Euphysilla Kramp, 1955

Maggioni, Davide, Schuchert, Peter, Arrigoni, Roberto, Hoeksema, Bert W., Huang, Danwei, Strona, Giovanni, Seveso, Davide, Berumen, Michael L., Montalbetti, Enrico, Collins, Richard, Galli, Paolo & Montano, Simone, 2021, Integrative systematics illuminates the relationships in two sponge-associated hydrozoan families (Capitata: Sphaerocorynidae and Zancleopsidae), Contributions to Zoology 90, pp. 487-525 : 502-504

Euphysilla Kramp, 1955

Diagnosis: Hydroids like in Sphaerocoryne .

Medusa umbrella ovoid, with apical chamber; manubrium with quadratic base; mouth circular; no gastric peduncle; mature gonads surrounding the whole manubrium; four equally developed tentacles with adaxial or abaxial nematocyst clasps and a terminal cluster; ocelli absent or underdeveloped and very inconspicuous. Medusa buds on manubrium usually present.

Genetic diagnosis: 20 molecular diagnostic characters differentiate Euphysilla from other genera in the family, specifically 5 in the 16S, 9 in the COX1, 4 in the COX3, and 2 in the 18S ( table 2 ).

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Remarks: Euphysilla is very similar to Sphaerocoryne , differing only in the medusa stage by the absence or reduction of the ocelli and the frequent presence of medusa buds. Although ocelli have not been reported in Euphysilla , we noted in some of the specimens of E. pyramidata faint orange-yellow spots on the abaxial side of the tentacle bulbs, just at the position where normally ocelli would occur ( fig. 4M ). The spots are very inconspicuous and easily overlooked as they have the same colour as the other pigmented tissues of the medusa. It is unclear if these spots are functional ocelli. These spots were apparently overlooked by Schuchert & Collins (2021). The genus comprises currently the following species: Euphysilla peterseni Allwein, 1967 , E. pyramidata Kramp, 1955 , and Euphysilla tubularia Huang, Xu & Lin, 2015 . The latter species appears indistinguishable from E. pyramidata ( Schuchert & Collins, 2021) .

Figures

FIGURE 4 Euphysilla pyramidata. A, B, C) Polyps from the Maldives.D) Close-up of a hydranth showing the typical colouration. E) Hypostome with nematocysts (arrowhead). F) Longitudinal organisation of tentacles.G) Polyps with medusa buds. H) Large stenoteles (ls), small stenoteles (ss), I) desmonemes, and J) heteronemes from the polyp.K, L) Medusae with medusa buds.M) Detail of a bulb showing a reduced abaxial ocellum (arrowhead). Scale bars: A) 0.5 mm; B-D, G) 0.2 mm; E, F) 0.1 mm; H-J) 5 Μm; K, L) ~ 1 mm; M) ~ 0.3 mm.