Chapter 31.2- Key Innovations in Animal Evolution

tissue

groups of cells sharing a common structure & function

parazoa

animals without tissues

eumetazoa

animals with tissues

endoderm

innermost layer that eventually becomes digestive system or respiratory system in some animals

ectoderm

the outer germ layer that develops into external body surface and nervous system

mesoderm

the middle germ layer that develops into muscle & most structures between gut and body surface

diploblasts

only have endoderm and ectoderm

triploblasts

have all three layers

Radiata

phyla Cnidaria & Ctenophora, have radial symmetry, usually sessile/slow-moving, netlike nervous system receiving sensory input from all directions

radial symmetry

body parts arranged around an axis

Bilateria

have bilateral symmetry with anterior, posterior, dorsal, and ventral ends

cephalization

development of an anterior head where sensory organs & nervous tissue are concentrated

acoelomates

don't have body cavity separating gut from body muscles

pseudocoelomates

have a fluid- or organ-filled space between the gut & body wall muscles, partially lined by tissues derived from the mesoderm

coelomates

have a fluid-filled body cavity between the gut and body wall completely lined by the peritoneum

peritoneum

thin tissue derived from mesoderm

mesenteries

membranous extensions of peritoneal inner and outer layers, surrounds the internal organs & suspend them within the coelom

protostomes

one of two clades of bilateria including most phyla of invertebrates

deuterostomes

one of two clades of bilateria including vertebrates & nearest invertebrate relatives

spiral

protostomes have ________ cleavage

radial

deuterostomes have _______ cleavage

segmentation

production of body parts as repeating units