Biol 108 - Topic 26: Introduction to chordates

Chordates (phylum Chordata) are ______ animals that belong to the clade ______

bilaterally symmetrical; Deuterostomia

Chordate body plan:

bilateral symmetry, a coelom as the body cavity, and segmented bodies

• share deuterostomes devl’mt w/ echinoderms

Most chordates have ______

vertebral columns (vertebrates)

Chordates consist of all vertebrates and two groups of invertebrates, the____ and _____

urochordates and cephalochordates.

Chordate shared derived traits:

1. Notochord: longitudinal, flexible rod located dorsally between the digestive tract and nerve cord that provides flexible skeletal support.
   The notochord develops from the dorsal mesoderm during embryogenesis (organ systems begin to develop from embryonic layers) and is present in all chordate embryos and some adults.

2. Dorsal, hollow nerve cord that develops from a plate of ectoderm during embryonic development.

3. Pharyngeal slits or clefts: embryonic pharyngeal clefts develop into slits that open to the outside of the body.
   Functions: filter-feeding structures (invertebrate chordates), gas exchange (vertebrates, excl. tetrapods), skeletal and muscle elements of the head and neck in tetrapods.

4. Muscular, post-anal tail: contains skeletal elements and muscles, and provides propulsive force in most aquatic chordates (swimming tail).
   The tail is greatly reduced during embryonic development in some chordates.

notochord (Chordate shared derived traits)

longitudinal, flexible rod located dorsally between the digestive tract and nerve cord that provides flexible skeletal support.

• The notochord develops from the dorsal mesoderm and is present in all chordate embryos and some adults.

dorsal hollow nerve cord (Chordate shared derived traits)

develops from a plate of ectoderm during embryonic development.

Pharyngeal slits or clefts: (Chordate shared derived traits)

embryonic pharyngeal clefts develop into slits that open to the outside of the body.

• Allows water entering the mouth to exit through the pharyngeal slits, preventing it from passing into the digestive tract

• Functions: filter/suspension-feeding structures (invertebrate chordates), gas exchange (vertebrates, excl. tetrapods), skeletal and muscle elements of the head and neck in tetrapods.

• Only present during embryonic devl’mt of tetrapods

• Gas exchange - Gills develop along the pharyngeal arches

Muscular, post-anal tail: (Chordate shared derived traits)

contains skeletal elements and muscles, and provides propulsive force in most aquatic chordates (swimming tail) and grip/balance.

• The tail is greatly reduced during embryonic development in some chordates.

• Most adult chordates have a tail posterior to the anus

  • The digestive tract of most non-chordates extends full body length

Invertebrate chordates (Two groups)

Lancelets (Cephalochordata) and Tunicates (Urochordata)

Lancelets (Cephalochordata):

• superficially resemble fish, but retain chordate characteristics as adults.

  • Feed by drawing water into the mouth and filtering food particles with mucus-covered pharyngeal slits; mucous net (with food) digested; water passes out via the atriopore.

Tunicates (Urochordata)

the living sister taxa of vertebrates: marine filter feeders (adult tunicates are sessile or pelagic).

• Larval tunicates show chordate shared derived traits, but most are lost in adult tunicates; adults filter-feed using a mucus-covered pharyngeal basket.

embryogenesis

(organ systems begin to develop from embryonic layers)