Best Echinothurioid
Phormosoma placenta is a deep Atlantic echinothurioid sea urchin described by Wyville Thomson in 1872, usually found below 500 m.
Calveriosoma hystrix is an echinothuriid sea urchin described by Thomson in 1872, notable for a digestive siphon running beside the stomach.
Phormosoma bursarium is an echinothurioid sea urchin described by Alexander Agassiz in 1881, recorded from about 170 to 2340 m depth.
Echinothuria floris is a fossil echinothuriid sea urchin described by Woodward in 1863, serving as the type species of Echinothuria.
Echinothuria diomedeae is not readily verifiable as an accepted current name; diomedeae is used for Caenopedina diomedeae, named in 1939.
Sperosoma antillense is a species of deep-sea regular sea urchin in the family Echinothuriidae, primarily identified from the bathyal waters of the Caribbean Sea.
Tromikosoma panamense is a species of deep-sea regular sea urchin in the order Echinothurioida, characterized by its remarkably flexible, thin test.
Phormosoma rigidum is a species of deep-sea sea urchin belonging to the family Phormosomatidae, scientifically described in 1879 by zoologist Alexander Agassiz.
Hygrosoma petersii is an Atlantic deep-sea echinothuriid sea urchin described by Alexander Agassiz in 1880, placed in Hygrosoma.
Sperosoma obscurum is a deep-sea sea urchin in the family Echinothuriidae, notable for its flexible, plate-covered test uniquely adapted to extreme ocean depths.
Kamptosoma asterias is a distinctive deep-sea sea urchin in the family Kamptosomatidae, notable for its sharp, heavily structured protective primary spines.
Hygrosoma hoplacantha is an Indo-Pacific deep-sea echinothuriid sea urchin described by Wyville Thomson in 1877.
