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| Animals - Echinoderms |
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Phylum Echinodermata:
Sea stars, sea urchins and brittle stars
Share a common ancestry with Chordata: deuterostomes
Triploblastic, coelomate
Radially symmetrical as adults (pentamerous)
Body covered with delicate epidermis stretched over an endoskeleton
Endoskeleton consisting of calcium rich movable or fixed plates (ossicles)
Plates (ossicles) bear spines (well developed or reduced)
Tube feet (for locomotion) emerge from perforations in the plates
Water vascular system connects to tube feet
Simple nervous system with no distinct brain
Main Classes:
Class Asteroida: Sea Stars e.g. Common Starfish Echinoster sepositus (Stilla Hamra)
Class Echinoidea: Sea Urchins e.g. Rock Urchin Paracentrolus lividus (Rizza)
Echinoderms of the Maltese Islands:
Common Starfish (Stilla Hamra) Echinaster sepositus
20cm. Lives among seaweed, almost up to the seashore. Has five arms and a bright red colour. Common.
Cushion-star (Stilla Hadra) Asterina gibbosa
4cm. Lives among seaweed and beneath stones. Small, with yellowish-green body. Arms very short, so that the body has a pentagonal shape. Common.
Red Starfish (Stilla Hamra Lixxa) Hacelia attenuata
15cm. Lives on rocks among seaweed. Resembles Common Starfish, but has a smoother skin. Frequent.
Violet Starfish (Stilla Hamra Kbira) Ophidiaster ophidianus
30cm. Lives on shallow, rocky bottoms among seaweed. Has swollen, round arms with blunt ends. Frequent.
Red Comb-star (Stilla tar-Ramel Kbira) Astropecten aranchiacus
30cm. Lives at depths of 5-50m. Largest species in this family. Bright orange. Frequent.
Blue Starfish (Stilla ta' Hafna Swaba') Coscinasterias tenuispina
9cm. Lives in shallow water down to 30m. Has more than five arms, usually seven, sometimes more. Arms not all the same lenght. Dark brown with bluish tones. Common.
Spiny Starfish (Stilla tal-Felul) Marthasteria glacialis
35cm. Lives in shallow and deep water, down to 180m. The dorsal surfaces of its very flexible arms have rows of warty protuberances, each bearing a hard spine. Brown or greenish. One of the largest starfishes. Common.
Brown Brittle-star (Stilla Qarnita Kbira) Ophioderma longicauda
25cm. Lives among rocks and seaweed, in both shallow and deep waters. Arms can be up to 15cm long, but body only grows to a diameter of 2.5cm. Dark, ranging from brown to olive green with darker blotches. Very common.
Rock-urchin (Rizza) Paracentrotus lividus
8cm. Lives on rock among seaweed and among Posidonia leaves, even in very shallow waters. Excavates a small depression by abrasion of the rock using teeth and spines. Covers itself with bits of shell and seaweed, probably to reduce its exposure to light. Colour very variable, usually greenish, but often brown, red or purple. Edible. Has almost disappeared from certain localities in recent years, probably because of a disease epidemic. Very common
Black Sea-urchin (Patri) Arbacia lixula
7cm. Prefers shallow rocky bottoms in rather dark places, such as vertical rock faces, rock crevices or among stones. Always black. Often wrongly believed to be the male Rock-urchin. Very common.
Violet Sea-urchin (Rizzun) Sphaerechinus granularis
16cm. Found singly in fairly deep waters. Spines are few, but long and very stout, preventing it from being engulfed by the sand or soft mud. Frequent.
Pea-urchin (Gurdien Zghir) Echinocyamus pusillus
1cm. Lives among gravel and small pebbles which collect around the bases of Posidonia plants. Has a felt-like covering of very short, dense spines. Greenish. After death, the spines drop off leaving only the whitish test. A handful of gravel may contain several empty tests. Very common.
Black Sea-cucumber (Buzzu tar-Ramel) Holothuria tubulosa
25cm. Lives on sand in Posidonia meadows, crawling along and ingesting the sediment, from which it retains any nutrient matter. The rest is eliminated at the posterior opening. Several specimens often encountered on sandy bottoms, each with its own trial of sand. Very common.
