Clytia brevithecata ( Thornely, 1904 )

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 : 581-582

Clytia brevithecata ( Thornely, 1904)

( Figure 5c, d )

Campanularia brevithecata Thornely, 1900: 454 , pl. 44, figs 8a, b.

Type locality

Papua New Guinea: New Britain, Blanche Bay ( Thornely 1904, as Campanularia brevithecata ) .

Material examined

Wafer Bay , 5.54618, −87.06318, 2 colonies, on two barnacles, to 3 mm high, without gonothecae, coll . I . Keith, #240600.

Remarks

Hydroids of Clytia brevithecata ( Thornely, 1904) have unusually shallow, cup-shaped hydrothecae with an entire hydrothecal rim and a subhydrothecal spherule. A whorl of about 20 filiform tentacles is borne on the hydranths. Pedicels are long and unbranched, with annulations at the base and occasionally elsewhere. Gonothecae, clavate with smooth walls and a truncated distal end, arise on short pedicels from the hydrorhiza ( Thornely 1904). In describing the species, Thornely commented on the remarkably large, trumpet-shaped hypostomes of its hydranths, reminiscent of those in species of Eudendrium Ehrenberg, 1834 . The species was originally described from Papua New Guinea, based on specimens overgrowing the barnacle Lepas , ropes and fish baskets. Other than this record from Cocos Island, hydroids assigned to C. brevithecata have been reported only once since the original description, from the Northwestern Hawaiian Islands ( Calder and Faucci 2021).

Clytia hummelincki ( Leloup, 1935) , originally described from the Caribbean Sea (type locality: Bonaire, the Netherlands), is essentially identical in morphology to C. brevithecata . The two have recently been taken to be conspecific, with the senior name C. brevithecata having priority ( Calder and Faucci 2021). Galea and Ferry (2015, p. 241) had noted earlier that they might be identical. Although a connection appears to exist between Indo-Pacific and Atlantic populations given the record of C. hummelincki from a buoy on Agulhas Bank at the southern tip of Africa ( Millard 1966, 1975), molecular comparisons are needed to confirm synonymy of the two names. Of its two synonyms, the species is much more widely recorded and better known under the name C. hummelincki . As such, it has been reported more than a dozen times across the Atlantic region and at least four times in the Indo-Pacific ( Calder and Faucci 2021). In the Tropical Eastern Pacific, it has been reported from Isla San Cristóbal and Isla Wolf in the Galápagos Islands ( Calder et al. 2003).

The generic affinities of C. hummelincki (= C. brevithecata ) appear unsettled on the basis of recent molecular studies. The species has been shown to be genetically distant from other included species of Clytia ( Govindarajan et al. 2006; Leclère et al. 2009; Maronna et al. 2016), and its assignment to Clytia and the family Clytiidae has been debated ( Cunha et al. 2017). However, in having a medusa stage that conforms with that of the genus ( Gravili et al. 2008, as C. hummelincki ; Gravili et al. 2015, as C. hummelincki ), the species is maintained here in both the family Clytiidae and the genus Clytia .

A recent overview of C. brevithecata has been given by Calder and Faucci (2021).

In concert with its status in the Galapagos Islands ( Carlton et al. 2019), we treat C. brevithecata as introduced on Cocos Island, and native to either the Western Atlantic Ocean or the Indo-West Pacific.

Reported distribution

Cocos Island: first record.

Elsewhere: currently taken to be circumglobal in tropical and warm-temperate waters ( 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.