Hydrichthys Fewkes, 1887

Calder, Dale R., 2010, Some anthoathecate hydroids and limnopolyps (Cnidaria, Hydrozoa) from the Hawaiian archipelago 2590, Zootaxa 2590 (1), pp. 1-91 : 24-26

Genus Hydrichthys Fewkes, 1887

Hydrichthys Fewkes, 1887: 604 .

Type species. Hydrichthys mirus Fewkes, 1887 , by monotypy.

Diagnosis. Pandeid hydroids with colonies ectoparasitic on fishes and on ichthyoparasitic copepods. Zooids monomorphic or dimorphic, atentaculate, clavate to tubular, arising from a basal encrusting plate or reticular hydrorhiza; perisarc absent.

FIGURE 12. Amphinema sp. : hydrocaulus and hydranth, ROMIZ B3824. Scale equals 0.5 mm.

FIGURE 13. Hydrichthys pietschi : part of colony on skin of host fish, Ceratias holboelli (after Martin 1975). Scale equals 60 µm.

FIGURE 14. (?) Merga sp. : hydrocaulus with hydranths and a medusa bud, USNM (without collection number). Scale equals 1.0 mm.

FIGURE 15. (?) Merga sp. : hydranth, USNM (without collection number). Scale equals 0.25 mm.

FIGURE 16. (?) Merga sp. : nematocysts, USNM (without collection number). a, desmoneme. b, heterotrichous microbasic eurytele. c, foreign nematocyst on colony.

Gonophores fixed sporosacs or free medusae, arising from hydranths or from gonostyles. Medusae, when present, with bell-shaped umbrella having an apical projection. Manubrium cruciform in cross-section; mouth with four prominent lips; radial canals jagged, four or more; mesenteries present. Newly liberated medusae with two opposite marginal tentacles; older medusae with up to six; tentacle bulbs conical. Gonads on interradii of manubrium, forming eight adradial masses. Ocelli absent.

Remarks. Diagnosis of the polyphyletic genus Hydrichthys Fewkes, 1887 as given here follows that in Bouillon et al. (2006) and Schuchert (2007). Bouillon et al. recognized seven species in this genus of parasitic hydroids, including Hydrichthys pietschi Martin, 1975 from Hawaii.

Hydroid species currently assigned to Hydrichthys are known to liberate medusae referable to several genera ( Schuchert 2007), and the genus is in need of revision.