Acoelomates and other groups Flatworms! Chapter 10

Basics Multicellular Primary bilateral symmetry Digestive system incomplete Most are monoecious Triploblastic- have three germ layers Lack a coelom or a pseudocoelom

Taxonomic Groupings P. Platyhelminthes P. Nemertea C. Turbellaria C. Trematoda C. Monogenea C. Cestodoa P. Nemertea

Acoelomate Characteristics No body cavity ectoderm mesoderm Gut endoderm

Acoelomate Characteristics Triploblastic Mesoderm (mesenchyme, parenchyma) Gut Ectoderm Endoderm

Parenchyma Form of tissue Loose Vacuolated Contains more cells and fiber than mesoglea of the cnidaria.

Acoelomate Characteristics Bilateral Symmetry Anterior: toward the front of the body Posterior: toward the rear of the body

Acoelomate Characteristics Cephalization the concentration of sensory organs in the head of the animal Eye spots Auricles

Flatworms are triploblasts with well-developed organ systems digestive excretory nervous reproductive

Excretory System Flame Cells or Protonephridia

Nervous System Ladder-type. Brain, and 1 or more ventral nerve cords and Transverse nerves.

Four Classes Class Turbellaria: (the planarians) mostly free-living. Class Trematoda: (the flukes) all parasitic. Class Monogenea: (monogeneans) all parasitic. Class Cestoda: (the tapeworms) all parasitic.

I. Class Turbellaria (planarians) photosynthetic endosymbionts Acoels Rhabdocoels Polyclads Triclads

Triclad flatworm with “3-branch” gut diatoms Triclad flatworm with “3-branch” gut Acoel flatworms do not have a well-formed gut cavity Polyclad flatworms have a many branched gut

Rhabdocoel turbellarian phalloidin stain (ventral body wall musculature) longitudinal and circumferential (circular) muscles bulbous, muscular pharynx © Matthew Hooge

Polyclads swimming with undulatory body waves statocyst of acoel

Turbellarians are often predatory specialists ascidian polyclads feeding bryozoans planarian feeding on a midge

Asexual reproduction and regeneration

Sexual Reproduction

Turbellarian Diversity

Variation in color patterns and shapes among polyclad turbellarians

Flatworm mimicry of nudibranchs Aposematic coloration in nudibranch families Chromodorididae and Phyllidiidae Mimicry by flatworm family Psuedocerotidae

Phylum Platyhelminthes, Class Turbellaria Bipalium

Terrestrial Planarians!

Lake Baikal Planarians Up to 2.0 feet long!

Temnocephalan Turbellarians Live as either ectocommensals or ectoparasites on the surface of crustaceans, insects, molluscs and turtles

Temnocephalan Turbellarians Live as either ectocommensals or ectoparasites on the surface of crustaceans, insects, molluscs and turtles