nearvertebrates

Nearvertebrates is an informal, nonstandard term used to describe chordate organisms that are closely related to vertebrates but are not themselves vertebrates. In this sense, nearvertebrates typically refers to two living subgroups within the phylum Chordata: tunicates (urochordates) and lancelets (cephalochordates). The term highlights evolutionary proximity to vertebrates rather than a formal taxonomic category.

In modern phylogeny, tunicates are commonly regarded as the closest living relatives of vertebrates, while cephalochordates are the sister group to the vertebrate lineage. Collectively, these groups provide crucial insights into the early evolution of chordates and the origins of vertebrate traits. They share key chordate features such as a notochord, a dorsal nerve cord, pharyngeal slits, and a post-anal tail, though the expression of these traits differs along their life cycles.

Anatomy and life cycles vary between the groups. Lancelets retain many primitive features throughout life and resemble small, eel-like marine animals that filter-feed with an elongated body. Tunicates exhibit drastic life-cycle changes; many adults are sessile and may lose some defining chordate traits, while their larval stage exhibits recognizable chordate characteristics, including a notochord and dorsal nerve cord.

Ecologically, nearvertebrates are primarily marine and inhabit shallow coastal environments worldwide. They are central to studies of developmental biology, genomics, and the evolution of vertebrate complexity, contributing essential perspectives on the origins of vertebrate features and gene regulation. The term remains informal and is used mainly in broader or introductory discussions of chordate relationships.