Balellidae Stechow, 1922

Calder, Dale R., 2010, Some anthoathecate hydroids and limnopolyps (Cnidaria, Hydrozoa) from the Hawaiian archipelago 2590, Zootaxa 2590 (1), pp. 1-91 : 28

Family Balellidae Stechow, 1922

Tubidendridae Nutting, 1905: 940 .

Balellidae Stechow, 1922: 142 .

Diagnosis. Filiferan hydroids with erect, irregularly branched, polymorphic colonies. Hydrocaulus polysiphonic. Hydrorhiza, hydrocaulus, and hydrocladia covered with perisarc, although naked coenosarc may also be present. Gastrozooids club-shaped to pyriform; tentacles filiform, in two widely separated whorls, one proximally and another mid-distally on hydranth; hypostome elongate. Gonozooids small, slender, with one or no tentacles; bearing medusa buds. Dactylozooids present on hydrocaulus and hydrocladia, digitate, solid, lacking perisarc over most or all of length.

Gonophores free medusae, borne on gonozooids; radial canals four; marginal tentacles four, solitary, short.

Remarks. The name Tubidendridae , first applied to this family by Nutting (1905), is not available [ICZN Art. 11.7.1.1] because it was not formed from the stem of an available generic name included in the taxon when it was established ( Calder 1988). It was replaced by the name Balellidae by Stechow (1922).

Affinities and classification of Balellidae have been difficult to resolve because little is known about the life cycle in species of the group. Jäderholm (1919) and Schuchert (2003) established the presence of medusa buds arising from gonozooids in Balella mirabilis ( Nutting, 1905) , but the adult medusa has yet to be described. Gonophores have not been observed in the only other putative species in the family, B. irregularis ( Fraser, 1938a) . Stechow (1923b) included the taxon as a subfamily of Clavidae McCrady, 1859 , while authors including Millard (1975), Hirohito (1988), and Bouillon (1995) included it in Bougainvilliidae Lütken, 1850 . Calder (1988) regarded it as a distinct family, closer to Clavidae [now Oceaniidae Eschscholtz, 1829 ] than to Bougainvilliidae . Recent authors have also recognized it as a distinct family ( Calder et al. 2003; Schuchert 2003; Bouillon et al. 2006). Schuchert (2003), and Nutting (1905) earlier, suggested that affinities of the family were with Hydractiniidae L. Agassiz, 1862 , given the polymorphic character of zooids and the occurrence of naked coenosarc on stems of both B. mirabilis and B. irregularis .

Balellidae includes the single genus Balella Stechow, 1919 , and two species.