ECHINODERMS

Phylum Echinodermata

This important phylum is entirely marine in origin and has many different family groups. Completely varied in form, they nevertheless all have common characteristics, such as calcareous plates, a water vascular system and tiny tube feet for locomotion and capturing food. Many are armed with some degree of protection. Most obvious of all are the sea urchins, which are surrounded by sharp spines.

BRITTLESTARS

BLACK BRITTLESTAR

Ophiocomino nigra

Fairly common in deeper water and not always black in colour as the name would suggest, this brittlestar has five to seven rows of short spines along each arm. Its arms are up to 10cm (4in) long. Feeding on detritus deposits, it is omnivorous and can occur in large numbers.

LONG-ARMED BRITTLESTAR

Ophioderma longicauda

This species has a circular disc, which is often patterned and up to 2.5cm (1in) in diameter with arms as long as 15cm (6in). Each arm has small rows of blunt spines. This species prefers low light and is most often found deep inside caves and caverns or in very deep water.

FRAGILE BRITTLESTAR

Ophiothrix fragilis

This is a colourful species with the disc and arms coming in almost every colour imaginable and often varied on each individual. Hairy in appearance, the arms, which grow up to 6.3cm (2½in) long, are characterized by having numerous rows of quite long spines. It can occur in extremely dense beds in deep water.

CRINOIDS

FEATHER STARFISH

Antedon mediterranea

This characteristically shaped crinoid has a tiny body with the mouth on the upper surface of the cup and surrounded by ten long flexible arms up to 10cm (4in) long, which have slender lateral branches. Under the cup-like body are a number of flexible feet or cirri with which it holds on. Usually reddish-orange in colour and sometimes with banded arms, it is commonly found on wrecks and likes strong current or well-aerated water.

STARFISH

BURROWING STARFISH

Astropecten irregularis

This is a fairly large burrowing starfish growing up to 20cm (8in) with five distinct arms. It is a pale cream in colour and is a uniform texture with the upper surface covered in paxillae. It has well-defined marginal plates bearing short, erect spines. It is found on fine sand and is usually partially or wholly buried. It feeds on small bivalves, worms and crustaceans.

IRREGULAR STARFISH

Coscinasterias tenuispina

This species can have 6–12 arms, often of different lengths, probably owing to damage inflicted whilst the starfish is young and its ability to regenerate limbs. It is usually light cream in colour, but mottled with brown, red and even bluish or purple blotches. Growing to around 20cm (8in) in diameter, it is found in most habitats and feeds on the rich algae found in shallow water.

RED STAR

Echinaster sepositus

This is a very common, rough-skinned, red starfish with five, pointed, circular-sectioned arms up to 18cm (7in) long. The rough skin is actually papulae or gill structures and it has a slimy feel. Found in most depths, it feeds on various algae.

SPINY STARFISH

Marthasterias glacialis

One of the largest of the starfish found in these waters, it has five, very long, subcylindrical arms that are roughly tapering and covered in longitudinal rows of thick, sharp spines. Each spine is surrounded by a raised group of pedicellariae. This species prefers a rocky substrate and is mottled greenish-brown in colour. It grows to over 70cm (2ft 4in) in diameter.

LONG-LIMB STARFISH

Ophidiaster ophidianus

Probably the most brilliantly coloured of the large starfish found, this species has long, cylindrical, blunt-tipped arms, which vary from red in colour to even more brilliant red, violet or orange. It can grow to over 50cm (1ft 8in) in diameter and is quite rough in texture with a slightly fuzzy appearance.

SEA URCHINS

BLACK SEA URCHIN

Arbacia lixula

Once thought to be the male version of the Rock Sea Urchin (see here), the Black Sea Urchin enjoys a well-lit, soft rock habitat where it burrows into the rock whilst eating the algae, which grow into the recess. It grows to around 8cm (3¼in) in diameter and has a black shell with black spines.

SEA POTATO

Echinocardium cordatum

The common name refers to the brittle empty test or shell, which is sometimes seen on the sandy seabed or shore. The animal when alive is covered in a mat of fine, cream spines almost like hairs. Slightly heart-shaped, fairly round and up to 7.5cm (3in) across, it burrows in the fine sand and is a deposit feeder.

PURPLE HEART URCHIN

Spatangus purpureus

Also heart-shaped, it can grow as large as 12cm (4¾in) and is coloured a brilliant purple with light, fine spines. It only burrows shallowly and prefers coarse sand and shell gravel.

LONG-SPINED URCHIN

Centrostephanus longispinus

This species is relatively rare in the Mediterranean, having been almost wiped out a few years ago by a virulent disease. Unmistakably recognizable by its long dark spines up to 13cm (5in) long, which are sometimes banded, this sea urchin prefers low light conditions and is usually seen in deep water.

ROCK SEA URCHIN

Paracentrotus lividus

One of the most common sea urchins in the western and central Mediterranean, it occurs in a variety of colour forms and has a rather flattened round test or shell. Growing to around 7cm (2¾in) in diameter, it burrows into soft limestone, leaving cavities in the rock wall, which it enlarges as it grows. It is a herbivore, feeding on algae around its hole or over rocky surfaces.

VIOLET SEA URCHIN

Sphaerechinus granularis

This is a large globular sea urchin growing to around 13cm (5¼in) in diameter and coloured a vivid purple. Usually with white-tipped spines, it is often all the one colour. It likes open, well-lit ground where it browses on algae and has the habit of attaching small pieces of detritus, shell fragments or algae to its spines for camouflage.

SEA CUCUMBERS

COTTON SPINNER

Holothuria forskåli

The most common of the cucumbers, this species comes in two colours, either jet black or varied tan and brown with brown spots on a cream base. Its name comes from its defence mechanism when it ejects sticky, white thread when threatened. It can reach over 20cm (8in) in length and has a dense, tubercle-covered body and numerous tube feet. Feeding on sand and mud particles, which it ingests and passes through its body cavity, the excreta is usually recognized easily as it resembles an egg-like necklace chain made of fine sand particles.

WHITE SPOT CUCUMBER

Holothuria polii

Also distinctively coloured, this species is black or dark brown in colour and is covered in tiny, white, spot-like spines. It grows to around 20cm (8in) and is an active detritus browser.

TUBULAR CUCUMBER

Holothuria tubulosa

The longest of the sea cucumbers found commonly, the Tubular Cucumber can grow over 30cm (12in) long and is varicoloured with dark brown on the top and light brown to peach shades on its flanks. It has conspicuous, pointed tubercles all over its body and prefers to live at the base of cliffs and amongst seagrass beds.