Enigmatic protostome taxa

Wiwaxia is a genus of prehistoric soft-bodied animals that were covered in carbonaceous scales and spines that protected it from predators. Wiwaxia fossils—mainly isolated scales, but sometimes complete, articulated fossils—are known from early Cambrian and middle Cambrian fossil deposits across the globe. The living animal would have measured up to when fully grown, although a range of juvenile specimens are known, the smallest being long.

Hyoliths are an extinct group of invertebrates with small conical shells, known from fossils from the Palaeozoic era. They are at least considered lophotrochozoans, possibly being lophophorates, a group which includes the brachiopods (hyoliths may even be brachiopods themselves), while others consider them as being basal lophotrochozoans, or even molluscs.

Odontogriphus (from , 'tooth' and , 'riddle') is a genus of soft-bodied animals known from middle Cambrian Lagerstätte. Reaching as much as in length, Odontogriphus is a flat, oval bilaterian which apparently had a single muscular foot and a "shell" on its back that was moderately rigid but of a material unsuited to fossilization.

Dinophilidae is a family of orbiniid annelids comprising the two genera Dinophilus and Trilobodrilus, first linked based on their sperm morphology.

Sialomorpha dominicana, also known as the mold pig, is a panarthropod genus of uncertain affinities discovered in 30-million year old Dominican amber by George Poinar at Oregon State University and Diane R. Nelson at East Tennessee University. It was placed in a new genus and family (Sialomorphidae) unto itself, and appears to represent a new phylum. S. dominicana shares some resemblance to tardigrades and mites. It is about 100 μm long and grew by molting its exoskeleton. It was probably an omnivore, feeding on minute invertebrates and fungi, including mold.

Typhloesus wellsi is an extinct species of enigmatic bilaterian animals from the Bear Gulch Limestone, United States. It was once thought to be the first body fossil of a conodont, based on what turned out to be its gut contents; it is now thought to exhibit a radula, which would make it a mollusc, although different types of animal have independently evolved radula-like features. Mark Purnell, of the Centre for Palaeobiology at the University of Leicester, said that it was not definitively known "what this weird thing is".

species of mollusc