Download Characteristics of Animal Phyla

Characteristics of Animal Phyla
Figure A. Descriptive characteristics (presence of tissues, symmetry, body cavity development, and segmentation) of 12 animal phyla. See
the next pages for explanations of the characteristics.
Descriptions of Characteristics
True Tissues
Tissues are groups of cells that work together to carry out a specific function.
Symmetry
Asymmetry- not symmetrical; no planes intersect the body to produce a mirror image (e.g. sponges)
Bilateral symmetry- a plane intersects the body to produce a single mirror image (e.g. humans)
Radial symmetry- a plane intersects the body at multiple points and produces mirror images; body parts
are arranged around one main axis (e.g. jellyfish)
Spherical symmetry- the animal has an infinite number of planes that intersect the body to produce a
mirror image; the simplest form of symmetry (e.g. Volvox)
Body Cavity
See Figure B.
Acoelomate- body cavity absent; the area between the gut and body wall (mesoderm) is filled with
masses of cells (mesenchyme)
Pseudocoelomate- body cavity (called the pseudocoelom) present; the organism has internal organs
suspended in fluid and enclosed by the muscular body wall (mesoderm)
Coelomate- body cavity (called the coelom) present; the organism has a body cavity lined with muscular
tissue (peritoneum) that contains organs lined with epithelial tissue
Figure B. Body plans for triploblastic, bilateral organisms.
Formation of the Coelom
Coelomate animals are further classified based on whether the blastopore, the first opening of the
embryo, develops into a mouth or the anus.
Protostome- the blastopore of the embryo develops into the mouth of the adult
Deuterostomes- the blastopore of the embryo develops into the anus of the adult
Segmentation
Body segments are specialized regions of the body that may lead to complex organ systems. For example,
insects (phylum Arthorpoda) have three major body segments, the head, thorax, and abdomen and
earthworms (phylum Annelida) have a segmented, ringed body.