Chapter 9 Flashcards
(20 cards)
Asymmetry
the lack or absence of symmetry
Radial Symmetry
symmetry around a central axis, as in a starfish or tulip flower
Bilateral Symmetry
symmetrical arrangement of an organism or part of an organism along a central axis so an organism can be divided into two equal halves
Ectoderm
one of three primary germ layers. The ectoderm is the most exterior layer of skin
Endoderm
Innermost of the primary germ layers. Gives rise to the respiratory tract, gastrointestinal tract.
Mesoderm
One of three primary germ layers. Middle layer giving rise to a number of structures including bone, muscle, connective tissue and middle layer of skin
Diploblastic
describing an animal with a body wall composed only of two layers, ectoderm and endoderm
Triploblastic
describing an animal having a body composed of three germ cell layers
Protostome
first opening in the embryo becomes the mouth. At this stage of development the later specialization of any given embryonic cell has already been determined.
Radial Cleavage
cleavage that is typical of deuterostomes and that is characterized by arrangement of the blastomeres of each upper tier directly over those of the next lower tier resulting in radial symmetry
Spiral Cleavage
cleavage that is typical of protostomes and that is characterized by arrangement of the blastomeres of each upper tier over the cell junctions of the next lower tier
Deuterostome
distinguished from protostomes by their deuterostomic embryonic development. The first opening becomes the anus rather than the mouth
Coelom
fluid filled body cavity that is completely lined by tissue created from the mesoderm.
Pseudocoelom
second body cavity which occupies a space between the mesoderm of the body wall and the endoderm of the gut
Acoelomate
an invertebrate lacking a coelom. such as flatworms and characterized by bilateral symmetry and a digestive cavity that is the only internal cavity
Lophotrochozoa
One of the two distinct clades within protostomes
Ecdysozoa
Other major grouping of clades including Arthropoda, Nematoda etc
Incomplete Gut
only have one opening for food intake and waste removal
Complete Gut
clear beginning and end with separate openings for food and waste
Metamerism
phenomenon of having a linear series of body segments fundamentally similar in structure. Each segment is called somites or metameres