BIO 370 Vertebrate Zoology
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Vertebrate Diversity
Invertebrate Chordates

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Phylum Chordata


  • Presence of notochord (internal supporting rod) at some stage in life
  • Pharyngeal gill slits
  • Post-anal tail
  • Segmented muscles
  • Dorsal hollow nerve cord

Subphylum Urochordata Tunicates


  • Notochord, dorsal nerve cord, and tail only present in larval stage
  • Adults usually soft-bodied sac-like, sessile filter feeders

Ascidian Larva
Ascidian "Tadpole" Larva, stained whole mount
See also labeled photo.
Mangrove Tunicate
Mangrove Tunicate, Ecteinascidia sp., stained whole mount.
See also labeled photo.
Sea Peach
Sea Peach, Halocynthia aurantium
Club-Shaped Ascidians
Club-shaped Ascidians, Euherdmania claviformis; La Jolla, CA
Tunicate, possibly Pyura sp.
Social Tunicate
Social Tunicate, Metandrocarpa taylori; La Jolla, CA.
Star Tunicate
Pacific Star Tunicate, Botryllus sp.; a colonial form; Encinitas, CA.
Sea Pork
Sea Pork, Aplidium sp.; a colonial form: each small orange spot is a single individual; La Jolla, CA.

Phylum Chordata
Subphylum Cephalochordata Lancelets


  • Elongate, laterally flattened, fish-like animals
  • Tail and notochord persist throughout life
  • Presence of tail (caudal) fin
  • Notochord extends anteriorly past nerve cord
  • Muscles segmented into myomeres
  • Burrow in marine sediments
Lancelet (aka Amphioxus), Branchiostoma lanceolatum, stained whole mount
See also labeled photo.
Lancelet cross section
Lancelet (aka Amphioxus), Branchiostoma lanceolatum, stained cross section from mid-pharynx
See also labeled photo.
Pikaia gracilens model; Cambrian (Burgess Shale)
Pikaia gracilens fossil cast; Cambrian Period, 505 mya; Burgess Shale, BC, Canada

Phylum Chordata
Subphylum Vertebrata Vertebrates


  • Brain enclosed in cartilagenous or bony cranium
  • Fewer pharyngeal gill slits (used for respiration instead of feeding)
  • Notorcord supplemented by or replaced with segmented vertebrae in most
  • Larger, more complex brain and sense organs
  • More complex visceral organs
  • Includes fishes (jawless, cartilagenous, and bony), amphibians, reptiles, birds, and mammals
  • Sometimes alternatively called the Craniata (with Vertebrata excluding the hagfishes)
Haikoulela Fossil
Haikouella lanceolata fossil; Early Cambrian, 520 mya (Yunnan, China); The fish-like shape and segmented muscles are visible in these poorly preserved fossils
Haikoulela model
Haikouella lanceolata model; Cambrian (Yunnan, China); This species is regarded as the most basal vertebrate (craniate) or the sister group of the vertebrates (craniates)
This page last updated 24 July 2015 by Udo M. Savalli ()
Images and text Udo M. Savalli. All rights reserved.