Staurodiscus kellneri ( Mayer, 1910 )

Schuchert, Peter & Collins, Richard, 2021, Hydromedusae observed during night dives in the Gulf Stream, Revue suisse de Zoologie 128 (2), pp. 237-356 : 285-287

Staurodiscus kellneri ( Mayer, 1910)

Fig. 31 A-H

Toxorchis kellneri Mayer, 1910: 229 , pl. 28 figs 1-2. – Vanhöffen, 1913a: 421. – Bigelow, 1917: 306. – Bigelow, 1926: 54. – Kramp, 1959a: 141, fig. 167. – Kramp, 1961: 150.

Dipleurosoma brooksii Mayer, 1910: 227 , fig. 118a-b, nov. syn.

Toxorchis brooksi . – Kramp, 1959a: 141, fig. 168b. – Kramp, 1961: 147.

Hebella furax . – Migotto & Andrade, 2000: 1873, figs 1-5. [? not Hebella furax Millard, 1957 ]

? Toxorchis milleri Bouillon, 1984b: 71 , fig. 20.

? not Staurodiscus kellneri . – Bouillon et al., 2004: 152, figs 82A-D.

Examined material: BFLA4050 ; 1 male; 01-APR- 2019; size 20 mm; preserved in formalin ( UF-013450 ) and small part in alcohol for DNA extraction; 16S sequence MW528661 . – BFLA4074 ; 1 specimen; 11-APR-2019; size 13 mm; preserved in formalin ( UF- 013784 ) and small part in alcohol for DNA extraction; 16S sequence identical to MW528721 . – BFLA4107 ; 1 specimen; 27-MAY-2019; size 10 mm, only 9 radial canals; preserved in formalin ( UF-013794 ) and small part in alcohol for DNA extraction; 16S sequence MW528675 . – BFLA4242 ; 1 specimen; 11-NOV- 2019; size 7 mm; preserved in formalin ( UF-013835 , sample macerated, only debris left) and part in alcohol for DNA extraction; 16S sequence MW528691 . – BFLA4399 ; 1 specimen; 17-MAY-2020; size 11 mm; preserved in formalin ( UF-014041 ) and small part in alcohol for DNA extraction; 16S sequence MW528721 . – BFLA4404 ; 1 specimen; 26-MAY-2020; size 8 mm; preserved in alcohol for DNA extraction; 16S sequence identical to MW528721 . – BFLA4424 ; 1 specimen; 28-MAY-2019; size 9 mm; preserved in formalin ( UF- 014050 ) and small part in alcohol for DNA extraction; 16S sequence MW528726 . – BFLA4452 ; 1 specimen; 08-JUN-2020; size 14 mm; preserved in formalin and deposited as UF-013450 . – 30-MAY-2020; 1 specimen; photographed but not collected; 10 mm, 9 radial canals, juvenile.

Observations: Umbrella diameter 10-20 mm, hemispherical or slightly flatter than hemisphere, lateral jelly thin but gradually thickening towards apex, the latter moderately thick. Manubrium rather flat, mouth wide open or a short tube with variable number of folded lips, manubrium base much enlarged and drawn out star-like into up to 12 basal extensions which may branch into two or three radial stomach extensions and reaching almost to circular canal, continued as short radial canals (about 1/6 of bell radius) and these all connected to circular canal, no blind ending radial canals or stomach extensions, 16-19 radial canals. Branching pattern variable and irregular, some radial canals not branching. Gonads develop on lateral walls of stomach extensions, reaching from branching points to beginning of radial canals, colour pale reddish-brown or brown-yellow. Tentacles 23-32, with distinct ovoid marginal bulb, black ocellus on adaxial side where joined to umbrella. Marginal bulbs independent of radial canals. Between each pair of tentacles usually one, sometimes 2-3 (especially in smaller animals) elongate cordyli, cordyli with a few terminal nematocysts, at attachment site on adaxial side a black ocellus. No statocysts.

16S Data: The six 16S sequences obtained represented four haplotypes with only 0.16 to 0.5% base pair differences. In the maximum likelihood tree ( Fig. 28 ) they are well separated from the other Staurodiscus species and also Melicertissa of this study.

