Staurodiscus luteus, Peter, 2021

Schuchert, Peter & Collins, Richard, 2021, Hydromedusae observed during night dives in the Gulf Stream, Revue suisse de Zoologie 128 (2), pp. 237-356 : 289

Staurodiscus luteus n. spec.

Fig. 33 A-H

Holotype: BFLA4284 ; 1 specimen; collected off Palm Beach , Florida, 06-DEC-2019; size 6 mm, ~32 tentacles; bell fragments preserved in formalin and deposited as UF-013842, fragment in alcohol used for DNA extraction (MHNG-INVE-0137382); 16S sequence MW528698 .

Other examined material: BFLA3819 ; 1 specimen; 24-OCT-2018; size ~ 2.5 mm, ~36 tentacles; preserved in ethanol for DNA extraction; 16S sequence identical to MW528698 . – BFLA4458 ; 1 specimen, no photos taken; 11-JUN-2020; size ~ 8 mm; preserved in ethanol for DNA extraction; 16S sequence identical to MW528698 . – 06-MAY-2017; 1 specimen photographed; 8 mm; not collected. – 26-JUL-2018; 1 specimen photographed; size ~ 5 mm ~38 tentacles; not collected. – 11-APR-2019; 1 specimen photographed; damaged, 8 mm, ~24 tentacles; not collected. – 27-MAY-2019; 1 specimen photographed; juvenile, ~ 2 mm, ~9 tentacles; not collected. – 27-MAY-2019; 1 specimen photographed; juvenile, 2.5 mm, ~6 tentacles; not collected. – 17-MAY-2020; 1 specimen photographed; ~ 4 mm, ~24 tentacles; not collected. – 13-JUN-2020; 1 specimen photographed; 5 mm, ~17 tentacles; not collected.

Type locality: Atlantic Ocean , USA, Florida, approximately 6.5 km east of Palm Beach, WGS84 rectangle between 26.70, -79.94 and 26.78, -79.94, occurrence depth 8-10 m.

Diagnosis: Similar to the sympatric Staurodiscus kellneri , but smaller (<10 mm), with intensively yellow colour of stomach and its radiating extensions, and marginal bulbs; more radial canals (up to 30 and more) due to more branching, stomach extensions narrower, radial canals broader.

Description: Staurodiscus medusa with bell somewhat flatter than hemisphere, largest diameter observed 8 mm, apical jelly thick, about half the umbrella height ( Fig. 33D ). Conspicuous, opaque, intensively golden-yellow colour of stomach, radial canals and marginal bulbs, colour fading in peripheral regions of radial canals; colour is partially preserved in alcohol. Stomach wide, up to half the diameter of the subumbrellar diameter, shallow, base irregularly starshaped, turning into basal stomach extensions which taper radially and branch irregularly 0 to 3 times and changing gradually into 30 to 40 radial canals which all reach the circular canal, radial canals very short. Gonad tissue (gametes) could not be seen in the preserved material, thus animals likely not reproductive. About 24 to 38 tentacles, long, contracted tightly coiled, their bulbs ovoid, clearly separated from rest of tentacles. Marginal bulbs positioned independently of radial canals. Usually only one cordylus between pairs of tentacles, also in younger individuals, sometimes cordylus on a marginal bulb without tentacle. Small, brown ocellus on base of adaxial side of bulb or on radial canal at attachment sites of cordylus. On aboral side of manubrium the cross-like marks of an original state with only four radial canals can be seen ( Fig. 33E ). Branching of the radial stomach extensions must occur early in development. Amphipods appear occasionally to associate with the medusa.

Etymology: The Latin adjective luteus means yellow and refers to the striking yellow colour of this medusa.

16S Data: The three 16S sequences obtained in this study were all identical. Staurodiscus kellneri haplotypes have about 9% base pair differences to the one of S. luteus . The two species are clearly separated in the maximum likelihood tree ( Fig. 28 ).

Distribution: Known from type locality only.

Remarks: The opaque, yellow or golden-yellow colour renders S. luteus rather conspicuous ( Fig. 33 ), although it resembles otherwise S. kellneri and S. milleri ( Bouillon, 1984b) . The latter has about the same size and is thus even more similar. The radial canals are more branched in S. luteus , resulting in 30 to 40 canals, while S. milleri has up to 18. Bouillon (1984b) usually also observed living animals for his studies in the Hansa Bay and he would certainly have noted any conspicuous colour as it is present in S. luteus . We therefore assume that S. milleri was not pigmented.

It is though possible that formalin preserved material – which loses colours after some time – has previously been mis-identified as S. kellneri in the western Atlantic. Both species can be separated based on their size, branching patterns of the radial canals, and proportions. The identification is more secure if 16S data are used.

Figures

Fig. 33. Staurodiscus luteus n. spec. (A) Holotype, BFLA4284, 6 mm diameter, oblique view on oral side. (B-F) BFLA3819, size 2-3 mm. (B) Oral view. (C) Oral view. (D) Lateral view. (E) Oblique view on aboral part, note cross-shaped mark of original radial canals. (F) Bell margin from oral side, cordyli and ocelli are visible. (G) Juvenile, 4 mm, oral view, photographed 17- MAY-2020. (H) Photo taken 26-JUL-2018, aboral view.

Fig. 28. 16S maximum likelihood phylogenetictree of Laodiceidae,Hebellidae,and Orchistomatidae,obtainedwith PhyML (GTR+G+I model) and based on about 600 bp positions of the mitochondrial 16S gene. Node-support values are bootstrap values of 100 pseudoreplicates (shown only if> 70%).All sequence labels start with the GenBank numbers (except for identical haplotypes) permitting the retrieval of more information. Red labels are new sequences from this study.