Phialellidae, Russell, 1953

Calder, Dale R., Carlton, James T., Keith, Inti, Ashton, Gail V., Larson, Kristen, Ruiz, Gregory M., Herrera, Esteban & Golfin, Geiner, 2022, Biofouling hydroids (Cnidaria: Hydrozoa) from a Tropical Eastern Pacific island, with remarks on their biogeography, Journal of Natural History 56 (9 - 12), pp. 565-606 : 578-579

Phialellidae (undetermined)

( Figure 5a )

Material examined

Wafer Bay , 5.54618, −87.06318, 2 colonies, on two barnacles, to 0.4 mm high, without gonothecae, coll . I . Keith , #240600 . – Chatham Bay , 5.55271, −87.03826, numerous hydrothecae, to 2 mm high, without gonothecae, coll . I . Keith , #240565 .

Remarks

Nothing morphologically similar to these hydroids has been reported before from the Tropical Eastern Pacific region. The closest to them is a specimen identified by Calder et al. (2021) as Opercularella sp. from La Libertad, Ecuador, but it differs in lacking a hydrothecal diaphragm and in having tapered rather than nearly cylindrical hydrothecae. Instead, they more closely resemble specimens identified as? Phialella quadrata ( Forbes, 1848) from the Seychelles by Millard and Bouillon (1973), and especially ‘ Phialellidae undetermined’ from Gardner Pinnacles in the Northwestern Hawaiian Islands by Calder and Faucci (2021). While likely referable to either Opercularella Hincks, 1869 or Phialella Browne, 1902 , in the family Phialellidae , the generic identity of our Cocos material could not be reliably determined in the absence of gonophores. These genera are distinguished largely on characters of the gonosome, with species of Opercularella said to have fixed sporosacs and Phialella a medusa stage ( Bouillon et al. 2006). As with the hydroid from Hawaii, specimens examined here have been identified simply as Phialellidae (undetermined).

Reported distribution

Cocos Island: first record.

Elsewhere: possibly from Gardner Pinnacles in the Northwestern Hawaiian Islands ( Calder and Faucci 2021) .

Figures

Figure 5. Leptothecata: Phialellidae, Cirrholovenia, Clytiidae. (a) Phialellidae (undetermined): three hydrothecae and pedicels, #240565. (b) Cirrholovenia tetranema: two hydrothecae and stolons, and a nematotheca, #240629. (c) Clytia brevithecata: hydrotheca and distal end of pedicel, #240600. (d) Clytia brevithecata: proximal end of pedicel and stolon, #240600. (e) Clytia linearis: hydrotheca and distal end of pedicel, #307693. (f) Clytia linearis: gonotheca, #307693. (g) Clytia obliqua: hydrotheca and distal end of pedicel, #240629.(h) Clytia obliqua: hydrotheca and distal end of pedicel,#253541. (i) Clytia obliqua: gonotheca, #253541. (j) Clytia obliqua: gonotheca, #240629. Scale bars: a, c–j = 0.1 mm; b = 0.05 mm.