Hydractinia armata Fraser 1940

Hydractinia armata Fraser, 1940 (Fig. 3C–E) Hydractinia armata Fraser, 1940: 39, pl. 1 fig. 1a–f. Type locality . USA: California, San Mateo County, Montara (misspelled as Mantara), encrusting corallines in tidepools (Fraser 1940: 40). Material . IHAK50, on Balanus glandula , with gonophores (BHAK 2474), RBCM 026-00035-001. Description . Colony stolonal; reticulating hydrorhiza coalescing into encrusting mat, on barnacle shell. Spines high (0.8–over 1 mm), mostly smooth but occasionally with external transverse lines; internal annular ridges visible from certain angles, tapering distally, straight, or slightly curved distally, tips blunt, arranged in loose clusters, or scattered. Gastrozooids large (over 2 mm high), 9–12 tentacles in two close whorls, hydranth with dome-shaped hypostome. Tentaculozooids not observed. Gonozooids smaller; about 2/3 height of gastrozooids, gonophores arising about half-way up the body of the zooid in two irregular whorls, on short pedicels, about 4–6 in number; sporosacs ovoid or spherical. Remarks . The present material conforms morphologically to type specimens of Hydractinia armata Fraser, 1940 (Lectotype: RBCM 976-00213-002 and paralectotype: BCPM 976-00213-001) held at the Royal BC Museum, designated by Calder & Choong (2018) from syntype material. The species is recognized as valid (Cairns et al. 2002, Mills et al. 2007, WoRMS Editorial Board 2026). Hydractinia armata is distinguished from its congeners in having numerous, long, slender, and hollow spines with a series of annular thickenings (Fraser 1940). According to Fraser, these annular thickenings are only visible when the tops of the spines are broken off. In the present material and in the type specimens, the internal annular ridges (thickenings) were also visible using transmitted light microscopy with contrast enhancement, if the specimen is viewed from certain angles (illustrated in Fig. 3E). In all material examined for this study, including the type specimens, the spines vary in shape from almost cylindrical, with a short tapering point to being variously curved (although never bent at acute angles), with longer tapering points. Fraser (1940) described encrusting colonies of H. armata from nonmotile hosts (coralline algae) in the intertidal zone. The present sample was collected on Balanus glandula . Miglietta & Cunningham (2012) consider encrusting Hydractiniidae on nonmotile hosts to be exceptions to reticulate colonies, as encrusting species such as Schuchertinia milleri (Torrey, 1902) occur on rougher environments as hermit crab specialists. However, coralline algae can withstand strong hydrodynamic forces (Kolzenburg et al. 2023), and Balanus glandula functions across various hydrodynamic conditions (Geierman & Emlet 2009), such as those found in the central coast of British Columbia where Calvert Island is located. The present record in the central coast of British Columbia represents the northernmost recorded occurrence of H. armata to date. Reported distribution . Pacific coast of North America: Montara, San Mateo County, California, USA (Fraser 1940); southwards to San Nicolas Island, California (Fraser 1948), northwards to Race Rocks, Strait of Juan de Fuca, British Columbia (Brinckmann-Voss 1996).

Source: Zenodo (CERN open repository) PDF: N/A Original Link: https://doi.org/10.5281/zenodo.23914509