Prey capture and digestion in the carnivorous sponge Asbestopluma hypogea (Porifera: Demospongiae)

Abstract

Asbestopluma hypogea (Porifera) is a carnivorous species that belongs to the deep-sea taxon Cladorhizidae but lives in littoral caves and can be raised easily in an aquarium. It passively captures its prey by means of filaments covered with hook-like spicules. Various invertebrate species provided with setae or thin appendages are able to be captured, although minute crustaceans up to 8 mm long are the most suitable prey. Transmission electron microscopy observations have been made during the digestion process. The prey is engulfed in a few hours by the sponge cells, which migrate from the whole body towards the prey and concentrate around it. A primary extracellular digestion possibly involving the activity of sponge cells, autolysis of the prey and bacterial action results in the breaking down of the prey body. Fragments of the prey, including connective cells and muscles, are then phagocytosed and digested by archaeocytes and bacteriocytes. The whole process takes 8–10 days for a large prey. This unique feeding habit implies the capture and digestion of a macro-prey without any digestive cavity. It would appear to be an adaptation to life in deep-sea oligotrophic environments. Carnivorous sponges provide actual evidence, through a functional example, that a transition is possible from the filter-feeder poriferan body plan towards a different organizational plan through loss of the aquiferous system, a transition that has been hypothesized for the early evolution of Metazoa.