An exclusively marine group of invertebrates, the echinoderms are striking and distinctive creatures. All are slow-moving and some are virtually sedentary. Representatives of all the main groups are easily found on the seashore.
WHAT ARE ECHINODERMS?
Echinoderms are characterised by having bodies that exhibit radial symmetry; this feature is obvious in most groups, but less so in the sea cucumbers, which have elongated bodies. The collective common name for the group, echinoderm, literally means ‘spiny skin’, and indeed this is the most distinctive feature of the sea urchins in particular. All echinoderms have an outer skeleton of calcified plates, which range in complexity from a few scattered plates embedded in the skin in sea cucumbers, to a rigid, calcified dome in sea urchins. Tube feet protrude from pores, located in radiating rows (typically, five rows); these are used for movement or anchoring, depending on the species, and are operated by an internal hydraulic system. There is a central mouth; some echinoderms are grazers while others are active predators.
THE RANGE OF ECHINODERMS
The phylum Echinodermata is divided into a number of sub-groups. Those found regularly on the seashore, or in shallow coastal seas, include the following: feather stars (class Crinoidea); starfish, sea stars and cushion stars (class Asteroidea); brittlestars (class Ophiuroidea); sea urchins (class Echinoidea); and sea cucumbers (class Holothuroidea).
Unusual echinoderms that comprise ten delicate, flexible arms radiating from a central cup; the cup is attached to a rock or other substrate by a branched ‘stalk’. The feather star mouth is located in the centre of the cup on the upper side.
Starfish, sea stars and cushion stars
Distinctive echinoderms that are typically star-shaped, usually with five radiating arms. The upper surface is tough and usually covered with tubercles or short spines. Underneath, rows of tube feet line grooves along the arms; between the feet are tiny gills and pincer-like cleaning appendages. Most starfish species have slender arms, usually five in number but sometimes more. Sea stars have a broad central body with many relatively short, radiating arms; cushion stars are overall pentagonal in outline, the projecting arms being reduced in length.
Common Brittlestar.
Easily recognised by the five slender, brittle, flexible arms that radiate from a central rounded disc. There are two rows of tube feet on the underside of each arm; the arms themselves comprise numerous spiny segments.
Edible Sea Urchin test, with spines removed.
Underside of Psammechinus miliaris, showing the mouth, tube feet and spines.
distinctive echinoderms whose skeletal plates are linked to form a rigid case called a ‘test’; depending on the species, this can be spherical, ovoid or flattish. The test is typically covered in spines, between which lie appendages. Tube feet are found on the underside, aligned in five rows and radiating from the central mouth; the mouth contains a five-jawed structure called ‘Aristotle’s lantern’.
Cotton Spinner, a typical sea cucumber.
sausage-shaped echinoderms with a mouth at one end, surrounded by retractile tentacles, and the anus at the other. The tough, leathery skin is embedded with skeletal plates; in some species, the skin is covered in spikes. There are five rows of tube feet, running the length of the body; three are on the ventral surface and two on the dorsal surface.
Common Starfish Asterias rubens Diameter to 30cm
Our most familiar starfish. Found on a wide range of shores but usually near prey (including polychaete worms and molluscs, often mussels). Seashore individuals are usually rather small. ADULT is usually orange-brown overall with 5 stout arms, each with white spines in a central row and in irregularly scattered clumps. STATUS Widespread and often locally common.
Leptasterias muelleri Diameter to 6cm
Small, well-marked starfish. Found on sheltered rocky coasts, on lower shore. ADULT has 5 stout arms. Seashore individuals are usually greenish (sometimes pinkish purple in deeper water). Arms have pale tips and margins, and rows of star-shaped clusters of pale spines. STATUS Locally common only in the N and NW.
Seven-armed Starfish Luidia ciliaris Diameter to 50cm
Seven-armed Starfish eating a Thick Top Shell
Impressive and distinctive starfish. Found on sheltered rocky coasts, on lower shore. Seashore individuals are usually relatively small. ADULT usually has diagnostic 7 arms (sometimes lost or partly regrown), orange with a fringe of white spines. STATUS Locally common only in the W, from Devon to N Scotland.
