Amphinema sp.

Calder, Dale R., 2010, Some anthoathecate hydroids and limnopolyps (Cnidaria, Hydrozoa) from the Hawaiian archipelago 2590, Zootaxa 2590 (1), pp. 1-91 : 24

Amphinema sp.

Fig. 12

Material examined. 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, to 2.5 mm high, without gonophores, coll. D.R. Calder, ROMIZ B3824 .

Description. Hydroid colonies stolonal, small, up to about 2.5 mm high, arising from a creeping hydrorhiza. Hydrocaulus simple, of varied length, exceedingly slender basally, gradually increasing in diameter towards terminal hydranth. Perisarc investing hydrorhiza and hydrocaulus thin, clear to straw-coloured, smooth except for a few wrinkles or annulations at base of hydrocaulus, ending perceptibly or almost imperceptibly below hydranth base; hydranths club-shaped, reaching about 1 mm long, widest at tentacular whorl, narrowest at base; tentacles filiform, amphicoronate, in two close whorls around distal end of hydranth, about 12–14 in number; hypostome dome-shaped to elongate. Endoderm of hydranths a conspicuous orange-red colour in life. When disturbed, hydranths bend over sharply, as noted in other described species of the genus.

Medusa buds not seen.

Remarks. Hydroids are known for only three of about 12 currently recognized species of the genus Amphinema Haeckel, 1879 . The specimens from Hawaii Kai cannot reliably be identified to species, especially in the absence of gonophores and information on their life cycle. Trophosomes are essentially identical with those of A. dinema ( Péron & Lesueur, 1810) and A. rugosum ( Mayer, 1900a) , two species that are morphologically indistinguishable in the absence of medusa buds ( Russell 1953; Schuchert 2007). Also similar is the hydroid of Amphinema sp. from Bodega Bay, California, described by J.T. Rees (2000). Unlike A. rollinsi Widmer, 2007 from deep waters of the Monterey Bay Submarine Canyon, California, colonies are strictly stolonal and perisarc investing the hydrocaulus is smooth and more slender. Hydroids referable to the genus Amphinema have not been reported before from Hawaii.

Reported distribution. Hawaii. New record.