Some more crabs
Depending on the shore you’re surveying you might well find some less than usual crabs on your survey. We start here with a fairly common one, but which is small and lives under rocks and therefore is commonly overlooked.
We finish with two species groupings, difficult to ID to species and commonly hidden due to camouflage.
The species in focus are:
long-clawed porcelain crab/cranc porslen (Pisidia longicornis)
Risso’s crab (Xantho pilipes)
Montagu’s crab (Xantho hydrophilus)
small spider crabs/crancod heglog (Inachus and Macropodia sp.)
medium-large spider crabs (several species)
You will get a close-up look at these crabs and find out more about where to find them, so when you do see them you will be able to recognise them.
You will then be tested.
A few more crabs
long-clawed porcelain crab/cranc porslen (Pisidia longicornis)
©Reece Halstead
- a small crab growing up to 1cm in size,
- very long claws relative to the carapace
- found under rocks
- red-brown, sometimes with patterning in colour
- carapace roundish
Risso’s crab (Xantho pilipes)
©North Wales Wildlife Trust
- up to 3cm wide carapace
- mottled colour, commonly yellow and reds
- relatively deep furrows-making it look like a body builder
- 5 teeth either side of eyes
- hairs on legs and under teeth nr eyes
- black-tipped claws
- carapace wider at front end, tapering slightly towards back
Montagu’s crab (Xantho hydrophilus)
©Paul Naylor www.marinephoto.co.uk
- up to 7cm wide carapace
- mottled colour, commonly yellow and reds
- relatively deep furrows-making it look like a body builder
- 5 teeth either side of eyes
- no hairs on legs nor under teeth nr eyes
- black-tipped claws
- carapace wider at front end, tapering slightly towards back
small spider crabs (Inachus and Macropodia sp.)
©North Wales Wildlife Trust
- small long-legged crabs
- often will cover themselves in sponge species
- have a triangular carapace, longer than broad
- low shore species, on rock, sand and mud
- 1 species can be found living within the tentacles of the snakelocks anemone
medium to large spider crabs (several species)
©Molly Jones
- medium species (carapace length 4cm) to larger species (10-20cm long carapace)
- triangular to teardrop-shaped carapaces
- carapace has either tubercles or spines
- has horns/spines at front of head
- some like to decorate with algae,
- carapace, if seen, is red-brown
The comparisons between the spider crab groups has been addressed to a degree within the individual descriptions.
The Xantho crabs, as well as being confused with each other, can also look and behave a bit like edible crabs. They are chunky-looking, have black-tipped claws and will readily bury themselves.
The differences are:
1. the Xantho crabs have body-builder type furrows on their carapace
2. the edible crabs are red-brown in colour the Xantho crabs can be a variety of colours and can be mottled
3. edible crabs can grow much bigger than Xantho crabs
Alternative factoids
Want to get to know more about the less common crabs you might find on shore? This section will not appear in the quiz as questions.
Montagu’s crab is one of the Climate Change Indicators; another species thought to be moving northwards as our seas are becoming generally warmer.
The Inachus species, scorpion spider crabs are thought to benefit from a symbiotic relationship with the snakelocks anemone. Gaining protection from the anemones sting, the anemone gains tasty bits of food from a messy-eating crab lurking within.
The long-clawed porcelain crab is related more to the lobster grouping of crustaceans than to true crabs
The next section is the quiz. You will be tested on what you’ve learnt so far. Don’t worry too much, as once you’ve been out on the shore, the ID features you’ve learnt about will make more sense and after a couple of visits you should feel more confident about your ID.
Good luck!