Spiny Starfish Marthasterias glacialis Diameter to 65cm
Impressive and distinctive starfish. Found on rocky coasts, on lower shore. Seashore individuals are usually relatively small. ADULT has 5 rather slender arms, greenish or greenish brown with longitudinal rows of spines, each spine arising from a swollen, minutely spiny base. STATUS Locally common only in the W, from Devon to N Scotland.
Common Sun Star Crossaster papposus Diameter to 35cm
Unmistakable starfish. Usually found on rocky and mixed coasts; generally sub-littoral but sometimes on lower shore, or washed up after gales. Active predator of other echinoderms. ADULT comprises a large central disc and usually 11–13 rather slender arms. Reddish orange with paler margin to disc. STATUS Widespread, but commonest N from Wales and N Norfolk; easiest to find on shores in the NW.
Purple Sun Star Solaster endeca Diameter to 35cm
Large, striking starfish. Found on rocky and mixed coasts; usually sub-littoral but sometimes washed up after gales. ADULT has a relatively smaller central disc than Common Sun Star, with usually 9–11 slender, long arms. Usually purplish but can be yellowish orange. Arms are rather rounded in cross section, with numerous small spines. STATUS Mainly N species, locally common only on coasts of NW and N Scotland.
Sand Star Astropecten irregularis Diameter to 20cm
Distinctive starfish. Found on sandy coasts, buried on lower shore and in sub-littoral zone. Sometimes washed up after gales. ADULT is very flat; the 5 stiff arms have marginal plates and spines, and a leathery upper surface. Usually orange or pinkish orange, arms often tipped violet. STATUS Widespread but locally common only off SW and W coasts.
Henricia sanguinolenta Diameter to 20cm
Bloody Henry Starfish
Bloody Henry Starfish
Attractive starfish. Found on sheltered rocky coasts, on lower shore. Seashore individuals are usually relatively small. ADULT has 5 narrow arms, rather rounded in cross section, with regular clusters of spines on upper surface. Usually reddish violet but often yellowish orange. STATUS Locally common on SW, W and N coasts; easiest to find on shores in the NW. SIMILAR SPECIES Bloody Henry Starfish H. oculata is very similar. Examine skin surface for certain identification: spines are covered by skin, creating a pock-marked texture. More widespread than H. sanguinolenta but mainly sub-littoral.
Cushion Star Asterina gibbosa Diameter to 5cm
Asterina phylacti
Distinctive starfish relative, found under rocks on lower shore. ADULT is shaped like a nativity star. Body is fleshy, usually mottled dark green or reddish brown. STATUS Locally common only in the SW and on W coasts. SIMILAR SPECIES A. phylactica is similar but smaller (diameter to 15mm), typically buffish overall with a dark central star-shaped pattern. Restricted to upper-shore pools with coralline algae, in the SW only.
Red Cushion Star Porania pulvillus Diameter to 10cm
Unmistakable. Found on rocky and mixed coasts; usually sub-littoral, sometimes washed up after storms. ADULT has a thick, fleshy body with relatively short, triangular arms. Reddish orange, adorned with white spots. STATUS Locally common only in the NW.
Feather Star Antedon bifida Length to 10cm
Feathery and delicate echinoderm. Found attached to undersides of rocks and in rocky gullies; lower shore and sub-littoral zone. Able to move around and attach itself at will. ADULT has 5 pairs of feathery arms arising from basal disc. Below this, 20–25 cirri attach animal to rock. Arms are usually reddish and banded. STATUS Locally common only in the W, from Devon to N Scotland.
Common Brittlestar Ophiothrix fragilis Disc diameter to 20mm
Well-marked and often colourful brittlestar. Found under stones on sheltered rocky shores. ADULT has spiny disc with pair of triangular plates (radial shields) at base of each leg; has distinct gap between each pair. Legs are fragile, roughly 5× disc diameter, and armed with spines. Colour overall is usually reddish, legs often banded. STATUS Widespread but commonest in the W. SIMILAR SPECIES Crevice Brittlestar Ophiopholis aculeata (disc diameter to 20mm) has angular disc with scales and granules (not spines) on surface; radial shields are not visible. Each leg segment has dorsal oval plate fringed by small scales. Mainly in the W, commonest in the NW.
