There were so many hermit crabs in these tide pools it was like Grand Central Crustacean
My marine biology nerd self could have watched them until the tide came in! I think they are all P longicarpus but one of them had a different color pattern, not sure of any other species that lives around there
image from the texan ID guide to marine species website here
Up to 2.5cm. Right claw slender and extremely elongated, highly variable colouring. Typically tan with a hint of green, top of legs and hands often described as iridescent, lighter claw tips.
Introduced from the coast of North America, likely through ballast water, and first noted in the north sea in 2020 when it seemed to have already established a small population. Going off beachexplorer data, so far they look to be confined to the south eastern north sea, though their range is clearly expanding. They seem to be coexisting with P. bernhardus just fine, according to Neumann et al. (2022).
Comparison photo from the (otherwise lackluster) Schutzstation Wattenmeer pdf.
Only present in some parts of the wadden sea at time of writing (march 2023), and thus not on Juist. Only time will tell when or whether they make it here at all, though there is a credible report of one from Langeoog from August of 2022 (and two false ones from Juist which clearly show the red claw marking of a P. bernhardus).
Shoutout to Beachexplorer user Rainer Schulz with his reliable and frequent reports.
Hermit crabs are crustaceans that first appeared at the start of the Jurassic, about 201 million years ago. Despite their common name they aren't actually true crabs, instead being a classic example of convergently evolving a crab-like body plan via carcinization.
They also have noticeably asymmetric bodies, with abdomens that coil to one side and differently-sized front claws.
Pagurus bernhardus by Arnstein Rønning | CC BY 3.0
And while modern hermit crabs are famous for inhabiting scavenged snail shells, their fossil record suggests this wasn't always the case.
Originally, they seem to have lived in ammonite shells.
Palaeopagurus vandenengeli lived in what is now northern England during the Early Cretaceous, about 130 million years ago. Around 4-5cm long (~1.6-2"), it was found preserved inside the shell of the ammonite species Simbirskites gottschei.
Its left claw was much larger than its right, and together they would have been used to block the shell opening when it was hiding away inside. And while the exact shape of its abdomen isn't known, it probably asymmetrically coiled to the side to accomodate the spiralling shape of the host shell.
Hermit crabs seem to have switched over to using gastropod shells by the Late Cretaceous, around 90-80 million years ago, possibly due to marine snails developing much stronger sturdier shells during this period in response to the increasing prevalence of specialized shell-crushing predators. The more upright snail shells would also have been much easier to drag around the seafloor than ammonite shells – and meant that they were ultimately less affected by the total disappearance of ammonites during end-Cretaceous mass extinction.
Cancer pagurus crabs causing havoc, which is something they do Very Well
During my experiment each one had their own separate tank…but after the experiment concluded they got really super good at escaping, so I reintroduced them into a group setting for a few days
Highlights of communal living included:
- smashing an air stone (property damage I had to apologize for on behalf of the crabs)
- whatever this was (???????)
- dancing in a circle (forming a cult???)
- actually eating in front of me for the first time (the ONE THING I was trying to observe the for WHOLE EXPERIMENT)
I adore them and their chaotic selves
just some Regular Crab Activities, you know how it be
The one with the dark, gold tipped protrusions on it's back (called cerrata) is Hilton's aeolid (Phidiana hiltoni), & the fluffy, cream colored one is a warty shag-rug nudibranch (Aeolidia loui). I don't know how aware they were of each other, but I was delighted that they bumped into each other & ran their oral tentacles over one another before going about their business. I was able to watch the Hilton's aeolid for a while, & it ended up briefly riding on a grainy hermit crab (Pagurus granosimanus), which then began pinching at it's cerrata before giving up on it.
What's your favorite crab species? Mine is Pagurus longicarpus, the longclaw hermit crab. We used to catch them up and down the beach all summer when I was a kid
I have a real soft spot for those huge Japanese spider crabs. They just defy logic with their hugeness and I like a crab that commands respect and strikes fear like that. Most people think of crabs as little guys but no. Not these. These are bigger than your dad. You're gonna respect them.
Yeti crabs also get props for their stylish leg warmers.
Red egg crab (Atergatis interrimus), a bashful crab belonging to the family Xanthidae, is a species of reef crab, which is colorful and round that can be very commonly seen on many shores in coral rubble areas and reefs. It looks like a cancer pagurus that many people prefer to cook and eat it. However, it is highly toxic and toxins mainly come from algae and shellfish, accumulating through the food chain. It contains tetrodotoxin (TTX), a paralytic shellfish toxin. It also contains saxitoxin (STX), which is the best-known paralytic shellfish toxin. These toxins, which are not destroyed by cooking and have no effective antidote, can cause muscle paralysis, respiratory failure, and death.
Pagurus bernhardus common hermit crab, soldier crab
Einsiedlerkrebs
Up to 8cm. The right claw is noticably larger than the other, older animals are covered in small prickles while young ones are smooth and light in colour. Reddish-orange with a characteristic stripe along the right claw.
Common in the entire north sea. Will bury themselves in the sand when disturbed, so watch your step!
Young individuals are predominantly found, older animals are rare on beaches. P. bernhardus are the only hermit crabs in the north sea large enough to live in whelk shells (Buccinum undatum). Dead crabs typically lack their softer abdomen.