{"id":145,"date":"2009-03-07T18:46:53","date_gmt":"2009-03-07T16:46:53","guid":{"rendered":"http:\/\/klqewmpxo.cyon.link\/?page_id=145"},"modified":"2026-03-01T18:37:06","modified_gmt":"2026-03-01T16:37:06","slug":"seeigel","status":"publish","type":"post","link":"https:\/\/azalas.de\/en\/sea-urchins\/","title":{"rendered":"Sea urchins"},"content":{"rendered":"

S<\/big>ea urchins are not the most popular sea animals. However, in moderate numbers, they are an important part of a healthy ecosystem.<\/p>\n

Here you can skip the introduction and go directly to the species.<\/a><\/p>\n

\"\"
\nBlack sea urchins in shallow water<\/small><\/p>\n

D<\/big>espite their simple body anatomy, sea urchins stand quite “high” in the “phylogenetic tree”, close to the vertebrates. With almost 1,000 species, they form their own class (Echinoidea)<\/em> and form the phylum Echinodermata<\/em> together with the sea cucumbers<\/a> and the starfish<\/a>. Like most members of the echinoderms, they show a five-rayed radial symmetry. They have an external skeleton made of calcium carbonate. This calcareous shell is covered with small tubercles on which the spines are attached. Five radial double rows of small ambulacral plates also run across the shell, through whose pores the sea urchins extend their thin ambulacral feet, which they use to move around and stir the water for breathing.<\/p>\n

\"\"
\nOn this skeleton of a Violet sea urchin, you can see the small tubercles on which the spines sit in living animals, and in between them the rows of ambulacral plates with their small pores.<\/small><\/p>\n

\"\"
\nThe extended ambulacral feet can be seen on this Black sea urchin.<\/small><\/p>\n

A<\/big>t the bottom of the body lies the mouth opening with a kind of chewing apparatus, known as Aristotle’s lantern, which the sea urchin uses to scrape algae off rocks. Inside the body, the five sections contain five male and five female gonads; the eggs and sperm are released into the sea water. There is also an intestine-like digestive system.<\/p>\n

\"\"
\nopened sea urchin with gonads and digestive system<\/small><\/p>\n

\"\"
\nAristotle’s lantern, the sea urchin’s chewing apparatus<\/small><\/p>\n

I<\/big>n the Mediterranean Sea occur several species of sea urchins. Like many sea animals, they are mostly nocturnal, crawling around on the rocks at night and grazing on the alga layer. They are eaten by many fish, some crabs and starfish.<\/p>\n

T<\/big>he spines of sea urchins have slight barbs at the tip, making them difficult to remove from the skin. The best way is to pour a little oil onto the skin where the spines sit. However, only the spines of a few species are poisonous. Sea urchins are not found in the sand or on sandy beaches, but live on rocks. If you want to go ashore in a rocky place, such as the small rocky island in our bay, it is advisable to wear plastic shoes and use a mask so that you can see if there are any sea urchins.
\n
<\/p>\n

\nSpecies of Sea urchins on Naxos<\/font><\/a><\/p>\n

Species on Naxos<\/h3>\n

The Photo gallery of the marine animals<\/strong><\/a> gives an overview over the species.<\/p>\n

A note on identification:<\/strong> Some species usually can be identified easily and reliably. In many cases, however, several related species are difficult to distinguish. Also not all species are included in the field guides; even using the internet, it is difficult to find information on some species. Accordingly, some of the identifications may not be correct.<\/small><\/p>\n

Here you can jump directly to the species<\/strong> (return with the back arrow or by swiping back):
\nBlack sea urchin, Arbacia lixula<\/em><\/a>  –  Arbaciella elegans<\/a>  –  Purple sea urchin, Paracentrotus lividus<\/em><\/a>  –  Violet sea urchin, Sphaerechinus granularis<\/em><\/a>  –  Hatpin urchin, Centrostephanus longispinus<\/em><\/a>  –  Long-spine slate pen sea urchin, Cidaris cidaris<\/em><\/a>  –  Big white heart urchin, Brissus unicolor<\/em><\/a>  –  Common heart urchin, Echinocardium cordatum<\/em><\/a><\/p>\n

Black sea urchin, Arbacia lixula<\/em>, L.<\/a><\/h6>\n

T<\/big>he Black sea urchin is by far the most common species in the Mediterranean. It can be recognised by its deep black colouring. It lives on rocks and feeds on the algae that grow on them, which it scrapes off with its chewing apparatus. It is mainly active at night.<\/p>\n

