Question

Are there any animals with an odd number of feet? Humans have two feet, dogs have four and spiders have eight. By feet, I mean external appendages. I realize starfish have five arms, but it turns out these arms are not actually used for locomotion.

Answer 1

snails and slugs come closest although the 'foot' is an integral part of their body, not an appendage

Answer 2

Here's a bit more information for you:

If one defines 'leg' as a bodily appendage, usually articulated, and used for locomotion, the short answer is 'no.' However, some would argue that gastropod molluscs (snails and slugs) have one 'leg' (actually called a 'foot') and/or that starfish have five (and sometimes a larger odd number) of limbs (usually referred to as 'arms'). However, these are not legs in the true sense, as (1) a gastropod's 'foot' is an integral part of their body, not an appendage per se, and (2) a starfish's 'arms' are not directly used for locomotion; rather they move about by the action of the numerous 'tube feet' that protrude from the ventral surface of the arms.
Hope this helps,

Sra