Chapter 10: Phylum Platyhelminthes

Phylum Platyhelminthes Contains over 34,000 animal species Can range from 1 mm (or less) to 25 m (beef tapeworm) Triploblastic Acoelomate (has organs) Mesoderm is called the parenchyma (loose tissue that fills in the space between tissues, organs and the body wall. Function of the parenchyma: skeletal support, nutrient storage, motility, may contain regenerative cells, oxygen storage, and transport of materials.

General Characteristics Triploblastic acoelomate Bilateral symmetry Unsegmented Incomplete gut Somewhat cephalized Monoecious Protonephridia Very simple nervous system

Class Turbellaria Free-living flatworms Bottom dwellers in marine and freshwater environments Named for the turbulence that their beating cilia create while swimming Predators and scavengers Mostly black, brown and gray Some have bright colored patterns.

Class Turbellaria Ventral surface contains gland cells Rhabdites- create a mucous sheath around the body Adhesive glands-Attaches worm to a substrate Releaser glands-secretes a chemical that dissolves the attachment Glide over substrates using muscles and mucous secreted by the gland cells.

Class Turbellaria: Digestion/Nutrition Digestive cavity varies from simple to highly branched Pharynx-ingestive organ Sensory cells help to detect food from a distance Digestion begins with enzymes released by the pharynx, then phagocytosis occurs

Class Turbellaria: Respiration/Excretion Respiration via diffusion across the body wall Excretion (ammonia) via diffusion Protonephridia Regulates osmotic pressure in freshwater environments Flame cells: specialized cells that are used to create a different pressure.

Class Turbellaria: Nervous System Similar to nerve net Statocyst Detects the body position in terms of gravity Cerebral ganglion (primitive brain) with neurons Auricles Sensory lobes (chemoreception) Ocelli Light sensitivity Negative reaction

Class Turbellaria: Reproduction Asexually Fission (produce zooids)

Class Turbellaria: Reproduction Sexually Monoecious Internal fertilization Exchange sperm and release eggs (cocoon)

Class Trematoda The Flukes ~8000 species Wide, flat shape Parasitic in vertebrates as adults Feed on host cells or fragments (blood/body fluids) Immature forms can be parasitic in vertebrates or invertebrates (or attached to plants).

Class Trematoda Epidermis called the tegument Glycocalyx Adaptation to allow for a parasitic lifestyle Outer layer is called the glycocalyx Glycocalyx Aids in transport of nutrients, gases and wastes across the body wall Protects the fluke from the host’s immune system

Class Trematoda Most flukes require at least two different hosts to complete their life cycles. Adhesive organs: Oral sucker (surrounds the mouth) Acetabulum (middle of the body) Important trematode parasites of humans: Chinese Liver Fluke (requires 2 intermediate hosts: snail and fish) Human eats raw or poorly cooked fish Schistosome Blood Fluke

Class Cestoidea Tapeworms ~3500 species Endoparasitic Two major endoparasitic adaptations Loss of the mouth and digestive tract (absorb nutrients across the body wall) Consist of repeating units called proglottids (each proglottid contains one or two complete sets of reproductive structures).

Class Cestoidea Body is divided into 3 regions: Scolex Neck Strobila Contains the suckers and hooks Tapeworm will use the scolex to attach itself to the intestinal wall of the host Neck Strobila Consists of proglottids Proglottids contain the reproductive organs Newer proglottids are added as the tapeworm grows Older proglottids mature as they move posteriorly from the neck and begin to produce eggs (gravid).

The testes mature before the eggs, so copulation generally occurs between different proglottids or between two different tapeworms (in the same host). Gravid proglottids break free and are released into the host’s feces.