Introductory Terms Flashcards
Biradial symmetry
A combination of radial and bilateral symmetry, as in the Ctenophores. Here, the body components are arranged with similar parts on either side of a central axis, and each of the four sides of the body is identical to the opposite side but different from the adjacent side.
Radial Symmetry
a basic body plan in which the organism can be divided into similar halves by passing a plane at any angle along a central axis, characteristic of sessile and bottom-dwelling animals, as the sea anemone and starfish.
Bilateral symmetry
a basic body plan in which the left and right sides of the organism can be divided into approximate mirror images of each other along the midline.
Dorsal
situated on or toward the posterior plane in humans or toward the upper plane in quadrupeds.
Ventral
situated on or toward the lower, abdominal plane of the body; equivalent to the front, or anterior, in humans.
anterior
pertaining to or toward the head or forward end of the body.
Posterior
pertaining to or toward the rear or caudal end of the body.
Lateral
Of or pertaining to the side; situated at, proceeding from, or directed to a side
Medial
situated in or pertaining to the middle; median; intermediate.
Reynolds number
a dimensionless number, v ρ l /η, where v is the fluid velocity, ρ the density, η the viscosity and l a dimension of the system. The value of the number indicates the type of fluid flow
Cilia
minute hairlike organelles, identical in structure to flagella, that line the surfaces of certain cells and beat in rhythmic waves, providing locomotion to ciliate protozoans and moving liquids along internal epithelial tissue in animals.
flagella
a long, lashlike appendage serving as an organ of locomotion in protozoa, sperm cells, etc.
hydrostatic skeleton
A structure found in many cold-blooded organisms and soft-bodied animals consisting of a fluid-filled cavity, the coelom, surrounded by muscles. The pressure of the fluid and action of the surrounding circular, longitudinal, and/or helical muscles are used to change an organism’s shape and produce movement, such as burrowing or swimming.
exoskeleton
an external covering or integument, especially when hard, as the shells of crustaceans
endoskeleton
the internal skeleton or framework of the body of an animal
sagittal plane
a vertical plane which passes from ventral (front) to dorsal (rear) dividing the body into right and left halves
frontal plane
A plane parallel to the long axis of the body and perpendicular to the sagittal plane that separates the body into front and back portions.
transverse plane
plane that divides the body into superior and inferior parts. It is perpendicular to the coronal and sagittal planes.
Bilateria
All animals having a bilateral symmetry, i.e. they have a front and a back end, as well as an upside and downside.
enterocoely
process by which some animal embryos develop in which a mesoderm is formed in a developing embryo, in which the coelom forms from pouches “pinched” off of the digestive tract (also known as the embryonic gut, or archenteron)
schizocoely
A process by which some animal embryos develop. Animals which develop through schizocoely are known as schizocoelomates. Schizocoely occurs when a coelom (body cavity) is formed by splitting the mesodermal embryonic tissue.
Pseudocoel
An internal body cavity of some primitive invertebrates, similar to a coelom but lacking a mesodermal lining.
Coelom
the body cavity of many multicellular animals, situated in the mesoderm and containing the digestive tract and other visceral organs
radial cleavage
holoblastic 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 around the pole to pole axis of the embryo
spiral cleavage
holoblastic 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 so that the blastomeres spiral around the pole to pole axis of the embryo
blastula
an early embryonic form produced by cleavage of a fertilized ovum and consisting of a spherical layer of cells surrounding a fluid-filled cavity.
Blastocoel
The fluid-filled, central cavity of a blastula. Also called segmentation cavity.
Gastrula
An embryo at the stage following the blastula, consisting of a hollow, two-layered sac of ectoderm and endoderm surrounding an archenteron that communicates with the exterior through the blastopore.
Gastrulation
the process in which a gastrula develops from a blastula by the inward migration of cells
Germ layers
each of the three layers of cells (ectoderm, mesoderm, and endoderm) that are formed in the early embryo.
Endoderm
the innermost layer of cells or tissue of an embryo in early development, or the parts derived from this, which include the lining of the gut and associated structures.
Ectoderm
the outermost layer of cells or tissue of an embryo in early development, or the parts derived from this, which include the epidermis and nerve tissue.
Mesoderm
the middle layer of an embryo in early development, between the endoderm and ectoderm.
Diploblastic
having a body derived from only two embryonic cell layers (ectoderm and endoderm, but no mesoderm), as in sponges and coelenterates.
Triploblastic
having a body derived from three embryonic cell layers (ectoderm, mesoderm, and endoderm), as in all multicellular animals except sponges and coelenterates
Larvae
the active immature form of an insect, esp. one that differs greatly from the adult and forms the stage between egg and pupa, e.g., a caterpillar or grub.
Indirect development
biologic development accompanied by a metamorphosis
Settlement
a place, typically one that has hitherto been uninhabited, where people establish a community.
Metamorphosis
a major change in the form or structure of some animals or insects that happens as the animal or insect becomes an adult
Epidermis
The outer, protective, nonvascular layer of the skin of vertebrates, covering the dermis.
Epithelium
Membranous tissue composed of one or more layers of cells separated by very little intercellular substance and forming the covering of most internal and external surfaces of the body and its organs.