Sea biscuit

Plagiobrissus grandis

ORDER Spatangida

FAMILY Brissidae

TAXONOMY

Plagiobrissus grandis Gmelin, 1788.

OTHER COMMON NAMES

English: Heart urchin, long-spined sea biscuit, great red-footed urchin.

PHYSICAL CHARACTERISTICS

One of the largest irregular urchins; longest dimension is their oval-shaped test that can reach 9.8 in (25 cm) in length. Colors vary from yellow or tan to reddish brown. Test covered with medium-sized spines, although some on the upper surface are up to 3.9 in (10 cm) long. Flat underneath with five rows of tube feet in ambulacral groove.

DISTRIBUTION

Found in shallow waters from Florida to the West Indies and Brazil. Common at depths less than 164 ft (50 m), but can occur in depths greater than 655 ft (200 m).

HABITAT

Inhabits sandy coastal lagoons.

BEHAVIOR

Burrows into the sediment. Its long spines are used to defend itself from predators when buried. Often associated with the commensal crab, Dissodactylus primitivus.

FEEDING ECOLOGY AND DIET

Deposit feeder; feeding is suspected to occur both night and day. Main predators are the large helmet conchs, Cassis tuberosa and C. madagascariensis spinella.

REPRODUCTIVE BIOLOGY

Sexual reproduction. Sexes are separate. Eggs and sperm are released into the water column, where they are fertilized and develop into free-living larvae.

CONSERVATION STATUS

Not listed by the IUCN.

SIGNIFICANCE TO HUMANS Known to have poisonous spines. ♦

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