Periphragella undetermined

Periphragella sp. (Figures 7–8) Material. Many dead specimens of Periphragella sp. and fragments with Ferro-Manganese covering of their frameworks. RV ‘Akademik Mstislav Keldysh’—22, sta. 2316, trawl, N from the Piip Volcano, 55 o 36.08’–35.0’ N 167 o 23.04’ –24.46’ E, depth 4294– 4200 m. Dead skeleton of Periphragella with numerous specimens of Caulophacus (C.) hyperboreus (Rossellidae) on it. RV ‘Akademik M.A. Lavrentyev’—75, ROV ‘Comanche’: sta. 16, off Piip Volcano, 55.5774 o N 167.3258 o E, depth 4277–4278 m; sta. 22, spec. 7, Piip Volcano, 55 o 30’36.1” N 167 o 19’27.1” E, depth 3578 m. Body. The most complete specimens reach about 150 mm high with central atrial cavity from 30 mm to more excavated specimens with walls 1–2 mm in thickness, the lateral tubular outgrowths are about 8 mm in diameter with walls 1–1.5 mm thick. Framework. The framework is multilayered, 2–4 layers. Remarks. Unlike the previously described species— Periphragella spiridonovi sp. nov. —these fossil fragments have multilayered walls, which does not allow to refer them to the same species. Nevertheless, their generic assignment is doubtless. The dead dictyonal skeletons of Periphragella were found to play an important role as substrata on silt bottom. Being relatively lightweight, having rigid dictyonal skeleton structure, the dead skeletons of Periphragella drift off from the rocky areas (Periphragella itself inhabits hard substrata only) to the surface covered by muddy silt and thus provide hard substrata for other benthic organisms, for instance for other hexactinellids—for example, numerous specimens of Caulophacus (C.) hyperboreus (Tabachnick et al., 2023).