Download Chapter 13 Invertebrates with Coeloms

Chapter 13 Invertebrates with Coeloms
Evolutionary Trends
1. The advantages to an animal having a coelom include:
• Organ expansion. Allows internal organs to expand and
contract in size as needed.
• Greater absorption. Allows for higher degree of folding and
therefore increased surface area for absorption. This translates
into more efficient uptake of nutrients and release of wastes.
• Flexibility of movement. Organs can slide past each other
while animal is in motion.
2. The advantage of an animal having an anus:
• Increased nutrient uptake. Having an opening at the opposing
end of an alimentary canal means one way transport of food
allowing for greater quantities of nutrients to be processed for a
given time. Increased nutrient uptake means greater resource
availability and hence greater size. This characteristic is often
referred to as a complete digestive tract.
3. It is thought by evolutionists that bilateral animals split into two
groups as they developed. These groups, the protostomes and
deuterostomes are classified by the way their embryos develop their
mouth and anus.
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Protostomes
"proto" - first
Deuterostomes
"deutero" - other
"stoma" - opening
"stoma" - opening
Mouth first, anus second
anus first, mouth second (other)
Spiral cleavage in embryo
Radial cleavage in embryo
A word on segmentation
Segmentation – the repetition of body parts containing similar
structures. The advantage of segmentation is that it permits greater
specialization of structures. E.g. insects are segmented into head,
abdomen and thorax (HAT). Each segment is responsible for different
functions.
¾ Head – information gathering and eating
¾ Thorax – locomotion and digestion
¾ Abdomen – reproduction, excretion and defence.
Phylum Annelida: The Segmented Worms
The Annelids are divided into three groups
• Oligochaeta – (oligo – few; chaeta – bristles) earthworms
• Polychaeta – (poly – many; chaeta – bristles)
• Hirudinea – leeches
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Oligochaetes
Important points:
• Closed circulatory system
• Respiration through skin, where blood picks it up and transports
throughout body
• Nephridia – like kidneys, they collect waste and dump it outside
the worm
• Heart – 5 aortic arches
• Ventral nerve chord
• Lateral/longitudinal muscles allow for paristalsis
• Hermaphroditic but fertilization via copulation
Figure 13.3
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Polychaetes
Important points:
• Marine dwellers
• Generally flattened
• Many lateral parapodia (para – side; podia – feet) which
provide movement and gas exchange. Parapodia are armed
with setae (bristles) which give protection and traction
Figure
Hirudinea
• Slow or still freshwater environments and on some vegetation
in humid jungles
• ~75% of species are external blood-sucking parasites
• produce hirudin which is an anticoagulant…it keeps the blood
from clotting
p328 Case Study
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Phylum Mollusca
Although molluscs are very diverse in adult form, they share common
embryonic characteristics (which have caused them to be grouped
into a common phylum). The four (of 7) largest classes are
• Chitons
• Gastropods- (stomach-foot) snails and slugs
• Bivalves – (two-shells) clams, oysters etc
• Cephalopods – (brain-foot) squids and octopi
,,,and the common embryonic characteristics include
• Protostomes – mouth developes first from gastrula opening.
• Trocophore larva stage – the trocophore larva has cilia at one
end for locomotion and a band of cilia for ‘beating’ food towards
its mouth.
Although not readily apparent, they also have some common
structures:
• foot - a large muscle used for locomotion
• mantle - a ‘cloak-like’ protective tissue
• shell • gills - outgrowths of the mantle used for breathing
• visceral mass - internal organ system
• radula - a ‘rasping’ mouth
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Home Assignment:
Figure 13.6 - Identify and compare common structures
A Special Word on Cephalopods
Easily the most complex molluscs are the cephalopods. Included with
the squid and octopus, is the intriguing nautilus. Because
cephalopods preys on faster-moving animals it has more complex
adaptations to accomplish the task.
• Streamlined shape
• Water-jet propulsion for short bursts
• Well developed digestive systems for efficient removal of all
possible nutrients
• Two true hearts - one to pump blood to gills and one to service the
organ system. Closed circulatory system can maintain high blood
flow and high blood pressure. This advanced circulatory system
along with large folded gills means efficient respiration and
circulation.
• Highly developed nervous system and true image-producing eye.
Octopods have a 10-lobed brain and are good learners.
How might these characteristics be useful to a predator of faster,
moving fish?
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Ecology
Molluscs use all types of feeding strategies (predator, decomposer,
herbivore, parasite) so they can be found almost everywhere in water
environments.
Many are filter-feeders and tend to concentrate pollutants in their
tissues. The benefit of this is that scientists can monitor pollution
levels by studying them. The problem is that if their eaten, they can
cause sickness and death.
Phylum Arthropoda
The arthropods are easily the most successful group on Earth
because they inhabit every nook and cranny of the globe.
Although they are often thought of as pests because they:
• destroy crops
• damage buildings
• carry disease
• cause direct harm to humans (as parasites, poisonous stings and
bites etc.)
They are also indispensable to life as we know it because they also:
• kill other pest organisms by the millions
• are important food source for higher organisms
• pollinate crops
• recycle nutrients back into the food chain
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Majour Characteristics
• SEGMENTED BODY plan - head, thorax, abdomen
• JOINTED APPENDAGES on each segment adapted for various
functions. E.g. sensory antennae, moving mouth parts for handling
food.
• EXOSKELETON composed of non-living chitin. Protective, but
cumbersome and requires molting in some species
• MALPHIGIAN TUBULES - aid in reabsorption of liquid and
nutrients
• NERVOUS SYSTEM may be simple (like annelids) or complex
(especially among social insects like ants and bees)
• Eyes - maybe simple photoreceptors or COMPLEX COMPOUND
EYES. ***Insect eyes lack a focussing mechanism and each lightunit ‘sees’ only one dot of light…so, they can’t see very well, but
sense movement well.
• ANTENNAE - touch (and possibly low-light) sensitive organs
• PITS - mechanical and chemical sensitive openings in the cuticle.
• OPEN CICULATORY SYSTEM - blood is pumped by the heart
into a hemocoel (coelom containing heme or blood) where it
circulates freely among the organs.
• RESPIRATORY SYSTEM - air enters body through tiny hoes in
each segment called spiracles and is transported through
complex tubing (tracheae)in the hemocoel where gas exchange
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takes place. Process is aided by air sacs which act as bellows,
pulling in fresh air and pushing out used air.
• REPRODUCTION is normally by internal fertilization.
Development can either be with definite stages (metamorphosis)
or without (larval stage resembles adult stage and only change is
increase in size)
Moulting Process
• Inner cuticle is softened and recycled to make a new, flexible
cuticle.
• Water is absorbed, swelling and stretching the animal
• Outer cuticle falls off
• ‘Inner’ cuticle (now the new outer cuticle) hardens. ***Critter is
vulnerable during this time!
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Phylum Echinodermata (starfish and sea urchins)
• Pentameric (penta - five; mere - unit) radial symmetry in adult
stage; bilateral symmetry in larval stage.
• Water vascular system allows movement and feeding
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