Arachnoides placenta

{{Short description|Species of sea urchin}}

{{Speciesbox

| image = Cake sand dollars (Arachnoides placenta).jpg

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| genus = Arachnoides

| species = placenta

| authority = (Linnaeus, 1758)

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Arachnoides placenta is a species of sea urchin of the family Clypeasteridae. Their armour is covered with spines. It is placed in the genus Arachnoides and lives in the sea. Arachnoides placenta was first scientifically described in 1758 by Carl Linnaeus.Kroh, A. (2010). Arachnoides placenta (Linnaeus, 1758). In: Kroh, A. & Mooi, R. (2010) [http://www.marinespecies.org/aphia.php?p=taxdetails&id=513113 World Echinoidea Database]. at the World Register of Marine Species.