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 Larsonia pterophylla ( Haeckel, 1879 ) Fig. 10 A-D Stomotoca (Stomotocanna) pterophylla Haeckel, 1879: 52 , pl. 4 fig. 10. Stomotoca pterophylla .– Mayer, 1910: 113 , pl. 29 figs 3-5, pl. 30 fig. 7. – Bigelow, 1918: 372 , synonymy, discussion of species. – Uchida, 1940: 284 , fig. 3. ‒ Kramp, 1959a: 119 , fig. 115. – Kramp, 1961: 115 . – Kramp, 1968: 44 , fig. 113. – Larson, 1982: 433 , fig. 183. – Wedler & Larson, 1986: 97 , fig. 11a-b, hydroid, young medusa. Stomotoca divisa Maas, 1897: 11 , pl. 1 figs 1-9. – Vanhöffen, 1913b: 14 , synonym. Larsonia pterophylla . – Boero et al ., 1991: 198 , new combination. – Woodstock et al., 2019 : fig. 1, hydroid. Stomotoca atra . – Vanhöffen, 1913b: 14 , pl. 2 figs 12-16. – Stampar & Kodja, 2007: 55 , figs 2-3. [not Stomotoca atra L. Agassiz, 1862 ] Examined material: BFLA4453 ; one formalin fixed specimen deposited under catalogue number FU-014064 ; collected 08-JUN-2020 ; height 27 mm . – 08-AUG-2018 , 1 specimen photographed; not collected... Observations: Medusa 27 mm , with low umbrella and big, conical, pointed apical process; subumbrella shallow; with broad gastric peduncle reaching to velum level; 4-5 ribbon-like radial canals; two opposite tentacles, long, whitish, with swollen base clasping bell margin, no ocelli; about 80-100 atentaculate bulbs along bell margin, small, wart-like, all about the same size, without ocelli ( Fig. 10C ); manubrium barrelshaped, with mouth drawn out into four long perradial lips, margin crenulated; gonads large, covering stomach in eight adradial series of about 10 branched folds directed towards interradial, pairs of adradial fold series connected perradially by a thick, vertical fold; adradial folds branching with up to four ends ( Fig. 10B ). Gonads and manubrium colour golden-brown or brown. Distribution: American coasts from Gulf of Maine to Brazil , West Africa, Pacific coasts of Panama to Peru , Japan , Papua New Guinea , Indian Ocean ( Kramp, 1968 ; Bouillon, 1980 ; Navas-Pereira & Vannucci, 1991 ; Stampar & Kodja, 2007 , as Stomotoca atra ). Type Locality: Caribbean Sea, 20.60°N 79.00°W . Remarks: The observed specimens agreed well with existing descriptions of Larsonia pterophylla , except that one had five radial canals instead of four. This surplus radial canal was interpreted as a developmental aberration or variation without taxonomic significance. Also other tetraradial hydromedusa species occasionally show three or five radial canals (see Clytia spec. ). Stomotoca atra L. Agassiz, 1862 is a very similar species and Vanhöffen (1913b) thought that they could be conspecific. However, S. atra is distinct from L. pterophylla , notably they have different polyp stages (comp. Larson, 1982 and Boero & Bouillon, 1989 ). The medusae are distinguishable: in L. pterophylla the mouth margin is crenulated and perradially drawn out into long lips, in S. atra it is not crenulated and the perradial lips are short. Additionally, the transverse gonad folds are branched several times in L. pterophylla , while they are mostly unbranched in S. atra (comp. Schuchert, 2017b ) or in loops in very mature animals (comp. Bigelow, 1918 ; Arai & Brinckmann-Voss, 1980 ). The Brazilian medusae depicted in Stampar & Kodja (2007) and identified as S. atra must thus belong to L. pterophylla .