Chapter 32- Animal Evolution Flashcards
cleavage
- a succession of mitotic cell divisions w/o cell growth b/w the divisions
- zygote undergoes cleavage to form the blastula
blastula
- multicellular stage of the development of most animals that usually takes the form of a hollow ball
- formed by cleavage of zygote
- undergoes gastrulation to become gastrula
gastrulation
- process during which the layers of embryonic tissues that will develop into adult body parts are produced
- one end of the embryo folds inward, expands, and eventually fills the blastocoel, producing germ layers
- preceded by the blastula stage
- results in gastrula stage
gastrula
- developmental stage resulting from gastrulation
- first stage to have germ layers
archenteron
- pouch inside gastrula that is formed by gastrulation
- opens to the outside via the blastopore
- develops into “gut”
larva
sexually immature form of an animal that is morphologically distinct from the adult, usually eats a different food, and may even have a different habitat that the adult
-eventually undergo metamorphosis
metamorphosis
developmental transformation of an animal larva into a juvenile that resembles an adult but is not yet sexually mature
Hox genes
- homeobox-containing family of genes unique to animals
- play important roles in the development of animal embryos, controlling the expression of dozens or even hundreds of other genes that influence animal morphology
- development of Hox genes proposed to be involved in the Cambrian explosion
Cambrian explosion
- a wave of animal diversification that occurred 535-525 million years ago
- great increase in the diversity of animal phyla
- decline in the diversity of Ediacaran life forms
- 3 popular hypotheses behind phenomenon: predator-prey relationships, atmospheric changes, and changes in the regulation of development
Ediacaran
- first generally-accepted macroscopic fossils of animals appear
- 565 to 550 million years ago
radial symmetry
- type of symmetry found in a pie
- has a dorsal/ventral orientation
- lacks anterior/posterior and left/right orientation
- commonly seen in sessile and planktonic animal
- equips animal to meet the environment equally well from all sides
bilateral symmetry
- two-sided symmetry seen in a shovel
- has 2 axes of orientation: dorsal/ventral and anterior/posterior
- typically found in actively moving animals
- most bilateral animals have a CNS that enables them to coordinate complex movements
cephalization
an evolutionary trend commonly seen in animals w/ bilateral symmetry in which sensory equipment is concentrated at the anterior end, including a CNS in the head
ectoderm
- germ layer covering the surface of the embryo
- gives rise to the outer covering of the animal and CNS
endoderm
- innermost germ layer that lines the archenteron
- gives rise to the lining of the digestive cavity and organs such as the liver and lungs
diploblastic
- describes an animal w/ only 2 germ layers (ectoderm and endoderm)
- includes cnidarians and ctenophorians
mesoderm
- 3rd germ layer found in all bilaterally symmetrical animals
- fills most of the space b/w the ectoderm and endoderm
- forms the muscles and most other organs b/w the digestive tract and the outer covering of the animal
triploblastic
- describes an animal w/ all 3 germ layers
- includes all animals w/ bilateral symmetry
coelom
-body cavity found in most triploblastic animals
body cavity
- a fluid- or air-filled space located b/w the digestive tract and the outer body wall
- holds internal organs
protostome development
- mouth 1st
- spiral and determinate cleavage
- solid masses of mesoderm split and form coelom
- blastopore becomes mouth
- eg, molluscs, annelids
deuterostome development
- mouth 2nd (anus 1st)
- radial and indeterminate cleavage
- folds of archenteron form coelom (outpockets)
- blastopore becomes anus
- eg, echinoderms, chordates
spiral cleavage
- cleavage in which the planes of cell division are diagonal to the vertical axis of the embryo
- smaller cells are centered over the grooves b/w larger underlying cells
determinate cleavage
- cleavage that rigidly casts the developmental fate of each embryonic cell very early
- isolated cell cannot form into a whole animal
radial cleavage
- cleavage in which the planes of cell division are either parallel or perpendicular to the vertical axis of the embryo
- tiers of cells are aligned, one directly above the other
indeterminate cleavage
- cleavage that produces cells with the capacity to develop into a complete embryo
- how multiple offspring are possible (e.g., twins)
blastopore
- indentation that during gastrulation leads to the formation of the archenteron
- opening of gastrula
metazoa
-monophyletic clade including all animals
eumetazoans
- clade of “true animals” with true tissues
- includes all animals except sponges
bilaterians
- clade of animals w/ bilateral symmetry and 3 germ layers
- contains the majority of animal phyla (all except porifera, cnidaria, and ctenophora)
- Cambrian explosion was primarily a rapid diversification of bilaterians
ecdysozoans
- clade of animals in molecular phylogeny that secrete exoskeletons
- dependent on a hormone
- includes nematodes and arthropods
lophotrochozoans
- clade of animals in molecular phylogeny that may develop lophophores or go through a trochophore larval stage
- dependent on feeding mode
- includes platyhelminthes, rotifers, ectoprocts, brachiopods, molluscs, and annelids
lophophore
- a structure consisting of a crown of ciliated tentacles that function in feeding
- found in some lophotrophozoans, such as ectoprocts
- “crest”“carry”
trochophore larva
-larval stage of development found in some lophotrophozoans
