drhoz
in
wtf_nature
Things I Get To ID at Work, Part 10 - Pea Crab
Not so much at work, as at the Xmas dinner arranged by my employers. One of the chilli mussels I was enjoying turned out to be unexpected crunchy, and what I had expected to be a fragment of mussel shell turned out to a crab, either a Zaops ( oyster crab ) or the closely related Pea Crab, genus Pinnotheres. Both genera used to be Pinnotheres, but have have since been split up a bit.
Pinnotheres pisum (Linnaeus, 1767) - Pea crab from the Southern North Sea. Photo Hans Hillewaert 2007
Pinnotherids live inside the shells of oysters, mussels, fan-shells, and other large molluscs, but they're also found inside sea urchins, sand dollars, the rectum of sea cucumbers, the tubes of parchment worms, in the burrows of mud shrimp, and the gills of sea squirts - any animal where they can get protection, food, and a flow of water. They're tiny little things - even the females, which are much bigger than the males, rarely get larger than a pea. Hence the name. The females are round and delicate critters, with greatly reduced eyes and fragile legs, and never leave the host. The males are much more 'normal'-looking, and apparently wander from mussel to mussel to visit their house-bound lady-friends.
This photo of a sea-otter happens to include a male pea-crab that presumably dropped out of the mollusc he or she is chewing on.
Photo by Mila Zinkova
There seems to be ongoing argument as to where these crabs are parasites, or simply inquilines that live inside the host's shell (or gills) and pick at the streamers of food-bearing mucus that flow past. Certainly, the pearl industry here in WA considers them good for the host's health, and try not to hurt the crabs when they're installing pearl seeds into the oysters they farm. I'm sure there's some studies out there that have tried to resolve the question, but I don't have anything authoritative to hand.
Pinnotheres pisum (Linnaeus, 1767) - Pea crab from the Southern North Sea. Photo Hans Hillewaert 2007
Pinnotherids live inside the shells of oysters, mussels, fan-shells, and other large molluscs, but they're also found inside sea urchins, sand dollars, the rectum of sea cucumbers, the tubes of parchment worms, in the burrows of mud shrimp, and the gills of sea squirts - any animal where they can get protection, food, and a flow of water. They're tiny little things - even the females, which are much bigger than the males, rarely get larger than a pea. Hence the name. The females are round and delicate critters, with greatly reduced eyes and fragile legs, and never leave the host. The males are much more 'normal'-looking, and apparently wander from mussel to mussel to visit their house-bound lady-friends.
This photo of a sea-otter happens to include a male pea-crab that presumably dropped out of the mollusc he or she is chewing on.
Photo by Mila Zinkova
There seems to be ongoing argument as to where these crabs are parasites, or simply inquilines that live inside the host's shell (or gills) and pick at the streamers of food-bearing mucus that flow past. Certainly, the pearl industry here in WA considers them good for the host's health, and try not to hurt the crabs when they're installing pearl seeds into the oysters they farm. I'm sure there's some studies out there that have tried to resolve the question, but I don't have anything authoritative to hand.