Ophiocomina nigra Disc diameter to 25mm
Distinctive dark brittlestar. Found on rocky coasts; lower shore and sub-littoral zone. ADULT has uniform granular disc (lacking radial shields) and relatively slender legs, roughly 5× disc diameter, with fine spines. STATUS Locally common only in the W, from Devon to N Scotland; commonest in the NW.
Small Brittlestar Amphipholis squamata Disc diameter to 5mm
Small, easily overlooked brittlestar. Found under stones and rocks on lower shore. ADULT has disc covered in small scales, with pale, closely abutting pair of radial shields at base of each leg. Legs are slender, roughly 4× disc diameter, with short spines. STATUS Widespread and locally common.
Amphiura brachiata Disc diameter to 12mm
Distinctive brittlestar. Lives buried in sand on lower shore, sometimes with leg tips projecting. ADULT has disc covered in scales, with prominent radial shields. Legs are species’ most striking feature: up to 15× longer than disc diameter. STATUS Local, mainly in W.
Edible Sea Urchin Echinus esculentus Diameter to 12cm
Edible Sea Urchin, empty case
Unmistakable sea urchin, found on rocky coasts; lower shore and shallow sub-littoral zone. ADULT has domed outline, pinkish overall with radial bands tinged green or purple. Spines usually red and white, tipped violet. STATUS Widespread and locally common, but absent from most of the SE, from Dorset to Norfolk.
Psammechinus miliaris Diameter to 5cm
Psammechinus miliaris, empty case
Purple Sea Urchin
Distinctive little sea urchin. Found under rocks and among seaweeds on lower shore. ADULT is relatively flattened in outline and greenish overall. Spines are green with purple tips. STATUS Widespread and locally common. SIMILAR SPECIES Northern Sea Urchin Strongylocentrotus droebachiensis (diameter to 7cm) has numerous rather fine spines, red, green or purple, but usually white-tipped; restricted to Shetland Isles. Purple Sea Urchin Paracentrotus lividus has numerous purple or green spines and often bores cavities in limestone rocks, where it resides; very locally common in W Ireland (mainly Co. Clare), rare in SW England.
Sea Potato Echinocardium cordatum Length to 5cm
Sea Potato, empty case
Unmistakable sea urchin. Lives buried in muddy sand on lower shore. Empty shells often washed up. ADULT is oval to heart-shaped in outline, with numerous close-packed buffish spines. STATUS Widespread and locally common.
Purple Heart Urchin Spatangus purpureus Length to 6cm
Distinctive sea urchin. Lives buried in sand and gravel. Occasionally found exposed at surface on very low tides, or washed up after gales. ADULT is heart-shaped in outline with numerous spines, shorter than those of Sea Potato, and purplish. STATUS Widespread and very locally common, mainly in the W and SW.
Green Sea Urchin Echinocyamus pusillus Length to 10mm
Tiny sea urchin. Lives buried in sand and is easily overlooked. ADULT is oval and flattened. Spines are short and closely packed. Empty shell shows 2 holes (mouth and anus) on ventral surface. STATUS Widespread but local; absent from much of the SE.
Sea Gherkin Pawsonia saxicola Length to 12cm
Ocnus lactea
Striking sea cucumber, found under rocks and among seaweed holdfasts on lower shore. ADULT has a smooth white body, with 5 rows of tube feet (ventral rows are double). Tentacles are branched; main stems are grey, tips flecked yellowish buff. STATUS Widespread and locally common, mainly in the SW and W, from Dorset to Shetland. SIMILAR SPECIES Ocnus lactea is smaller (length to 4cm). Body is white and smooth, with irregular rows of single tube feet; tentacles are yellowish buff. Local, mainly in the W.
Brown Sea Cucumber Aslia lefevrei Length to 12cm
Rather undistinguished-looking sea cucumber, found under rocks and in crevices on lower shore. ADULT has wrinkled brown body with tube feet in 5 double rows. Tentacles are branched and dark. STATUS Widespread and locally common, mainly in the SW and W, from Dorset to Shetland.
Cotton Spinner Holothuria forskali Length to 25cm
upper surface
underside
Unmistakable large sea cucumber, found in rock crevices on lower shore of rocky coasts. When disturbed, can eject a mass of sticky cotton-like threads that entangle would-be predators. ADULT is soft and brown to black, paler below than above. Has 3 ventral rows of tube feet and relatively short, branched tentacles. STATUS Widespread and locally common only in the W.
