Holasteroida is an order of irregular sea urchins.
ORDER
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Holasteroida is an order of irregular sea urchins.
== Characteristics == thumb|upright=1.1|Ceratophysa ceratopyga by A. Agassiz (1881) These irregular sea urchins are characterized by a particularly marked bilateral symmetry, including for the apical system, which is highly elongated. In some contemporary abyssal groups such as Pourtalesiidae, some species are even bottle-shaped. The mouth (peristome) does not contain an Aristotle's lantern. The anus (periproct) has migrated towards the periphery of the test. The plastron is never amphisternous.
Discovered by embedding cosine similarity (sentence-transformers MiniLM, 384-dim).