''Haplophrentis'' is a genus of tiny shelled

hyolithid Hyoliths are animals with small conical shells, known as fossils from the Palaeozoic era. They are at least considered as lophotrochozoan, and possibly being lophophorates, a group which includes the brachiopods, while others consider them as b ...

which lived in the

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...

Period. Its shell was long and conical, with the open end protected by an operculum, from which two fleshy arms called ''helens'' protruded at the sides. These arms served to elevate the opening of the shells above the sea floor, acting like stilts.

Morphology

Shell length of ''H. reesi'' reached up to while ''H. carinatus'' reached up to . Juveniles could of course be smaller. It is distinguished from ''

Hyolithes Hyoliths are animals with small conical shells, known as fossils from the Palaeozoic era. They are at least considered as lophotrochozoan, and possibly being lophophorates, a group which includes the brachiopods, while others consider them as be ...

'' by the presence of a longitudinal septum on the middle of the inner surface of the top of the shell. Its soft anatomy comprises 12(H. carinatus) to 16 (H. reesi) tentacles attached to a horseshoe-shaped lophophore. A pair of wide structures of uncertain function extend along the length of the conical shell. A larval shell is attached to the shell apex.

Affinity

The soft anatomy of ''Haplophrentis'' was key to establishing the hyoliths as members of the

Lophophorata The Lophophorata are a Lophotrochozoan clade consisting of the Brachiozoa and the Bryozoa. They have a lophophore. Molecular phylogenetic analyses suggest that lophophorates are protostomes, but on morphological grounds they have been assessed a ...

, the group containing brachiopods and phoronids. While some studies supported this interpretation, other studies considered hyoliths as basal

lophotrochozoan Lophotrochozoa (, "crest/wheel animals") is a clade of protostome animals within the Spiralia. The taxon was established as a monophyletic group based on molecular evidence. The clade includes animals like annelids, molluscs, bryozoans, brachiopo ...

mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...

Ecology

''Haplophrentis'' was a filter feeder, using its lophophore to extract organic matter from passing seawater. Specimens of ''Haplophrentis'' have been found in the gut of the predator ''

Ottoia ''Ottoia'' is a stem-group archaeopriapulid worm known from Cambrian fossils. Although priapulid-like worms from various Cambrian deposits are often referred to ''Ottoia'' on spurious grounds, the only clear ''Ottoia'' macrofossils come from th ...

''.

Occurrence

186 specimens of ''Haplophrentis'' are known from the Greater

Phyllopod bed The Phyllopod bed, designated by USNM locality number 35k, is the most famous fossil-bearing member of the Burgess Shale fossil ''Lagerstätte''. It was quarried by Charles Walcott from 1911–1917 (and later named Walcott Quarry), and was t ...

, where they comprise 0.35% of the community. It is also known from several specimens in the Spence Shale, and occurs prolifically at the Marble Canyon locality. Many specimens at Stanley Glacier display soft tissue well.

References

External links

* * {{Taxonbar, from=Q2309087 Hyolitha Burgess Shale fossils Protostome enigmatic taxa Fossil taxa described in 1988 Cambrian genus extinctions Paleozoic life of the Northwest Territories