Silicularia pedunculata Jaderholm 1904

Silicularia pedunculata (Jäderholm, 1904)

(Fig. 3U– Y, Z3)

Campanularia pedunculata — Jäderholm, 1904: vi.

Silicularia pedunculata — Jäderholm, 1905: 18, pl.7 figs 4–7. — Nutting, 1915: 90, pl. 24 figs 6–8. — Blanco, 1967a: 229. — Ralph, 1956: 290.

Orthopyxis pedunculata — Ralph, 1956: 291.

not Silicularia pedunculata — Fraser, 1938: 39.

Silicularia divergens Hartlaub, 1905: 578, fig. B2.

Material examined. Stn. PNS — 15.ii.2011, Ant.16/2011 (0–1 m): male and female colonies detached from boulders (MHNG-INVE-79781). Stn. SHO — 17.ii.2011, Ant.24/2011 (1 m): male and female colonies detached from boulders (MHNG-INVE-79779).

Description. Creeping, branched and anastomozing hydrorhiza giving rise to crowded hydrothecate pedicels and gonothecae; pedicels 1–8 mm high, 120–205 µm wide; perisarc either spirally twisted throughout, or only basally and/or distally, smooth elsewhere; a subhydrothecal spherule. Hydrotheca inverted conical, radially symmetrical, 720–995 µm high, walls smooth, perisarc slightly thickened basally to delimit a subhydrothecal chamber, elsewhere thin; rim even, circular, aperture 545–670 µm wide. Hydranths with big, rounded proboscis, 26–28 tentacles, and no "caecum"; able to retract completely within their hydrothecae. Gonothecae narrow and elongate, tapered proximally and distally, borne on long, spirally grooved pedicels; aperture terminal, slit-like; female 5–6 mm long, 545–665 µm wide; male 3.5–4.5 mm high, 490–605 µm wide. Gonophore, a medusoid with four radial canals, perradial gonads and no mouth; embryonic development takes place within the female gonotheca, eggs divide at least up to the morula stage. Nematocysts: likely two types of microbasic mastigophores (none seen discharged), large capsules (8.0–9.1) × (2.4–2.7) µm and smaller capsules (6.3–6.6) × (1.7–1.8) µm.

Remarks. Jäderholm (1905) is probably right in including S. divergens Hartlaub, 1905 in the synonymy of his species, and we follow his view. The sole difference between the two relies in the comparatively thickened perisarc in S. divergens. The sterile material from Panama examined by Fraser (1938) is unidentifiable and most probably do not belong to the present species, due to its geographically remote origin.

Based on characters of the trophosome11, Ralph (1956) recognized Jäderholm's species as a member of Orthopyxis L. Agassiz, 1862, though she acknowledged that the morphology of its gonothecae would require an emendation of the diagnosis of that genus12.

However, we maintain the present species in Silicularia Meyen, 1834 until more material, especially with thickened hydrothecae (as in S. divergens), becomes available for study. It is likely that such specimens would have hydrothecae bilaterally symmetrical and hydranths no longer capable of completely retracting within their corresponding thecae, and possibly provided with a basal "caecum".

Geographical distribution. South Shetland islands (Jäderholm 1904, 1905, present study), South Georgia (Hartlaub 1905).