Chapter 34: Vertebrates (Chordates and Vertebrates [Gnathostomes])

Sister group

Closest relative of another evolutionary group

Phylum Chordata

Contain all vertebrates and some invertebrates, bilaterian and deuterostomes

Chordate

Animals that at some point during development possess a notochord, dorsal, hollow nerve cord, pharyngeal slits, and muscular post anal tail

Bilaterian

Animal that has bilateral symmetry

Deuterostome

Animal that forms anus first mouth second

a vertebral column

What do invertebrate chordates lack

Derived Character

A trait that arose in the most recent common ancestor of a lineage and was passed on to all of its descendants

Notochord

dorsal hollow nerve cord

pharyngeal slits

muscular post anal tail

What are the derived characters of chordates

Notochord

Longitudinal, flexible rod made of tightly packed mesodermal cells that runs anterior-posterior axis of the dorsal part of the body, offers skeletal support

Mesodermal cells

Cells that originate from the mesoderm

Anterior

Refers to the front of the body, near the head

Posterior

Refers to the back of the body near the tail

Dorsal

Relating to the back/upper side of an animal

Dorsal hollow nerve cord

Develops from the ectoderm to form the central nervous system

Ectoderm

Outer germ layer

Pharyngeal slits/clefts

Series of arches separated by grooves that forms along the outer surface of the pharynx can later develop into slits that open into the pharynx, allows water entering the mouth to exit the body

Pharynx

Hollow area behind the mouth and nose that connects the mouth to the esophagus

Gills

Respiratory organ believed to have evolved from pharyngeal slits

Muscular, post-anal tail

Helps to propel many aquatic species, contains skeletal and muscular elements; greatly reduced in many species

Phylum Cephalochordata

Contains lancelets, invertebrate chordates; sister group to all living chordates, often used for showing derived characteristics of vertebrates

Invertebrate chordate

Chordates that lack a vertebrae

Phylum Urochordata

Contains tunicates (sea squirts), sessile marine invertebrate chordates; more closely related to other chordates than lancelets

Hox genes

Genes that regulate body plants in animals

Italicized

How do you write genes

Normal

How do you write products of genes (ex. proteins)

Vertebrate

A chordate with a backbone

2 or more sets of *Hox* genes and a neural crest

What are the derived characters of vertebrates

Neural crest

Collection of cells that appears along the edges of the closing neural tube of an embryo

Phylum Myxini

Contains hagfishes, marine jawless with rudimentary vertebrae; produce slime to escape predators

Rudimentary vertebrae

Backbone made of cartilage instead of bone

Clade Cyclostoma

Living jawless vertebrates; hagfishes and lampreys

Slime

Sticky substance produced by hagfishes as defense, clogs gills of predators

Phylum Petromyzontida

Contains lampreys, marine or freshwater and can be parasitic; jawless with rudimentary vertebrae

Inset

Mouth of parasitic lampreys

Clade Gnathostoma

Living jawed vertebrates, includes every other vertebrate chordate besides lampreys and hagfish

They have derived characteristic of chordates yet lack a backbone they instead possess a notochord

Why are all chordates not vertebrates

They have a rudimentary backbone made of cartilage and possess all the other derived characters of vertebrates

How are lampreys and hagfishes grouped under vertebrates if they don't have a backbone?