Lecture 22 Invertebrates 3 pdf

Lecture 22 Invertebrates 3 pdf - Invertebrates 3:...

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1 Invertebrates 3: Bilaterian Lophotrochozoa Concept 33.3 Lophotrochozoans Clade identified by molecular data have the widest range of animal body forms Belong to clade Bilateria Most members possess structure called a lophophore or go through a trochophore larval stage Very diverse group that includes 18 animal phyla Lophophore Concept 33.3 Lophotrochozoans, a clade identified by molecular data, have the widest range of animal body plans Very diverse group that includes 18 animal phyla Phylum Platyhelminthes or flatworms ~20,000 species of flatworms, living in marine, freshwater, and damp terrestrial habitats. – Includes many parasitic species, such as flukes and tapeworms They may be flat, but they range in length from microscopic to tapeworms over 20 m long
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2 The Simplest Bilaterians Though structurally more complex than cnidarians or ctenophores, flatworms are simpler than other bilaterians Flatworms are the simplest triploblastic animals, with a middle embryonic tissue layer, mesoderm – Mesoderm gives rise to several internal organs and to true muscle tissue – Unlike other bilaterians, flatworms are acoelomates Four Classes of Flatworms Turbellaria Nearly all free-living (nonparasitic) and mostly marine Pseudobiceros Polycladids (many reach 15 cm in length. These are from Guam) Freshwater. Genus Dugesia commonly known as planarians Dugesia sp. Planarian Anatomy Planarians and other flatworms lack organs specialized for gas exchange and circulation – Their flat shape places all cells close to the surrounding water, and fine branching of the digestive system distributes food throughout the animal – Nitrogenous wastes are removed by diffusion and simple ciliated flame cells help maintain osmotic balance – Like Radiata, most flatworms have a gastrovascular cavity with only one opening and waste is egested through mouth Figure 33.10
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3 Planarian Anatomy Planarians move using cilia on the ventral epidermis, gliding on a secreted mucus film Paired eyespots detect light and lateral flaps provide chemical sensing Nervous system is more complex and centralized than the nerve net of cnidarians – Planarians can learn to modify their responses to stimuli Lateral flaps Planarian reproduction Planarians can also reproduce sexually – These hermaphrodites cross-fertilize Planarians can reproduce asexually through regeneration – The parent constricts in the middle, and each half regenerates the missing end Freshwater turbellarians of genus Dugesia are major model for regeneration Can cut a flatworm into a maximum of 279 pieces - and each one will grow into a new planarian! Time-course of planarium undergoing cephalic regeneration The blastema is the unpigmented area and is the area that is filled with stem cells (numbers refer to days after decapitation) Use of RNAi to identify genes linked to regeneration
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4 Animals that are starved will reduce their size, while maintaining their form and function. Feeding will reverse this condition and return the animals to
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Lecture 22 Invertebrates 3 pdf - Invertebrates 3:...

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