Eudendrium capillare Alder, 1856

Calder, Dale R., 2010, Some anthoathecate hydroids and limnopolyps (Cnidaria, Hydrozoa) from the Hawaiian archipelago 2590, Zootaxa 2590 (1), pp. 1-91 : 39-40

Eudendrium capillare Alder, 1856

Figs. 24 , 25

Eudendrium capillare Alder, 1856: 355 , pl. 12, figs. 9–12.– Nutting, 1905: 939.

Eudendrium sp. — Cooke, 1977: 87.

Type locality. UK: Northumberland, Embleton Bay ( Alder 1856) .

Material examined. Oahu: Kaneohe Bay, pier at Hawaii Institute of Marine Biology , 2 m, on wood pilings, no date, two colony fragments, to 0.6 cm high, with male gonophores, BPBM (without collection number) .— Oahu: Kaneohe Bay, pier at Hawaii Institute of Marine Biology , 2 m, on wood pilings, no date, fragment of colony above, with male gonophores, ROMIZ B3834 .– Oahu: Hawaii Kai, on pilings of bridge over Highway 72, 21º17’06.60”N, 157º43’07.21”W, 0.1 m, 27.vii.2009, on small oyster shell, one colony, with cormoids up to 0.5 cm high, without gonophores, coll. D. R. Calder, ROMIZ B3826 .

Description. Colonies small, with both stolonal and erect forms, up to 0.6 cm high, arising from a creeping hydrorhiza; colonies with erect hydrocaulus sparsely and irregularly to more or less alternately branched. Hydrocaulus monosiphonic, branched or simple, when branched with branches and ultimate branchlets relatively long, straight to sometimes contorted, resembling hydrocaulus. Perisarc relatively firm, becoming thinner in younger parts, terminating at perisarc groove on base of hydranths, annulated at bases of hydrocaulus, branches and ultimate branchlets, a few annulations and wrinkles elsewhere but mostly smooth. Hydranths urn-shaped, up to 0.35 mm long from base to hypostome, 0.30 mm wide; base with perisarc groove; gastroderm with numerous black pigment spots; ring of nematocysts above perisarc groove lacking; hypostome large, knob-shaped to flared. Tentacles solid, filiform, in one whorl, about 18–22 in number.

Gonophores fixed sporosacs, borne on atrophied blastostyles. Male gonophores with one chamber or a linear pair of two chambers; terminal chamber with an apical tubercle; blastostyles with a tuft of as many as 20 strings of gonophores. Female gonophores not seen.

Nematocysts. Heterotrichous microbasic euryteles (7.0–7.7 µm long × 2.8–3.3 µm wide).

Remarks. Material with male gonophores, corresponding with the characters of Eudendrium capillare Alder, 1856 , were present in collections at the Bishop Museum (BPBM, without collection number) from shallow waters in Kaneohe Bay. Cooke (1977) also found minute specimens in shallow waters that resembled E. capillare , but he concluded that species identification was impossible in the absence of gonophores. From his description, these hydroids are thought to be the same species as specimens examined here. The Hawaiian population and should be studied further, however, because a preponderance of colonies from the region were stolonal rather than erect as usual in the species.

Nutting’s (1905) hydroids from Albatross Stn. 3854 were infertile, and he assigned them to Eudendrium capillare with considerable reservation. They are regarded as a different species herein, identified as Eudendrium sp. 2 .

The cnidome of Eudendrium capillare is usually thought to comprise only heterotrichous microbasic euryteles. Schuchert (2008b) also discovered small isorhizas in material from Europe, although numbers varied and they were sometimes absent. I was unable to confirm the presence of isorhizas in material from Hawaii.

Reported distribution. Hawaii. Oahu: Kaneohe Bay and Honolulu Harbor ( Cooke 1977).

Worldwide. Virtually cosmopolitan in warm and temperate waters; 0–82 m ( Fraser 1946; Calder 1988; Schuchert 2008b).

Figures

FIGURE 24. Eudendrium capillare: part of colony with hydranth and male gonophore, ROMIZ B3834. Scale equals 0.5 mm.