Staurocladia dzilamensis, Ahuatzin-Hernández & Hernández-Solís & León-Deniz, 2024

Ahuatzin-Hernández, José María, Hernández-Solís, Pablo Alberto & León-Deniz, Lorena Violeta, 2024, First record of the genus Staurocladia (Hydrozoa: Cladonematidae) in the Gulf of Mexico with the description of Staurocladia dzilamensis sp. nov., a new species of crawling hydromedusa, European Journal of Taxonomy 921, pp. 251-275 : 255-259

Staurocladia dzilamensis sp. nov.

urn:lsid:zoobank.org:act:AF3C5967-0A3D-4123-AABF-3A2852FC73BC

Figs 3–5

Diagnosis

Staurocladia medusae with flattened-hemispherical to occasionally dome-shaped umbrella, with medusa buds on exumbrella, dorsally placed. A thickened and continuous marginal nematocyst ring on subumbrella; 6–11 bifid tentacles, branching proximally, with lower branch up to two times as long as upper one. Upper branch with three nematocyst clusters, one apical, and two opposite placed alternately on its aboral and oral sides. Lower branch with terminal adhesive pad. Cnidome composed of stenoteles (two size classes) and desmonemes.

Etymology

The name is derived from the type locality, Dzilam de Bravo.

Material examined

Holotype

MEXICO • Yucatán, Dzilam de Bravo ; 21°23.7′ N, 88°53.1′ W; depth 1 m; 14 May 2022; José María Ahuatzin Hernández leg.; macroalgae; YUC-CC-254-11-001655 .

Paratypes

MEXICO • 1 spec.; same collection data as for holotype; 7 May 2022; YUC-CC-254-11-001656 • 1 spec.; same collection data as for holotype; 7 May 2022; YUC-CC-254-11-001657 • 1 spec.; same collection data as for holotype; YUC-CC-254-11-001658 .

Description

Medusa bell flattened-hemispherical to dome-shaped, ca 0.43 mm wide (0.25 ± 0.60 mm, n = 100); brown-olive coloured, commonly with medusa buds on exumbrella, dorsally located; manubrium conical, extending beyond the margin, occupying a great part of the subumbrellar cavity, distally with simple, circular mouth; gonads surrounding the upper part of manubrium; neither pouches nor nematocyst knobs were observed on the manubrium; some specimens with visible eggs; a continuous and thickened nematocyst ring present on subumbrella; velum fully closing subumbrella; 5–7 short, unbranched radial canals, hard to see in most specimens and rarely corresponding to the number of marginal tentacles; 6–11 (usually 8) bifid tentacles with a black-reddish ocellus at their aboral base; tentacles branching a short distance after their origin, with the lower branch up to 2 times as long as the upper one, the former with a terminal adhesive pad; upper branch short, with 3 nematocyst clusters, one apical, knob-like shaped, and 2 additional, crescent-shaped, placed alternately on the aboral and oral sides of the branch. Cnidome: stenoteles of two size classes, class 1 = (15.00– 17.50) × (12.50–15.00) μm, class 2 = 10.00 × 7.50 μm, and desmonemes = 7.50 × 5.00 μm, all in the upper branch, capsules restricted to both the terminal knob and the crescent-shaped clusters; no nematocysts were observed in the adhesive pad of the lower branch; marginal ring with stenoteles and desmonemes.

Histology: mesoglea reduced, not noticeable; velum evident, fully closing subumbrella; subumbrellar cavity wide, ca 149.18 µm (SD = 33.60); gonads like an external thin layer that surrounds the upper part of the manubrium, without any apparent division; radial canals short and broad, originating laterally from the gastric cavity, ending in a ring canal located immediately above the thickened continuous nematocysts ring; nematocysts ring ca 38.30 µm wide (SD = 3.92); internal walls of the manubrium with a layer of gastrodermis, gastrodermis ca 6.34 µm wide (SD = 0.72); gastric cavity wide, occupying ⅔ of subumbrella, ca 110.46 µm (SD = 22.31).

Remarks

A large cover of filamentous algae and Dynamena sp. hydroids occurred at the site, so a possible association between S. dzilamensis sp. nov. and Dynamena hydroids must be studied in the future. Of the 110 specimens, most were observed alive, and their morphology did not considerably change post-fixation. Most specimens had eight tentacles (n = 57), followed by nine (n = 25), seven (n = 22), six (n = 3), ten (n = 2), and eleven (n = 1). Two specimens showed tentacles with two aboral crescent-shaped nematocyst clusters on the upper branch of some tentacles. Two specimens presented a trifid tentacle. The origin of the third bifurcation was on the distal part of the lower branch, with both lower branches of equal length and with adhesive pads. Most specimens had exumbrellar medusa buds (n = 61). Thirty-eight specimens had one medusa bud, twenty had two buds, and only three specimens had three buds. Budding was the only way of asexual reproduction observed.

The third day of sampling (May 28) recorded the highest values of the measured variables and their greatest variation. The average temperature showed the highest values on the first day of sampling, ranging between 28.25 and 29.35°C. Dissolved oxygen recorded the highest values on the third day of sampling; this variable ranged between 0.10 and 0.67 mg /L. Salinity showed euhaline characteristics, since its values ranged from 36.07 to 38.94 ppt. Finally, the pH showed a higher acidity during the first two days, while on the third day, it showed alkaline ( Table 1 ). Unfortunately, the polyp stage was not found in the samples (Appendices).

Figures

Fig. 3. Diagnostic features of Staurocladia dzilamensis sp. nov. A. Lateral view. B, G. Aboral view. C. Tentacle lower branch. D, F. Tentacle upper branch. E. Oral view. H. Cnidome. Abbreviations: dms = desmonemes; egs = eggs; lnc = lower nematocyst cluster; ltp = adhesive pad; mbd = medusa bud; mnr = marginal nematocyst ring; mth = mouth; mtl = bifid marginal tentacles; ocl = ocellus; rcl = radial canal; sts1 = stenoteles class 1; sts2 = stenoteles class 2; tnc = terminal nematocyst cluster; unc = upper nematocyst cluster.

Fig. 4. Sagittal histological sections from different specimens of Staurocladia dzilamensis sp. nov. Abbreviations: gct = gastric cavity with a prey; gds = gastrodermis; mbd = medusa bud; mnr = marginal nematocyst ring; mth = mouth; mtl = marginal tentacle; rcl = radial canal; suc = subumbrellar cavity; vlm = velum.

Fig. 5. Staurocladia dzilamensis sp. nov. A. Lateral view. B. Oral view. C. Aboral view. D. Sagittal section. Abbreviations: gct = gastric cavity; mnr = marginal nematocyst ring; mth = mouth; rcl = radial canal; vlm = velum.