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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 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.
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
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
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”
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
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.
‘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.
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
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.
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!)
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 !
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.
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!)
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)
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
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
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
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
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
Tubeworm (Spirorbis tridentatus) Batten Bay, Mount Batten, Plymouth, Devon.)
Trochophore larvae of a bristle worm Note the bristles anchored in the body for swimming and the reddish eye spots.
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.
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
Oligochaeta • Found in mud/sand bottoms • Usually deposit feeders • Lack parapodia • Includes the common earthworm
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
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
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
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
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>