Hydranthea margarica ( Hincks, 1862 )

Watson, Jeanette E., 2011, New species, new records and redescriptions of Thecate hydroids (Cnidaria: Hydrozoa: Leptothecata) from Southern Australia, Zootaxa 3122, pp. 1-36 : 6-8

Hydranthea margarica ( Hincks, 1862)

Fig. 3 A–E

Hydranthea margarica Hincks, 1868: 100 , pl. 19, fig. 1.– Huvé, 1954: 178, pls 3–6.– Cornelius, 1995: 302, fig. 71.– Millard & Bouillon, 1973: 45, fig. 6A.

Material examined. NMV F171355, fertile colony of c.15 hydrothecae on rhizome of the green alga Caulerpa scalpelliformis, St Leonards pier, Port Phillip, depth 1 m, coll: J. Watson, 6/04/2006; material ethanol preserved.

Description (from live material). Colony stolonal, hydrorhiza creeping, stolons tubular, walls thin, fairly smooth with a thin coating of adventitious material. Hydrophores small, vasiform, smooth, arising at irregular intervals along hydrorhiza, variable in length but typically short.

Hydrotheca shallow saucer-shaped, expanding from a transverse diaphragm to margin, rim sometimes everted. Secondary hydrophores rare but when present arising from diaphragm of primary hydrotheca. Column of hydranth tall, slender, expanding just below tentacles; c. 30 tentacles in a single whorl, long and slender, surrounding a dome-shaped hypostome; tentacles connected at their bases by a conspicuous intertentacular web; two or three large nematocysts on web between each set of tentacles.

Gonophores borne on hydrorhiza, on a short pedicel, ovoid in shape, with an aureole of large nematocysts; contents too immature for more detailed description.

Cnidome comprising mastigophores of two categories:

i) macrobasic mastigophores, capsule banana-shaped, 39– 42 x 8–9 µm, shaft thick, with a row of large spines at c. 100 µm above capsule, tubule long; in tentacle web, hydranth column and hydrorhiza. ii) microbasic mastigophores, capsule elliptical, 8– 9 x 3 µm, shaft 6–8 µm, tubule fairly short, grouped in circlets in tentacles.

Hydranth body pale gold with a narrow white band below hypostome, tentacles colourless. Perisarc thin throughout.

Remarks. The hydranth is very active and extensile, often bending over to touch the substrate when disturbed. Bouillon et al. (2006) transferred Hydranthea from the Haleciidae to the Lovenellidae . Known species of Hydranthea are: Hydranthea margarica ( Hincks, 1862) , Hydranthea aloysii ( Zoja, 1893) and Hydranthea phialiformis Antsulevich, 1983 . Hydranthea margarica is known from the British Isles, France, the Mediterranean Sea ( Cornelius 1995a) and the Seychelles ( Millard & Bouillon 1973), H. aloysii is known from the Mediterranean Sea ( Huvé 1954) and H. phialiformis from the Sea of Japan ( Antsulevich 1983). Hydranthea aloysii and H. phialiformis were considered but the hydranth of H. aloysii has only 12 tentacles and the intertentacular nematocysts are only 15 x 5 µm, much smaller than those of the present material. The gonophores of H. phialiformis are borne on the body of the hydranth.

Hydrorhiza diameter 60–72

Hydrophore

length of primary hydrophore 86–162

Hydrotheca

depth, diaphragm to rim 20–50 diameter at rim 120–168

Hydranth

length of extended body ~ 1250 diameter of column 75 width across extended tentacles ~ 1000

Gonophore, immature

height 240–228 maximum width 160–200 length of pedicel 120 diameter at rim 100

Millard & Bouillon’s (1973) description of H. margarica from the Seychelles closely matches the present specimen in dimensions of the hydrotheca, the number of tentacles and absence of desmocytes. The major difference between their description and the present material is that they did not mention nematocysts which are in the intertentacular web of the present material; this is puzzling as these are considered diagnostic of the species. If the British, Mediterranean, Indian Ocean and southern Australian material is H. margarica , then the distribution is quite broad and some degree of change may have occurred in some populations, perhaps eventually leading to speciation. Despite this uncertainty, I assign the present material to H. margarica . Genetic studies could further elucidate population structure of this widespread species.

Distribution. This is a new record of the genus Hydranthea from Australia.

Figures

FIGURE 3. Hydranthea margarica. A, hydrotheca with extended hydranth, drawn from live material. B, replicated hydrotheca. C, immature gonophore. D. macrobasic mastigophore in tentacle web, hydranth and hydrorhiza. E, microbasic mastigophore in tentacles. Scale bar: A – C, 0.2 mm, D, E, 20 µm.