Marine hitchhikers: a preliminary study on invertebrates ...
Chapter 7: Marine Invertebrates
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Transcript of 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.
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
gecko.gc.maricopa.edu/.../platyhelminthes/ platyhel.htm
Planaria
Bilateral Symmetry
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).
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
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.
A Tube-Within-A-Tube
‘Tubular’ Terminology
Animals can either be Acoelomate – no body cavityPseudocoelomate – 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.
Flatworms
Turbellarians– Planarians– Marine, free-living
Trematodes – Flukes– Mostly parasitic
Cestodes– Tapeworms– Parasites that live in the
intestines of vertebrates (including humans!)
Anatomy of a Flatworm
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
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
PHYLUM: AnnelidaSegmented Worms
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
Serpula vermicularis – reef building tube worm
Common lug worm (Arenicola marina) Plymouth, Devon, England
Lug worm casts on the coast of North Ireland
King Ragworm (Nereis virens)
Tubeworm (Spirorbis tridentatus) Batten Bay, Mount Batten, Plymouth, Devon.)
Myrianida pachycera, a polychaete (worm) (60x)
Christmas tree worms on coral head
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.
Feather duster worms, Bimini, Bahamas
Polychaete epitokes swarming . Glover’s Reef, Belize
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
proboscis
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
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 CitationsBrown, 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>