Staurodiscus tetrastaurus Haeckel, 1879

Schuchert, Peter & Collins, Richard, 2021, Hydromedusae observed during night dives in the Gulf Stream, Revue suisse de Zoologie 128 (2), pp. 237-356 : 287-288

Staurodiscus tetrastaurus Haeckel, 1879

Figs 32 A-D

Staurodiscus tetrastaurus Haeckel, 1879: 145 , pl. 9 figs 1-3. – Mayer, 1910: 214, pl. 22 figs 7-8, pl. 25 fig. 5, pl. 26 figs 10-11. – Uchida, 1927b: 167. – Menon, 1932: 14, pl. 2 figs 14, 19. – Nair, 1951: 60. – Kramp, 1959a: 140, fig. 165. – Kramp, 1961: 148. – Kramp, 1962: 321. – Kramp, 1968: 70, fig. 182. – Migotto & Andrade, 2000: table 6.

Staurodiscus heterosceles Haeckel, 1879: 146 . syn. nov.

Examined material: BFLA3831 ; 1 specimen; 15-NOV- 2018; size 7 mm; preserved in ethanol for DNA extraction; 16S sequence MW528662 . – BFLA4406 ; 1 specimen; 26-MAY-2020; size 8 mm; preserved in ethanol for DNA extraction; 16S sequence MW528722 . – BFLA4433 ; 1 specimen; 30-MAY-2020; size 5 mm; preserved in ethanol for DNA extraction; 16S sequence identical MW528722 . – BFLA4440 ; 1 specimen; 07-MAY-2020; size 10 mm; preserved in ethanol for DNA extraction; 16S sequence identical to MW528662 . – BFLA4444 ; 1 specimen; 07-MAY-2020; size 15 mm; part preserved in formalin and deposited as UF-014059, small part preserved in ethanol for DNA extraction; 16S sequence identical to MW528662 . – 11-DEC-2017; 1 specimen photographed; juvenile, gonads not yet developed, not collected.

Observations: Bell hemispherical, 8 to 15 mm when mature, apical jelly about 1/3 of total height. Manubrium composed of central, cylindrical part and four basal, perradial extensions each with two lateral outgrowths in about middle of bell. Central part of manubrium tubular, with cruciform mouth opening drawn into four lips, margin slightly undulated. Basal, perradial extensions of stomach reaching almost to circular canal and thus length of radial canals to circular canal is short (1/4); stomach outgrowths relatively thick, giving off lateral diverticula in about the middle, these paired outgrowths opposite or not, oblique to radial axis or slightly curved, towards ends somewhat irregularly folded or undulating, not connecting to circular canal. Gonads in walls of stomach outgrowths. Mature animals with 23-30 tentacles and 1-3 cordyli between each pair of tentacles. Young animal with four perradial tentacles only and 7-9 cordyli per quadrant ( Fig. 32A ). Tentacles with conical bulbs. Small, inconspicuous ocelli present on adaxial side of tentacles bulbs and attachment sites of cordyli ( Fig. 32F ). Animal colourless or with greenish tint. Amphipods appear often to associate with the medusa ( Fig. 32 ).

16S Data: The five obtained 16S sequences represented 2 haplotypes differing only one position (an insertion/ deletion). In the maximum likelihood tree ( Fig. 28 ) they are well separated from the other Staurodiscus species and also Melicertissa of this study. It is part of a well supported clade comprising the Staurodiscus species of this study and some Hebellidae .

Distribution: Canary Islands, Florida, Caribbean Sea, coast of Mozambique, coasts of India, Singapore, Taiwan Strait, Bismarck Sea ( Kramp, 1959a, 1968; Bouillon 1978a, 1984b; Navas-Pereira & Vannuci, 1991; Zhang, 1999; Segura-Puertas et al., 2003). Type locality: Atlantic Ocean, Canary Islands, near Lanzarote.

Remarks: Haeckel (1879) introduced two nominal Staurodiscus species , S. tetrastaurus and S. heterosceles , both collected at the same time and near Lanzarote Island. The former had 8-16 tentacles, 48 cordyli, and a bell diameter of 4-6 mm, the latter 8-32 tentacles, 40-80 cordyli, and a bell diameter of 6-8 mm [note that the figures in Kramp (1959a, 1968) depict a juvenile S. tetrastaurus with four tentacles, compare Fig. 32A ]. Additionally, Haeckel distinguished both nominal species based on the branching pattern of the radial canals (= actually basal extensions of the manubrium, comp. Fig. 32A, E, G ): S. tetrastaurus has opposite pairs, while they were not opposite in S. heterosceles . Haeckel (1879) also observed intermediate forms and explicitly expressed doubts that they are “ bona species ”, but nevertheless named both forms [Haeckel used an artificial, typological species concept and did not distinguish biological species, comp. comments in Haeckel, 1879: XXV, 109]. Kramp (1962, 1968) too thought that both names refer likely to the same species.

One of our specimen (BFLA3831) was also intermediate as it had the size and tentacle numbers of S. heterosceles , but the outgrowths of the stomach had opposite sidebranches ( Fig. 32E ). Others ( Fig. 32G ) had a variable branching pattern. The observed juvenile specimen ( Fig. 32A ) had three opposite and one alternate pairs of side-branches. It is thus quite clear that S. tetrastaurus and S. heterosceles must be regarded as conspecific, S. tetrastaurus being the valid name. Medusae identified as Staurodiscus heterosceles have – to our knowledge – not been recorded anymore since Haeckel’s time.

Andrade & Migotto (1997) reared the initial stages of medusae released from a hydroid referable to Hebella scandens ( Bale, 1888) and found that they resembled our S. tetrastaurus . Our 16S phylogeny ( Fig. 28 ) also suggests a more close relationship to Hebellidae than to Laodiceidae . Staurodiscus tetrastaurus is the type species of the genus, thus decisive to which family the genus belongs.

Figures

Fig. 32. Staurodiscus tetrastaurus. (A-C) Young animal observed 11-DEC-2017. (D-E) BFLA3831, size 7 mm. Some amphipods are associated with the animal. (F) BFLA4440, size 10 mm, bell margin seen from adaxial side, ocelli are barely visible. (G) BFLA4440, oral view, note variation of position of lateral diverticula.

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.