Gymnangium hians ( Busk, 1852 )

Chakraborty, Oishinee & Raghunathan, C., 2020, Notes on seven Aglaopheniids (Cnidaria: Hydrozoa: Aglaopheniidae) from Andaman and Nicobar Islands with three new records to India, Zootaxa 4790 (2), pp. 291-317 : 297-298

Gymnangium hians ( Busk, 1852)

( Fig. 2b , 3 a–c)

Plumularia hians Busk, 1852: 396 ; Kirchenpauer, 1876: 30.

Halicornaria hians .— Bale, 1884: 179–180, pl. 13: fig. 6, pl. 16: fig. 7; Kirkpatrick, 1890: 604; Stechow, 1909: 101, pl. 1: fig. 11, pl. 6: figs. 16, 17; Billard, 1913: 68, 69; Stechow, 1913: 94–95, fig. 61; Jäderholm, 1916: 8, fig. 5; Briggs, 1918: 47; Stechow, 1919: 125; Bedot, 1921: 347; Jarvis, 1922: 355; Nutting, 1927: 237; Vervoort, 1941: 222–225, figs. 7–8; Millard, 1958: 219–220, fig. 15G–H; Pennycuik, 1959: 186.

Aglaophenia balei Marktanner-Turneretscher, 1890: 272–273 , pl. 7: figs. 19–20; Billard, 1905: 334.

Halicornaria flava Nutting, 1906: 955 , pl. 6: fig. 2, pl. 13: figs. 11–12.

Halicornaria hians var. profunda Ritchie, 1909: 528 ; Ritchie, 1910a: 24, pl. 4: figs. 13–14; Jäderholm, 1919: 26, pl. 6: fig. 6.

Halicornaria balei .— Ritchie, 1910a: 22–23.

Halicornaria balei var. flava, Nutting (?) Ritchie, 1910a: 23, pl. 4: fig. 12.

Halicornaria haswellii Bale, 1884: 180–181 , pl. 13: fig. 5, pl. 16: fig. 8.

Halicornaria hians var. laxa Ritchie, 1910b: 835–836 , fig. 81; Rees & Thursfield, 1965: 197; Smaldon, Heppell & Watt, 1976: 23.

Halicornaria hians var. balei Billard, 1913: 70 , fig. 56; Bedot, 1921: 347; Van Gemerden—Hoogeveen, 1965: 70–73, figs. 39–41.

Halicornaria hians var. flava .- Bedot, 1921: 347.

Gymnangium hians .— Stechow, 1923: 19; 1925: 254; Yamada, 1959: 84; Ooishi, 1964: 191; Rees & Thursfield, 1965: 171; Rho, 1967: 346, fig. 6; Millard & Bouillon, 1973: 92–93; Rho & Chang, 1974: 147; Millard, 1975: 444–445, fig. 134G–H; Rho, 1977: 279, 425, pl. 93: fig. 93; Vervoort & Vasseur, 1977: 84–86, fig. 35; Millard, 1978: 193; Hirohito, 1983: 77; Rees & Vervoort, 1987: 172–175, fig. 41; Hirohito, 1995: 287–290, fig. 101 a.b; Watson, 2000: 58–60, fig. 47; Vervoort & Watson, 2003: 292, fig. 69F; Ronowicz et al., 2017: 27–30, fig. 7c, 7d, 13a–13e.

Gymnangium hians var. balei .— Schmidt, 1972: 41; Mergner & Wedler, 1977: 24, pl. 6: fig. 38, pl. 10: figs. 64–69.

Gymnangium hians var. flava .— Mammen, 1965b: 311.

Material examined. Stn. 1: 09.ix. 2017, 7 m; Stn. 6: 21.i. 2017, 3 m; Stn. 7: 09.i. 2019, 5 m; Stn. 8: 27.v. 2017, 7 m; Stn. 10: 14.i. 2019, 6 m; Stn. 11: 20.i. 2017, 5 m; Stn. 16: 10.i. 2019, 4 m; Stn. 18: 13.i. 2019, 4 m; Stn. 20: 29.x. 2016, 6 m; Stn. 26: 29.xii. 2018, 8 m; Stn. 28: 23.ii. 2017, 11 m; Stn. 30: 06.x. 2016, 20 m; Stn. 39: 15.xii. 2016, 7 m; Stn. 43: 18.x. 2018, 6 m; Stn. 47: 27.xii. 2017, 3 m; Stn. 48: 28.xii. 2017, 13 m.

