Although they look like they are nudibranchs, the two snail species featured in today’s posting are surely not nudibranchs, even if one is kind of sluggish in form and fashion. The larger of the two, Gastropteron pacificum, is a bubble shell, meaning it has a shell that looks quite like a soap bubble and it is about as durable. When sitting on the bottom, the animal is about the size of a grape. The sides of the animal’s foot are expanded into two long lateral lobes that are normally folded up over the animal, but virtually nothing of the animal is normally visible as it is generally covered in a mucous sheet which, in turn, is covered by sediment particles. The animal looks like a lump of mud on a bottom that is covered in lumps of mud, and so this is pretty good camouflage.
Gastropteron pacificum, a stationary lump of pseudo-mud. The pink structure is a fleshy, tubular, siphon that brings in breathing water.
Gastopteron pacificum individuals are found frequently in the spring in waters of the North American “Pacific Northwest” and if a diver ventures into its gorpy, mucky, muddy habitat – otherwise known when I was working in these areas, as a “Shimek study site” – one can often see the trails left by these little guys as they move around, presumably in search of food or a mate.
Gastropteron pacificum, leaving a trail in the mud as it crawls from there to here.
They are probably detritivores, as they are reported to eat detritus and diatoms in the laboratory, but I am not sure what they eat in nature, and neither, to the best of my knowledge, is anybody else. I don’t think they have been studied in any detail which, if true, is quite a pity as they are neat little critters. When something startles them – a diver (me) in my case for the photograph, or the presence of a bottom-feeding fish, such as the ratfish, Hydrolagus colliei, the little snail unfolds its foot flaps and flaps away. They are quite strong swimmers and this appears to often be an effective escape response.
Hydrolagus colliei
This “rat fish,” or “chimerid,” is a cartilaginous-skeletoned fish but obviously not a shark. Individuals in this particular species can reach about 70 cm (28 inches) in length. Rat fishes are some of the most common predators in the soft-sediment ecosystems of the NE Pacific, and some of my unpublished data indicate they feed on mollusks, annelids, and echinoderms.
A Gastropteron pacificum individual.
This little animal is swimming away from the most fearsome and horrific predator of all, a diver – in this case, of course, me. I was sensed, probably by my water disturbances, and it then took off, and stayed waterborne for about 2 minutes. Although Gastropteron swimming appears to be undirected, given the currents in the region, it will likely cover some distance before it quits swimming and falls back to the bottom.
If the Gastropteron is successful in its life, it find a good friend and they will do the snaily version of the “wild thing” resulting some time later in the deposition of some jelly-like “egg masses” attached to the bottom. These are filled with small fertilized eggs (zygotes) that develop within the misnamed egg mass, which eventually dissolves releasing the larvae into the plankton.
A group of Gastropteron “egg,” actually embryo, masses. I don’t know if all of these are deposited by one individual or if they aggregate during spawning to deposit the jelly-like masses (many snails in this region do form spawning aggregatations).
However, they don’t get a break! There is a small sacoglossan slug, Olea hansinensis, in the area that searches out and eats the eggs of Gastropteron and its relatives.
Olea hansinensis.
This is a small sacoglossan slug that eats eggs of cephalaspidean snails, such as Gastropteron. This one was about 3 mm (1/8th inch) long, but larger individuals are said to reach about 13 mm, or half an inch in length.
More later,
Until then,
Cheers,
