Priapulida

Priapulida is a phylum of marine, unsegmented worms with a retractable, spiny proboscis. Most species live in seafloor sediments.

Introvert: A retractable anterior body region found in priapulids and several other ecdysozoan animals. Its retraction and eversion expose the spiny proboscis used to explore and capture food.
Deposit feeding: Feeding on organic particles and microorganisms within sediment or deposited material. Many priapulids ingest sediment while extracting food from the seafloor.
Cambrian explosion: A major diversification of animal life recorded in the fossil record around the beginning of the Cambrian Period. Priapulid-like fossils occur in Cambrian deposits from this interval of animal diversification.
Marine sediment: Particulate material that accumulates on the seafloor, including mineral grains and organic matter. The sediment is both priapulid habitat and a source of food and shelter.
Scalids: Cuticular spines or hooks arranged in rings on the introvert of priapulids and related animals. These structures arm the priapulid proboscis and help distinguish its body regions.
Burrowing: Locomotion through or beneath a substrate by displacing its material. Priapulids use muscular body movements and their introvert to move through sediments.
Sirius Passet: A Cambrian fossil site in North Greenland known for exceptionally preserved marine organisms. Its fossils include early priapulid-like forms that clarify the group's deep history.
Benthic zone: The ecological region at or near the bottom of a body of water. Priapulids are benthic animals, living on or within the seabed.
Trunk (zoology): The main body region behind an animal's head or anterior structures. Priapulids have an unsegmented trunk that follows the introvert.
Ecdysis: The periodic shedding of an animal's outer cuticle or exoskeleton. A new cuticle must form before a growing priapulid sheds the old one.

Linked from 5 pages