Obelia pseudodichotoma ( Vervoort, 1959 ), 2025

Gil, Marta & Ramil, Fran, 2025, Hydroids (Cnidaria, Hydrozoa) from Guinea Bissau, Zootaxa 5577 (1), pp. 1-89 : 36

Obelia pseudodichotoma ( Vervoort, 1959) comb. nov.

( Fig. 6A–C )

Laomedea (Eulaomedea) pseudodichotoma Vervoort, 1959: 316–318 , figs 56, 57. Laomedea pseudodichotoma : Redier, 1971: 505.— Cornelius, 1982: 111–112, fig. 21.— Ramil & Vervoort, 1992a: 240–241, fig.

67E.— Álvarez Claudio, 1993: 376–377, fig. 65.— Medel & Vervoort, 2000: 44–46, figs 10B, 11.— Peña Cantero & García

Carrascosa, 2002: 156, fig. 30A–B. Obelia dichotoma : Ritchie, 1907: 502–503.

Material examined. BISSAU-0810, stn BS181, 10º14'20"– 10º13'43"N, 17º02'14"– 17º01'34"W, 223–224 m, 1-XI-2008: one colony 12 mm high without gonothecae, substrate unknown.

BISSAU-0810, stn BS191, 10º18'25"– 10º19'20"N, 16º08'47"– 16º08'47"W, 24–25 m, 3-XI-2008: nine colonies (one with gonothecae), 13–21 mm high, of which two growing on crustaceans and another one on Idiellana pristis .

Additional material. Mauritania, CCLME 2012-404 , stn SL-13, 16º19’51’’N, 16º36’51’’W, 34 m, 30-V-2012: several colonies 9−35 mm high, some with gonothecae .

CCLME 2012-404 , stn SL-20, 19º18’22’’N, 16º44’50’W, 30 m, 08-VI-2012: three colonies (one with gonothecae), 20−30 mm high, substrate unknown .

Remarks. Vervoort (1959) included this species in the genus Laomedea due to the presence (in the preserved material) of putative sessile heteromedusoid gonophores in the female gonotheca and apparently styloid gonophores in the male. However, we observed fully formed medusae within the gonothecae in our material from station SL-13 ( Fig. 6C ). The development of the gonophores as free medusae is a diagnostic feature of the genus Obelia , but not of Laomedea , in which the gonophores develop as fixed sporosacs ( Bouillon et al. 2006). This finding implies the placement of this species within Obelia , under the binomen Obelia pseudodichotoma ( Vervoort, 1959) comb. nov.

Our finding represents the first record of this species for Guinea-Bissau.

Biology. This species has been found growing on Sertularelloides cylindritheca ( Allman, 1888) and ascidians ( Vervoort 1959; Peña Cantero & García Carrascosa 2002). In the northern hemisphere, fertile material has been collected in January, March−August and in December ( Vervoort 1959; Vervoort 1966; Medel & Vervoort 2000; Peña Cantero & García Carrascosa 2002; Gil & Ramil 2017a).

In our material, some colonies were growing on I. pristis and on crustaceans. Gonothecae were found in November for the first time in this species.

Distribution. Obelia pseudodichotoma comb. nov. is an East-Atlantic species distributed from the Bay of Biscay to Ghana with one record from the West Mediterranean, where it seems restricted to the Alboran Sea (Álvarez-Claudio 1993; Peña Cantero & García Carrascosa 2002). The species is mainly known from the West African coast, where it has been recorded from Mauritania ( Gil & Ramil 2017a), the Cape Verde Islands ( Ritchie 1907), Senegal [ Vervoort 1959, as L. (Eulaomedea) pseudodichotoma ], the Ivory Coast ( Redier 1971) and Ghana ( Vervoort 1959). Its bathymetric distribution ranges from 15 ( Peña Cantero & García Carrascosa 2002) to 230 m ( Gil & Ramil 2017a).

Our material was collected at depths between 24–224 m.

Figures

FIGURE 6. A–C. Obelia pseudodichotoma (Vervoort, 1959) (stn SL-20): portion of colony with hydrotheca and gonotheca (A); (stn BS191), portion of colony with hydrothecae and gonothecae (B); (stn SL-13), gonotheca with medusa bud (C). D–E. Halecium beanii (Johnston, 1838) (stn BS216); portion of colony with female gonotheca (D); male gonotheca (E). Scales: a–e, 0.5 mm.