Hydromedusae observed during night dives in the Gulf Stream Author Schuchert, Peter Muséum d’histoire naturelle, C. P. 6434, CH- 1211 Genève 6, Switzerland peter.schuchert@ville-ge.ch Author Collins, Richard 880 NE 33 rd Street, Boca Raton, Florida, USA rc6684@icloud.com text Revue suisse de Zoologie 2021 2021-10-21 128 2 237 356 journal article 10.35929/RSZ.0049 172fa5c5-c0c4-4bd7-b710-d608237b8458 0035-418 5639938 Euphysilla pyramidata Kramp, 1955 Fig. 17 A-I Euphysilla pyramidata Kramp, 1955b: 245 , pl. 1 fig. 1, pl. 2 fig. 3. – Kramp, 1959a: 90 , fig. 42. – Kramp, 1961: 39 . – Kramp, 1965: 4 . – Kramp, 1968: 17 , fig. 33. – Vannucci & Santhakumari, 1969: 40 . – Schmidt, 1973: 16 . – Hamond, 1974: 554 , figs 4-6. – Segura-Puertas, 1984 : pl. 2 fig. 2. – Petersen, 1990: 135 , fig. 7B. – Xu & Huang, 2004: 560 , fig. 9. ? not Euphysilla pyramidata . – Bouillon, 1978b: 259 , figs 7 & 8.1-2. Examined material: BFLA4396 ; 1 specimen ; 17-MAY-2020 ; size 2.5 mm ; preserved in ethanol for DNA extraction; 16S sequence MW528719 . – BFLA4397 ; 1 specimen ; 17-MAY-2020 ; size 2 mm ; preserved in ethanol for DNA extraction; 16S sequence MW528720 . – BFLA4402 ; 1 specimen ; 26-MAY- 2020 ; size 3 mm ; preserved in formalin and deposited as UF-014043. – BFLA4468 ; 1 specimen ; 17-JUN- 2020 ; size 3 mm ; preserved in formalin and deposited as UF-014073 . – BFLA4478 ; 1 specimen ; 18-JUN-2020 ; size 4 mm ; preserved in ethanol for DNA extraction; 16S sequence identical MW528719 . Observations: Umbrella 2-4 mm in height, oviform, with apical thickening of very variable height, lateral walls thin, exumbrella with scattered nematocysts. Above manubrium an apical chamber, without apparent connection to gastric cavity, size variable depending on size of apical process ( Fig. 17 A-C). Manubrium an inverted cone, as long as bell cavity, base broad and cruciform in life ( Fig. 17D ), more square-shaped when preserved, upper part of manubrium cylindrical, narrowing to tubular lower part of manubrium ending in small, circular mouth. All observed medusae were budding medusae, buds in groups on all four perradial sides of the manubrium in about the middle of the manubrium. Gonad-like opaque tissue layer covers manubrium above buds. Colour of manubrium intensively yellow-orange. Radial canals connected to manubrium by apparent short mesenteries (giving cruciform manubrium base), thin; circular canal more rectangular than circular. Four tentacles, contracted about half the length of the bell height, each with 8-12 crescent-shaped, clasping nematocyst pads, all in one row on adaxial side, terminal button ovoid, as wide as rest of tentacle. Four tentacle bulbs relatively small, orange-yellow, without well visible ocelli, but a faint reddish spots may be present on abaxial tentacle base ( Fig. 17A ). Nematocyst ( Fig. 17 F-I, preserved tissue, sizes approximative): small stenoteles (7x10 µm), large stenoteles (12x13 µm), desmonemes (4x9 µm), spherical microbasic eurytele with barbed filament, shaft appears without barbs (7x10 µm). 16S Data: The three obtained 16S sequences represented two haplotypes, differing in only one base pair of 588. A blastn search in GenBank singled out a sequence ( LT 714182 ) with very high similarity (99.3%, Fig. 21 ). The sequence was obtained from a Sphaerocoryne polyp collected in the Maldives archipelago. Distribution: Circumglobal in tropical seas. Western Africa ( Kramp, 1955b ); Gulf of Mexico (Segura- Puertas et al ., 2003); Indian Ocean ( Kramp, 1965 ; Vannucci & Santhakumari, 1969 ; Hamond, 1974 ); Red Sea ( Schmidt, 1973 ); Bismarck Sea ( Bouillon, 1978b ); Taiwan Strait ( Xu & Huang, 2004 ); tropical eastern Pacific Ocean from Peru to Mexico ( Segura-Puertas, 1984 ). Type locality: Atlantic Ocean, Gulf of Guinea , off the coast of Bénin ; WGS84 6.01667 , 2.35000 ; depth 0-10 m. Remarks: Euphysilla pyramidata has not been recorded frequently, this despite its apparent circumglobal distribution. Kramp’s type specimen had no medusa buds, but he states that it had developed gonads. Euphysilla pyramidata with medusa buds were then reported in nearly all descriptions subsequent to Kramp (1955 b, 1965 ) (see synonymy above). Hammond (1974) found both forms. Except for the medusa buds, our specimens matched Kramp (1955b) quite well, including the yellow manubrium colour, although in Kramp’s formalin preserved material the remaining colour had become faint. The differences of our specimens and Kramp’s description in the shape of the manubrium (quadratic versus cruciform manubrium base, wide mouth versus narrow) can easily be attributed to fixation artefacts, viz . the type specimen having been preserved with an inflated stomach. Moreover, the stomach base depicted by Kramp (1955b : pl. 2 fig. 3) is more cruciform than quadratic. Kramp (1955b) did not mention an apical chamber, but his figure 1 on plate 1 shows such a chamber, although only faintly. Euphysilla pyramidata medusae reported from the Pacific Ocean by Bouillon (1978b) have some differences to our material. First, the apical thickening, hence likely also the apical chamber, is absent and the umbrella is more spherical, thus unlike the type specimen figured in Kramp (1955b) . Second, Bouillon (1978b) also describes the colour of the manubrium as rose-orange and the one of the bulbs as having a hue of red. Whether these are species level or population level differences remains to be investigated by genetic examinations. Perhaps Bouillon’s medusae are referrable to Euphysilla tubularia Huang, Xu & Lin, 2015 , from which they appear not objectively separable. The tubular part of the manubrium in the mouth region in Euphysilla tubularia is certainly only a fixtion artefact. We observed the same in the present material. It is thus probable that E. pyramidata as currently perceived is a complex of species. As in other genera, including information on the polyp stage might change its scope. The 16S sequences gave a surprising match with a hydroid of the genus Sphaerocoryne from the Maldives ( LT 714182 , Maggioni et al ., 2017 ). The author of this sequence, Dr Davide Maggioni, kindly let us know that a publication describing this colony is currently in preparation.