Opabiniidae

Opabiniidae Temporal range: Middle Cambrian - Middle Ordovician,
File:20220213 Opabiniidae Opabiniids.png
Opabinia (top) and Utaurora (bottom)
Scientific classification Edit this classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	†Dinocaridida
Order:	†Opabiniida
Family:	†Opabiniidae Walcott, 1912
Genera
†Opabinia †Utaurora †Mieridduryn †Myoscolex?

Opabiniidae is an extinct family of marine stem-arthropods. 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 are also distinguishable from radiodonts by setal blades covering at least part of the body flaps and serrated caudal rami.

File:20210807 Opabiniidae opabiniid trunk cross section.png

Cross section of the trunk of Utaurora and Opabinia

File:20220214 Opabiniidae size.png

Size comparison of Utaurora and Opabinia

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. 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. In 2022, two more opabiniids were discovered, those being Utaurora and Mieridduryn.

Myoscolex from Emu Bay Shale is sometimes suggested to be an opabiniid, but morphological features supporting this interpretation are controversial.