Leptosynapta inhaerens Length to 12cm
Slender, delicate sea cucumber. Lives buried in sandy mud on lower shore. ADULT is pink and worm-like, body capable of great contraction and extension. Has 12 much-branched tentacles. STATUS Widespread but scattered; absent from much of the SE. SIMILAR SPECIES Labidoplax digitata is also worm-like and lives buried in sandy mud; each of its 12 tentacles have just 2 pairs of branches at tip. Scattered and local, mainly in the W.
Ciona intestinalis Length to 12cm
Ciona intestinalis, orange form
Striking sea squirt. Solitary, but often in groups on suitable substrates: attaches basally to rocks, large seaweeds and pier pilings. ADULT has soft, tubular, retractile body with 2 openings close together. Typically translucent whitish (sometimes orange) with yellow around rim of openings. STATUS Widespread and locally common, except in E England.
Ascidiella aspersa Length to 10cm
Tough, gristly sea squirt, attached on 1 side to rocks and seaweeds on lower shore. ADULT is irregularly ovoid and usually milky white; surface is rough, often with attached and embedded debris. Has 2 siphons, 1 at top, the other 
way down body. STATUS Widespread and locally common, except in the E.
Ascidiella scabra Length to 4cm
Small sea squirt; lives attached to seaweeds, notably Serrated Wrack, on lower shore. ADULT is roughly ovoid and slightly translucent white, sometimes tinged pink; surface is wrinkled but smooth. Has 2 siphons, 1 at top, the other ¼ way down body; openings sometimes flushed red. STATUS Widespread, commonest in the W and NW.
Leathery Sea Squirt Styela clava Length to 10cm
Tough, strange-looking sea squirt. Lives attached to rocks and hard substrates, but often washed up after gales. ADULT is irregularly club-shaped, with a leathery, warty surface and tough, slender stalk. STATUS Alien and introduced. Now locally common in the S and SE, particularly around harbours.
Neptune’s Heart Sea Squirt Phallusia mammillata Length to 14cm
Large and distinctive sea squirt. Lives attached on 1 side to rocks on lower shore in silty areas. ADULT is whitish and irregularly flask-shaped, with a knobbly surface. STATUS Locally common only in Dorset and S Devon.
Ascidia mentula Length to 15cm
Tough sea squirt, attached on 1 side to rocks and Laminaria holdfasts on lower shore. ADULT is rubbery and elongate. Usually reddish but much of surface can be coated with detritus. Has 1 terminal siphon, the other ¾ way down body; siphon lobes are often marked with white. STATUS Widespread and locally common only on S and W coasts. SIMILAR SPECIES A. conchilega has a flattened-ovoid greenish-white body; 1 siphon is apical, the other 2/3 way down body; both usually point upwards. Widespread, commonest on S and W coasts.
Baked Bean Ascidian Dendrodoa grossularia Length to 15mm
Baked Bean Ascidian on Common Whelk
Distinctive sea squirt. Attaches singly or in aggregates to rocks, holdfasts and larger mollusc shells. ADULT is irregularly spherical, surface often encrusted; has 2 siphons. STATUS Widespread and locally common, least so on E coasts.
Morchellium argus Length to 40mm
Intriguing sea squirt, attached to rocks on lower shore. ADULT colony comprises club-shaped lobes with distinct flat-topped head and stalk. Zooids are embedded inside; apical inhalant siphons have 8 lobes. STATUS Widespread on S and W coasts.
Aplidium punctum Length to 20mm
Compact sea squirt. Lives attached to seaweeds on rocky shores. ADULT comprises irregularly rounded lobes, zooids with 6 lobes around siphons and apical red spot. STATUS Locally common, mainly in S and W. SIMILAR SPECIES Polyclinum aurantium (length to 25mm) comprises rounded, flat-topped and sand-encrusted lobes. Widespread but scattered, mainly S and W.
Lightbulb Sea Squirt Clavelina lepadiformis Length to 20mm
Distinctive colonial sea squirt. Lives attached to rocks and seaweeds; mainly sub-littoral. ADULT comprises groups of transparent zooids, each with internal yellow-white and brown lines, recalling lightbulb filaments. STATUS Widespread and locally common, least so on coasts of E England.
