Dykning med Långryggade havssurglar

Lanta Marina Liv | Diadematidae

Longspine Sea Urchins are a family of around 32 species of spiny, spherical, or globe shaped animals with hard shells which live on the seabed. Spotted everywhere, on all of our Koh Lanta dive trips.

As with other echinoderms, most urchins have a five part symmetry, with five equally sized parts radiating out from their central axes. The mouth is at the base, and the anus at the top.

The long spines are usually hollow, and most species have two series of spines, primary (long) and secondary (short), distributed over the surface of the body, with the shortest at the poles (top and bottom) and the longest at the equator (middle).

Liksom sjöstjärnor och sjögurkor har sjöborrar små rörfötter som kan användas för att 'gå' över havsbotten, ofta med hjälp av rörliga taggar. En inverterad sjöborre med lång rygg kan räta upp sig genom att använda sina rörfötter och manipulera sina taggar för att gradvis rulla kroppen uppåt.

Liksom andra sjöborrar är den långryggade sjöborren känslig för beröring och kemikalier och kan känna ljus. De har ögonfläckar som kan upptäcka ljus, och taggarna kan manipuleras så att ljuset faller på ögonfläckarna. När de upptäcker skuggor kan de fly från ett upplevt hot eller röra sig mot ett upplevt skydd.

Sjöborrar livnär sig främst på alger, men äter även andra långsamma eller stillastående ryggradslösa djur som de kan stöta på. Liksom andra familjer av sjöborrar äts de av sjöstjärnor och avtryckarfiskar.

Täta populationer av långsprötade havssurchiner kan snabbt sluka viktiga marina algsamhällen i ett korallrevs ekosystem och förstöra balansen i ekosystemet i de särskilda områden där dessa ansamlingar förekommer.

2 arter finns på denna sida:

Double-Spined Urchin (Echinothrix calamaris)
Black Longspine Sea Urchin (Diadema setosum)

Double-Spined Urchin

(Echinothrix calamaris)

Double-Spined Urchin @ Koh Bida

The Double-Spined Urchin, or Banded Sea Urchin, has a slightly oval test (shell) which can grow up to 5 cm in diameter. As with all other members of the family Diadematidae, the hollow spines are two different lengths, and very obvious in this species.

The short spines are yellow to dark brown and can deliver a very painful sting. The longer spines can be light coloured, dark coloured, or banded light and dark, and grow to 15 cm in length. Juvenile cardinal fish (family Apogonidae) may hide in the spines for protection.

As with other sea urchins and echinoderms, the Double-Spined Urchin displays five-part symmetry which is clearly visible with the shorter spines.

The mouth is on the lower body surface, and the large anal opening on the top is a generally light colour, with many black and white speckles and spots. The anus is surrounded by a ring of light sensitive receptors which provide rudimentary vision.

The Double-Spined Urchin is nocturnal, feeding at night and usually seeking shelter during the day.

Black Longspine Sea Urchin

(Diadema setosum)

Diadema setosum @ Koh Bida

The Black Longspine Sea Urchin is common to all dive sites in Thailand. The central test (body shell) is almost spherical in shape (slightly squashed vertically), normally black, sometimes dark grey, and grows to 8 cm in diameter.

As with other Echinoderms, this species displays five-fold symmetry which can be seen in the five equally-spaced white dots on the body.

The Black Longspine Sea Urchin has long, hollow, black or white, occasionally banded spines. The spines are slightly venomous and can easily inflict a painful sting, though non fatal.

There is an orange to white ring around anal sac opening, and the body is covered with light receptors (eye spots) providing rudimentary vision. The entire body, is in effect, a very basic ‘eye’.

This species is found on sandy, rubble or rocky bottoms and can use it’s longer spines to move quickly along the seafloor.