Spatangoida
Spatangoida is an order of irregular sea urchins. They are a diverse group of echinoderms, with over 500 species found in all the world’s oceans. Spatangoids are characterized by their flattened, oval-shaped bodies and their elongated, heart-shaped test (the shell). They are often called “heart urchins” because of their shape.
Common Names
Spatangoids are commonly known as "heart urchins", "sand dollars", "cake urchins", and "sea biscuits".
Characteristics
Spatangoids have several distinctive characteristics that set them apart from other sea urchins:
- Flattened, oval-shaped body: This shape allows spatangoids to burrow into the sand or mud.
- Elongated, heart-shaped test: The test is the hard, protective shell of the sea urchin. It is typically made of calcium carbonate plates.
- Mouth on the underside of the body: Spatangoids are adapted to feed on organic matter in the sediment, so their mouth is positioned on the underside of their body.
- Tube feet: Spatangoids have tube feet on the underside of their body that help them move and burrow.
- Spines: Like other sea urchins, spatangoids have spines that cover their body. Their spines are often short and blunt, but can be long and sharp in some species.
- Petaloid ambulacra: These are five grooves on the upper surface of the test that radiate from the mouth. They contain tube feet and help the urchin to breathe.
Environment
Spatangoids are found in a variety of marine habitats, including:
- Intertidal zone: This is the area between high and low tides, where spatangoids may be exposed to air at low tide.
- Subtidal zone: This is the area below the low tide mark, where spatangoids are permanently submerged.
- Deep sea: Some species of spatangoids live in deep water, where they may feed on organic matter that falls from the surface.
References
Wikipedia: Spatangoida
World Register of Marine Species: Spatangoida
Britannica: Heart Urchin