Eudendriidae L. Agassiz, 1862

Calder, Dale R., 2010, Some anthoathecate hydroids and limnopolyps (Cnidaria, Hydrozoa) from the Hawaiian archipelago 2590, Zootaxa 2590 (1), pp. 1-91 : 37-38

Family Eudendriidae L. Agassiz, 1862

Eudendroidae L. Agassiz, 1862: 342 [emended to Eudendriidae by Hincks (1868)].

Diagnosis. Filiferan hydroids colonial, sometimes stolonal but usually erect and branched; hydrocaulus monosiphonic or polysiphonic, arising from a creeping hydrorhiza; growth monopodial with terminal hydranths. Perisarc usually firm, enveloping hydrocaulus, hydrocladia, pedicels, and hydrorhiza, extending upward to groove at hydranth base. Hydranths urn-shaped, often large; tentacles filiform, usually in one whorl but with two or more very close whorls in some taxa; hypostome large, flexible, knob-shaped to flared.

Gonophores fixed sporosacs, arising from hydranth proximal to tentacles; reproductive hydranths sometimes reduced. Male gonophores with from one to several bulbous chambers in a linear series. Female gonophores, with one exception ( Eudendrium vervoorti Marques & Migotto, 1998 ), having a curved spadix enclosing an egg.

Remarks. The family Eudendriidae L. Agassiz, 1862 presently comprises two genera, the ubiquitous, familiar, and species-rich Eudendrium Ehrenberg, 1834 , and the circumtropical but much less frequently encountered Myrionema Pictet, 1893 , with its four nominal species (now including Perigonimus multicornis Allman, 1876 : see Schuchert 2008b). The number of valid species of eudendriids has been estimated at about 85 ( Daly et al. 2007), all of them having fixed gonophores. The family and its two genera are thought to be monophyletic ( Marques, Mergner et al. 2000). A detailed review of the family, and of species occurring in European waters, has been given recently by Schuchert (2008b).

Eudendriids are easy to recognize by the distinctive morphology of their hydranths and gonophores. Hydranths tend to be large and urn-shaped to barrel-shaped, with a prominent, pedunculated, knobbed to strongly flared hypostome apically and a shallow perisarc groove basally. Gonophores are styloid and arise from the gastric column of normal to reduced hydranths. Those of the male often comprise a linear series of bead-like chambers, while those of the female consist initially of a spadix enveloping a single egg ( Eudendrium vervoorti Marques & Migotto, 1998 is an exception, reportedly having gonophores that lack a spadix).

Hydroids referable to Myrionema differ from those of the better-known Eudendrium in having more elongated hydranths with a greater number of tentacles, often 40 or more in several close whorls. Zooxanthellae are present in the tissues ( Calder 1988) of Myrionema , but such symbionts are also known to occur in a species of Eudendrium ( E. moulouyensis Marques, Peña Cantero, & Vervoort, 2000 from the Mediterranean Sea). Of the two genera, only Eudendrium is currently known from Hawaii, although colonies of Myrionema might eventually be discovered there in shallow, sheltered environments.