Tubular Sea Cucumber

On a sandy bottom, at the edge of a seagrass bed, a brown mass bristling with papillae advances so slowly it seems motionless. At the front, its short tentacles nonetheless draw sediment toward its mouth.

Holothuria tubulosa selects elements rich in organic matter, ingests them, then rejects the sediment in recognizable cords. This passage through its digestive tract thus rearranges the sea floor surface and participates in the recycling of organic matter.

But this apparently simple body can hide another animal. The pearlfish, Carapus acus, sometimes uses H. tubulosa as shelter: this slender fish enters through the anus, stays in its intestine then exits to feed.

Even stranger, an experiment conducted on ten H. tubulosa revealed what this body is capable of when artificial transverse fission is induced. Surviving portions regenerated the missing structures, even reforming a functional mouth or anus.

The experiment demonstrates a remarkable capacity for regeneration, but not that the species naturally divides this way in the sea. Under your lamp, nothing betrays the fish that might hide there nor this power of reconstruction: only a sea cucumber slowly pursuing its path across the sand.