Opabiniidae

Opabiniidae is an extinct family of marine stem-arthropods.^[1] Its type and best-known genus is Opabinia. It also contains Utaurora, and Mieridduryn. Opabiniids closely resemble radiodonts, but their frontal appendages were basally fused into a proboscis. Opabiniids also distinguishable from radiodonts by setal blades covering at least part of the body flaps and serrated caudal rami.^[2]

Cross section

Size comparison

Opabiniidae Temporal range: Middle Cambrian - Middle Ordovician, 507–464 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Opabinia (top) and Utaurora (bottom)
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Stem group:	†Dinocaridida
Family:	†Opabiniidae Walcott, 1912
Genera
†Opabinia †Utaurora †Mieridduryn †Myoscolex?

History of study

Opabiniidae was named by Charles Doolittle Walcott in 1912, alongside its type species Opabinia. Walcott interpreted Opabiniidae as a family of anostracan crustaceans, most closely related to Thamnocephalidae.^[3] Opabinia was restudied in the 1970s, and reinterpreted as a stranger animal. Stephen Jay Gould referred to Opabinia as a "weird wonder", and an illustration of Opabinia prompted laughter when it was first revealed at a paleontological conference.^[4] In 2022, more opabiniids were discovered. That being Utaurora, and Mieridduryn.^[2]

Myoscolex from Emu Bay Shale is sometimes suggested to be an opabiniid,^[5] but morphological features supporting this interpretation are controversial.^[6][2]