Prenasteridae Family of Heart Urchins
One Heart Urchine from the Prenasteridae Family can be found in this website:
Grooved Heart Urchin, Agassizia scrobiculata. A representative of the Prenasteridae Family of Heart Urchins
Phylogeny: Heart Urchins of the Prenasteridae Family, like Basket Stars, Sea Cucumbers, Sea Stars, and Sea Urchins are in the phylum Echinodermata. They are in the subphylum Echinozoa, the class Echinoidea, the subclass Euchinoidea, the infraclass Irregularia, the subterclass Atelostomata, the order Spatangoida, and the suborder Paleopneustina. The Prenasteridae Family is one of two families in the superfamily Paleopneustoidea. The Prenasteridae Family contains only three genera and four species. The name Prenasteridae comes from the Greek and Latin words meaning “pre-star” or “before star”, referring to the primitive, star-shaped forms of these early echinoids.
Morphology: Prenasterid Heart Urchins are irregular sea urchins that have bilateral symmetry instead of the radial symmetry of regular sea urchins. Their bodies have a somewhat elongated oval or heart-shaped outline. The tests (skeleton) are flat on the oral surface (bottom) and rounded on top and are covered with short spines. The spines are utilized for movement, including helping the urchin burrow into the sand. Heart urchins have tube feet that extend from petal-shaped (ambulacral) grooves in their test that are used for feeding, movement and respiration. Heart Urchins lack the complex mouth parts (Aristotle’s Lantern) found in regular urchins. Their mouths that are located towards one end of the animal, and the anus towards the other. Prenasterid Heart Urchins reach a maximum length of around 6 cm (2.3 inches).
Habitat and Distribution: Most Prenasterid Heart Urchins are found buried in the sand, with their front end pointing downward. They may burrow as deep as 20 cm (7.9 inches) under the substrate surface. Some species are also found on, or under, rocks. They live in the intertidal zone, and to depths up to 900 m (2,952 feet). Live animals are seldom seen by humans but their tests are found, on occasion, washed ashore. Sources differ regarding the geographic range for Prenasterid Heart Urchins. Some sources say they have a global distribution in boreal to tropical seas. Other sources limit them to the subtropical to tropical Eastern Pacific and Western Atlantic. At least three species from this family are found in Mexican waters.
Reproduction: Prenasterid Heart Urchins are gonochoric (females or males for life). They reproduce sexually through broadcast spawning, with external fertilization. The fertilized eggs hatch into planktonic larva. These larva eventually settle to the sea floor and develop into their adult form.
Ecosystem Roles: Prenasterid Heart Urchins are deposit feeders and detritivores that feed on organic particles found in the sediment. They are preyed upon by fish and starfish. Heart Urchins also have pedicellariae (minute pincers) that help deter predators. They are preyed upon by fish and starfish. Their deposit-feeding activities play a key role in nutrient cycling and sediment dynamics within benthic communities.