Cytaeis tetrastyla Eschscholtz, 1829

Schuchert, Peter & Collins, Richard, 2021, Hydromedusae observed during night dives in the Gulf Stream, Revue suisse de Zoologie 128 (2), pp. 237-356 : 242-243

Cytaeis tetrastyla Eschscholtz, 1829

Fig. 2 A-C

Cytaeis tetrastyla Eschscholtz, 1829: 104 , pl. 8 fig. 2. – Schuchert, 2007: 275, fig. 32, synonymy, references, taxonomic details.

Examined material: BFLA4066 ; 1 specimen; 10 -APR- 2019; size 2 mm; preserved in ethanol for DNA extraction; 16S sequence MW528664 . – BFLA4069 ; 1 specimen; 11 -APR-2019; size 1.5 mm; photographed and preserved in formalin and deposited as UF-013780. – BFLA4073 ; 1 specimen; 11 -APR-2019; 2 mm; preserved in ethanol for DNA extraction; 16S sequence MW528667 . – BFLA4418 ; 1 specimen; 28 -MAY-2020; size 4 mm; preserved in ethanol for DNA extraction; 16S sequence MW528725 . – 16-NOV-2017; 1 specimen photographed, not collected.

Observations: Cytaeis medusa with bell height 1.5- 2 mm, apical jelly not much thickened and without apical process, but often with apical funnellike depression; subumbrella with shallow gastric peduncle. Manubrium spindle-shaped, reaching to velum level, with more than 10 capitate tentacles originating distinctly above mouth margin; in upper third of manubrium several medusa buds, in lower two thirds apparently with developing gonad. Four perradial tentacles, fully contracted about as long as bell height, solid, bases widened to ovoid bulbs which adhere just above bell margin, giving the impression of the tentacles being connected by a flared end ( Fig. 2B ); the tentacle arises at an acute angle to the bulb and curve towards aboral.

Distribution: Circumglobally in tropical to subtropical seas, partly oceanic ( Schuchert, 2007). Type locality: Atlantic Ocean, south of Equator.

16S Data: The three obtained 16S haplotypes have a maximal divergence of 2.2% and are thought to represent intraspecific variation ( Table 1 ). Blastn searches in GenBank did not yield matches at specieslevel identities. The closest matches were with several samples of Cytaeis uchidae Rees, 1962 from Japan (about 95% identity), followed by other Cytaeis species , though with lower identity values.

Remarks: The taxonomic situation and identification of Cytaeis medusae is currently not resolved (see discussion in Schuchert, 2007). The opinion of Bouillon et al. (2004) that the “ Cytaeis tetrastyla -like”medusae should not be given a specific name until the taxonomy has been sorted out properly is still valid, in particular if they do not come from the tropical Atlantic Ocean. However, the current material does come from the same tropical waters of the Atlantic Ocean as the type material and no named or distinct Cytaeis polyps are known from this region. We can thus be reasonably sure that Cytaeis tetrastyla is most likely the correct name. The taxonomic ambiguity relating to C. tetrastyla needs to be resolved using DNA sequence data of several populations and the present samples will hopefully contribute to this end.

Many cytaeidid medusae have a quite characteristic connection of the tentacles to the bell margin. The proximal ends of the tentacles are widened to an ovoid bulb which adheres along its long axis to the exumbrella just above bell margin, giving the impression of the tentacle being connected to the exumbrella by a flattened end ( Fig. 2B ).

The hydroid stage of this species is not known.A potential candidate is the Cytaeis hydroid from Bermuda Island described by Calder (1988).

Figures

Fig. 2. Cytaeis tetrastyla, bell height 2 mm. (A) Lateral view, note medusa buds on upper part of manubrium, BFLA4066. (B) Lateral view with focus on the frontal exumbrella showing the typical flared tentacle bases of Cytaeis medusae, BFLA4073. (C) BFLA4069, note green tentacle tips, a colour likely due to interference effects and not pigments.