protochordate

protochordate
/proh'toh kawr"dayt/, n. Zool.
any of the nonvertebrate chordates, as the tunicates, cephalochordates, and hemichordates.
[1890-95; < NL Protochordata name of the group; see PROTO-, CHORDATE]

* * *

      any member of either of two invertebrate subphyla of the phylum Chordata: the Tunicata (tunicate) (sea squirts, salps, etc.) and the Cephalochordata (cephalochordate) (amphioxus). Like the remaining subphylum of the chordates, the Vertebrata, the protochordates have a hollow dorsal nerve cord, gill slits, and a stiff supporting rod, the notochord, the forerunner of the backbone. The protochordates differ chiefly from the vertebrates in not having a backbone. Recent protochordates are thought to have evolved from the same ancestral stock as that which gave rise to the vertebrates.

      Two main theories have gained general acceptance as to how the vertebrates may have evolved. One theory proposes that the ancestral form was sessile (attached), perhaps like a pterobranch (q.v.) but with an unspecialized larva. This larva adapted to an independent pelagic life and became sexually mature. Subsequently, the sessile stage was lost, and the vertebrates evolved from this free-swimming animal. The other, more recent theory postulates that the chordates evolved from a small fossil group called the mitrates.

      For more information on protochordate groups, see amphioxus; larvacean; salp; sea squirt; tunicate.

* * *


Universalium. 2010.

Игры ⚽ Нужно сделать НИР?

Look at other dictionaries:

  • protochordate — pro·to·chordate …   English syllables

  • protochordate — /proʊtoʊˈkɔdeɪt/ (say prohtoh kawdayt) noun any of the non vertebrate chordates, as the tunicates, cephalochordates, and hemichordates …  

  • protochordate — adjective or noun see protochordata …   Useful english dictionary

  • Irving Weissman — Irving L. Irv Weissman M.D. is a Professor of Pathology and Developmental Biology at Stanford University [ [http://med.stanford.edu/profiles/Irving Weissman/ Faculty Researcher Profiles Stanford University Medical Center ] ] where he is the… …   Wikipedia

  • skeleton — skeletonless, adj. skeletonlike, adj. /skel i tn/, n. 1. Anat., Zool. the bones of a human or an animal considered as a whole, together forming the framework of the body. 2. any of various structures forming a rigid framework in an invertebrate.… …   Universalium

  • reproductive system, animal — Introduction       any of the organ systems by which animals reproduce.       The role of reproduction is to provide for the continued existence of a species; it is the process by which living organisms duplicate themselves. Animals compete with… …   Universalium

  • prochordate — I. “+ adjective Etymology: New Latin Prochordata : protochordate II. noun : protochordate …   Useful english dictionary

  • Eye — For other uses, see Eye (disambiguation), Ocular (disambiguation), Ocular, and Oculus. For taxon specific articles, see human eye, simple eye in invertebrates, mollusc eye, and arthropod eye. Eye …   Wikipedia

  • Ainiktozoon — Taxobox | name = Ainiktozoon loganense fossil range = Silurian image caption = Calymene blumenbachi Ainiktozoon loganese regnum = Animalia phylum = Arthropoda subphylum = Crustacea classis = Thylacocephala ordo = Concavicarida genus = Ainiktozoon …   Wikipedia

  • SIRPB1 — Signal regulatory protein beta 1, also known as SIRPB1, is a human gene. SIRPB1 has also recently been designated CD172B (cluster of differentiation 172B). PBB Summary section title = summary text = The protein encoded by this gene is a member of …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”