Ventromma halecioides ( Alder, 1859 )

Mendoza-Becerril, María A., Estrada-González, Mariae C., Mazariegos-Villarreal, Alejandra, Restrepo-Avendaño, Luisa, Villar-Beltrán, Rogelio D., Agüero, José & Cunha, Amanda F., 2020, Taxonomy and diversity of Hydrozoa (Cnidaria, Medusozoa) of La Paz Bay, Gulf of California, Zootaxa 4808 (1), pp. 1-37 : 17

Ventromma halecioides ( Alder, 1859)

Figs. 6 A–E

Plumularia halecioides Alder 1859: 353 , pl. 12, figs. 1–4.

Plumularia inermis .— Fraser 1948: 278.

Ventromma halecioides .— Humara-Gil & Cruz-Gómez 2018: 462 , fig. 6.

Type locality. Cullercoats and Roker, England ( Alder 1859) .

Material examined. Polyp—PB7_42, sampling site 3 (1), mature, 26.5°C, on a rock, coralline alga Amphiroa beauvoisii J.V.Lamouroux , and calcareous organisms.

Description. Colony erect from 5 to 20 mm high, with creeping hydrorhiza. Hydrocaulus branched, monosiphonic, divided at regular intervals into internodes 364.1–445.0 µm long, each with one distal nematotheca and one hydrocladial apophysis. Exoskeleton with a visible layer corresponding to perisarc. Perisarc thin (4.1–13.3 µm wide). Hydrocladia alternate, unbranched, with up to four thecate internodes, and occasionally with one short athecate internode proximally. Thecate internodes 335.8–633.5 µm long, each with a distal hydrotheca, a median inferior nematotheca, and a median superior nematothecae; athecate internodes 85.5–177.8 µm long. All nematothecae small (37.8–46.6 µm long), bithalamic and conical. Hydrotheca 83.3–99.7 µm long, cup-shaped, margin entire, with a circular aperture, 94.7–117.0 µm wide. Gonotheca 1102.6 µm long, 540.5 µm wide, with distinct transverse ridges and truncated on top, with short pedicel arising from hydrocaulus, exoskeleton thick (9.3–13.3 µm wide).

Nematocysts (length x diam.). Microbasic mastigophore (5.7–6.3 x 2.0– 2.8 µm).

More detailed description in Calder (1997) and Peña Cantero & García Carrascosa (2002).

Taxonomic status. Unaccepted (see remarks). AphiaID 117678.

Remarks. There is controversy about the identity of this species being assigned to the genus Kirchenpaueria Jickeli, 1883 or Ventromma Stechow, 1923 . While Stechow (1923) differentiated Ventromma from Kirchenpaueria Jickeli, 1883 by the presence of naked sarcostyles in the latter, some authors have argued that these genera cannot be confidently separated based on the structure or number of nematothecae, which is variable ( Bouillon 1985; Millard 1962; Schuchert 2020b). However, recent molecular studies support the validity of V. halecioides with sufficient genetic divergence from Kirchenpaueria , forming a sister clade to the rest of the family Kirchenpaueriidae ( Peña Cantero et al. 2010; Maronna et al. 2016; Moura et al. 2018). In light of this evidence, we follow Calder (1997) and consider our specimens to belong to Ventromma based on the presence of two bithalamic nematothecae. However, we stress the necessity of studying the amplitude of variation of the structure and number of nematothecae in both genera, to determine the extent of overlap between these characters and contribute to their delimitation.

Distribution. Species widely distributed in warm and temperate waters ( Peña Cantero & García Carrascosa 2002). In the Mexican Pacific, it has been reported in Baja California (Cedros Island) ( Fraser 1948) and Oaxaca (Santa Cruz Bay) ( Humara-Gil & Cruz-Gómez 2018).

Figures

FIGURE 6. A–E Ventromma halecioides (Alder, 1859): A, erect colony; B, hydrocaulus; C, hydrocladia; D, gonothecae; E, nematocysts microbasic mastigophore. F–J Plumularia floridana Nutting, 1900: F, erect colony; G, hydrocaulus; H, hydrotheca and nematothecae; I, nematothecae between hydrocaulus and hydrocladia; J, male gonophore. Scale equals A—2 mm; B, G— 500 µm; C—100 µm; D—200 µm; E—13 µm; F—1 mm; H–J—50 µm.