English: Basal spicule of the deep-sea glass sponge Monorhaphis chuni
(a) Young specimens are anchored to the muddy substratum by one single giant basal spicule (gbs). The body (bo) surrounds the spicule as a continuous, round cylinder. (b) Schematic representation of the growth phases of the sessile animal with its GBS (gbs) which anchors it to the substratum and holds the surrounding soft body (bo). The characteristic habitus displays linearly arranged large atrial openings (at) of approximately 2 cm in diameter. With growth, the soft body dies off in the basal region and exposes the bare GBS (a to c). (c) Part of the body (bo) with its atrial openings (at). The body surface is interspersed with ingestion openings allowing a continuous water flow though canals in the interior which open into oscules that are centralized in atrial openings, the sieve-plates. (d) M. chuni in its natural soft bottom habitat of bathyal slopes off New Caledonia (photograph taken by Michel Roux, University of Reims; reproduced with permission). The specimens live at a depth of 800–1,000 m [23]. In this region, the sponge occurs at a population density of 1-2 individuals per m2. The animals reach sizes of around 1 m in length. (e) Drawing from different hexactinellids.