Description. Colonies erect and stiff with no secondary branching. Hydrocladia alternately arranged on the hydrocaulus ( Fig. 3b ). Hydrocaulus monosiphonic and internodes not clearly visible. Three nematothecae present at the base of each hydrocladium; one axillary nematotheca on the posterior side and two anteriorly located nematothecae, one basal and one axillary. Hydrocladia divided into segments by oblique nodes and internal thickenings absent. Hydrotheca cup-shaped and margin interrupted by two to three pairs of lateral cusps ( Fig. 2b ). Abcauline shelf present, curving upwards at the end. Median nematotheca variable in length, always reaching beyond the hydrothecal margin. Median nematothecae tubular, pointed outwards with a gutter shaped opening. Lateral nematothecae sacshaped, opening directed upwards. Gonothecae arranged in double rows on the anterior side along the hydrocaulus on short peduncles inserted on hydrocladial apophysis ( Fig. 3a ).

Remarks. Ritchie (1909, 1910a) reported this species under the names; Halicornaria balei ( Marktanner-Turneretscher, 1890) , H. balei var. flava (Nutting?) and H. hians var. profunda Ritchie, 1909 . He differentiated H. balei from its variety, H. balei var. flava , based on “the compression of its hydrothecae”. Further, Ritchie (1910a) distinguished H. balei from H. hians based on “the strong convexity of its median sarcotheca, by its deeper hydrotheca, and by the position of the intrathecal ridge which is situated at a greater distance from the base of the hydrotheca”. Also, H. hians var. profunda was distinguished from H. hians based on “the greater length of the thecate internodes compared to their diameter, greater depth and more erect posture of the hydrothecae and greater distance which separate the intrathecal septum from the base of the hydrotheca”. This is known to be a highly variable species in terms of morphology and all the above names have been synonymised to Gymnangium hians ( Busk, 1852) following molecular taxonomy ( Ronowicz et al. 2017). In Mammen (1965b), Gymnangium hians var. flava has been listed, however no formal description or locality of the species was provided. Thus, the record of the species from mainland India remains doubtful. In terms of bathymetric distribution, this species was observed from 3 to 20 m.

Associated fauna. The bivalve, Pterelectroma physoides (Lamarck, 1819) , was observed to be attached to the main stem ( Fig. 3c ). Thornely (1904) also reported that some specimens of Gymnangium pennatulum (Ellis and Solander, 1786) had small bivalves attached to them, Avicula (Margaritifera) zebra, Reeve, 1857 , a name synonymised with P. physoides .

Substrate. Frequently observed to be growing in a “bunch” and the colonies were found growing on rocks, boulders, dead corals, in crevices and depressions.

Distribution. Type locality; Torres Strait.

India; Andaman and Nicobar Islands ( Ritchie 1909; 1910a and present study)

Elsewhere; South Africa ( Millard 1975); East Indies, Japan, Hawaii, Indian Ocean, Red Sea, Sagami Bay ( Stechow 1909), China Sea ( Nutting 1927).

Figures

FIGURE 2. Illustrations of hydrothecae. a, Aglaophenia cupressina Lamouroux, 1816. b, Gymnangium hians (Busk, 1852). c, Lytocarpia brevirostris (Busk, 1852). d, Lytocarpia delicatula (Busk, 1852). e, Macrorhynchia philippina Kirchenpeuer, 1872. f, Macrorhynchia phoenicea (Busk, 1852). g, Monoserius pennarius (Linnaeus, 1758). Scale bar, a, b, g= 200µm, c, d, e, f, h, i=100µm.

FIGURE 3. a–c, Gymnangium hians. a, In-situ photo of colony at Paget Island. b, Gonothecae arranged in two rows on the hydrocaulus. c, associated bivalve, Pterelectroma physoides, attached to the main stem. d–f, Lytocarpia brevirostris. d, In-situ photo of colony at Sir Hugh Ross Island. e, Gonothecae borne on modified hydrocladia. f, Hydrocaulus showing cauline nematothecae. Scale bar, b, e= 2mm, c= 5mm, f= 200µm