Orange Lights Sea Squirt Pycnoclavella aurilucens Length to 6mm
Smaller than Lightbulb Sea Squirt, with different markings. Attaches to rocks and seaweeds from lower shore to sub-littoral zone. ADULT comprises groups of semi-transparent buffish zooids with orange-yellow internal lines. STATUS Locally common, in SW England and Wales only.
Star Ascidian Botryllus schlosseri Width to 8cm or more
Distinctive colonial ascidian. Forms encrusting sheets on rocks and large seaweeds on rocky coasts. ADULT colony comprises star-shaped groups of narrowly oval zooids; these are typically yellowish buff and set in a colourful test, usually blue, purple or orange-brown. STATUS Widespread and locally common, least so on coasts of E England.
Botrylloides leachi Length to 8cm or more
Striking ascidian. Forms fleshy, encrusting sheets and masses on seaweeds and rocks, on lower shore. ADULT colony colour is variable but often orange or grey. Zooids are paler than test and arranged in convoluted parallel chains. STATUS Widespread and locally common, least so on coasts of SE and E England.
Sea Mat Membranipora membranacea Length to 7cm or more
Distinctive bryozoan. Forms flat, encrusting mats on fronds of Laminaria seaweeds. ADULT colony is white and lacy-looking, with zooids arranged in regimented grid; individual openings are rectangular. STATUS Widespread and locally common, least so in E England.
Striking bryozoan. Forms flat, encrusting mats on seaweeds, notably Irish Moss and Grape Pip Weed. ADULT colony is whitish and irregularly circular to star-shaped. Individual zooid openings are oval, the combined effect vaguely recalling miniature chainmail. STATUS Widespread and locally common, least so on coasts of E England.
Tubulipora plumosa Diameter to 20mm
Encrusting, calcified bryozoan, found on seaweed fronds, notably Laminaria and Saccorhiza. ADULT colony is roughly circular but lobed, the individual zooids forming fan-shaped radiations of tiny upswept pipes. STATUS Local, in the SW only.
Disporella hispida Length to 10mm
Encrusting, calcified bryozoan, found under rocks at low water. ADULT colony resembles a flattened cup, encrusting on rocks, often among coralline seaweeds. Close view reveals spiky texture, with zooids opening via tiny pores and tubes. STATUS Widespread but local, mainly on S and W coasts.
Alcyonidium hirsutum Length to 8cm
Alcyonidium hirsutum, close-up of polyps
Superficially sponge-like, encrusting bryozoan, often with a lobed appearance. Found on Serrated Wrack and Grape Pip Weed. ADULT colony is tough, gelatinous and usually buffish. Out of water, surface is slightly textured. In water, zooids emerge (like tiny sea anemones), each with 16–20 tentacles. STATUS Widespread and locally common in the W and N, scarce or absent elsewhere.
Flustrellidra hispida Length to 30mm
Flustrellidra hispida, colony out of water
Encrusting bryozoan found on seaweeds, mainly Serrated Wrack. ADULT colony out of water resembles a gelatinous patch, like a blob of dried glue; close inspection reveals tightly packed zooid chambers with tiny spikes around each opening. In water, zooids emerge (like tiny sea anemones), each with 28 tentacles. STATUS Widespread and locally common, mainly in the W and N.
Hornwrack Flustra foliacea Length to 15cm
Branched, colonial bryozoan with a passing resemblance to tough, leathery seaweed. Sub-littoral, attached to rocks; living and bleached dead specimens often washed up. Fresh specimens smell of lemon. ADULT colony appears bushy, with much-divided Fucus-like lobes that twist irregularly. STATUS Widespread and locally common.
Bugula turbinata Length to 5cm
Bushy, rather seaweed-like colonial bryozoan. Lives attached to stones and rocks on lower shore. ADULT has main ‘stems’ branching from base, along which are arranged spiral whorls of smaller branches that bear zooids. STATUS Widespread and locally common, mainly in the S and SW.
Cellepora pumicosa Diameter to 5cm or more
Colonial bryozoan. Encrusts rocks and kelp holdfasts on lower shore. ADULT colony forms nodular patches; circular openings are seen with hand lens. Texture is hard and coarse, and will graze human skin. Typically orange-red. STATUS Widespread and locally common.