Patterns of Organization

Just like body symmetry, body patterns are another form of organization used to classify animals. Unicellular Diploblastic Triploblastic

Diploblastic OrganizationDerived from 2 embryological layers:

Figure 7.10

Ectoderm: gives rise to the epidermis (outer layer of body wall)

Endoderm: gives rise to the gastrodermis (lining inside the gut)

Diploblastic Organization

Figure 7.10

Functionally interdependent tissue layers.

Gastrodermis-digestive and muscular cells

Epidermis-epithelial and muscular cells

Ex: Hydra & jellyfish

Triploblastic OrganizationDerived from 3 embryological layers

Mesoderm: gives rise to supportive, contractile, and blood cells

Most have organ-system level organization (excretory, nervous, digestive, reproductive, circulatory, etc.)

Triploblastic Organization

Body cavity is a fluid-filled space in which the internal organs can be suspended and separated from the body wall.

3 subgroups………….

Coelomate(SEE lom ate)

Body cavity completely surrounded by mesoderm

• Organs suspended in the body cavity

Pseudocoelomate

Body cavity not entirely lined by mesoderm

No suspended organs, muscular or connective tissue

Without a coelom

Mesoderm forms a solid mass between ectoderm and endoderm called parenchyma (no particular function)

Acoelomate

The Triploblastic, Acoelomate Body Plan

Chapter 10

Triploblastic, Acoelomate Body Plan

1st animals to exhibit bilateral symmetry and a body organization more complex than that of the sponges.

Triploblastic (3 primary germ layers) Acoelomate (without a coelom)

Phyla

Platyhelminthes Nemertea Gastrotricha

PlatyhelminthesGreek platys=flat and helmins=worms

“Flat Worms”

Phylum Platyhelminthes

34,000 species Range from 1 mm or less to 25 m Mostly worm like creatures that are flattened

body design Tapeworms, Flatworms, Flukes and

Planarian.

Characteristics

Bilateral symmetry Usually flattened &

unsegmented Degree of

cephalization Sac-like digestive

system; absorb food Ladder nervous

system Monoecious: complex

reproductive systems

Varies from simple unbranched chamber to a highly branched system of tubes

Digestion

Class Turbellaria

Freshwater & marine free living bottom dwellers

Crawl on rocks, sand and vegetation Predators and scavengers Colorization mostly black, brown & gray

(marine groups brightly colored) Blind gut (one-way gut); mouth but no anus Photophobic; have eyespots that detect light

Outer Body Covering Covered by a ciliated epidermis Rhabdites: rod-shaped cells that swell to

form a protective mucous sheath around the animal, possibly in response to attempted predation or desiccation

Adhesion glands: produce a chemical that attaches part of the animal to a substrate

Releaser glands: secrete a chemical that dissolves the attachment

Locomotion

Bottom dwellers glide over substrate using cilia and muscular contractions help twist & turn

Lay down a sheath of mucous that aides in adhesion and helps the cilia gain traction

Nutrition Most are carnivores and feed on

small, live invertebrates or scavenge on larger dead animals

Chemoreceptors (auricles): Sensory cells on their head help detect food

Feeding is via a pharynx: muscular opening to the one-way gut that is located mid-body

The pharynx will pin down the prey while enzymes secreted from the mouth soften the tissue. The mouth sucks in the food and digestion is completed inside the cells.

Figure 10.5

Class TurbellariaInternally, no body cavity: organs are held in parenchyma,non-contractile muscle cells that take up space

Reproduction & Environment

Use cross-fertilization

Monoecious: Hermaphroditic

Can reproduce asexually by transverse fission

Produce zooids Figure 10.8