Patterns of Organization n Just like body symmetry

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

Diploblastic Organization Derived from 2 embryological layers: Ectoderm: gives rise to the epidermis (outer layer of body wall) Endoderm: gives rise to the gastrodermis (lining inside the gut) Figure 7. 10

Diploblastic Organization Functionally interdependent tissue layers. Gastrodermis-digestive and muscular cells Epidermis-epithelial and muscular cells Ex: Hydra & jellyfish Figure 7. 10

Triploblastic Organization Derived 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

Acoelomate Without a coelom Mesoderm forms a solid mass between ectoderm and endoderm called parenchyma (no particular function)

The Triploblastic, Acoelomate Body Plan Chapter 10

Triploblastic, Acoelomate Body Plan n 1 st 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 n Platyhelminthes n Nemertea n Gastrotricha

Platyhelminthes Greek platys=flat and helmins=worms “Flat Worms”

Phylum Platyhelminthes n n 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 n n n Bilateral symmetry Usually flattened & unsegmented Degree of cephalization Sac-like digestive system; absorb food Ladder nervous system Monoecious: complex reproductive systems

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

Class Turbellaria n n n Freshwater & marine free living bottom dwellers Crawl on rocks, sand 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 n n 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 n n 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 n n 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 Turbellaria Internally, no body cavity: organs are held in parenchyma, non-contractile muscle cells that take up space

Reproduction & Environment n n Use crossfertilization Monoecious: Hermaphroditic Can reproduce asexually by transverse fission Produce zooids Figure 10. 8