Capitella teleta is a small, cosmopolitan, segmented annelid worm. It is a well-studied invertebrate, which has been cultured for use in laboratories for over 30 years. C. teleta is the first marine polychaete to have its genome sequenced.

For many years researchers believed that Capitella capitata was the only representative of this genus that survived, and flourished, in polluted environments. After the oil spill that occurred near Cape Cod in West Falmouth, Massachusetts in 1969, researchers collected sediment and found an abundance of what they believed to be C. capitata. However, subsequent research showed that while the individuals collected from that region had very similar gross morphology, their life histories, methods of reproduction and genetics indicated there were at least six distinct species. Capitella species I, eventually described as Capitella teleta in 2009, was one of the initial species identified from these surveys.

After 30 years of research on the group, Capitella teleta was officially described in 2009 by Blake et al. The species name is derived from the Greek word teleta, meaning "initiation". This word symbolizes that it was the first alternative Capitella species that was identified.

A 2018 molecular phylogeny of the family Capitellidae established clear monophyly and showed 8 genera. The phylogeny utilized 36 capitellid species and combined data from 18S, 28S, H3, and COI gene sequences. This study also established Capitellidae as the sister group to Echiura. While the study attempted to map morphological characters to the molecular phylogeny, this was not phylogenetically informative and a more detailed re-evaluation of morphology could help to elucidate character trait evolution.

Capitella teleta has a narrow, segmented body with reduced parapodia and is red in color. There are nine anterior thoracic segments and many more abdominal segments. New segments are added throughout the lifespan from a posterior subterminal growth zone called the posterior growth zone. Like other polychaetes, C. teleta has fine bristles or setae. Setae are segmentally repeated along the body, with morphologically distinct setae in the thoracic (hooded hooks) and abdominal segments (capillary setae). This animal exhibits sexual dimorphism and males have dorsally-positioned genital spines on setigers 7–8 while females have paired ovaries in the abdominal segments. Generally, there are separate sexes; however, hermaphroditism is possible when there are low densities of females. Males, females and hermaphrodites are of similar size (maximum size collected was a male that is 24 mm in length).

Capitella teleta lives in the shallow-water or intertidal marine environment. It is also found in salt marshes and is often found in high concentrations in disturbed soft sediments. It is a member of the infaunal benthic community. C. teleta burrows through the sediment by peristalsis, using its hydrostatic skeleton and contraction of longitudinal and circular muscles in the body wall. The thoracic segments of C. teleta also contain helical muscles that are proposed to generate additional force for burrowing. Capitellids are commonly thought of as opportunistic in nature, due to their ability to inhabit and flourish in organically enriched marine sediments.

This organism is commonly found in sediments along the east and west coasts of North America. Additional reports have placed this group in the Mediterranean region as well as Japan.

Capitella teleta embryos and early larval stages develop in a brood tube that surrounds the mother. The embryos are approximately 200 μm in diameter. Over the course of approximately a week, the embryos develop into non-feeding larvae which form musculature, a centralized nervous system, two circular ciliary bands, two eye spots, segments, and setae. The larvae are non-feeding and the digestive system develops at a later stage than other organs. Pre-metamorphosis larvae can be categorized into nine stages, with each stage lasting approximately one day. Upon further body elongation and gut maturation, the larvae emerge from the brood tube, and swim forward with a rotational turn via the beating of cilia organized within two circular bands, the prototroch and telotroch. Larvae exhibit positive phototactic behavior in which they swim towards light, potentially an adaptation to aid in larval dispersal C. teleta is an indirect developer and undergoes metamorphosis from a swimming larva into a burrowing juvenile. Metamorphosis is characterized by cilia loss, body elongation, and crawling behavior. Marine sediment functions as a cue to initiate metamorphosis into juvenile worms that thereafter grow into mature adults. Competent larvae can be induced to metamorphose into juveniles when exposed to the B vitamins Nicotinamide (B3) and Riboflavin (B2), suggesting that these chemical compounds may be responsible for the inductive role of the marine sediment in larval metamorphosis. The number of offspring in each brood tube can vary between 50 - 400 individuals, and is influenced by food quality.