Complete List of Terms and Definitions for Chapter 32

Terms Definitions
cleavage (1) The process of cytokinesis in animal cells, characterized by pinching of the plasma membrane. (2) The succession of rapid cell divisions without significant growth during early embryonic development that converts the zygote to a ball of cells.
spiral cleavage A type of embryonic development in protostomes, in which the planes of cell division that transform the zygote into a ball of cells occur obliquely to the polar axis, resulting in cells of each tier sitting in the grooves between cells of adjacent tiers.
bilateral symmetry Characterizing a body form with a central longitudinal plane that divides the body into two equal but opposite halves
Arthropods A group of organisms that have jointed appendages, an exoskeleton, bilateral symmetry, and reproduce sexually; insects, arachnids, millipedes and cenitpedes, and crustaceans
Gastrulation In animal development, a series of cell and tissue movements in which the blastula-stage embryo folds inward, producing a three-layered embryo, the gastrula.
acoelom has endoderm, mesoderm, and ectoderm, but no body cavity
pseudocoelom A body cavity that is not completely lined by tissue derived from mesoderm
lophotrochozoans Member of a group of animal phyla identified as a clade by molecular evidence. Lophotrochozoans include organisms that have lophophores or trochophore larvae.
pluripotent Stem cells with the potential to differentiate into most any type of cell
Gastrula An embryonic stage in animal development encompassing the formation of three layers: ectoderm, mesoderm, and endoderm.
ectoderm The outermost of the three primary germ layers in animal embryos; gives rise to the outer covering and, in some phyla, the nervous system, inner ear, and lens of the eye.
Porifera coextensive with the subkingdom Parazoa: sponges
protostome development In animals, a developmental mode distinguished by the development of the mouth from the blastopore; often also characterized by spiral cleavage and by the body cavity forming when solid masses of mesoderm split.
mesoderm the middle germ layer that develops into muscle and bone and cartilage and blood and connective tissue
Evo-devo Evolutionary developmental biology; a field of biology that compares developmental processes of different multicellular organisms to understand how these processes have evolved and how changes can modify existing organismal features or lead to new ones.
diploblastic having 2 germ layers: ectoderm and endoderm.
archenteron The endoderm-lined cavity, formed during the gastrulation process, that develops into the digestive tract of an animal.
mollusks Invertebrates with soft, unsegmented bodies that are often protected by a hard outer shell
Ecdysozoans Animals that have an exoskeleton that is a thick non living covering. It provides protection and support, it does not grow with the organism. Some exoskeletons contain chitin and the exoskeleton allows for new mechanisms for locomotion and respiration.
radial symmetry a body plan in which the body parts are arranged in a circle around a central point
differentiation process in which cells become specialized in structure and function
chordata phylum characterized by a dorsal nerve chord, notochord, post anal tail and pharyngeal slits
Eumetazoa Members of the subkingdom that includes all animals except sponges. (true tissues)
blastula The hollow ball of cells marking the end stage of cleavage during early embryonic development
coelom a body cavity completely lined with mesoderm.
endoderm the inner germ layer that develops into the lining of the digestive and respiratory systems
echinoderms invertebrates with an internal skeleton and a system of fluid-filled tubes called a water vascular system
deuterostome development In animals, a developmental mode distinguished by the development of the anus from the blastopore; often also characterized by radial cleavage and by the body cavity forming as outpockets of mesodermal tissue.
Metazoa first real animal, multicellular animals having cells differentiated into tissues and organs and usually a digestive cavity and nervous system
radial cleavage A type of embryonic development in deuterostomes in that the planes of cell division that transform the zygote into a ball of cells are either parallel or perpendicular to the polar axis, thereby aligning tiers of cells one above the other.
nematodes roundworms
annelida segmented worms: earthworms
flatworms A group of often parasitical worms that have bilateral symmetry, a one opening digestive system, and the beginnings of a brain; tapeworm
triploblastic Possessing three germ layers: the endoderm, mesoderm, and ectoderm. Most eumetazoa are triploblastic.
blastopore The opening of the archenteron in the gastrula that develops into the mouth in protostomes and the anus in deuterostomes