Concept 34.1: Chordates have a notochord and a dorsal, hollow nerve cord

Flashcards from Concept 34.1 of Pearson's Campbell Biology, Twelfth Edition.

Vertebrate characteristics

Includes:

• Skull and backbones composed of vertebrae

• Jaws and a mineralized skeleton

• Lobed fins

• Limbs with digits

• Amniotic eggs

Vertebrates

Animals with a backbone; includes over 60,000 species

• Include the largest and heaviest animals to have ever lived

  • Smallest is less than a centimeter long

Chordates

Animals belonging to phylum Chordata, made of all vertebrates, urochordates, and cephalochordates

All exhibit, at some point in their life, a:

• Notochord

• Dorsal, hollow nerve chord

• Pharyngeal slits or clefts

• Muscular tail

Chordate characteristics

Includes, at some point in their life, a:

• Notochord

• Dorsal, hollow nerve chord

• Pharyngeal slits or clefts

• Muscular tail

These may appear only during developmental periods

Notochord

A longitudinal, flexible rod between the digestive tube and nerve cord

• Provides flexible skeletal support; may be replaced by a jointed skeleton in adulthood

Nerve cord

Develops from a plate of ectoderm rolled into a neural tube dorsal to the notochord

• After embryonic period, this develops into the central nervous system (brain and spinal cord)

Central nervous system

The nervous system comprising the brain and spinal cord, developed from the fundamental nerve cord

Pharyngeal clefts

Grooves along the outer surface of the pharynx in chordate embryos, later developing into pharyngeal slits opening into the pharynx

Pharyngeal slits

Slits that develop from the pharyngeal clefts that allow water to pass from the mouth to the outside of the body, bypassing the digestive tract

Can function as:

• Suspension-feeding structures in invertebrates

• Gills for gas exchange

• Parts of the ear, head, and neck when developed as arches

Pharyngeal slit functions

Includes:

• Suspension-feeding structures in invertebrates

• Gills for gas exchange

• Parts of the ear, head, and neck when developed as arches

Muscular tail

This is contained posterior to the chordate with skeletal elements and muscles

• Provides propelling force in many species, but can be greatly reduced during embryonic development

Lancelets (Cephalochordates)

Marine suspension feeders named for their bladelike shape, swimming using a simplified fish mechanism

• Retain many of the key chordate characteristics

• Ancestral chordates likely resembled these

Tunicates (Urochordates)

Organisms more closely related to other chordates than lancelets

• Chordate characteristics are most apparent during larval stage, lasting only a few minutes

• Use tail muscles and notochord to swim until settling for metamorphosis

• Adults (sea squirts) are sessile, filtering in and shooting out water for feeding and defense

Sea squirts

Adult tunicates; these draw in and shoot out water to filter out food particles and repel attackers

• These have fewer Hox genes compared to other vertebrates