Clytia obliqua ( Clarke, 1907 )

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 : 583-586

Clytia obliqua ( Clarke, 1907)

( Figure 5g –j )

Campanularia (?) obliqua Clarke, 1907: 9 , pl. 5, figs 1–4.

Type locality

Panama: Perico Island, on the hydroid Disertasia crisioides ( Lamouroux, 1824) ( Clarke 1907) .

Material examined

Chatham Bay , 5.55208, −87.0431, several colonies, to 4 mm high, with gonothecae, coll . I . Keith , #253541 . – Chatham Bay , 5.55208, −87.04308, several colony fragments, to 6 mm high, with a gonotheca, coll . I . Keith , #253540 . – Chatham Bay , 5.55208, −87.04308, several colony fragments, without gonothecae, coll . I . Keith , #253539 . – Wafer Bay , 5.5456, −87.06235, 1 colony, on a barnacle, 3 mm high, without gonothecae, coll . G . Ashton , #240584 . – Wafer Bay , 5.5456, −87.06235, 4 colonies on 4 barnacles, to 2 mm high, with gonothecae, coll . G . Ashton , #240585 . – Wafer Bay , 5.54535, −87.06185, 1 colony, on a barnacle, 4 mm high, with a gonotheca, coll . G . Ashton , #240629 . – Wafer Bay , 5.54535, −87.06185, 1 colony fragment, 2 mm high, without gonothecae, coll . G . Ashton , #240630 . – Wafer Bay , 5.5456, −87.06235, 1 colony, on a barnacle, 3 mm high, with gonothecae, coll . G . Ashton , #240587 . – Wafer Bay , 5.54618, −87.06318, 2 colony fragments, 2 mm high, without gonothecae, coll . I . Keith , #307706 . – Chatham Bay , 5.55208, −87.04308, 2 colony fragments, to 2 mm high, without gonothecae, coll . I . Keith , #307715 . – Chatham Bay , dock 004, no coordinates, 1 colony, on Macrorhynchia philippina , 2 mm high, without gonothecae, coll . G . Ashton , #266335 .

Remarks

Clarke (1907) applied the binomen Campanularia (?) obliqua to a hydroid collected at Perico Island off the Pacific coast of Panama. Its prime distinguishing characters included (1) a small, creeping colony form, with pedicels 1.0– 1.5 mm high and with annulations at proximal and distal ends and sometimes in between; (2) hydrothecae having nearly cylindrical walls above the base; and (3) marginal cusps that are prominent and pointed at an oblique angle. Gonothecae were lacking in Clarke’s specimens, and the species was assigned by him, with uncertainty, to Campanularia Lamarck, 1816 .

Specimens listed above from Cocos Island, indistinguishable from Clarke’s (1907) brief description and illustrations of C. (?) obliqua , have been assigned to that species here. This hydroid was re-assigned from Campanularia to Clytia Lamouroux, 1812 by Fraser (1936), who found gonothecae in colonies from Japan that he identified as belonging to the species. Gonothecae were also observed in material from Japan by Hirohito (1969, 1995), although some uncertainty was expressed by him about their identification. Fertile specimens from Cocos Island ( Figure 5i–j ), with gonothecae arising from the hydrorhiza, confirm inclusion of the species in Clytia rather than Campanularia .

The validity of C. obliqua has often been questioned. On examining presumed type material (syntype, USNM 29616) of the species, Cornelius (1982) concluded that it differed only in the slope of the hydrothecal cusps from C. gravieri Billard, 1904 , now considered a synonym of C. linearis ( Thornely, 1904) . He therefore considered the two to be conspecific, a proposed synonymy that has been widely followed (e.g. Gibbons and Ryland 1989; Calder 1991; Watson 2000; Zhenzu et al. 2014; Wedler 2017; Choong et al. 2018). However, C. linearis clearly differs from the account of C. obliqua by Clarke (1907) in having colonies that are usually erect and sympodially branched, hydrothecae that are large and deep, and marginal cusps with distinctive inward-folding pleats that extend onto the distal wall of the hydrotheca ( Lindner and Migotto 2002; Cunha et al. 2020). By contrast, illustrations of C. obliqua by Clarke depict hydroids with unbranched pedicels, hydrothecae that were not particularly tall, and hydrothecal cusps that had no keel-like infolded pleats.

Gibbons and Ryland (1989, p. 400), in remarks on a hydroid identified as ‘ C. (?) gracilis (M. Sars) ’, also reported examining syntype material of C. obliqua . The types were described, in contradistinction to Clarke’s (1907) account of C. obliqua , as branched and with tall hydrothecae. Although no infolding pleats were observed on the hydrothecal cusps, Gibbons and Ryland concluded that C. obliqua was conspecific with C. linearis . Based on the account of Clarke (1907), however, characters of C. obliqua appear to have more in common with those of C. hemisphaerica ( Linnaeus, 1767) , C. gracilis and especially C. elsaeoswaldae Stechow, 1914 ( Lindner et al. 2011) than with C. linearis . Thus, while C. obliqua is a poorly known species, it is considered a valid one here. Moreover, if it should prove to be conspecific with C. elsaeoswaldae , a putative species having many of the same characters, the name C. obliqua has priority.

Clytia obliqua has been mentioned infrequently in studies on hydroids. Surprisingly, it was never included in accounts by Fraser (1938a, 1938b, 1938c) of species from the Tropical Eastern Pacific region. Meanwhile, a record by Fraser (1948) from southern California seems suspect on zoogeographic grounds. As noted above, reports of the species from Japan ( Fraser 1936; Hirohito 1969, 1995) are open to question and this material should be re-examined. A record of it from the Mediterranean coast of France ( Picard 1950) appears to have been based on another species and has been discounted ( Picard 1958; Bouillon et al. 2000). Finally, C. obliqua was included in a paper by Calder et al. (2019) on hydroids from the Galápagos Islands. It was one of the most common species in the current collection from Cocos Island.

Reported distribution

Cocos Island: first record.

Elsewhere: questionably from Point Fermin, California ( Fraser 1948) to the Galápagos Islands ( Calder et al. 2019), including the type locality of Perico Island, Panama ( Clarke 1907); other questionable reports include those of Fraser (1936) and Hirohito (1969, 1995) from Sagami Bay, Japan.

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.