Symplectoscyphus aggregatus Jaderholm 1917

Symplectoscyphus aggregatus (Jäderholm, 1917)

(Fig. 12 B)

Symplectoscyphus aggregatus — Peña Cantero, 2010a: 35 (synonymy).

Material examined. Stn 112, strongly polysiphonic stem 12 mm high, three incipient monosiphonic and unbranched stems up to 4 mm high on pebble (NIWA 117571); Stn 198, fragment 6 mm long, in bad condition (MNCN 2.03/632).

Description. Stem 12 mm high, strongly polysiphonic, ca. 2 mm in diameter at base. Planar rhizoidal hydrorhiza, indicating attachment on hard substrate. Hydrothecae alternately arranged in one plane, forming two longitudinal rows, strongly packed, branches with planar aspect. Hydrothecal distal part surpassing basal part of following hydrotheca and about half of alternate one.

Lower-order branches originating at hydrothecal base, on one side of preceding branch. In some cases branching alternate.

Hydrotheca (Fig. 12 B) almost cylindrical, straight, directed upwards, adnate to internode in more than half (usually about two thirds) of adcauline length. Free portion of adcauline hydrothecal wall roughly straight. Abcauline wall straight or with slight basal swelling. Hydrothecal aperture directed upwards, provided with three blunt cusps.

Measurements (in µm). Hydrothecae: length of abcauline wall 440–450, length of free adcauline wall 210–250, length of adnate adcauline wall 220–240, diameter at aperture 160–180, diameter at diaphragm 120, maximum diameter 220. Cnidome: larger microbasic mastigophores, range 10.5– 11 x 2.5–3, mean 10.7±0.2 x 2.7±0.2 (n=10); ratio, range 3.5–4.4, mean 4.1±0.3 (n=10).

Remarks. Although, as indicated above, the hydrothecae are alternately arranged in one plane and form two longitudinal rows, there are irregularities. In some parts of the colony, there is a tendency for the hydrothecae of each row to be slightly alternately arranged, consequently forming four longitudinal rows. In other parts, there is a change in the plane formed by the two rows of hydrothecae.

In the type material of this species, the hydrothecal distal part almost reaches the basal part of the following hydrotheca and approximately the middle of the adcauline wall of the alternate one (cf. Peña Cantero et al. 2002). In the material here studied the hydrothecae are even more packed, clearly overpassing the basal part of the following hydrotheca (cf. Fig. 12 B).

Ecology and distribution. Shelf species (Peña Cantero 2010a), collected at a depth of 150 m (Jäderholm 1917); present material found between 222 and 351 m.

It was known only from off Graham Land, in the Antarctic Peninsula region (Jäderholm 1917), in West Antarctica. Present material is the first record from the Ross Sea, collected off Cape Adare and Adare Peninsula, pointing to a circum-Antarctic distribution.