Science Art: Holothuria tubulosa (Sjogurka stor ugglan, a sea cucumber) from Nordisk Familjebok, 1919.

Scientific illustration of a sea cucumber
Scientific illustration of a sea cucumber

The sea cucumber doesn’t look like much until you really look at it. They’re complicated little creatures. They have complicated little parts. In this case, they are labeled as: a – Tentacles, b – Cloaca, c – Ambulacral feet on the ventral side, d – Papillae on the back.

This diagram came from the classic encyclopedia Nordisk Familjebok, which you can peruse in this subsection here, on Wikimedia Commons.