Halecium exaggeratum Pena Cantero, Boero & Piraino 2013

Halecium exaggeratum Peña Cantero, Boero & Piraino, 2013

(Fig. 5 K)

Halecium exaggeratum Peña Cantero, Boero & Piraino, 2013: 743 –745, fig. 6d, e. Halecium sp.1 Peña Cantero, 2008: 455 –456, fig. 1J.

Halecium sp. Peña Cantero & Vervoort, 2009: 85, fig. 1I.

Halecium delicatulum — Vervoort, 1972b: 341 –343, Fig. 2 a.

Halecium antarcticum — Blanco, 1984: 7 –10, pl. 4 figs 8–11, pl. 5 figs 12–13 (in part).? Halecium tenellum — Hartlaub, 1904: 13 –14, pl. 1 fig. 5.

? Halecium delicatulum —Blanco & Bellusci de Miralles, 1972: 7 –10, pl. 1 figs 3–5.

Material examined. Halecium tenellum by Hartlaub (1904). RBINS Code 563502, INV 40984, Expédition antarctique Belge S. Y. Belgica 1897–1899, Stn 243, 27 April 1898, 70°48’S, 91°54’W (Bellingshausen Sea), 350 m, one stem c. 8 mm high, on tube of polychaete.

Diagnosis. Monosiphonic, scarcely branched, slightly geniculate stems, up to 15 mm high. Hydrothecae alternately arranged in one plane. Stem giving rise either to paired or single branches originating from hydrophore of primary hydrothecae. Hydrotheca at the end of extremely long, free hydrophore. Hydrothecal diameter widening distally; rim everted. A secondary hydrotheca present. Gonothecae flattened, triangular, narrowing at base and opening along an irregular slit at apex. Cnidome consisting of microbasic mastigophores? and microbasic euryteles?

Description (H. tenellum by Hartlaub). Stem c. 8 mm high, unbranched, and provided with nine hydrothecae. Internodes relatively long and slightly arranged in a zigzag pattern (Fig. 5 K).

Hydrothecae placed at the end of long free hydrophores (Fig. 5 K); ratio between adcauline length of hydrophore and diameter at diaphragm c. 1.7. Hydrophores straight, regularly diverging from internode. Hydrothecae considerably surpassing distal node of internode (Fig. 5 K).

Hydrotheca low, distinctly widening distally, more at adcauline side (Fig. 5 K). Rim everted. Hydrothecal height slightly smaller at abcauline side. No pseudodiaphragm. Three hydrothecae with one secondary hydrotheca resting on long hydrophores (Fig. 5 K).

Measurements (in µm). Hydrothecae: diameter at aperture 190–200, diameter at diaphragm 125–130, height 30–50. Cnidome: microbasic euryteles? with rounded ends (7 x 3) and microbasic mastigophores? with sharp ends (6.5–7 x 2).

Remarks. For a complete description and discussion of this newly described species see Peña Cantero et al. (2013).

The material assigned to Halecium delicatulum by Vervoort (1972b) belongs to H. exaggeratum. It agrees in colony structure, with long and thin internodes (1080–1215 µm long and 105–115 µm wide), arranged in zigzag fashion, and in the shape and size of the hydrothecae (215–245 µm in diameter at aperture and 48–55 µm high), resting on very long hydrophores. Although gonothecae were not present in the material studied by Peña Cantero et al. (2013), Vervoort’s (1972b: fig. 2a) material is provided with them, being described as “flattened, triangular structures, narrowing at the base and opening along an irregular slit at the apex”. They are 675–745 µm high and 510–530 µm wide.

Part of the material assigned to H. antarcticum by Blanco (1984) seems to correspond to H. exaggeratum. As Peña Cantero (2013) pointed out, that record is based on material from different localities and seems to be based on specimens of several species. Peña Cantero (2013) indicated that the material represented in pl. 4 figs 10 and 11 and pl. 5 fig. 13 by Blanco (1984) could belong to H. frigidum. I believe now that Blanco’s material represented in pl. 5 fig. 13 undoubtedly belongs to H. exaggeratum. This material was also provided with gonothecae, c. 649 µm high and 568 µm wide.

The material assigned to H. delicatulum by Blanco & Bellusci de Miralles (1972) also seems to correspond to H. exaggeratum, agreeing in colony structure, with long and thin internodes (920–1290 µm long and c. 130 µm wide), shape and size of the hydrothecae (180–240 µm in diameter at aperture, 110–150 µm diameter at diaphragm, and 37–92 µm high) and, particularly, in the distinctly long hydrophores (ratio between adcauline length of hydrophore and diameter at diaphragm 2.3). One of the two stems studied by Blanco & Bellusci de Miralles (1972) differs in being slightly polysiphonic basally, but it was 30 mm high, two-fold the maximum height reported for H. exaggeratum and, therefore, this difference could be related to development. Concerning the absence of paired branches, this also is present in part of the material studied by Peña Cantero et al. (2013).

The examination of Hartlaub’s material of H. tenellum Hincks, 1861 has clearly shown that it does not belong to Hincks’ species. Instead it seems to be conspecific with H. exaggeratum. Although reported from Antarctic waters in several occasions, Halecium tenellum seems to be absent from this area (see also below under H. interpolatum).

Ecology and distribution. Halecium exaggeratum has a circum-Antarctic distribution (cf. Peña Cantero et al. 2013), being known from Arthur Harbour, Palmer Archipelago (Vervoort 1972b), off Livingston Island, the South Shetland Islands area (Peña Cantero 2008), Bransfield Island, Antarctic Peninsula (Peña Cantero & Vervoort 2009) and Rod Bay and Tethys Bay, Ross Sea (Peña Cantero et al. 2013). Hartlaub’s (1904) material was collected in the Bellingshausen Sea and that of Blanco & Bellusci de Miralles (1972) off Peter I.