Crabs

of Sligo and Leitrim (Donegal Bay)

 
 
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Masked Crab (Corystes cassivelaunus)


There are several common names for this species including Masked Crab, Long-clawed crab and Sand Crab.  This can lead to confusion but there is only one scientific name!  The name ‘Masked Crab’ is a reference to the pattern on the carapace that resembles a mask that may be worn over a human face.  The only likely confusion is when an old carapace is found that like the masked crab is longer than wide, and then Portumnus latipes that is of a similar size and is also quite common, has to be eliminated.  Corystes cassivelaunus burrows into soft sand near the low water mark.  On occasion I have seen this species rapidly burrowing into the sand at Yellow Strand during low water and there are reports of them washing up after storms when the sand is churned up by the waves.  Adaptations include the hind legs that allow it to burrow backwards into the sand and the distinctive long antennae that join together to make a breathing tube.  This crab is a predator that searches out worms and small bivalve seashells living in the sand. 


In County Sligo it seems to be frequent at Bunduff Strand, Yellow Strand and Dunmoran Strand.  There is also a 1994 record for Tullaghan Point, Co Leitrim (Picton & Costello 1997).  The Masked Crab is found all the way along the west coast of Ireland and has a wider distribution that includes the north-east Atlantic, North Sea and Mediterranean Sea.

References


Crowe, W.A. (1995)  A Survey of the Macro Fauna and Flora of a selection of the foreshore area at Culleenamore strand in Ballysadare Bay, in the vicinity of the outlet pipe, from the salmon hatchery, located at Glen Lodge, Co. Sligo.  Unpublished report to Sligo County Council.  34 pages + 30 pages of appendices.


Doyle, T.K.; W. Helps & J. Davenport (2013)  Columbus crab (Planes minutus (L.)) from the leg pouch of a Loggerhead Turtle (Caretta caretta (L.)).  Irish naturalists’ Journal 32(2):106-107.


Holmes, J.M.C.; D. McGrath, B.E. Picton & N. Mulligan (1983)  Records of some interesting crabs from the coast of Ireland.  Irish naturalists’ Journal 21(2):79-81.


Holt, E.W.L. (1892)  Survey of fishing grounds, west coast of Ireland, 1890-1891.  Report on the results of the fishing operations.  Scientific Proceedings of the Royal Dublin Society 7:225-477.


Ingle, R.W. (1980)  British Crabs.  British Museum (Natural History), London.


McGrath, D.; A. McCarthy, D. Minchin & J.P. Molloy (2008)  Zoological Notes.  The swimming crab Polybius henslowii Leach in Irish waters.  Irish Naturalists’ Journal 29(1):55-56.


Picton, B.E. & M.J. Costello (eds.) (1997)  BioMar biotope viewer: a guide to marine habitats, fauna and flora of Britain and Ireland. Environmental Sciences Unit, Trinity College, Dublin. (CD-ROM).


Picton, B.E. and Morrow, C. C. (2006)  BioMar Survey of marine species and habitats of Ireland. Ulster Museum, Belfast.  BioMar survey of South Donegal Bay area, May 1994.


Picton, B.E. and C.C. Morrow (2010) [In] Encyclopedia of Marine Life of Britain and Ireland. http://www.habitas.org.uk/marinelife/ accessed 27 January 2014).


Silke, J.; F. O’Brien & M. Cronin (2005)  Karenia mikimotoi: an exceptional dinoflagellate bloom in western Irish waters, summer 2005. Marine Environment and Health Series No.21 (44 pages).


Thompson, W. (1842)  The Crustacea of Ireland.  Order Decapoda.  Annual Magazine of Natural History 10:274-287.


Wikipedia http://en.wikipedia.org/wiki/Crabs_of_the_British_Isles (accessed 18 October 2013)

Pennant’s Nut Crab (Ebalia tuberosa)


There are five similar species of ‘nut crabs’ genus Ebalia recorded from the west coast of Ireland so care is needed to to ensure a correct identification.  If possible the specimen should be taken and preserved, but a good photograph may also allow accurate identification.  These nut crabs are all very small with a carapace length of around 10 mm.  They live on the sea bed from sub-littoral to quite deep water selecting substrates of marl, muddy sand, gravel or stones depending in the species.  Here they feed as carnivores on other marine animals.  Nut crabs are only likely to be seen by SCUBA divers but they can be hard to spot as they tend to be coloured to merge in with their habitat.


Pennant’s Nut Crab (E.tuberosa) is the largest species in our area and has a carapace length up to about 17 mm but is more usually about 13 mm long.  It has not yet been recorded from Sligo or Leitrim but in 1984 the BioMar survey team made a record from Donegal Bay at a site off St. John’s Point which is across the bay from Mullaghmore (Picton & Costello 1997).  This species has also been recorded from Mayo, Galway Bay and Fastnet and more widely it is recorded from all the way around the Irish and British coasts.

Harbour Crab (Liocarcinus depurator)


This species could easily be confused with the Flying Crab (Liocarcinus holsatus) and even with the Shore Crab (Carcinus maenas) so care needs to be taken.  The Shore Crab differs in not having the arcs of white spots on the carapace and the three points between the eyes are gently rounded and not so pronounced (see picture below).  Another difference can be seen if the hind legs are present, then Liocarcinus crabs have paddle-like last segments whilst the Shore Crab has slender and pointed last segments to the hind leg.  The Harbour Crab carapace is covered in small tubercles giving it a rough texture whilst the Flying Crab carapace is quite smooth with a rather translucent milky-green or -blue colour.  Also the three projections between the eyes are all equal in length on a Harbour Crab but the middle one is slightly longer on a Flying Crab.  This species grows up to 40 mm in length and 50 mm wide which is a size to make it large enough to be commercially fished in North America.











The habitat of this crab is sub-littoral sand, muddy sand and gravel.  It is scarce in Donegal Bay having been recorded once from St. John’s Point, Co. Donegal (Pickton & Costello 1997) and twice from Bunduff Strand, Co Sligo.  There are also records from Mayo and Galway Bay.  The wider distribution includes both sides of the Atlantic Ocean, the North Sea, Mediterranean Sea and Black Sea.

Pennant’s Swimming Crab (Portumnus latipes)


This distinctive shape of this crab being longer than wide, makes it quite distinctive with the only other species that could be mistaken for it being the Masked Crab (Corystes cassivelaunus).  The carapace length doesn’t seem to exceed about 30 mm.  It is of a light brown to grey brown colour with a fine mottled pattern on the shiny carapace.  These markings gives it excellent cryptic colouration for its habitat which is just below the sand on beaches from near the low water mark down to the sub-littoral.


I have found it alive on Yellow Strand on two occasions and dead specimens have been noted on Bunduff Strand, Trawalua Strand, Lower Rosses Strand and Inishcrone Strand.  Ingle (1980) did list Donegal Bay and Silke et al. (2005) found some dead on the beach at Bunduff Strand when carrying out a survey after a red tide.  Interestingly in was not recorded during BioMar surveys (Picton and Costello 1997; Picton & Morrow 1996).  It would seem to be quite an uncommon species but there are records from all around the coasts of Ireland and Britain.

Shore Crab (Carcinus maenas)


The Shore Crab also has several other common names including European Green Crab.   It is by far the most commonly seen species in rock pools and washed up dead on the shore or just found as a shell (carapace) on sandy strands.  It is easily mistaken for the Velvet Swimming Crab or members of the genus Liocarcinus so two or three distinctive features can be examined to make the correct identification.  The most easily seen is the form of the carapace edge between the eyes which is represented by three gently curving ‘teeth’.  Compare the detail in the photograph below with three Liocarcinus species of the Harbour crab, the Flying Crab and the Marbled Crab that are shown above.  If the hind legs are present then the last segment is not flattened to form a paddle but is slender and ends in a point.  Close examination of the carapace also reveals a rather rough texture with many small papillae.  The shore crab is quite large being up to 60 mm long and 90 mm wide so it occasionally is fished commercially.











This shallow water species is a predator feeding on young bivalves, worms and crustaceans.  Because it lives in the littoral zone it is easily recorded and occurs commonly along the entire coast of Sligo and Leitrim, in rock pools, harbours and in estuaries where it is tolerant of dilution of the sea water by fresh water.  It is easily the most common crab to be washed up on sandy beaches in this area.  This species had a natural distribution throughout the north-east Atlantic Ocean including the Baltic Sea.  It has now been spread by people to become an invasive species along the eastern and western shores of North America and also in temperate Australia, South Africa and Argentina.

Marbled Swimming Crab (Liocarcinus marmoreus)


It is distinguished from other similar species by the presence of three similarly-sized teeth on the edge of the carapace, between the eyes, and by the marbled colouration on the carapace. It reaches a carapace length of 35 mm.  L.marmoreus is found on sand and gravel in the sublittoral and lower littoral zones, down to a depth of 84 m.  It has been recorded from all sea areas on the west coast of Ireland apart from Mayo.  In Sligo there are records from Yellow Strand and Lower Rosses Strand.  The wider distribution includes the northern Atlantic Ocean from the Azores as far north as the Shetlands; it is also in the North Sea and the western Mediterranean Sea.

Acknowledgements

Many of the specimens described herein were collected with the assistance of, or by Jean Dunleavy.  To the photographers who so generously allowed use of their superb pictures through Wikimedia Commons and Creative Commons and in particular to Hans Hillewaert, I would like to say what a great resource they have made available to the internet community.  I also thank Bernard Picton, Malcolm Storey, Steven Campbell and people who donated pictures to WoRMS and MarLIN for the use of their photos.

Edible Crab (Cancer pagurus)


This is the second most common species in the Sligo area and it is one of the largest.

Spiny Spider-crab (Maia squinado)


At the top of this page there is a photograph of someone holding a specimen of the Spiny Spider-crab that shows this is a very large crab; and in fact it can be up to 210 mm long.  It has long limbs, hence the name ‘spider crab’ and is of a distinctive red colour when alive or freshly dead.  The old carapace in the photograph below has become bleached with age.  It lives below the low water mark down to depths of about 75 m.  It feeds on other marine invertebrates including molluscs and echinoderms such as sea urchins.  It occasionally finds its way into lobster pots in Sligo.  This species is commercially fished In France, Great Britain, Spain and several other countries.


On three occasions I have found this species washed up on the shore at Yellow Strand, Co. Sligo.  Every time they were whole animals and once the animal was still just alive.  It is possible that these specimens were disguards from lobster pots.  The spiny spider crab is found all the way down the west of Ireland from Mayo, Galway Bay, Fastnet and Cork (Ingle 1980) and has a wider distribution in the north-east Atlantic from Denmark to Morocco and into the Mediterranean Sea.  Apparently this species is migratory moving over 150 km south in autumn and north again in the spring.


This species may be named in the literature as Maja.

Spiny Spider-crab (Maja squinado) found washed up on Yellow Strand

Summary of species of crabs recorded from Sea Area 34 Donegal Bay

Defined Sea Areas around the coasts of Ireland.  Sea Area 34 (Donegal Bay) includes all of the coastline of County Sligo and Leitrim as well as parts of Donegal and Mayo.

Locations along the coast of Counties Sligo and Leitrim sampled during the BioMar study.

There are 43 sites in Sligo and 2 in Leitrim

Crabs and crab allies recorded from Sea Areas 34 - 37 down the west of Ireland


Data compiled from Ingle (1980), BioMar sources (Picton et al. 1997 and 2006), Holmes et al. (1983); McGrath et al. (2008), Doyle et al (2013) and personal records (Cotton unpublished)

Map showing the locations of beaches from which crabs have been recorded

Great Spider Crab (Hyas araneus)




There is an old record for Donegal Bay (Ingle 1980) and in Sligo this species has been recorded washed up on Yellow Strand on two occasions and from the Lower Rosses sand flats once.

Hairy Crab (Pilumnus hirtellus)


Length up to about 15 mm long

The hairy crab would appear to be quite common along rocky shore.

By searching under large rocks and boulders near low spring tides on wave-cut platforms

Agharrow near Streedagh; Loughaun Bay, Serpent’s Rock, Ballyconnell; Long Rock, Dunmoran Strand; and Rathlee Head, Lenadoon Point, Killala Bay


Galway Bay, Fastnet

Columbus’s Crab (Planes minutus)


This is a very interesting little crab, which like the name suggests is minute generally being less than 10 mm long.  For such a tiny creature it is amazing to think that its habitat is amongst materials being carried on ocean currents around the North Atlantic Ocean.  For this reason P.minutus is a good swimmer and has distinctive flattened limbs to act as paddles.  The diet of this crab is varied from being a predator and eating other small marine creatures, to scavanging on the waste products of turtles etc., and even being a herbivore feeding on some marine algae.


This pelagic way of life means that if one wants to find one of these crabs it is necessary to search for it on logs and other debris washing ashore on our beaches.  Very few people would notice a tiny crab in these circumstances so there are very few records of it from Irish shores but its occurrence must be quite frequent.  The specimen below is one of 3 found at Mermaid’s Cove, Mullaghmore Bay on 25 July 2015 amongst Smooth Gooseneck barnacles.  Two further occurrences on the Sligo coast are at Tra Bui on 23 November 2015 (John-Mark Dick) and a male and a female at Yellow Strand on 25 November 2015 (Don Cotton).  Irish records on the west coast come from Mayo, Galway Bay, Fastnet; and now Donegal Bay.  A recent paper added a new record and summarised historical records in Ireland for this species (Doyle, Helps & Davenport 2013).

Montagu’s Crab (Xantho hydrophilus)


Generally much larger than X pilipes this crab reaches 45 mm in length and 70 mm in width.  It is hairless with black ‘pincers’ unlike the similarly shaped but smaller X.pilipes that has distinctive hairy fringes to some of the limbs and to the shell margins, and has dark brown ‘pincers’.


X.hydrophilus is quite easy to find under rocks and boulders during low water all along the rocky shores of Sligo i.e. Trawalua Strand; Rinnadoolish Point, Streedagh; Agharrow near Streedagh; Loughaun Bay and Ballyconnell Strand, Ballyconnell; Long Rock, Dunmoran Strand; Carrickfadda east of Aughris Head; Tra Bui Strand and Carricknacranny rocks; Lackavarna and Donagh near Dromore West; Coanmore Bay near Easky; and Rathlee Head, Lenadoon Point, Killala Bay. 


If one is exposed when a rock has been lifted it will aggressively hold its pincers up and wide open, a threat that will result in a nasty nip if clumsily handled!  Apparently this crab is a herbivore that feeds on seaweeds.  Montagu’s crab has been recorded all the way down the west coast of Ireland, having a wider distribution that extends from the west of Scotland down to the Canary Islands off the west African coast.


In much of the older literature his species was called Xantho incisus.  It was recently discovered that in 1790, 24 years before it was described as Cancer iscisus, that it was correctly described and named Cancer hydrophilus, so this name that takes presidence with a but with a more modern change of genus to Xantho.  The name hydrophilus means ‘water lover’.

Pea crab (Pinnotheres pisum)


This tiny crab lives inside the shells of living mussels (Mytilus edulis) and many other bivalve molluscs.  Here it scavanges on the food taken in by the bivalves.  Because it does no service for the host animal but takes away the hosts food, it is considered to be a commensal, or some authors suggest it is a parasite.  This crab is just 6 to 10 mm long or exceptionally up to 13 mm and is thus the size of a pea hence the scientific name of pisum meaning a pea.  The smooth exterior, translucent shell and habitat within bivalve mollusc shells make this crab unmistakable.  The infection of mussels in a study carried out in the south of England varied from less than 1% to 43% with higher infestation rates being associated with larger mussels and mussels lower down on the shore.


P.pisum is recorded from Donegal Bay but has not been found by myself yet.  There is no record to ascribe it’s presence to either Sligo or Leitrim.  It occurs all around the coasts of Ireland and Great Britain and throughout European coastal waters.  Other very similar species of pea crabs are found all over the world.

Contracted Crab (Hyas coarctatus)


This species has been recorded from Donegal Bay according to Ingle (1980) but the source of this record is not known to me.  It is also recorded from Mayo and Galway Bay.

Scorpion Spider Crab (Inachus dorsettensis)


The only record for Donegal Bay was west of Pound Point, Co Donegal in July 1996 (Picton & Costello 1997).

Long-legged Spider Crab (Macropodia rostrata)


It has been recorded from Donegal Bay at St. John’s Point, Co. Donegal in May 1994 (Picton & Costello 1997).  There is so far no record from Co. Sligo.

Strawberry Crab (Eurynome aspera)


This is a compact relative of the spider crabs with relatively short limbs.  Its carapace measures about 15-20 mm long.  The whole animal has a rather scruffy appearance being rather rough, slightly hairy and with mud and other dirt stuck to its back for camouflage.    It lives on muddy sand.  The only record I know of from Donegal Bay was from Streedagh Point in May 1994 (Picton & Costello 1997).  Leach’s Spider Crab (Inachus phalangium) was found at the same place during the same dive.

Leach’s Spider Crab (Inachus phalangium)


It has been recorded from Donegal Bay at St. John’s Point, Co. Donegal as well as off Streedagh Point, Co Sligo in May 1994 in about 10 m depth of water (Picton & Costello 1997).  Strawberry Crab (Eurynome aspera) was found during the same dive.

Maia squinado

Yellow Strand, County Sligo on 07 June 1998

Photographs by Don Cotton

Eurynome aspera

Belgian Coastal Waters on 17 March 2006

Photograph Hans Hillewaert.

Licensed under CC BY-SA

In addition to the records published in Ingle and those in the BioMar reports, crabs washed up along the seashore or found in rock pools by Cotton and Dunleavy (unpublished) are included in this web page.  Records of crabs washed up on sandy beaches are mainly of of carapaces (shells) or dead whole specimens.  Although these dead specimens can be assumed to be of local provenance this may not be the case and some may have been washed in from deeper waters or from places further along the coast.  Some records are of living specimens found in rock pools or under rocks and boulders along rocky shores.  Whether the specimens were dead or living is always stated in the descriptions.

In his book ‘British Crabs’, Ingle (1980) describes 67 species as occurring in the seas around the coasts of Britain and Ireland.  Some of these are only in the very south in warmer waters, some are only in the very north in cooler waters, and some are only found offshore in deeper waters.  A list of species published in Wikipedia shows 65 species, Chaceon affinis (syn Geryon affinis) and Cymonomus normani as having been removed from the list for this area (http://en.wikipedia.org/wiki/Crabs_of_the_British_Isles accessed 18 October 2013).


The coast of Sligo and Leitrim are within the Marine Census Area of Donegal Bay (area 34) that stretches from Aran Island in north-west County Donegal all the way to Erris Head in the west of County Mayo.  The fauna of the seas in this region were quite poorly known when Ingle wrote his book (1980) and he relied upon sources such as Thompson (1842) and Holt (1892) for information about this area when he listed 9 species.  The adjacent Sea Area of Mayo had 20 species and North Donegal had just one species recorded.  Since then I have come across just one more published record for a species in Donegal Bay (Holmes et al. 1983) other than those in the BioMar study (Picton & Costello 1997).

Necora puber

Dead specimen washed up on Yellow Strand 04 January 2014

Photograph Don Cotton

Risso’s Crab (Xantho pilipes)


Xantho pilipes is a small crab with a maximum length up to 30 mm and width of 40 mm.  It is ‘built like a tank’ with thick shell and stout legs.  The first pair of legs are particularly large with distinctive brown ‘nippers’.  It looks very similar to Xantho hydrophilus but X.pilipes has distinctive fringes of hairs on the 4th and 5th pairs of walking legs and also on the sides and back of the shell (carapace).

It lives under rocks or buried in gravel or sand on the lower shore.  If you want to find one it has to be at a low spring tide and by turning over rocks.  There are currently only two records for County Sligo with one from Long Rock, Dunmoran and the other from Lislary south of Streedagh.  It is undoubtedly more common than these records would suggest.  Its wider distribution is all of the way around the Irish coast; along the entire west coast of Britain right up to the Shetland Islands; and apparently it occurs from Scandanavia right down to the west African coast.  The common name for this crab (and for Risso’s dolphin) is in honour of Antoine Risso from Monaco who named 549 species of marine life.

Xantho pilipes

Ilfracombe, North Devon, England

by Bob Alexander http://www.glaucus.org

Xantho hydrophilus

by NicoDesSables is licensed under CC BY-SA 3.0

Pinnotheres pisum

Photograph by Malcolm Storey

http://www.discoverlife.org/

Planes minutus

Beached at Mermaid’s Cove, Mullaghmore Bay, Co. Sligo on 25 July 2015 (Don Cotton).

Above : amongst Smooth Gooseneck barnacles

Left : crab removed and

length measured

Toothed Pirimela (Pirimela denticulata)


Only record Muckross Head, north Donegal Bay

Circular Crab (Atelecyclus rotundatus)


The Circular Crab (or Round Crab) is well named because that is its shape and for this reason it is of unique appearance in this geographical area.  The 9 to 11 teeth on either side of the carapace are reasonably even in size and are also a very distinctive identification feature.  This is a medium-sized species with a carapace length of up to 40 mm but more usually of about 30 mm.  I have never found this species washed up on the shore and apparently it lives on sand and gravel from about 20 m to about 90 m under water.  I will have to rely on SCUBA divers to find it for me.


It is recorded from St John’s Point in Co. Donegal where it was ‘frequent’ but so far there is no record made for it in Sligo or Leitrim.  Other records for the west of Ireland are from Galway Bay and Fastnet.  The wider distribution goes all of the way from Shetland and Orkney down to the Canary Islands and Cape Verde and it is also throughout the Mediterranean Sea.

Arch-fronted Swimming Crab (Liocarcinus navigator)


This species previously called L.arcuatus because the frontal margin of the carapace between the eyes is a smooth arc which has a fringe of hair but no teeth (see detail of photograph shown below). It has a dark brown carapace approximately 33 mm wide, with lighter coloured walking legs. Like other swimming crabs in Necora and Liocarcinus the ends of the hind legs are flattened to make paddles.










Recorded from all the way around Ireland including Donegal Bay, Mayo and Galway Bay (Ingle 1980).  I don’t know in which county the record from Donegal Bay was made.  It is found chiefly around Britain and Ireland, however its wider range covers the north-east Atlantic Ocean, including the North Sea as far north as Norway, and as far south as the west African coast at Mauritania.  It also occurs in the Mediterranean.

Velvet Swimmimg Crab (Necora puber)


The velvet swimming crab was previously called Liocarcinus puber but was placed in its own genus of Necora in recent times.  Its common name is sometimes simply given as the Velvet Crab because the body is coated with short hairs, giving the animal a velvety texture. Like other swimming crabs, the last pair of pereiopods are flattened to facilitate swimming.  Pay especial attention to the front edge of the carapace between the eyes when making an identification (see detail of photograph shown below).  This is the largest swimming crab occurring in Irish coastal waters, with a carapace length up to 80 mm and width of up to 100 mm.










Its habitat is reported as being on rocky bottoms from the shoreline to a depth of about 65 m.  It is one of the major crab species for Irish fisheries and is marketed from Mullaghmore.  In Sligo dead specimens and old carapaces are often found on Yellow Strand and it is also recorded from Inishmurray; Mullaghmore Bay; Conor’s Island; mouth of Streedagh Estuary; Lislary; Cloonagh; Rosses Point Strand; Long Rock, Dunmoran Strand and Donagh near Dromore West.  The velvet crab is found down the west coast of Ireland in all sea areas.  The wider distribution stretches from southern Norway to the Western Sahara of North Africa, in the North Sea and north Atlantic, as well as western parts of the Mediterranean Sea.

Flying Crab (Liocarcinus holsatus)


The Flying Crab has a carapace which is brownish-grey with a green or blue tinge. It is very similar in appearance to the Harbour Crab Liocarcinus depurator.  Old carapaces on the beach have a smooth pearly grey-white appearance with a tinge of green or pale blue.  I have also seen a mauve coloured specimen.  If the shells are filled with sand the green/pale blue colour is enhanced.  The curved rows of whitish dots are a very obvious identification feature shared only with the Harbour Crab.  Between the eyes the trident of projections are all about equal or sometimes the middle one is slightly larger than the ones on either side.  The carapace reaches up to 40 mm wide.













The diet comprises crustaceans, especially juvenlie shrimps (Crangon) and bivalve molluscs such as Spisula elliptica, and fish.


Recorded from North Donegal, Mayo and Galway Bay.  In Co Sligo it has been picked up on Bunduff Strand, Mullaghmore Bay; Trawalua Strand; Yellow Strand; Lower Rosses Strand; Rosses Point beaches; and Inishcrone Strand.  It is found chiefly in the North Sea, Irish Sea and English Channel.

Crabs are well known to everyone.  Most people also know that they are crustaceans closely related to lobsters and shrimps.  When walking along a sandy beach the shells of crabs are one of the things thrown up by the sea that are frequently observed.  Most of the time it is just the shell that surrounded the body (the carapace) that is found and the legs are all lost.  The carapace may have been moulted by the crab in which case the animal is probably still alive under the water with a new and larger shell.  Alternatively the animal may have died and this is often when one finds the legs still attached to the carapace.


Crabs have 10 legs (5 pairs).  The scientific Order that crabs and their allies are placed in are the Decapoda which means ‘10-legged’.  The front pair (the chelipeds) carry the claws or pincers; then there are 3 pairs of walking legs; and the last pair are swimming legs.


In Ireland all native crabs live in salt water but recently an invasive fresh water crab has been found in some southern rivers.  Information on the occurrence and distribution of crabs around Britain and Ireland was gathered together by Raymond Ingle of the British Museum (1980) who presented distribution records based on Marine Census Areas (see map shown below).  The coastline of Counties Sligo and Leitrim along with parts of the Donegal and Mayo coastlines are in Marine Census area ‘34 Donegal Bay’.  Since Ingle’s book was published the main source of new data about crabs in this area has come from a comprehensive study called ‘BioMar’ and published on a Compact Disc (Bernard Picton & Mark Costello (eds.) 1997) as well as on a web site (Picton and Morrow 2006).

Descriptions of Crabs recorded from the Sligo and Leitrim coast


The length of crabs is measured from the point between the eyes back to the rear edge of the carapace.  Measurements on this website follow this method.

However be aware that in some reports it is the width of the carapace that is reported.

Descriptions of Hermit Crabs and Porcelain Crabs

recorded from the Sligo and Leitrim coast

Long-clawed Porcelain Crab (Porcellana longicornis)


This tiny relative of the true crabs lives under stones and rocks low down on the shore and can be searched for at low spring tides.  Records from Co. Sligo include Streedagh at Rinnadoolish Point; Agharrow near Streedagh; Carricknacranny rocks at western end of Tra Bui; and Lackavarna near Dromore West.

Broad-clawed Porcelain Crab (Porcellana platycheles)


These distinctive ‘crabs’ are very flattened as an adaptation to squeezing in crevices under rocks.  Although their body may only be about 10 mm across, when the front limbs are taken into consideration the whole animal is perhaps 30 to 40 mm across.  Broad-clawed Porcelain Crabs are very common in and around rock pools and underneath boulders and large loose rocks on the lower shore.  You must wait for a low spring tide and then turn over rocks on the lower shore to find them.  It is not unusual to see perhaps 10 of them clinging to the underside of a rock where they almost seem to be a part of the rock as their colour so well matches the worm tubes and other encrustations.  After a few seconds they then begin to scuttle away.  They are one of the wonderful creatures that you will find in this fascinating inter-tidal habitat along rocky shores.


In Sligo and Leitrim this species is common along all rocky shores where there are loose boulders and particularly where there is a broad wave-cut platform.  These animals are found all the way around the Irish coast and their wider distribution includes almost all European shores including the Mediterranean Sea.

Xantho hydrophilus

Lackavarna near Dromore West on 15 September 1984 Photograph by Don Cotton

Xantho pilipes

Long Rock Dunmoran Strand on 29 March 1987

Photograph by Don Cotton

Pilumnus hirtellus

Long Rock, Dunmoran Strand on 29 March 1987

Photograph by Don Cotton

Portumnus latipes

Yellow Strand on 01 December 2013

Photograph by Don Cotton

Portumnus latipes

Trawalua Strand on 20 October 2013

Photograph by Don Cotton

Porcellana platycheles

Agharrow near Streedagh on 16 September 1984

Photograph by Don Cotton

In the following descriptions I sometimes suggest that you turn over rocks in order to search for crabs, porcelain crabs and hermit crabs.

