As tedious and eye-straining as it is to clean my Ceratostoma foliatum shells of epibionts (So I can get accurate weights), I keep coming across all sorts of wonders.
Yesterday my prize was a tiny slipper limpet (Calyptraeidae). It is too small (3mm in length) to be sure of an identification, but Crepidula sp. seems most likely due to the shape of the ‘shelf’ on the inside of the shell. Once I peeled him off (chipping his shell), he motored around the dish a good pace, making photography difficult. Once I flipped him upside-down, he struggled valiantly, so I still had a hard time capturing his charm.
Snails in the family Calyptraeidae are not true limpets, but have convergently evolved the same low profile, high expansion shells good for sticking strongly to the substrate. The limpet morphology has evolved at least seven times (depending on the phylogeny you use) in Gastropods.
Calyptraeids are sequential hermaphrodites, most famous for the stacking Crepidula fornicata, in which many smaller males stack on top of a larger females in a mating aggregation. As the males grow, they transform into females and can start their own stack. This little guy is probably too young to be sexually mature, and is perhaps more properly addressed as ‘it’.
The gills are so large and prominent because most Calyptraeids are filter feeders, using their gills to trap plankton, and sucking it in their mouth on a stream of mucous from their radula.