Thecocodium quadratum ( Werner, 1965 )

Schuchert, Peter & Collins, Richard, 2021, Hydromedusae observed during night dives in the Gulf Stream, Revue suisse de Zoologie 128 (2), pp. 237-356 : 259-260

Thecocodium quadratum ( Werner, 1965)

Fig. 13 A-B

Ptilocodium quadratum Werner, 1965: 11 , figs 4-5. – Werner, 1984: 139, fig. 85.

Thecocodium quadratum . – Jarms, 1987: 59, fig. 8.1-8.4. – Kubota, 1993: 89, fig. 1. – Akiyama et al., 2013: 113, figs 1-2.

Thecocodium aff. quadratum . – Kubota et al., 2018: 7, fig. 2A- B.

Thecocodium spec. – Kubota & Meldonian, 2016: 77, fig. 1.

Examined material: 21-JUL-2018, 1 specimen photographed; not collected. – BFLA4461 ; 1 specimen; 13 -JUN-2020; size 5 mm; preserved in alcohol for DNA extraction; 16S sequence MW528730 . – BFLA4466 ; 1 specimen; 13 -JUN-2020; size 4 mm; preserved in alcohol for DNA extraction; 16S sequence MW528731 . MHNG-INVE-0039477; schizoholotype, polyps obtained from original culture of Werner (courtesy Dr G. Jarms), origin of material Kenya; cultivated and reared medusae, preserved in Feb- 2006; 16 sequence FN422379 .

Observations: Medusa with bell-shaped umbrella, up to 5 mm, mesoglea thick, including lateral walls, height of apical jelly at least 1/3 of total height, not delimited as apical process. Bell margin with deep perradial clefts continued as canal-like furrows to midheight of bell and housing tentacle. Bell margin appears lobed through the clefts, between the furrows on each lobe 5-7 meridional nematocyst tracks originating from near circular canal and curving around bell margin to exumbrella and then dissolving into arrays a few isolated nematocysts clusters,>100 additional nematocyst buttons scattered on entire exumbrella. Four smooth radial canals widened to funnels at the junction to the manubrium. Four tentacles, directed upwards, lying in the canal-like exumbrellar furrows, usually contracted to length shorter than bell height, but able to extend to length at least>3 times the bell height. Tentacles at origin with a small bulb with a pink to red colour, bulb adnate to exumbrella; main trunk of tentacles appears chordoid and is transparent, tapering to tip which is whitish-opaque and sometimes slightly swollen. Manubrium large, with a spherical stomach and a small neck-like oral region, small cruciform mouth; gonads much developed surrounding the manubrium entirely, with a brilliant, intense yellow-orange colour, subdivided in 8 adradial, vertical bulges ( Fig. 13B ), the whole appearing like a peeled orange composed of 8 wedges, perradial and interradial clefts deep. Females with> 200 eggs.

Distribution: Coast of Kenya ( Jarms, 1987); Japan ( Kubota, 1993); Taiwan ( Kubota et al., 2018); Florida ( Kubota & Meldonian, 2016; this study). Type locality: Indian Ocean, NE of Mombasa (hydroid, substrate unknown).

16S Data: The two obtained 16S haplotypes differed in 0.5% of their base pairs, the divergences to the type material were 4.3 to 4.5% ( Table 1 ).

Remarks: The descriptions of this species ( Werner, 1965; Jarms, 1987) were based on a cultivated hydroid colony and its released medusae reared to subadult stage. It was therefore with some hesitations that subsequent findings of the medusa in the plankton where attributed to this species or they were even only identified to genus level (see synonymy above). The observed specimen from Florida differed from the type material in having a slightly higher umbrella and many more exumbrellar nematocysts clusters. Moreover, the gonads are much more developed. The species has been recorded from Florida waters before ( Kubota & Meldonian, 2016). Like Kubota & Meldonian (2016) we are also aware that the identification of the Florida specimens as Thecocodium quadratum is to some degree questionable for biogeographic reasons. However, comparing our photos with a medusa from Taiwan published by Kubota et al. (2018) it is evident that there are no taxonomically significant differences and this morphotype has likely a very widespread distribution. The 16S sequences from the Florida specimens differed about in 4.5% of the base pairs compared to the type specimen ( Table 1 ). In comparison with other medusae this appears to us as intermediate between intraspecific or interspecific variation, but these few samples and just one marker alone cannot provide conclusive information. Because the morphology of Pacific and Atlantic medusae match, we think it should be attributed to T. quadratum until more detailed genetic data prove the contrary.

Figures

Fig. 13. Thecocodium quadratum, females. (A) Specimen photographed 21-JUL-2018. Lateral view of whole animal. (B) BFLA4461, an apparently fully mature female.