Molpadia musculus

Background

Molpadia musculus is found in the northern Atlantic Ocean, living buried in mud on the seabed with its anterior (mouth end) directed downwards and its posterior (rear end) at the sediment surface. It can be very common, with up to 220 individuals per square metre recorded. As a detritivore, it ingests mud, extracts nutritious fragments as the mud passes through its gut, and voids the rest onto the sediment surface. The mud contains high levels of bacteria, archaea, and other prokaryotes, especially in the top centimetre.

Research has shown that the micro-organisms in the sea cucumber's gut differ from those in the surrounding sediment, leading to the hypothesis that the gut fauna live as commensals, to the mutual benefit of both. It appears that a gut community of bacteria is not needed where sediment is rich in organic matter, as in the Nazaré Canyon, but is necessary where sediment quality is poor, as in the Cascais Canyon. Like other sea cucumbers, Molpadia musculus has separate sexes, with external fertilization; the larvae are planktonic and settle on the seabed when sufficiently developed, undergoing metamorphosis into juveniles.