without adaxial cnidocyst cushion, while P. menoni has 60 terminal branches and tentacles as many, each with an adaxial cnidocyst cushion.

Key to medusae of all known species in genus Proboscidactyla .

1. With 20 radial canals, some bifurcated; gonads extending along proximal half of all radial canals; no tentacles.................................. .................................................................................................................................................................. P. abyssicola Uchida, 1947 With 4–8 primary radial canals ............................................................................................................................................................2

2. With more than 4 primary radial canals ...............................................................................................................................................3 With 4 primary radial canals ................................................................................................................................................................4

3. Normally with 6 primary radial canals, up to 24 terminal branches and tentacles as many, with adaxial basal cnidocyst cushions ...... ..................................................................................................................................................................... P. stellata ( Forbes, 1846) Normally with 8 primary radial canals, 24–54 terminal branches and tentacles as many, without adaxial basal cnidocyst cushions .... ................................................................................................................................................................ P. mutabilis (Browne, 1902)

4. With medusa buds, arising from corners of manubrium base or forks of radial canals; radial canals with 16–20 terminal branches, and same number of tentacles .................................................................................................................... P. ornata (McCrady, 1859) Without medusa buds ........................................................................................................................................................................... 5

5. Gonads restricted to manubrium wall .................................................................................................................................................. 6 Gonads at base of manubrium wall, extending along lateral wall of gastric lobes ...............................................................................7

6. Gonads extending slightly onto proximal part of radial canals; lips of manubrium with highly folded and hang; 4 primary radial canals, 54–70 or more terminal branches and same number of short tentacles ..................................................... P. flavicirrata Brandt, 1835 Gonads masses, each with a pair of swollen lobes on adradial side of manubrium wall; mouth lips fold, simple; 4 primary radial canals; 24–32 terminal branches and as many tentacles.......................................................................... P. circumsabella Hand, 1954

7. Manubrium with 8 to 16 radial gastric lobes; 4 primary radial canals, 60 terminal branches and tentacles as many, each with an adaxial cnidocyst cushion; gonads extending to secondary branches of radial canals....................... P. menoni Pages, Bouillon & Gili, 1991 Manubrium with 4 radial gastric lobes; 4 primary radial canals, 24 terminal branches and tentacles as many, each without adaxial cnidocyst cushion; gonads extend slightly onto proximal part of primary radial canals ...... P. trifurcata Xu, Huang & Guo , 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.