Diving with Toxopneustidae Sea Urchins

Lanta Marine Life | Toxopneustidae

Toxopneustidae Sea Urchins have an internal skeleton (test) made of overlapping plates which form a globular shape. Occasionally spotted during our Koh Lanta dive trips.

The outer shell of this family are covered with short moveable spines, with tiny pedicellariae (pincers) located between the spines. Some species have a toxic venom within these pincers which is used for defence.

As with all other Sea Urchins, the mouth of Toxopneustidae Sea Urchins contains a complex chewing apparatus consisting of 5 jaws, known as an Aristotle's Lantern.

Toxopneustidae Sea Urchins use their tube feet and movable spines to move and are found in various colours, including black, blue, green, orange, pink and green up to 15 cm in diameter.

The Toxopneustidae Sea Urchins are herbivorous grazers, feeding on algae, detritus and sea grasses. In turn they are preyed upon by fish, gastropods and sea stars.

Another unusual adaptation in this Family is the attaching of foreign objects on to the top (arboral) surface of the shell. These species use their pedicellariae (tiny pincers) to pick up, and hold onto, pieces of algae, coral rubble, human rubbish or shell fragments. These objects may help to provide camouflage, armor, or sun protection for the urchin.

1 species found on this page:

Collector Urchin (Tripneustes gratilla)

Collector Urchin

(Tripneustes gratilla)

Tripneustes gratilla @ Koh Haa

Collector Urchins (sometimes known as Cake Urchins) have a blue, purple to brown body, covered with mostly short white or reddish/brown spines sometimes tipped with orange, and brownish-red tube feet.

The spines are alternated by vertical bands of tiny pincers (pedicillaria) which allow Collector Urchins to collect debris from around the reef (hence the common name).

Collector Urchins grow to 10 cm and generally feed on algae and seagrass. They are themselves preyed upon by pufferfish and octopus and are less commonly seen at the dive sites around Koh Lanta.