description Phormosoma placenta Overview
Phormosoma placenta is a species of deep-sea sea urchin belonging to the order Echinothurioida, first described by Charles Wyville Thomson in 1872. It is primarily found in the Atlantic Ocean, typically inhabiting benthic environments at depths of 500 meters or more. Like other echinothurioids, it possesses a flexible test, or shell, which often causes specimens to collapse into a flat, pancake-like shape when removed from the high-pressure deep-sea environment. This species is of interest to marine biologists studying deep-sea benthic fauna.
help Phormosoma placenta FAQ
What kind of animal is Phormosoma placenta?
Phormosoma placenta is a deep-sea sea urchin in the order Echinothurioida and the family Phormosomatidae. Its scientific authority is Charles Wyville Thomson, who described the species in 1872, as recorded by [NatureServe](https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.948905/Phormosoma_placenta).
Where does Phormosoma placenta live?
It lives on the Atlantic continental slope, from the northern Atlantic toward the Caribbean and Gulf of Guinea. It is seldom found above 500 metres, making it a genuine deep-water species rather than a shallow coastal urchin.
What is unusual about the body of Phormosoma placenta?
Its test, or shell, is flexible, dome-shaped above, and flattened underneath. The plates overlap and are joined by membrane, so collected specimens can collapse into disk-like shapes when brought out of deep water.
How large can Phormosoma placenta become?
The species is yellowish-brown and can reach about 12 centimetres in diameter. Its lower surface carries slender, club-shaped spines enclosed in membranous sacs, a feature described in the [NOAA echinoid report](https://www.st.nmfs.noaa.gov/spo/SPO/tr33.pdf).
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