Misollardiids

Misollardiids are a extinct group of marine invertebrates belonging to the phylum Mollusca. They are known primarily from fossil evidence, with their earliest occurrences dating back to the Devonian period. Misollardiids are characterized by a distinctive shell morphology, typically coiled and symmetrical. Their exact phylogenetic placement within Mollusca has been a subject of debate among paleontologists, with some considering them to be an early offshoot of gastropods or a distinct class altogether.

The shell of misollardiids is often bellerophontiform, meaning it is planispiral or helicoidal and commonly involute, with earlier whorls enclosed by later ones. This shape is reminiscent of the well-known Bellerophontida, though misollardiids possess unique internal shell structures and apertural features that differentiate them. Studies of their internal anatomy are limited due to the nature of fossilization, but evidence suggests they likely possessed a soft body within the protective shell, similar to other mollusks.

Misollardiids are found in marine sedimentary rocks across various paleocontinents. Their distribution indicates they inhabited a range of seafloor environments. The group experienced a decline in diversity during the Carboniferous and eventually went extinct by the Permian period, contributing to the broader pattern of marine faunal turnover during the Paleozoic Era. The reasons for their extinction are not definitively known but likely relate to environmental changes and competition with other marine invertebrates.