Opisthobranch of the Week Data
The onchidids are intertidal marine slugs, oval in outline, with a dorsally arched notum bearing warts and papillae. There are glands which apparently secrete noxious fluids at the sides of the body, and tentacles which bear eyes at their tips. Onchidium sp. 1 is considered to be very common on Okinawa's main island. These well-camouflaged pulmonate snails are commonly found during all months of the year here. Relatively few of the animals have been collected, if for no other reason than they are so commonly encountered in the intertidal zone during low tide conditions. I've added several different images of the same animal, one showing its appearance on a rock of the tidal flat as exposed to air.
This week's featured animal could perhaps be Onchidium verruculatum, a common species throughout the Indo-Pacific. I'm not certain if there is but a single species here on Okinawa or several species. The animals appear to be quite variable in both color and appearance of the upper notum. For the time being I'll call this animal Onchidium sp. 1. It's secreted in crevices during high waters and emerging at low tide to graze over algae-covered rock. The featured animal was found during a modest low daytime tide on the upper surface of an alga (Ulva sp.) covered rock.
Onchidium sp. 1 is of course not an opisthobranch but is rather an opisthobranch-appearing gastropod, found in Okinawan waters. I've previously featured several of these opisthobranch-appearing slugs in the past. Five of these non-opisthobranchs are featured at: