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The Seashore


Spider Crabs - the Majidae

The spider crabs have a carapace that is longer than it is broad, especially to the rear. They are a small group but range from tiny ones living in rockpools covered with weed to the largest crustacean found on the shore, Maja squinado. All tend to be omnivorous feeding on sedentary animals attached to the rocks. Spider Crabs - the Majidae

The Spider Crab (Hyas araneus), photo above, is from a weedy rockpool. Note how it has camouflaged itself with pieces of seaweed, sponges and even tubeworms. This spider crab has a very triangular body around 4 cm long. The colour is a browny-purple. The exoskelton is not smooth but covered in small, projecting bumps called tubercles. The legs and pincers are quite narrow, with claws at the end of the legs. They cut pieces of seaweed and stick them all over the body and can be difficult to find. This species has superb camouflage which it makes for itself. It is little more than a walking "forest" and with all of the seaweeds that it attaches all over the body it soon becomes colonised by a variety of small animals like hydroids and caprellids. The spider crab sits very still amongst the surrounding weed, an essential part of the crypsis.

Spider Crab (Macropodia rostrata)

Spider Crab (Macropodia rostrata) is another species which attaches a host of seaweeds and sponges on the body. This spider crab is one of the smallest at 2 cm across and has a triangular carapace. The limbs are long and thin, in fact the second pair are three times the length of the body. The body is a yellowish brown. This spider crab is a walking larder of food. The sponges and weed it attaches to the carapace keep it well camouflaged and they soon spread. These lumps are its food and so it just needs to nibble on the growths of sponge rather than go in search of food. An example of a cultivator crab. With a wide distribution pattern along the European coast it can be found in the far north right down into the Mediterranean. It is mainly found in deep water but does extend to the lower shore, especially in the north. In the latter case it will be sheltered rocky seashores.


A Spider Crab

Spiny Spider Crab (Maia squinado) - not pictured. With a carapace length of up to 20 cm this is the largest of the European spider crabs. Unlike the others it does not attach seaweeds or animals on to its back. It is a red colour when alive and the carapace is covered in spines and projections. There are two points between the eyes. The legs are long and narrow and the pincers are quite small. Dead specimens are often washed in and after storms live ones appear on the seashore. It is an impressive animal which moves slowly and relies on its size and spines for protection. This can be a very common spider crab living off shore, rarely found on the seashore. It likes sandy and flat areas beyond the breakers. However, it does investigate crevices and boulders and often turns up in lobster pots. In recent years it has been caught for a continental market, especially Spain. Common in the Mediterranean and up to the western Channel and Ireland.

 


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