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Chapter 7: Marine Invertebrates

Chapter 7: Marine Invertebrates. Bilateral Symmetry and the Advancements of the Worms. Oh, to be a Worm!. Adaptive trends exhibited by worm phyla: Bilateral symmetry Cephalization –development of a head region Coelom development Increasing development of nervous sensory systems .

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Chapter 7: Marine Invertebrates

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  1. Chapter 7: Marine Invertebrates Bilateral Symmetry and the Advancements of the Worms

  2. Oh, to be a Worm! Adaptive trends exhibited by worm phyla: • Bilateral symmetry • Cephalization –development of a head region • Coelom development • Increasing development of nervous sensory systems.

  3. Bilateral Symmetry • “Bilateral symmetry refers to a basic animal body plan in which one plane of symmetry exists to create two mirror-image halves.” Sumich (1999) An Introduction to the Biology of Marine Life Planaria gecko.gc.maricopa.edu/.../platyhelminthes/ platyhel.htm

  4. Organisms with bilateral symmetry have developed an anterior “head” region and a posterior “tail” region. In addition they also display a top or back side (dorsal) and a belly or underside (ventral). Bilateral Symmetry

  5. Worms with Direction • “Animals with a front end [anterior] region generally move in a forward direction.” Villee, et. Al. (1989) Biology • Thus the tendency would naturally be to concentrate sensory organs in this anterior region to detect changes in the environment. • Leads to more active predation • More sophisticated behaviors • This process is termed “cephalization” • from the Greek for “getting a head”

  6. A Bit About Germ Layers • Early in embryonic development, the structures of most animals develop from three tissue layers call germ layers. • Ectoderm – outer layer • Mesoderm – middle layer • Endoderm – inner layer Digestive cavity

  7. A Tube-Within-A-Tube • As organisms become more sophisticated anatomically, the development of a body cavity or coelom [see-luhm] is observed. • The coelom is lined by mesoderm tissue and is essentially an open tube within the organism’s body in which digestive, reproductive and other organs arise.

  8. ‘Tubular’ Terminology • Animals can either be Acoelomate – no body cavity Pseudocoelomate – a body cavity develops between the body wall (ectoderm) and the internal organs (endoderm). Usually filled with fluid. Coelomate – the body cavity is completely lined with tissue from the mesoderm.

  9. Advantages of a Coelom • It allows for more extensive growth of the organs such as those of the digestive tract. • It permits the formation of an efficient circulatory system with a heart that can drive the blood through the vessels without them being restricted by a compact body. • The fluid in the coelom can transport or move materials faster than by diffusion. • The fluid can also generate a more efficient hydrostatic force against which muscles can act. • The muscles of the digestive tract can become independent of the muscles of the body wall permitting more variation in movement of both sets of muscles. • The coelom provides a space for gonads to develop during breeding season or for young to grow in those animals which give birth to live young. From Dr. Kent Simmons, Campus Manitoba Web

  10. PHYLUM: PlatyhelminthesFlatworms – A Tiny “Inch” Forward • Exhibit bilateral symmetry and cephalization • Acoelomate • Mouth and anus are still shared • Simplest organisms with well-developed organs • Have a simple brain called a ganglia in the head with two nerve cords that extend the length of the body.

  11. Anatomy of a Flatworm Flatworms • Turbellarians • Planarians • Marine, free-living • Trematodes • Flukes • Mostly parasitic • Cestodes • Tapeworms • Parasites that live in the intestines of vertebrates (including humans!)

  12. Flatworms – Another Look Anatomical diagram of a planarian – a typical flatworm found in both fresh and marine waters as well as terrestrial habitats Flatworm Media Planaria Swimming Turbellarians Trematode infection of salamanders Warning: Colonoscopy showing tapeworm !

  13. PHYLUM: NemertineaProboscis Worms/ Ribbon Worms • Simplest animals to possess definite organ systems. • Almost exclusively marine • Possess a proboscis – a long, hollow, muscular tube which can be everted from the head to capture food or for defense.

  14. Proboscis Worms/ Ribbon Worms • Are truly a “tube-within-a-tube.” The digestive tract is a complete tube with mouth at one end and anus at the other. • First example of separate circulatory and digestive systems • Acoelomates • Non-parasitic, mostly benthic • Claim to fame – one species has been observed up to 30 m long (the longest invertebrate!)

  15. PHYLUM: NematodaRoundworms • Most common worms in the world – inhabit almost every species of plant and animal. • Mostly parasitic, some benthic • Have a tough, outer covering called a cuticle which keeps them from drying out. • Sexes separate and dimorphic – separate male and females that look different (male smaller)

  16. Roundworms • Pseudocoelomates • Have a cavity filled with incompressible fluid which acts as a hydrostatic skeleton. • Cavity is not completely lined by mesoderm. • When muscles in the body wall contract they flex and squeeze against this fluid causing the shape of the worm to deform and therefore move. • Excellent technique for sediment burrowing. Roundworm in cat gut Marine roundworm Good slide show of various roundworm images

  17. PHYLUM: AnnelidaSegmented Worms • 20,000 species including marine and terrestrial species (e.g. earthworms) • Defining characteristics • Body divided into segmented units called metameres. • Chaetae (or setae) – hair-like structures on each segment

  18. Other Innovations of Annelids • Digestive tract (or gut) extends through all segments. • Coelomates • Acts as a hydrostatic skeleton • Organism can move each segment individually. This permits localized and more efficient movement. • Have a closed circulatory system • In aquatic species, respiratory exchange is through gills