It is very important that you try to turn the rock back to its original position after having enjoyed seeing the fascinating animals that live underneath.

Porcellana longicornis

Lackavarna near Dromore West on 15 September 1984

Photograph by Don Cotton

Hyas araneus

Lower Rosses on 12 March 1985

Photograph by Don Cotton

Cancer pagurus

Yellow Strand on 28 June 2011

Photograph by Don Cotton

Liocarcinus marmoreus

Lower Rosses on 24 November 2013

Photograph by Don Cotton

Carcinus maenas carapace with barnacles

Rosses Point on 21 October 2013

Photograph by Don Cotton

Carcinus maenas

Ardtermon Strand on 24 October 2013

Photograph by Don Cotton

Liocarcinus holsatus

Bunduff Strand on 26 November 2013

Photograph by Don Cotton

Liocarcinus holsatus

Bunduff Strand on 19 June 2013

Photograph by Don Cotton

Liocarcinus depurator

Bunduff Strand on 27 November 2013

Photograph by Don Cotton

Corystes cassivelaunus

Dunmoran Strand on 10 July 1997

Photograph by Don Cotton

Ebalia tuberosa

Photograph by IMARES

Licensed under CC BY-NC-SA 3.0

Ebalia tumefacta

Roscoff, France in 1985

Photograph by Hans Hillewaert Licensed under CC-BY-SA-3.0

Corystes cassivelaunus

Belgian coastal waters 09 March 2007

Photograph by Hans Hillewaert

Licensed under CC BY-SA 3.0

Necora puber

Carapace found on Yellow Strand on 14 October 2013

Photograph Don Cotton

Liocarcinas navigator

Westdiep on the Belgian Continental Shelf 28 September 2005

Photograph by Hans Hillewaert.  Licensed under CC BY-SA 3.0

Liocarcinus depurator

Westdiep on the Belgian Continental Shelf on 28 September 2005

Photograph by Hans Hillewaert.  Licensed under CC BY-SA 3.0

Liocarcinus marmoreus

Photograph Hans Hillewaert.

Licensed under CC BY-SA 3.0

Atelecyclus rotundatus

Belgian coastal waters in 2006

Photograph Hans Hillewaert.

Licensed under CC BY-SA 3.0

Pirimela denticulata

Southern North Sea on 17 January 2007

Photograph Hans Hillewaert.

Licensed under CC BY-SA 3.0

Pilumnus hirtellus

Southern North Sea on 17 January 2007

Photograph Hans Hillewaert.

Licensed under CC BY-SA 3.0

Hyas araneus

Fisheries and Oceans Canada

Photograph by Catriona Day

Licensed under CC BY-NC-SA 3.0

Hyas coarctatus

Southern North Sea on 02 January 2007

Photograph Hans Hillewaert.

Licensed under CC BY-SA 3.0

Inachus dorsettensis

Southern North Sea on 18 January 2007

Photograph Hans Hillewaert.

Licensed under CC BY-SA 3.0

Inachus dorsettensis

West coast of Scotland

Photograph Fiona Crouch

Macropodia rostrata

Belgian Continental Shelf on 27 October 2005

Photograph by Hans Hillewaert.  Licensed under CC BY-SA 3.0

Xantho pilipes

Detail of hind leg showing fringe of hairs

Photograph by Don Cotton

Red Swimming Crab (Bathynectes longipes)


This would seem to be a rare crab down the west of Ireland but perhaps it is not so well known because it is generally a deep water species.  When it is occasionally found in shallower water its habit of hiding in crevices in the sub-littoral and only coming out at night has meant that it has evaded being seen by many SCUBA divers.


There is only one record for Donegal Bay in 1981 which was from St. John’s Point, Co. Donegal (Holmes et al. 1983; Picton and Morrow 2010).

Bathynectes longipes

St. John’s Point, Co. Donegal

Photograph by Bernard Picton