Pluteus

·noun The free-swimming larva of sea urchins and ophiurans, having several long stiff processes inclosing calcareous rods.

pluteus
plŭtĕus, i, m., less freq. plŭtĕum, i, n. I A penthouse , shed , or mantlet , made of hurdles cove...

A New Latin Dictionary by Charlton T. Lewis Ph.D. and Charles Short, LL. D.
pluteus
pluteus ī, m —As a cover for besiegers, a penthouse, shed, mantlet: pluteos ad alia opera abduxerun...

An Elementary Latin Dictionary