\"Black<\/p>\n

\"Black
\nThe Black sea urchin is the most common species in our reagion.<\/small><\/p>\n

Arbaciella elegans<\/em>, Mortensen<\/a><\/h6>\n

T<\/big>his small sea urchin species is only about half a centimeter in size. Often it was considered to be young specimens of the black sea urchin Arbacia lixula<\/em>. However, recent studies suggest that it is a species of its own, the only one of its genus.<\/p>\n

\"Arbaciella
\nThe species Arbaciella elegans<\/em> can be recognised not only by its very small size, but also by the fact that its shell carries spines only around the middle; these are short and flattened.<\/small><\/p>\n

Purple sea urchin, Paracentrotus lividus<\/em>, Lamarck<\/a><\/h6>\n

T<\/big>he Purple sea urchin is rarer than the Black sea urchin, but also occurs regularly. It is usually brownish or purple in colour, but can also be almost black. It can be distinguished from the Black sea urchin by the fact that it always holds some objects with its ambulacral feet on its back for camouflage: a few algae, a mussel shell, etc. Both species are found in the Mediterranean Sea and the eastern Atlantic from the water surface to a depth of about 50 meters, with the Purple sea urchin also found at depths of up to 80 meters. Purple sea urchins can use their Aristotle’s lantern to burrow holes in limestone, where they spend the day. They feed on algae growing on the rocks, as well as seagrass.<\/p>\n

\"Purple<\/p>\n

\"Purple
\nPurple sea urchin with camouflage<\/small><\/p>\n

\"Purple
\nThe Purple sea urchin has a more or less purplish colour.<\/small><\/p>\n

\"Purple
\nOn the underside you see the mouth opening and the “teeth”.<\/small><\/p>\n

\"Purple
\nSometimes one finds a greenish specimen of the Purple sea urchin, also green sceletons are quite common.<\/small><\/p>\n

Violet sea urchin, Sphaerechinus granularis<\/em>, Lamarck<\/a><\/h6>\n

T<\/big>he Violet sea urchin is much rarer on Naxos than the two previous species. It can be recognised by its violet colouring and numerous, rather blunt spines with white tips. Violet sea urchins are mainly found in calmer waters or at greater depths. Between the spines sit small pincers that can release a toxin; however, they are not strong enough to penetrate human skin.<\/p>\n

\"Violet
\nThe Violet sea urchin has rather blunt, violet spines with white tips.<\/small><\/p>\n

Hatpin urchin, Centrostephanus longispinus<\/em>, Philippi<\/a><\/h6>\n

T<\/big>he Hatpin urchin has particularly long, extremely thin spines that are very mobile. The spines are not smooth, but covered with numerous tiny nodules. They easily penetrate the skin and then usually break off and are difficult to remove. Hatpin urchins live mainly at greater depths. We occasionally find a shell on a sandy beach.<\/p>\n

\"Hatpin
\nThe Hatpin urchin has very long and thin spines.<\/small><\/p>\n

\"Hatpin
\nIts chewing apparatus shows especially long and sharp teeth.<\/small><\/p>\n

Long-spine slate pen sea urchin, Cidaris cidaris<\/em>, L.<\/a><\/h6>\n

T<\/big>he Long-spine slate pen sea urchin has only a few and rather thick spines. The spines grow very long, up to twice the diameter of the body. Between the large primary spines sit small, blunt secondary spines. This species also occurs at greater depths, where it lives mainly on rocks and coral beds.<\/p>\n

\"Long-spine
\nThe Long-spine slate pen sea urchin has only a few long and thick primary spines with short secondary spines in between. In the specimen on the right you can see the Aristotle’s lantern with its small teeth.<\/small><\/p>\n

\"Long-spine<\/p>\n

\"Long-spine
\nSkeleton of the Long-spine slate pen sea urchin; you can see the very large tubercles of the primary spines, the smaller tubercles of the secondary spines and the rows of ambulacral plates.<\/small><\/p>\n

\"Long-spine
\nlive Long-spine slate pen sea urchin<\/small><\/p>\n

Heart urchins<\/h3>\n

C<\/big>losely related to the sea urchins are the heart urchins (subclass Irregularia<\/em>), whose skeletons can also occasionally be found on beaches. These are not round, but oval in shape; their spines are soft and almost fur-like. The ambulacral plates with the ambulacral feet do not cover the entire body, but are located in star-shaped grooves around the apical field on the upper side and around the mouth opening on the underside.<\/p>\n

