Nick Upton's picture

Spider crab moulted shells

Observed: 22nd July 2012 By: Nick UptonNick Upton’s reputation in InvertebratesNick Upton’s reputation in InvertebratesNick Upton’s reputation in InvertebratesNick Upton’s reputation in Invertebrates
Moulted crarapaces and legs of Spiny spider crabs (Maja squinado) washed up on Rhossili Bay, with the Worm's Head in the background, The Gower Peninsula, UK, July.
Description:

I found masses of Spider crab shells with legs attached washed up on Rhossili beach recently; all moulted shells I think. I read that north Atlantic spider crabs are now considered to be Maja brachydactyla rather than Maja squinado. http://www.marlin.ac.uk/speciesinformation.php?speciesID=4688

Identifications
Species interactions

No interactions present.

Comments

ChrisMcA's picture

eg their very knobbly

eg their very knobbly carapace.(& for more Ispot photos see them under former name Maja squinado)

Nick Upton's picture

brachydactyla confirmation

Thanks for the confirmation of what the taxonomists now call what I used to know as M. squinado (I've often come across them while snorkelling in Cornwall too and they're a popular catch there for crabbers) though I'm not sure why you didn't just click on I agree rather than repeating the ID! I do appreciate the feedback, though, as few people react to seashore invert postings for some reason.

Nick Upton, naturalist and photographer.

nightfly's picture

Yeah Nick its that

Yeah Nick its that distribution map of MarLIN'S that keeps mucking me up (if squinado is definitely not found here, is that just based on those few lines by MarLIN or is it from more reputable sources also, I hope so!?!)

When I go onto that page and view the map, I then find I automatically misinterpret the text below as the 2 contradict each other. I think I decide that its saying squinado's biggest density is found in the Med and brachydactyla's is in the north east Atlantic, but the map says squinado is here so it must be?- which is my mistake. I could point out a few really obvious misID's on MarLIN, I used to love it but its sort of disappointing me now.

Do you know of anywhere there are more reliable distribution maps for our marine species or is MarLIN what weve got?

Cathal.

Nick Upton's picture

distribution info

I think Marlin is being inconsistent. My take is it has accepted the M. brachydactyla name for our Spider crabs and used it's old squinado distribution map, but hasn't yet updated the squinado page and map. I came across a similar confusion on many sites when Chris McA queried what British Cornish sucker fish should be called. I contacted the UK fish expert who'd stated it should be Lepadogaster purpurea to find out how sure he was. If you're feeling strong, there is an epic string here: http://www.ispot.org.uk/node/289896 which makes clear that all our Cornish sucker fish should now be considered as Lepadogaster purpurea if the findings of a Portuguese study are accepted. WORMS has accepted it, but has yet to update its distribution maps, hence the confusion there... Only by reading the new paper about spider crab species distributions may it become completely clear, but my reading of the summaries is that ours are now considered M brachydactyla (though they're bound to referred to as M. squinado for years to come by many, whatever!)

Nick Upton, naturalist and photographer.

nightfly's picture

Yeah Nick I know what you

Yeah Nick I know what you mean about feeling strong! I had a few looks at that clingfish debate and I needed strong liquor afterwards. I was going to put up a horribly juvenile unmarked clingfish I have photographed just to really throw a curveball into an already interesting discourse. Mine was IDed and Dipladogastor? dipladogastor (you know what I mean) and then subsequently as Diplecogaster bimaculata, but I dont see any 2 spots on my 'Two spotted Clingfish' and all those purpurea have 2 nice big spots on top so the mind boggles.

I'll share this thing soon, hope I havent got it up already.

Cathal.

Nick Upton's picture

taxonomical tangles

After a certain point, I give up on these precise ID debates, as often the taxonomists can't agree anyway... These days I mainly want to know what I should call species when I have images of them I want to place with photo libraries/ get published in books without looking an eejit for giving it the wrong name/ an ancient name. As a former scientist, I sometimes get sucked in deeper than I should, or if I think my observations can help establish changed distributions, eg for insect species moving north from Europe. My head does spin though as so many species (especially shoreline species for some reason) that I thought I knew well now have new names...

Nick Upton, naturalist and photographer.

nightfly's picture

Hi Nick and Chris, Just

Hi Nick and Chris,

Just trawling through old stuff and noticed there are 10 Maja squinados on iSpot. Shouldn't they be Maja brachydactlya?

Cathal.

Nick Upton's picture

Renaming

Strictly yes, as I understand it if they were UK records...

The splitters have defined that M. squinado has a more mediterranean distribution, M. brachydactyla NE Atlantic .

The key paper seems to be this Spanish 2008 DNA sequencing study: http://darwin.uvigo.es/download/papers/61.brachydactyla.08.pdf which confirmed a suggestion made by Neumann in 1998 based on some morphological differences that crabs considered then as M. squianado comprised 2 species.

MARLIN seems to have accepted the new M. brachydactyla name for NE Atlantic spider crabs and shows its distribution around the UK. What it hasn't yet done is remove M. squinado from its site where it shows the same distribution for this crab in the UK. This is clearly out of date.

WORMS records both species (and M. brachydactyla was first described in 1922, though it's not clear where the type specimen was collected) and list both as UK species as they are both on some UK species list from 2011. Again, they have failed to update the records based on the new information. Just possibly WORMS doesn't accept the new evidence... and only a crustacean taxonomist, which I'm not, could tell you if the 2008 paper I cited is fully accepted by them that should know. I suspect it is, and various marine register sites haven't updated all their data. I guess they have a lot to keep on top of!

Nick Upton, naturalist and photographer.

ChrisMcA's picture

There's scientific names & UK scientific names!

Wikipedia's maja squinado mentions the split, & Habitas.org has brachydactyla; & WoRMS seems the accepted standard (eg google follows it).
But the Natural history musm's datab. of uk sp's doesnt have it; eg
http://www.nhm.ac.uk/research-curation/scientific-resources/biodiversity...
It's the same with Lepadogaster purpurea (however both say updated 1999)