Turritopsis McCrady, 1857

Calder, Dale R., 2010, Some anthoathecate hydroids and limnopolyps (Cnidaria, Hydrozoa) from the Hawaiian archipelago 2590, Zootaxa 2590 (1), pp. 1-91 : 14

Genus Turritopsis McCrady, 1857

Turritopsis McCrady, 1857: 58 .

Type species. Turritopsis nutricula McCrady, 1857 , by monotypy.

Diagnosis. Oceaniid hydroids sometimes stolonal but usually with erect and irregularly branched colonies. Hydrocaulus polysiphonic or less frequently monosiphonic, branched or less often simple; hydrocladia, if present, adnate to hydrocaulus or to other hydrocladia over part of their length basally. Perisarc with firm outer primary and more filmy inner secondary layers, covering hydrocauli and hydrocladia, terminating near hydranth bases. Hydranths club-shaped, lacking perisarc; tentacles filiform, scattered over most of hydranth.

Gonophores, where known, free medusae, borne on pedicels or branches. Medusa thimble-shaped; radial canals surrounded by mass of vacuolated cells at apex of manubrium; marginal tentacles solitary, simple, eight or more; ocelli present.

Remarks. With the publication date of McCrady’s account of Turritopsis established as 1857 instead of 1859 ( Calder et al. 1992), earlier concerns ( Calder 1988) that this familiar generic name was threatened by the nearly forgotten Clavula Wright, 1859a are removed.

Transformation of medusae into polyps has been described in species of this genus ( Bavastrello et al. 1992; Piraino et al. 1996). Although reported relatively infrequently, this peculiar phenomenon has been known for more than a century. Hincks (1865) reported it in a hydractiniid, and other early accounts of such “retrograde metamorphosis” were reviewed by Hincks (1868: xxviii–xxix).