O<\/big>ne usually never encounters a living heart urchins: they live buried in the sandy soil at a depth of 10 to 30 meters.<\/p>\n

Big white heart urchin, Brissus unicolor<\/em>, Leske<\/a><\/h6>\n

T<\/big>he most common species of heart urchin in our area is the Big white heart urchin which can reach a length of 13 cm. One can find the skeletons on the sandy floor in the sea, as the heart urchins are living buried in the ground.<\/p>\n

\"Big
\nSkeleton of Brissus unicolor<\/em>, here with particularly attractive colouring (most skeletons we find are plain grey). The apical field, where the animal takes in water for respiration through four small pores, lies in the middle of the so-called fasciole, which is delimited by a curved line and encloses the star-shaped grooves with the ambulacral plates.<\/small><\/p>\n

\"Big
\nHere you see the underside with the mouth opening; on the left, not visible here, lies the anus.<\/small><\/p>\n

\"Big
\nOn this shell fragment, you can still see part of the soft, fur-like spines.<\/small><\/p>\n

Common heart urchin, Echinocardium cordatum<\/em>, Pennant<\/a><\/h6>\n

T<\/big>he Common heart urchin is much rarer. Its slightly heart-shaped skeleton is smaller (up to 5 cm) and less elongated. The Common heart urchin also lives buried 10 to 15 cm deep in the sandy soil, being connected to the sand surface via a tube that it creates with the help of its ambulacral feet and stabilises with a mucus secretion; it uses this tube to take in breathing water. The locations of heart urchins in the sand can be recognised by the slight cone-shaped hollows around the tube openings. The heart urchin slowly digs through the seabed with its soft spines and feeds on the small organisms it encounters. Certain species of mussels often live in association with the heart urchin: they attach themselves to its spines with byssus threads and feed on the detritus that is carried in with the water stream that the urchin creates for breathing.<\/p>\n

\"Kleiner
\nskeleton of the Common heart urchin, upperside<\/small><\/p>\n

\"Kleiner
\nskeleton of the Common heart urchin, underside<\/small><\/p>\n

\"Common
\nOnce we found a live Common heart urchin in the shallow water. This species has light-coloured spines that are flexible and do not sting. The photo shows the underside. Clearly visible are the fine red ambulacral feet which the urchin uses for breathing. They are arranged in a star-like pattern on the spines-free ambulacral plates around the kidney-shaped mouth opening. The anal opening lies on the left.<\/small><\/p>\n

To the photo gallery<\/a><\/p>\n

continue: Starfish<\/a><\/p>\n

back: Marine animals (Overview)<\/a><\/p>\n

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Sea urchins are not the most popular sea animals. However, in moderate numbers, they are an important part of a healthy ecosystem. Here you can skip the introduction and go directly to the species. Black sea urchins in shallow water Despite their simple body anatomy, sea urchins stand quite “high” in the “phylogenetic tree”, close […]<\/p>\n","protected":false},"author":4,"featured_media":60493,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[21,1987,11,9,22],"tags":[35,869,154,34,143,144,48,50,865,153],"class_list":["post-145","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-sea","category-marine-animals","category-nature","category-naxos","category-animals","tag-agais","tag-griechenland","tag-herzigel","tag-kykladen","tag-meeresfauna","tag-meerestiere","tag-mittelmeer","tag-mittelmeerfauna","tag-naxos","tag-seeigel"],"_links":{"self":[{"href":"https:\/\/azalas.de\/en\/wp-json\/wp\/v2\/posts\/145","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/azalas.de\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/azalas.de\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/azalas.de\/en\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/azalas.de\/en\/wp-json\/wp\/v2\/comments?post=145"}],"version-history":[{"count":14,"href":"https:\/\/azalas.de\/en\/wp-json\/wp\/v2\/posts\/145\/revisions"}],"predecessor-version":[{"id":77920,"href":"https:\/\/azalas.de\/en\/wp-json\/wp\/v2\/posts\/145\/revisions\/77920"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/azalas.de\/en\/wp-json\/wp\/v2\/media\/60493"}],"wp:attachment":[{"href":"https:\/\/azalas.de\/en\/wp-json\/wp\/v2\/media?parent=145"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/azalas.de\/en\/wp-json\/wp\/v2\/categories?post=145"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/azalas.de\/en\/wp-json\/wp\/v2\/tags?post=145"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}