Phylum Annelida

Tree of Life

Related Interest:
Annelid Fossils

Class PolychaetaPhylum Annelida is an extremely diverse group of animals commonly called segmented  Rhaphidiophorus hystrix Mazon Creek Polychaete Worm Fossil with Preserved Bristlesworms. Comprising some 15,000 extant species, annelids are ubiquitous on earth and are found in marine, fresh water and terrestrial habitats, and have an enormous range of size from less than a mm to several meters. Some species use sexual reproduction, and others use asexual reproduction.

Among the three predominant annelid classes, Class Oligochaeta (earthworms) and Class Hirudinea (leeches) are the most commonly known, but Class Polychaete that is represented in essentially all marine environments contains the greatest diversity. Because the creatures have soft bodies, fossilization is exceedingly rare. Equivocal forms such as the Dickinsonia are known from the Precambrian. The best-preserved and oldest specimens come from Cambrian Lagerstätte such as the Burgess Shale of Canada, and the Middle Cambrian strata of the House Range in Utah. The Annelids are also well Polychaete worm Glycera represented among the Pennsylvanian-age Mazon Creek fauna of Illinois. The hard jaws of some polychaete worms, such as Fossundecima konecniorum from Mazon Creek, are sometimes common enough to have utility for stratigraphic correlation.

The Echiura (the distinct Phylum Echiura is recognized by some scientists) were initially regarded as an annelid group, were then excluded, but newer evidence suggests they are in fact annelids (Hessling and Westheide, 2002), albeit this placement remains unresolved. The Echiura fossilize poorly and the earliest known specimen is Coprinoscolex ellongimus from Mazon Creek dating to the Pennsylvanian.

Phylum Annelida
Class Polychaeta Bristle worms, diverse, mainly marine worms with parapodia that have bristles
Class Clitellata Subclass Oligochaeta Earthworms
Subclass Hirudinea Leeches
Subclass Branchiobdellida Leeches
Class Myzostomida Parasitic worms
Class Echiura Spoon worms, also considered a separate phylum