Ryan Photographic - Echinoidea - Sea Urchins

Sea Urchins

The sea urchins are other worldly-looking creatures. It seems to me that they belong to some exotic planet far-far-away. There are around 950 species of sea urchin and they are found in all of the world's oceans, even into the abyssal depths. They typically feed on algae, or rotting wood which they graze using a five toothed jaw, controlled by an elaborate structure called Aristotle's lantern. (Aristotle was arguably the world's first marine biologist).

Sea urchins possess the same five-fold symmetry (pentamerous) as the other echinoderms (featherstars, sea stars and sea cucumbers). Like most other echindoerms they possess a water vascular system which enables them to inflate balloon-like tube feet. The tube feet, often with suckers on the end, enable the sea urchin to move, albeit quite slowly. They protect themselves by virtue of their long spines which, in some species, are venomous. They can react to shadow and it is quite alarming to wacth a long-spined sea urchin realign its spines to point at you ... In addition to spines most species possess a three-jawed grapnel-like set of jaws set on a long stalk. Called pedicellariae they protect the sensitive upper surface from fouling organisms or simply debris. In the flower urchin the pedicellariae are capable of injecting venom and at least one person is believed to have died from this envenomation - although in fairness it is hard to know whether the person died from the venom or from drowning.

In the slate-spined sea urchins the thick, strong spines prevent most mouths from getting close enough to do damage - but it won't deter a triggerfish. Humans also eat sea urchins - primarily the roe. All the sea urchins have a calcareous endo-skeleton which is covered in a thin layer of tissues. Small holes in this test allow the tube feet to protrude.

There are male and female urchins. They reproduce by releasing eggs and sperm into the sea. The fertilized egg develops into a pluteus larva which, depending on the species, may stay feeding in the water column for several months before settling on the bottom and undergoing metamorphosis into the adult form.

Asthenosoma ijimai Magnificent fire urchin

Astropyga radiata

Colobocentrotus atrata sea urchin

ECHIN 6382 Colobocentrotus atrata inter-tidal sea urchin, Kona, Hawaii.

ECHIN 6379 Colobocentrotus atrata inter-tidal sea urchin, oral surface, Kona, Hawaii.

ECHIN 6374 Colobocentrotus atrata inter-tidal sea urchin, Kona, Hawaii.

ECHIN 6389 Colobocentrotus atrata inter-tidal sea urchin, Kona, Hawaii.

Diadema sauvignyi

Echinometra mathaei sea urchin

ECHIN 5940 Echinometra mathaei, sea urchin, Kona, Hawaii.

Echinothrix calamaris Sea urchin

Echinothrix diadema Sea urchin

ECHIN 5916 Echinothrix diadema, sea urchin, Kona, Hawaii.

ECHIN 7157 Echinothrix diadema, sea urchin, Kona, Hawaii.

ECHIN 7147 Echinothrix diadema, sea urchin, Kona, Hawaii.

Eucidaris thouarsii Slate pencil sea urchin

ECHIN 5986 Eucidaris thouarsii Slate pencil sea urchin, Sea of Cortez.

Evechinus chloroticus - Kina New Zealand sea urchin

Heterocentrous mammillatus Slate pencil sea urchin

ECHIN 7177 Heterocentrotus mammillatus,slate pencil sea urchin, Kona, Hawaii

Heterocentrotus species Slate pencil sea urchin

Heterocentrotus sp. Slate pencil sea urchin, Fiji.

Toxopneustes roseus Flower sea urchin

ECHIN 6281 Toxopneustes roseus Flower sea urchin covered in algae and shells, Sea of Cortez.

ECHIN 5487 Toxopneustes roseus Flower sea urchin pedicellariae detail, Sea of Cortez.

Tripneustes gratilla collector urchin

ECHIN 5929 Tripneustes gratilla, collector urchin, Kona, Hawai'i.

ECHIN 7117 Tripneustes gratilla, collector urchin, Kona, Hawai'i.

ECHIN 7116 Tripneustes gratilla, collector urchin, Kona, Hawaii.

Tripneustes ventricosus West Indian sea egg

Echinoderms

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