Sertularella robustissima Horia R. Galea & Dirk Schories & Verena Häussermann & Günter Försterra 2017, sp. nov.

Sertularella robustissima Galea, Häussermann & Försterra, sp. nov.

Fig. 16 A-D

Sertularella argentinica. – Galea, 2007: 59, fig. 14A-C. – Galea et al., 2007c: 312, fig. 3I [non Sertularella argentinica El Beshbeeshy, 2011 = Sertularella clausa (Allman, 1888)].

Holotype material: MHNG-INVE-53268; Chile, Región de Aysén, Guaitecas Archipelago, NW of Melinka, -43.88333° -73.71667°, 10-15 m, coll. HSFS, HF1; 08.03.2005; a 8 cm high, sterile colony.

Additional material: HRG-0611; Chile, Región de Magallanes y de la Antártica Chilena, Canal Copihue, -50.33979° -75.37834°, 16 m, coll. HSFS, HF16, lot #084; 16.04.2013; a 8 cm high, sterile colony.

Diagnosis: Colonies bonsai-like, with strongly fascicled stems and dark brown perisarc; internodes slightly demarcated, short, almost collinear; hydrothecae short, tubular, curved outwards, marginal cusps separated by large, shallow embayments.

Etymology: A superlative of the Latin rōbustus, -a, -um, with reference to the sturdiness of the stems of this species.

Description: Colonies bonsai-like, up to 8 cm high, arising from well-developed, rhizoid mass of stolonal fibers firmly attached to substrate; composed of single, thick, strongly fascicled stem, unbranched in lower half, and forming numerous, irregularlydirected side branches in upper half; main branches polysiphonic proximally, giving rise to bundles of 2-4 basally parallel, distally diverging, monosiphonic branchlets, up to 3 cm long, each branched again up to 2 times; branching almost regular, alternate, every 3 consecutive hydrothecae (rarely 2). Both stem and branches delimited into rather short, almost collinear internodes by means of oblique nodes slanting in alternate directions; a hydrotheca, or a hydrotheca and a lateral apophysis below its base, confined to the distal end of each internode. Hydrothecae rather short, tubular, distinctly curved outwards, adnate to the corresponding internode for slightly more than half their length; free adaxial wall smooth to slightly undulated; aperture with 4 small, triangular cusps separated by very shallow embayments; operculum composed of 4 triangular flaps with concentric striae; 1-2 closely-set renovations of the margin. Gonothecae unknown.

Dimensions: Internodes 310-493 μm long and 310- 352 μm wide at nodes. Hydrothecal free adaxial length 337-393 μm, adnate adaxial length 356-477 μm, abaxial length 477-573 μm, maximum width 399-444 μm, diameter at aperture 337-376 μm.

Remarks: The colony structure is illustrated in both Galea (2007, fig. 14A) and Galea et al. (2007c, fig. 3I).

Distribution: Chile – Región de Aysén [Guaitecas Archipelago (Galea, 2007, as S. argentinica)]; Región de Magallanes y de la Antártica Chilena [Canal Copihue (present study)].