Hydrodendron chilense

Description. Colony arising from a creeping, branching, anastomosing hydrorhiza; perisarc with irregular, thick, internal projections. Hydrocauli upright but small, not surpassing ca. 3 mm in height. Stems monosiphonic, divided into internodes by transverse constrictions of the perisarc. Internodes broadly cylindrical, of varied length, each with a proximal bulge, with or without a lateral apophysis supporting the following internode or a hydrophore, and with or without a nematotheca; perisarc moderately thick, surface smooth to locally wrinkled. Branching pattern clearly sympodial, with additional internodes or hydrophores given off at acute angles from the apophyses of preceding internodes; apophyses not in one plane, but arising from any side of the stems. Hydrophores of varied length, with a basal bulge, widening gradually distally to merge into hydrotheca; both separated by a thin diaphragm projecting into the lumen of hydrophore. Hydrotheca tronconical, obviously deep, rim flaring, margin conspicuously everted. Ring of desmocytes irregular, placed at a fair distance above diaphragm. Hydranths reduced to mere buds, possibly due to reproductive exhaustion. Nematothecae irregular and scarce, given off from both the stolon and some stem internodes or hydrophores; beaker shaped, rather large and deep, with a distinctly everted rim; nematophores long (up to ca. 2 mm) and slender, with solid core and a large, distal capitulum. Gonothecae, male in the present material, borne abundantly on the stolon; elongated tubular for most of their length, tapering abruptly proximally into a short, indistinct pedicel; truncate distally above a narrowed neck; walls provided with 7 – 8 distant, spiral grooves.

Remarks. The new species is characterized, among others, by the presence of spirally twisted gonothecae. Four congeners, namely H. alternatum (Fraser, 1938), H. expansum (Fraser, 1948), H. mirabile (Hincks, 1866), and H. sympodiformis Millard & Bouillon, 1974, share the same character. Both H. alternatum and H. expansum were described from the eastern Pacific. Similarly to H. chilense, the internodes of the former are given off sympodially at sharp angles from the preceding internodes, but there is reportedly a characteristic alternate arrangement of the hydrothecae along both sides of the stems and, when present, side branches (Fraser 1938), a situation not met in the new species. In addition, H. alternatum is further distinguished through the apparently exclusive and abundant occurrence of nematothecae on its stems [“ commonly one to each pedicel ” (sic)], and its uncommon ability to give rise to gonothecae, not only from the stolon, but also from the hydrophores and the stem internodes. Unlike H. chilense, H. expansum is a species with polysiphonic stems, collinear internodes delimited by oblique nodes, and large gonothecae with strongly ringed walls, which are given off “ from the fascicled portion of the stem, projecting at right angles to it ” (Fraser 1948).

Distribution in Chile. Only known from Corral. 15. The stems of H. mirabile were originally described as “ rudely annulated at the base, and jointed at intervals throughout ”, with the “ branching […] usually consisting of a single division of the stem ”, at most two (Hincks 1866). A modern illustration of the neotype (BMNH 1899.5.1.169) is given by Cornelius (1995 a, Fig. 73 C), who showed the characteristic sympodial growth pattern of the colonies. The description and illustration of the gonotheca goes back to Hincks (1868). It is worth underlining that the description of H. mirabile provided by Cornelius (1975) resulted undoubtedly from pooled data based, among others, on material dealt with earlier by Ritchie (1908, as Ophiodissa caciniformis) and Millard (1957, 1966 b). In Cornelius’ (1975, 1995 a) view, widely held by subsequent authors, H. caciniformis represents not more than a junior synonym of H. mirabile, and it appears that he mainly focused his attention to the similarities between them, rather than to certain, though not less important differences that are related to their respective growth patterns. Indeed, his illustration (Cornelius 1975, Fig. 14 A) of the paralectotype of O. caciniformis shows a species with almost collinear internodes delimited by slightly oblique nodes, thus differing from the sympodial growth pattern characteristic of Hincks’ species. In addition, the type material of H. caciniformis is sterile. A careful check of the relevant literature shows that specimens with both sympodial [e. g. Babić (1913), García Corrales et al. (1978), Rho & Park (1980), Hirohito (1974, 1995), Ramil Blanco & Iglesias Diaz (1988), Altuna (1994), Peña Cantero & García Carrascosa (2002)] and alternate [e. g. Millard (1957, 1966 b), Ralph (1958), Vervoort (1959), Gili (1986), Medel et al. (1998), Vervoort & Watson (2003)] growth patterns were equally included in either H. mirabile or H. caciniformis. It therefore becomes obvious that some of the records cited above, especially certain based on sterile material, are either incorrect or belong to unidentifiable species. - total length 1350 – 1720 (♂) 830 – 855 (♂) 670 – 830 (♂) 630 – 800 (♀) – ca. 1120 (♀) FIGURE 6. A, B: Sertularella asymmetra sp. nov. — colony fragment (A); hydrotheca in lateral (B 1) and apical (B 2) views. C: Sertularella blanconae El Beshbeeshy, 2011 — colony fragment. D, E: Sertularella curta sp. nov. — colony fragment (D); hydrotheca in lateral (E 1) and apical (E 2) views. F, H: Sertularella pauciramosa sp. nov. — colony fragment (F), and comparison with S. polyzonias (Linnaeus, 1758) (G); four hydrothecae (H). Scale bars: 200 µm (B, E, H), 1 mm (A, C, D, F, G). FIGURE 7. A: Sertularella asymmetra sp. nov. — female (A 1) and male (A 2) gonotheca; B: Sertularella blanconae El Beshbeeshy, 2011 — male gonotheca. C: Sertularella curta sp. nov. — male gonotheca. D: Sertularella pauciramosa sp. nov. — male (D 1) and female (D 2) gonotheca. E, F: Symplectoscyphus flexilis Hartlaub, 1901 — colony fragment (E 1) and hydrotheca (E 2); gonotheca (F). G ‒ J: Symplectoscyphus semper sp. nov. — stem fragment with beginning of side branch (G 1), and portion of cladium (G 2); hydrotheca (H); gonotheca (I), and details of the distal part (J). K ‒ M: Symplectoscyphus cf. subarticulatus (Coughtrey, 1875) — colony fragment (K); hydrotheca (L); gonotheca (M). Scale bars: 200 µm (H, L), 500 µm (A ‒ D, F, I, J, M), 1 mm (E, G, K).

Etymology. The new species is named after the country of its origin.

Material examined. Corral, Chaihuin / Huiro, lat. - 39.95000, long. - 73.61667, 17. x. 2011, 8 ‒ 12 m, sample 36: a male colony on seaweed (holotype: MHNG-INVE- 86227). France, Port d’Alon creek, lat. 43.146369, long. 5.707545, 20. v. 2009, 0.5 m, sample HRG- 0020: a female colony of H. mirabile (Hincks, 1866) on seaweed. France, Cap Taillat, lat. 43.174040, long. 6.640635, 09. vi. 2011, 0.5 m, sample HRG- 0567: a male colony of H. mirabile on seaweed. France, Martinique, Anse Dufour, lat. 14.527162, long. - 61.090033, 12. i. 2014, 0.5 m, sample M 277: several colonies, some fertile, of H. mirabile on seaweed.