Ectopleura cf. viridis ( Pictet, 1893 )

Calder, Dale R., 2010, Some anthoathecate hydroids and limnopolyps (Cnidaria, Hydrozoa) from the Hawaiian archipelago 2590, Zootaxa 2590 (1), pp. 1-91 : 48-49

Ectopleura cf. viridis ( Pictet, 1893)

Figs. 32 , 33

Tubularia viridis Pictet, 1893: 17 , pl. 1, figs. 10, 11.

Type locality. Indonesia: “ Port d’Amboine …” ( Pictet 1893) .

Material examined. Oahu: Kaneohe Bay, anchor cable, 3 m, 4.i.1978, one large clump, 15 cm in diameter, with medusa buds, coll. W.J. Cooke, BPBM (without collection number).–Oahu: Kaneohe Bay, anchor cable, 3 m, 4.i.1978, one small fragment of sample above, with medusa buds, coll. W.J. Cooke, ROMIZ B3827.

Description. Hydroids colonial, forming a dense aggregation of hydrocauli with numerous hydranths, arising from a hydrorhizal mat. Hydrorhizae creeping, wrinkled to smooth. Hydrocauli smooth, unbranched, up to 3.5 cm high, 0.6 mm wide, tangled together basally, free elsewhere, nearly straight to variously contorted, each terminating distally with a bulbous neck region supporting a hydranth. Perisarc of hydrorhiza thick; that on hydrocauli fairly thick basally, becoming thinner distally, filmy over neck region, terminating at base of hydranth; light straw-coloured, essentially clear in thin areas. Hydranths 3 mm high from basal constriction to mouth, 2.5 mm wide, vase-shaped, with proximal half bulbous, distal half tapering, becoming slender orally; bearing one aboral and one oral whorl of tentacles. Aboral tentacles of mature hydranths gradually tapering from base to tip, to 6 mm long, about 25–30 in number, in a single whorl; oral tentacles filiform, digitate, up to 0.9 mm long, about 25 in number, in a single whorl, bases adnate to hypostome, forming longitudinal ridges on it.

Gonophores free medusae. Medusa buds developing in clusters on short, slender blastostyles arising on hydranth immediately distal to aboral tentacles. Well-developed medusa buds thimble-shaped, 0.3 mm high, 0.25 mm wide, with an apical stalk attached to blastostyle; mesoglea thin; exumbrella with eight meridional tracks of nematocysts; manubium simple, large, tubular, stubby, reaching about ¾ distance to velar opening; radial canals four; tentacle bulbs four, with an opposite pair having well-developed marginal tentacles, each with a terminal knob and a single abaxial nematocyst cluster.

Remarks. Identification of hydroids of Ectopleura L. Agassiz, 1862 having medusa buds with two opposite tentacles is virtually impossible based on current limited knowledge of the group. Although assigned provisionally to Ectopleura viridis ( Pictet, 1893) , the identity of the hydroid studied here is uncertain in the absence of information on its medusa stage. Several species of Ectopleura besides E. viridis have medusa buds or medusae with two opposite tentacles ( Petersen 1990; Xu et al. 2007), but life cycles are unknown or inadequately known for all of them. Medusa buds and trophosomes in specimens examined here generally correspond with those ascribed to E. minerva Mayer, 1900b by Hirohito (1988). However, that species was originally described from the Atlantic Ocean (Florida) and records of it from the Pacific Ocean are considered doubtful.

Ectopleura viridis , apparently endemic to the Indo-west Pacific region (see Reported Distribution below), has been reported infrequently. Schuchert (2003, 2009) has been followed in regarding Ectopleura pacifica Thornely, 1900 as a synonym of it. A record of E. pacifica from India by Mammen (1963) is erroneous because medusa buds were described as having four tentacles rather than two. It was considered a new species, E. indica , by Petersen (1990).

The colony examined here, a clump reaching almost 15 cm in diameter, is much larger than specimens of E. viridis described previously by Pictet (1893), Thornely (1900, as E. pacifica ), Borradaile (1905, as E. pacifica ), Billard (1905), and Schuchert (2003), as well as those ascribed to E. minerva by Hirohito (1988). Individual hydrocauli were up to 3.5 cm in length.

Hirohito (1988) and Calder (1988) considered E. pacifica and E. minerva to be conspecific, but Xu et al. (2007) recognized both as valid based on differences in the medusa stage.

Reported distribution. Hawaii. New record.

Worldwide. Indonesia ( Pictet 1893; Schuchert 2003), Papua New Guinea ( Thornely 1900, as Ectopleura pacifica ), Mangareva, French Polynesia ( Billard 1905), Suvadiva Atoll, Maldives ( Borradaile 1905, as Tubularia pacifica ); 1–68 m.

Figures

FIGURE 32. Ectopleura cf. viridis: hydranth with medusa buds, BPBM (without collection number). Scale equals 2 mm.