Zanclea mayeri n. spec. Figs 18 A-E, 19A-H Zanclea costata. – Mayer, 1910: 87, pl. 8 fig. 6, perhaps also 2, 3, 7. [not Z. costata Gegenbaur, 1857] Holotype: BFLA4061; photographed (Fig. 18 A- E) and collected 10-APR-2019; 6 mm high, 3 mm wide; preserved in alcohol and used entirely for DNA extraction; frozen DNA solution deposited in MHNG under the catalogue number MHNG-INVE-0137375; 16S sequence MW528663. Paratypes: BFLA4219; 1 specimen; 27-SEP- 2019; height 5 mm; preserved in alcohol for DNA extraction; frozen DNA solution deposited as MHNG- INVE-0137377; 16S sequence MW528687. – BFLA4281; 1 specimen; 06-DEC-2019; height 7 mm; preserved in alcohol for DNA extraction; frozen DNA solution deposited as MHNG-INVE-0137378; 16S sequence MW528697. – BFLA4297; 1 specimen; 09-DEC-2019; height 6 mm, width 4 mm; preserved in alcohol for DNA extraction; frozen DNA solution deposited as MHNG-INVE-0137380; 16S sequence MW528703. Type locality: USA, Florida, 5.5- 12 km east of Palm Beach; WGS84 26.70, -79.94 to 26.78, -79.94; depth 10 m. Etymology: The name honours Alfred Goldsborough Mayor [Mayer] who described this species in his outstanding work of 1910 (for a biography see Stephens & Calder, 2006). Description: Mature medusa 4 to 7 mm high and 3-4 mm wide, bell bullet-shaped, apex rounded, lateral wall straight. Mesoglea relatively thick, thicker at apex. Exumbrella with four thick, white perradial nematocyst bands, protruding from surface, reaching from circular canal to apex, two opposite bands often recurved at apex (Fig. 18 A-C). Subumbrella with interradial pockets projecting into apical mesoglea (Fig. 18 A-B). Manubrium large, composed of a larger upper part and a thinner, short, cylindrical mouth region. Upper part of manubrium with cruciform cross-section (Fig. 19B), gonads cover surface entirely as a thin layer, but separated perradially. Radial canals smooth. Only two tentacles, opposite, other two perradial positions without bulbs. Tentacles at base thick, without bulb formation, evenly tapering to very fine end, very contractile or extensible to more than 35 mm (Fig. 18E). Tentacles with abaxial row of cnidophores, these relatively large, spherical, with long, contractile stalk (Figs 18E, 19D). No ocelli present. Colours: manubrium orange (females) or faintly orange (males), tentacles faint pink-orange. Nematocysts: macrobasic euryteles and stenoteles (Fig. 19 F-H). One medusa (Fig. 19E) with a hydroid colony growing on upper part of manubrium, polyp with one whorl of few capitate tentacles, stolon-like processes in the manubrium tissue. It is not evident if this hydroid is derived from medusa or if it is a parasitic hydroid. 16S data: The four available samples gave four different 16S haplotypes with divergences of 0.8-1.2%. A blastn search in GenBank with the obtained sequences yielded numerous Zanclea sequences, but all with less than 92% identity. A maximum likelihood tree using part of the 16S sequence data of Maggioni et al. (2018) did not associate the sample with any other (Fig. 21). Remarks: Mayer (1910) described and figured a single Zanclea medusa from Florida which he attributed to Zanclea costata Gegenbaur, 1857. His figure (pl. 8 fig. 6) obviously depicts the same medusa as shown here in Figs 18-19. Also, the size was the same (6 mm) and the umbrella shape matches. The scope of Z. costata has changed since then, although the identity of Gegenbaur’s medusa from the Mediterranean is still not entirely resolved (Brinckmann-Voss, 1970; Boero et al., 2000; Cerrano et al., 1997; Schuchert, 2010; Maggioni et al., 2018). Gegenbaur’s medusae were relatively big (2-5 mm), had four tentacles, and the nematocyst bands reached up to the apex. However, medusae that exactly matched Gegenbaur’s medusa have never been found again and the current scope of Z. costata goes back to Brinckmann-Voss (1970). The Mediterranean Z. costata has four marginal bulbs even in younger stages and with optimal growth it will develop four tentacles (Gegenbaur, 1857; Brinckmann-Voss, 1970; Schuchert, 2010). Zanclea mayeri is even larger than Z. costata but has only two tentacles and two bulbs. The divergence of the 16S from Z. costata (GenBank entry FN687559) is 9% and 8.5% from an unidentified Mediterranean Zanclea with four tentacles (GenBank entry KP776810). Zanclea mayeri is distinct and does not match any of the known nominal Zanclea species. We therefore introduce it as a new nominal species. The holotype specimen of Zanclea mayeri n. spec. was used entirely to extract its DNA. The deposited type material is thus not a preserved specimen but only part of it as an extract of its genomic DNA in a buffered solution. A DNA solution serving as type specimen has so far not been used for any hydrozoan, but it is in accordance with the International Code of Zoological nomenclature as it can be regarded as a part of the type specimen (Article 72.5.1). Moreover, photos of the living holotype specimens are given in Fig. 18A-E and applying article 72.5.6 of the ICZN the depicted specimen becomes the type specimen.

Published as part of Schuchert, Peter & Collins, Richard, 2021, Hydromedusae observed during night dives in the Gulf Stream, pp. 237-356 in Revue suisse de Zoologie 128 (2) on pages 268-271, DOI: 10.35929/RSZ.0049, http://zenodo.org/record/5639938