BIO 385 Invertebrate Zoology
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Invertebrate Diversity
Phylum Chordata Chordates

(Click on any image for larger version)

Chordate Characteristics

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

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
  • Note: Pikaia may be either a cephalochordate or a stem-chordate, more basal than any extant group
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 fossil
Pikaia gracilens fossil replica; Cambrian (Burgess Shale)

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 (2 views shown)
Club-Shaped Ascidian
Club-shaped Ascidians, Euherdmania claviformis; La Jolla, CA.
Tunicate, possibly Pyura sp.
Sea Peach
Sea Peach, Halocynthia aurantium
Social Tunicate
Social Tunicate, Metandrocarpa taylori; La Jolla, CA.
Star Tunicate
Pacific Star Tunicate, Botryllus sp.; a colonial form; La Jolla, CA.
Sea Pork
Sea Pork, Aplidium sp.; a colonial form: each small orange spot is a single individual; La Jolla, CA.
Colonial Tunicate, probably Didemnum sp.; La Jolla, CA.

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

Vertebrates are not covered in this class.
To learn more about this subphylum, consider enrolling in BIO 370.
This page last updated 18 March 2017 by Udo M. Savalli ()
Images and text Udo M. Savalli. All rights reserved.