Zancleopsis dichotoma ( Mayer, 1900 )

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 : 509-510

Zancleopsis dichotoma ( Mayer, 1900)

Gemmaria dichotoma Mayer, 1900: 35 , pl. 17 fig. 40.

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Zancleopsis dichotoma . Hartlaub, 1907: 115, fig. 105; Schuchert & Collins, 2021 (small form): 272, fig. 22.

Examined material: Sample SN 035, Singapore, 28/11/2017, polyps in ethanol and formalin. – Sample BFLA4170 , off Florida, 09/08/2019, medusa in ethanol and in situ photos. – Sample BFLA4171 , off Florida, 09/08/2019, medusa in ethanol and in situ photos. –S ample BFLA4248 , off Florida, 23/11/2019, medusa in ethanol and in situ photos .

Description: Polyp. Colonies monomorphic, living in association with sponges ( fig. 7A ). Hydrorhiza tubular and covered by a thin perisarc, embedded by the sponge host. Pedicels short and completely embedded in the sponge host, unbranched, covered by a thin perisarc. Hydranth slightly pyriform, up to 0.7 mm long, with variable diameter (110–170 Μm) ( fig. 7A, B ). Hypostome proboscis-like ( fig. 7B ). Tentacles organised in two alternating whorls of 4–5 tentacles ( fig. 7A ). Each tentacle with terminal and sub-terminal capitula (diameter: 60–100 Μm in the distal whorl; 40–50 Μm in the proximal whorl) ( fig. 7C ). Tentacles about 260–400 Μm long in the distal whorl, shorter in the proximal whorl (about 150–220 Μm). Nematocyst clusters 50–100 Μm distant from one other. Living hydranths transparent. Desmonemes, microbasic euryteles, small and large stenoteles ( figs. 7D, E ) occurring simultaneously and concentrated in the capitula, as well as scattered in the hydrorhiza; microbasic euryteles also in the hydranth.

Polyp cnidome. i) Desmonemes (undischarged: 7–9 × 4 Μm; discharged capsule: 6 × 3 Μm). ii) Microbasic euryteles (undischarged: 14–15 × 5–6 Μm; discharged capsule: 13–14 × 5–6 Μm; shaft: 17–20 Μm). iii) Large stenoteles (undischarged: 22–23 × 14–16 Μm; discharged capsule: 13 × 20 Μm). iv) Small stenoteles (undischarged: 9–10 × 6–7 Μm; discharged capsule: 7 × 9 Μm).

Adult medusa (from Schuchert & Collins, 2021, small form only). Total bell height up to 3 mm, 1/4 to 1/3 of the height taken by pointed apical process ( fig. 7F, G ); umbrella bell-shaped to conical, relatively thick walls, with shallow interradial subumbrellar pockets, tip of apical process green. Manubrium height about half the subumbrellar height when gonads start to develop, pear-shaped, short tubular oral part, mouth rim with four perradial white regions, upper part of manubrium (stomach) ochre coloured, with about 10 longitudinal, shallow gonad folds, folds mostly adradial, irregular ( fig. 7H ). Radial canals not forming mesenteries, smooth. Tentacle bulbs all equally developed, almost spherical, placed adaxial of origin of tentacles, white or faintly yellow. Two long, opposite tentacles, much extendable/contractible, with up to 25 short, abaxial, side branches ending in capitula, size of capitula gradually increasing towards distal ( fig. 7I ). The other tentacle pair very short, ending in spherical nematocyst knob. In young animals these short tentacles either missing or just beginning to develop. All tentacle bases with a red ocellus on abaxial side.

Adult medusa cnidome (preserved tissue). i) Desmonemes (8.5 × 5 µm). ii) Small stenoteles (18–21 × 14–17).iii) Larger stenoteles (24–26 × 22–23 µm). iv) Macrobasic euryteles (15–16 × 6–7 µm.

Distribution: Atlantic Ocean (Florida) and Indo-West Pacific ( Singapore).

Remarks: Schuchert & Collins (2021) found that Z. dichotoma medusae were genetically similar to A. cabela polyps. However, they found two genetically divergent morphs, one smaller (bell height of 3 mm) and the other larger (bell height up to 15 mm). The small morph better agrees with the original description of Z. dichotoma by Mayer (1900), and it was here linked through genetic data to Astrocoryne -like polyps from Singapore, supporting the synonymisation of the genus Astrocoryne with Zancleopsis .

Figures

FIGURE 7 Zancleopsis dichotoma. A) Polyp from Singapore (fixed in formalin).B) Close-up of a polyp.C) Tentacle with terminal and sub-terminal capitula.D) Large stenoteles (ls), small stenoteles (ss), desmonemes (d), and microbasic euryteles (e). E) Discharged microbasic eurytele. F, G) Medusae.Details of the H) manubrium with gonads and I) tentacles.Scale bars: A-C) 0.1 mm; D, E) 5 Μm;F-I) ~ 0.3 mm.