Chapter 2 Origin of Chordates

Protostomes

Blastopore becomes mouth

Spiral Cleavage

Schizocoelic Coelom

Determinant Cells

Deuterostomes

Blastopore becomes anus

Radial Cleavage

Entercoelic Coelom

Indeterminate Cell

Blastocyst

An early stage of embryo described as a 'ball of cells'

Cleavage

The division of cells from the egg/zygote

Radial Cleavage

cells are aligned as they divide

Spiral cleavage

cells are offset from each other

Gastrulation

Cells growing inward (invagination) to form the gut.

Blastopore

The first opening into the indentation of gastrulation.

In protostomes, what does the blastopore become?

The mouth.

In deuterostomes, what does the blastopore become?

The anus.

What are the three primary germ layers formed after gastrulation?

Ectoderm

Endoderm

Mesoderm

Ectoderm

outer layer

Endoderm

inner layer that forms the lining of the gut

Mesoderm

middle layer between the ectoderm and endoderm

Coelom

internal body cavity.

Schizocoelom

body cavity made from solid mass of mesodermal cells splitting

Enterocoelom

body cavity forming from the outpocketing of the gut that pinches off

What is the notochord?

A slender rod that forms from mesoderm, dorsal to the coelom and ventral of the nerve cord.

hydrostatic organ

outer fibrous sheath encloses incompressible fluid (prevents axial compression)

Pharyngeal Slits

In the pharynx, used for Filter feeding and in some cases, respiration.

Dorsal hollow nerve cord

Formed by invagination of the ectoderm into the neural plate, it will form the CNS (Central Nervous System)

Endostyle

A glandular groove in the floor of the pharynx used in filter feeding.

Thyroid gland

produces thyroid hormones and calcitonin

What are the Endostyle and the Thyroid Gland both involved in?

iodine metabolism

Postanal tail

A posterior elongation of the body extending beyond the anus.

larval stage of Protochordates

pelagic (residing in open water between the surface and the bottom)

Planktonic

riding from place to place primarily in currents and tides rather than their own efforts

Phylum Echinodermata

Includes sea star (starfish), sea urchin, sand dollar, sea cucumber, sea lily

Phylum Echinodermata Characteristics

Unsegmented adult body

Endoskeleton of calcium carbonate

No head or brain, but has a nerve ring

Pentaradial symmetry

Sex Organs of Protochordates

dioecious (Sperate sex organs) or monoecious (Have both sex organs)

Phylum Hemichordata

half chordate or marine benthic "worms"

benthic

living on or within a marine substrate

What are the two major classes of Hemichordata?

Enteropneusta (acorn worms) and Pterobranchia.

What is the larval stage of hemichordates called?

Tornaria larva.

Hemichordates similarities to echinoderm characteristics

Tornaria larva of hemichordata resembles auricularia larva of echinoderms

Hemichordates similarities to chordate characteristics

Pharyngeal slits and Dorsal nerve cord in collar region invaginated into deeper collar chord

Class Enteropneusta

acorn worms, under Phylum Hemichordata

Class Pterobranchia

tube worms, under Phylum Hemichordata that may have evolved from acorn worms

Patterning

specifying general regions of an embryo which determines where body parts are positioned

Patterning in Chordates

The reverse of those in all other animals, including hemichordates (i.e., ventral gene action in non-chordates is dorsal in chordates

Cephalochordata

A subphylum of chordates that includes Burrowing filter feeders.

oral hood

supports food-processing equipment of Cephalochordata, including the wheel organ, ciliated tracts that sweep food into the mouth

What are cephalochordates also known as?

Amphioxus or lancelets.

Hatschek's pit or groove

a ciliated invagination that secretes mucus to help collect food particles in Cephalochordatas

Urochordates

Subphylum of Chordata with simple, saclike body (as adults)

What are Urochordates also known as?

tunicates

What is the outer body covering of urochordates called?

Tunic or test.

What are the two classes of Urochordata?

Ascidiacea (sea squirts) and Larvacea (Appendicularia).

Annelid Chordate theory

Chordates evolved from from annelids or arthropods

Auricularian hypothesis

The hypothesis that chordates evolved from echinoderms.

What is the hypothesis regarding the evolution of chordates?

They may have evolved from echinoderms (auricularian hypothesis) or from annelids or arthropods.

What is the fate of the pharyngeal arches in chordates?

They become ventral, unlike in hemichordates where they were dorsal.

What are the three groups included in protochordates?

Hemichordata, cephalochordates, and urochordates.

What is the significance of Hatschek's pit in cephalochordates?

It is a ciliated invagination that secretes mucus to help collect food particles.

What distinguishes the larval stage of protochordates?

It is pelagic and usually planktonic, while the adult stage is benthic.