I. Protostomia - Pseudocoelom

Transcription

1 Z202-Unit3 Chapter 15 Pseudocoelomate Animals I. Protostomia - Pseudocoelom A. Structure - Embryonic blastocoel persist as a space or cavity - Pseudocoel internal cavity surrounding the gut, lacks mesoderm (peritoneal lining) of true coelom - Polyphyletic group (derived from more than 1 ancestor) B. Biological Contributions - Pseudocoel filled w/ fluid or gelatinous material - Provides greater freedom of movement - Space for development of digestive, excretory, & reproductive system - Simpler to distribute materials throughout body - Provides storage area (temporarily) for waste products - Cavity provides hydrostatic skeleton & base for muscles (provide movement)

2 II. Pseudocoelomates A. Diversity - less complex than eucoelomates - all have body call that is often syncytial, a dermis & muscles surrounding the pseudocoel - digestion is extracellular complete (except the parasitic Acanthacephala) - digestive tract, gonads, & excretory organs are within the pseudocoel bathed in perivisceral fluid - epidermis secretes nonliving cuticle (collagen) in some III. Phylum Gnathostomulida Jaw worms A. General Characteristics - Over 80 species: marine & brackish waters (intertidal) - Delicate worm-like animals range mm long, ciliated (one per cell) - Live in sandy coastal sediments; survive low oxygen - Previously classified with planaria - Pharynx has lateral jaws scrape fungi & bacteria from substrate - Sexual reproduction (internal fertilization) IV. Phylum Rotifera A. General Characteristics - Found worldwide w/ over 2000 species - Most are freshwater; few marine, terrestrial or parasitic - Aquatic species are mostly benthic, some pelagic - Ciliated crown w/ the corona beating like a rotating wheel

3 - Highly diverse in color, shape, & size; some colonial - 2 forms: Floaters (globular, creepers elongated) Sessile (vase-like) - Many endure dessication & temp by encystment (resemble sand grains until rehydrated) - Cyclomorphosis (regular variation in body form to accommodate seasonal and food changes) B. Form & Function - rotifer head has head, trunk, & tail or foot/toes (only corona ciliated & aid in feeding & locomotion) - non-ciliated central area (below corona) has sensory bristles & mouth - all have a fibrous epidermis layer; some secrete cuticle C. Internal Features 1. Pseudocoel - large, filled w/ fluid and amoeboid cells 2. Digestion - Corona cilia filter out unsuitable particles muscular pharynx (mastax)equipped w/ hard jaws (trophi) Strategies: Trappers - funnel-shaped area to entrap prey Hunters - project trophi to seize prey

4 3. Protonephridial tubules w/ flame cells empty into common bladder - Bladder pulsates & empties into cloaca then released out anus 4. Osmoregulation - water enters by mouth 5. Bilobed ganglion dorsal w/ paired nerves leading to organs 6. Sensory organs include eyespots, sensory bristles & papillae, ciliated pits & dorsal antennae 7. Reproduction: - Dioecious (males are smaller than females) - In some classes, males occur briefly or are unknown - Females provide yolk to developing egg - Some cases of parthenogenesis (asexual), or haplodiploidy (unfertile eggs developed into male) - Internal fertilization (sperm enters pseudocoel)

5 V. Phylum Nematoda "Roundworms" A. Diversity - Approximately 25,000 species described; perhaps 1/2 million exist - live virtually everywhere; topsoil may contain billions per acre; polar to tropics, mtn. tops to deep sea - parasitize nearly all animals & plant species (economically important) - predatory forms eat rotifers, tardigrades, annelids & other worms - important food source for mites, insects, larvae, fungi - often studied for models of genomes & cell development & differentiation B. Form & Function 1. Distinguishing Characteristics - cyclindrical shape (fusiform) - nonliving cuticle (collagen) above well developed muscle layer - lack motile cilia or flagella (except 1 species) = undulate - longitudinal muscles in body wall (lack circular muscles) 2. Hydrostatic skeleton (pseudocoel) order of magnitude greater than any other invertebrate Ascaria avg mm Hg Sea Anemone avg mm Hg Earthworm avg mm Hg 3. Lack Protonephridia (one or more large glands excrete)

6 4. Nervous - ring of nerve tissue and ganglia around the pharynx - 2 nerve cords (one dorsal, one ventral) - Sensory perception: Papillae (head & tail sensory) Amphids (bare nerve endings) 5. Digestion Extracellular Complete - muscular pharynx w/ triradiate lumen - alimentary canal consists of mouth, pharynx, intestine, short rectum & anus - pharynx sucks food in 6. Metabolism (anaerobic & aerobic forms) = parasitic 7. Reproduction - most dioecious (male smaller than female, hooked end in some) - internal fertilization and eggs stored in uterus - often have complex life cycles

7 Hookworm: Filarial Worms:

8 8. Some nematodes parasites: - Ascaris (vegetable ingestion) - Hookworms (water borne, skin entry) - Trichina worms (dormancy in meat, ingestion) - Pinworms (fecal contamination) - Filarial worms (mosquito vectors) VI. Phylum Ectoprocta Bryozoa or Moss animals A. General Characteristics - Sessile or slow sliding/crawling colonial aquatic animals, typically less 0.5mm - large colonies with each member (zooids) feeding by extension of lophophores - produce exoskeleton around colony (gelatinous, chitinous, or calcified, siliceous) makes them resemble corals VII. Phylum Brachiopoda Lamp Shells A. General Characteristics - Ancient group of 12,000 fossils and 325 species; considered living fossils - sessile, bottom-dwelling marine animals seen at nearly all ocean depths - resemble bivalved mollusks possess 2 calcareous shell valves (dorsal & ventral valves instead of right & left) - typically ventral valve is slightly larger than dorsal - flourished and dominated during Paleozoic & Mesozoic periods (fossil indicators)

9 VIII. Phylum Phoronida A. General Characteristics - small (30 cm) worm-like animals consisting of approximately 20 species - most live on substrate in shallow coastal water - each worm secretes a leathery or chitinous tube to live in

10 VI. Phylogeny & Classification A. Phylogeny - After ancestral deuterostomes diverged, protostomes split into 2 large groups: Ecdysozoa Lophotrochozoa - nematodes are by far the most adaptive of this set of organisms; mostly due to their ability to survive suboptimal conditions - wide range of unusual strategies including: cryptobiosis hermaphroditism alternation of generations, etc - aids groups to survive and adapted B. Classification Phylum Gnathostomulida Phylum Micrognathozoa Phylum Rotifera Phylum Acanthocephala Phylum Cycliophora Phylum Gastrotricha Phylum Entoprocta Phylum Ectoprocta Phylum Brachiopoda Phylum Phoronida Phylum Nematoda Phylum Nematomorpha Phylum Kinorhyncha Phylum Priapulida Phylum Loricifera Phylum Onychophora Phylum Tardigrada