  19. Annelid Classes • Polychaeta • All marine, may be free-swimming or live in benthic aggregations • Include bloodworms, sandworms, lugworms, bristle worms, fan worms, feather duster worms, beard worms, etc. • Oligochaeta • Aquatic or terrestrial, live in mud or sand bottoms’ • Include earthworms • Hirudinea • Mostly freshwater, but some marine species • Leeches

  20. Polychaete Biology • Anatomy: • Chaetae emerge from flat parapodia which are stiff extensions on each body segment • Life History: • Have a planktonic larval stage called a trochophore • As adults, some crawl on bottom, others burrow, others build tubes and live in aggregations, while still others remain planktonic • Feeding: • Some are carnivorous, some are suspension feeders, and others are deposit feeders. • Crawling worms have well developed parapodia, a proboscis, and jaws. • Suspension feeding worms often have tentacles, cilia, or mucus to capture prey

  21. Serpula vermicularis – reef building tube worm

  22. Common lug worm (Arenicola marina) Plymouth, Devon, England

  23. Lug worm casts on the coast of North Ireland

  24. King Ragworm (Nereis virens)

  25. Tubeworm (Spirorbis tridentatus) Batten Bay, Mount Batten, Plymouth, Devon.)

  26. Myrianida pachycera, a polychaete (worm) (60x)

  27. Christmas tree worms on coral head

  28. Trochophore larvae of a bristle worm Note the bristles anchored in the body for swimming and the reddish eye spots.

  29. Polychaete sandworms - Notice the tubes sticking up from the mud. Some sandy beaches can contain up to 32,000 polychaete worms/m2 that consume 3 tons of sand/ year.

  30. Feather duster worms, Bimini, Bahamas

  31. Polychaete epitokes swarming . Glover’s Reef, Belize

  32. Pogonophora beard worms • Deep water species – live near hydrothermal vents • No mouth or gut • Tuft of tentacles absorbs dissolved nutrients from the water • Symbiotic bacteria inside the worm use these nutrients to make food. • Formerly classified in their own phylum

  33. Oligochaeta • Found in mud/sand bottoms • Usually deposit feeders • Lack parapodia • Includes the common earthworm

  34. Hirudinea leeches • Usually parasitic and blood-sucking • Inject a chemical into prey that is both an anticoagulant and an anesthetic. • Have a sucker on anterior and posterior. • Lack parapodia

  35. Sipuncula peanut worms • Strictly marine • Unsegmented • Burrow in shallow water soft bottom sediments • Possess a long anterior portion that can be retracted into the body. • Deposit feeder • 1-35 cm long • Approximately 320 species

  36. Echiura innkeepers/ spoon worms • Strictly marine • Unsegmented, though now classified with annelids • Have a non-retractable, spoon-like proboscis for gathering organic material. • One species creates a U-shaped burrow that is often shared with other organisms. • Deposit feeder • Approximately 135 species proboscis

  37. Unifying Characteristics of Worms • Ubiquitous in marine environment (benthic, parasitic, free swimming) • Usually small • Responsible for mixing marine sediments. • Recycle bacteria and detritus into the food chain. • Have highly developed feeding appendages and digestive systems. • Important food for higher invertebrates and some fish. • May have important health effects on marine vertebrates

  38. Image Citations Brown, Hugh. “Serpulid polychaete worm” Digital Image. Serpulid reefs. The Scottish Association for Marine Science (SAMS). 5 January 2009. <http://www.sams.ac.uk/research/departments/ecology/ecology-projects/reef-ecology/researchproject.2007-04-18.1807501867> Fiege, Dieter. “Glyceridae” Digital Image. Senchenbergische Naturforschende Gesellschaft. 2008. 5 January 2009. <http://www.senckenberg.de/root/index.php?page_id=2301> “Leech.” Digital Image. Annelids Live Invertebrates – Niles Biological, Inc. 2006. Niles Biological, Inc. 5 Jaunary 2009 <http://www.nilesbio.com/subcat288.html> Rouse, Greg. “Chaetae of an Annelid” Digital Image. Annelida 2004. Tree of Life Web Project. 5 January 2009 <http://www.tolweb.org/Annelida> Rouse, Greg. “Myrianida pachycera, a polychaete.” Digital Image. Nikon Small World – Gallery. 2008. Nikon Small World – Photomicrography Competition. 5 January 2009. <http://www.nikonsmallworld.com/gallery.php?grouping=year&year=2003&imagepos=2> Siddal, Mark. “Medicinal leech” Digital Image. Leech on Me. 2007. Science Friday Newsbriefs. 5 January 2009. <http://www.sciencefriday.com/newsbriefs/read/120> “Social feather duster worm close-up” Digital Image. ReefNews. 2001. 5 January 2009. http://www.reefnews.com/reefnews/photos/bimini/sfdust2.html “Swarming polychaetes” Digital Image. Rpolychaete epitokes Ryan Photographic. 5 January 2009. <http://www.ryanphotographic.com/epitoke.htm> “Trocophore larvae” Digital Image. Bristleworms and their larva. 1995. Mic-UK: Bristle worms. 5 January 2009. <http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artmar99/poly2.html> Veitch, Nick. “Lug worm casts” Digital Image. Wikimedia Commons. 2008. 5 January 2009. <http://commons.wikimedia.org/wiki/File:Lugworm_cast.jpg>

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