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Zoology

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skull parts

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Vertebrate structure and morphology

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Concepts:

Questions?

Primative animals:

Retained primative features:

Shared characters

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Characters shared by related phyla:

Related "phyla":

Except: one group has no internal skeleton, another: no digestive tract. Another: lacks a coelom (body cavity).

Chordata

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Characters:

  1. notochord (= back + cord)
  2. dorsal hollow nerve cord (nerve cord)
  3. pharynx
  4. ventral heart
  5. cephalization
  6. tail extending posterior to the anus
  7. metamerism
    • segmentation of some features of the body



Figure 2.1 Stylized larval urochordata drawing
Left Right

Primative vs derived

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Agnatha

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Cyclostomata

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Hagfishes

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Hagfish

  • exclusively marine
  • evolved Lower cambrian, at least 550 myo, probably.
  • eyes are vestigial
  • gills in pouches
  • primarily scavengers
  • sister group of all animals to follow
  • craniata (phylum) is hagfishes combined with sister group vertebrata (subphylum)
  • Myxinoidea (Myx = slime) is the first subclass of Agnatha (the dubious class)

Lamprey

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Lamprey

Pteraspidomorpha

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Pteraspidomorpha (= wing + shield + form)

  • appear 500myo, before any other vertebrates except conodonts
  • principal representative: pteraspids (order Heterostraci)
  • pteraspids have heavy armour covering head and anterior of body.
  • most have rostrum projecting over the mouth
  • bizarre spines on the shield
  • no paired fins
  • lateral eyes
  • two nostrils, common exit from all of the gill pouches (unlike other agnathans)
  • possibly slow swimmers, but not bottom feeders
  • most were marine

Anaspids

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Chordata species ranking

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Other agnathans

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Actinopterygii

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Actinopterygii, the ray-finned fishes. Most bony fishes belong to this subclass, but they do not include the ancestors of land vertebrates. We know from cranial bone patterns, and the nature of the venous system and reproductive ducts.

Panderichthyida

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Mesoderm

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Mesoderm formed by:

see: embryogenesis

Recommended references:

  • Gilbert, and Ranio (eds.). 1997. Embryology: constructing the organism One of the few comparative texts. Invertebrate embryology is followed by chapters on cephalochordates, fishes, amphibians, reptiles, and birds, and mammals. (amazon)

Secretory glands

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Secretory gland

mucous cell: (epidermal)

proteinaceous cell: (epidermal)

Pigment cells

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chromatophores of the epidermis:

chromatophores of the dermis: