Helcionelloida

Taxobox
color = red
name = Helcionelloida
fossil_range = fossil range|540|360 Early Cambrian – Devonian


image_caption = "Latouchella costata"
regnum = Animalia
phylum = Mollusca
subphylum = Conchifera
classis = †Helcionelloida
subdivision_ranks = Orders & Families
subdivision =
*Order †Helcionellida
**Family †Scenellidae
**Family †Helcionellidae
**Family †Yochelcionellidae
**Family †Stenothecidae

Helcionelloida is the name given to an extinct group of ancient molluscs (phylum Mollusca). These are the oldest known conchiferan molluscs, that is, they had a mineralised shell. Some members of this class were mistaken for Monoplacophorans.

Anatomy

These animals were untorted and they had a coiled, cone-shaped shell. Most species were small (about two millimeters) and in the modern day, they are often reconstructed to resemble snails. They also possessed a "snorkel"-like opening which was most likely used for breathing.

ources

http://www.palaeos.com/Invertebrates/Molluscs/BasalMollusca/Conchifera/Helcionelloida.html