Distribution: Florida and Gulf of Maine ( Kramp, 1959a). Type locality: USA, Florida, Dry Tortugas archipelago. The Mediterranean occurrence given in Bouillon et al. (2004) is based on records of the hydroid Hebella furax Millard, 1957 and is most likely incorrect because the medusa is not known to occur in this well investigated area. It is by no means evident that the simple hydroid Hebella furax corresponds to Staurodiscus kellneri in all regions it has been reported. It is highly probable that Hebella furax represent a species complex (see also Remarks below).

Remarks: This is a rare medusa, only a few individuals have been described so far and the variation of the number of tentacles, radial canals, and the branching of the stomach extensions were not well known. Migotto & Andrade (2000) reared medusae released from a hydroid they collected in coastal waters of Brazil and identified as Hebella furax Millard, 1957 . The resulting adult medusae were clearly identifiable as S. kellneri , although the authors hesitated somewhat with this identification, presumably because the branching pattern of the radial canals/stomach extensions were more variable than documented before. This trait was rather variable in our specimens too ( Fig. 31 A-G) and confirms the observations of Migotto & Andrade (2000). However, Hebella furax cannot simply be synonymized with Staurodiscus kellneri . Hebella furax [see Millard (1975) and also Boero et al. (1997)] was originally described from South Africa and is a widespread, rather simple hydroid offering few diagnostic features. It is very likely that it does not produce S. kellneri medusae over its whole distribution range, just like the “ Campanulina ”- type hydroids produce medusae belonging to different genera (see Schuchert et al., 2017 for similar cases).

Staurodiscus brooksii ( Mayer, 1910) (see description in Kramp, 1959a) from the Bahamas appears very similar to S. kellneri . The former has fewer tentacles and also fewer radial canals because four radial canals are unbranched. BFLA4399 had exactly this condition ( Fig. 31F ), while others like BLFA4050 ( Fig. 31A ) had it partially. Mayer (1910) described S. brooksii based on drawings made by the late William K. Brooks of a medusa collected from Nassau, Bahama Islands. The drawing did not show ocelli, but they were probably overlooked by Brooks as they are rather small and not well visible ( Fig. 31H ). Kramp (1959a) pointed out that also the cordyli were also not mentioned in Mayer (1910), but they are shown in Mayer’s figure (1910: 118aA). Staurodiscus brooksii must evidently be a younger stage of Staurodiscus kellneri and we regard both as conspecific. Both names were introduced in Mayer (1910), with S. brooksii appearing on page 227, S. kellneri on page 229. As the current ICZN does not enforce page precedence for synonymized names appearing in the same work, acting as first revisors we prefer to use the name Staurodiscus kellneri for the present species. It is the better and more precisely known nominal species and has been reported subsequently, while S. brooksii is incompletely described and has not been reported anymore (based on Kramp, 1961).

With the new data on the variability of the radial canals and their branching pattern in Staurodiscus kellneri , S. milleri ( Bouillon, 1984b) becomes hardly distinguishable. They could well be conspecific. The only tangible difference remaining being the smaller size of S. milleri (up to 8.5 mm versus 10-20 mm). Although we think that both names should be synonymized, we hesitate to do so for biogeographic reasons. Staurodiscus milleri is only known from the Bismarck Sea, thus both nominal species have a very disjunct distribution.

Figures

Fig. 31. Staurodiscus kellneri. (A-C) BLFA4050, size 20 mm. (A) Oral view, the oval, white body is a crustacean on the exumbrella. (B) Mouth part. (C) Bell rim, ocelli and cordyli are visible. (D) BFLA4107, size 10 mm, young animal with only nine radial canals reaching the circular canal. (E) BFLA4399, contracted bell, lateral view, size 11 mm. (F) BFLA4399, oral view, not all radial extensions are branched. (G) Animal photographed 12-OCT-2020, 10 mm, juvenile with 9 radial canals. (H) BFLA4242, bell diameter 7 mm, bell margin with bulbs and cordyli.

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.