Fig 5. Views of lithistid reef at Stone Sponge Seamount (SSS).

(A-B) General view of the lithistid mounds, showing intertwined growth and a complex 3D structure. Translucent "a-b" and "c-d" lines indicate sponge clumps measuring respectively 118 cm and 94 cm, relative to sediment bottom. Note the occurrence of dead sponges (d) and bare skeletal remains (sr) buried in the sediment. A squat lobster (s) is also shown. (C) View of sponge plates, showing how the sediment rain accumulates on the convex (in = inhalant) side, while the concave (ex = exhalant) side has no silt. The abundant hispidating spicules on the inhalant side appear to facilitate the accumulation of sediment on the sponges. Note the presence of the starfish Peltaster placenta, thought to be also a suspension feeder. (D) Common invertebrates growing on the lithistid are hydroids (h), the alcyonacean octocoral Muriceides lepida (m), and the scleractinian coral Desmophyllum dianthus (c) with abundance of newly settled recruits (r). (E) Group of lithistid individuals laying on the sediment. Note the superimposing structure of the clump. One of the individuals is already dead (d), buried in sediment. On the other sponges, growth marks (g) are seen on the bodies, probably reflecting periodical pulses of food and silicate in the sponge habitat. (F) Aggregation area seriously damaged, with large sponges broken and laying on the side (arrows) while being buried under the sediment rain.