coelomate invertebrates chapter 34. 2 introduction coelomates have a body design that: 1....
TRANSCRIPT
Coelomate Invertebrates
Chapter 34
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Introduction
Coelomates have a body design that:
1. Repositions the body’s fluid
2. Allows complex tissues/organs to develop
3. Allows for a larger body size
Coeloms evolved multiple times during animal evolution
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Phylum Mollusca
Mollusks are second in diversity only to arthropods
-Exhibit a wide variety of sizes and body forms
-Live in many different environments
-Include snails, slugs, clams, octopuses and others
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Phylum Mollusca
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Phylum Mollusca (Cont.)
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Phylum Mollusca
Mollusks evolved in the oceans and most groups have remained there
They are an important source of human food
They are economically significant in other ways
-Pearls are produced in oysters
-Mother-of-pearl is produced in the shells of abalone
Mollusks can also be pests
-Zebra mussel (Dreissena polymorpha)
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Mollusk Body Plan
Mollusks are bilaterally symmetrical
-Characterized by a reduced coelom surrounding the heart and excretory organs
The digestive, excretory and reproductive organs are concentrated in a visceral mass
Mollusks may have a differentiated head at the anterior end of the body
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Mollusk Body Plan
Mantle = A thick epidermis that covers the dorsal side of the body
-Forms a cavity which houses the respiratory organs (ctenidia, or gills) and the openings of excretory, reproductive & digestive organs
The muscular foot of a mollusk is adapted for locomotion, attachment, food capture
-Or a combination of the above
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Mollusk Body Plan
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Mollusk Body Plan (Cont.)
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Mollusk Body Plan
Most mollusks produce an external calcium carbonate-rich shell
-Used for protection
-Some species have internalized or reduced shells
Most mollusks have a rasping tongue-like organ called the radula
-Used for feeding
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Mollusk Body Plan
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Mollusk Body Plan
Nephridia = Special excretory structures that remove nitrogenous wastes
-Consist of cilia-lined openings called nephrostomes
Except for cephalopods, all mollusks have an open circulatory system
Cephalopods have a closed circulatory system
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Mollusk Reproduction
Most mollusks have distinct male and female individuals
Most engage in external fertilization
In marine mollusks, embryos develop through spiral cleavage
-Trochophores: Free-swimming larval stage
-Veliger: Second free-swimming larval stage
-Only in bivalves and snails
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Mollusk Reproduction
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Classes of Mollusks
There are eight recognized classes
-Four are representatives of the phylum
1. Polyplacophora
2. Gastropoda
3. Bivalvia
4. Cephalopoda
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Classes of Mollusks
Class Polyplacophora (Chitons)
-Marine mollusks that have oval bodies with eight overlapping dorsal calcareous plates
-Body is not segmented under the plates
-Most chitons are grazing herbivores
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Classes of Mollusks
Class Gastropoda (Snails and slugs)-A primarily marine group-Heads typically have pairs of tentacles with eyes at the ends-During embryological development, gastropods undergo
1. Torsion – Mantle cavity and anus are moved from the posterior to the front
2. Coiling – Spiral winding of the shell
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Classes of Mollusks
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Classes of Mollusks
Class Bivalvia (Bivalves)
-Includes clams, scallops, mussels, oysters and others
-Have two lateral (right and left) shells (valves) hinged together dorsally
-Most are sessile filter-feeders
-Water circulation is mediated by siphons and rhythmic beating of cilia on
gills
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Classes of Mollusks
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Classes of Mollusks
Class Cephalopoda
-Active marine predators
-Foot has evolved into a series of arms equipped with suction cups
-Squids have 10; octopuses, 8; and nautiluses, 80 to 90
-Have highly developed nervous systems
-Exhibit complex patterns of behavior and a high level of intelligence
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Classes of Mollusks
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Classes of Mollusks
Class Cephalopoda
-Many have an ink sac and are capable of expelling ink to confuse predators
-Octopuses and squids can change color using pouches of pigment called chromatophores
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Phylum Annelida
Annelid worms exhibit segmentation (building of body from repeated units)
-Allows for specialization
Members of this phylum are not monophyletic
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Phylum Annelida
An annelid consists of a series of ring-like elements running the length of the body
-Divided internally by septa
The anterior (front) segments contain specialized sensory organs
A ventral nerve cord connects the ganglia in each segment with each other and the brain
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Phylum Annelida
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Phylum Annelida
Annelids move using their hydrostatic skeleton -Each segment contains chitin bristles (chaetae) that help anchor the worms
Most have a closed circulatory system
They exchange O2 and CO2 through their body surfaces
Excretory system consists of a pair of ciliated, funnel-shaped nephridia per segment
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Phylum Annelida
Annelids have traditionally been classified into three classes:
1. Class Polychaeta
2. Class Oligochaeta
3. Class Hirudinea
Hirudinea is now considered a sub-class of Oligochaeta
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Phylum Annelida
Class Polychaeta (Polychaetes)
-Mostly marine worms, such as tubeworms
-Unusual forms and iridescent colors
-Have a differentiated head
-Have paired parapodia on most segments
-Used in swimming, burrowing, crawling
-Sexes are usually separate
-Typically lack permanent gonads
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Phylum Annelida
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Phylum Annelida
Class Oligochaeta (Earthworms and leeches)
-Mostly terrestrial
Earthworms
-Consist of 100-175 segments, with a mouth on the first and an anus on the last
-Lack eyes, parapodia and head
-Have fewer setae than polychaetes
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Phylum Annelida
Earthworms are hermaphroditic
-Clitellum secretes mucus that holds the worms together during copulation
-Also secretes a mucus cocoon, in which the fertilized egg develops
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Phylum Annelida
Leeches
-Occur mostly in freshwater
-Usually flattened dorsoventrally
-Cross-fertilization is obligatory
-Have no chaetae (except for one species)-Medicinal leech, Hirudo medicinalis
-Secretes anticoagulant
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The Lophophorates
Include two phyla of mostly marine animals: Bryozoa and Brachiopoda
Both convergently evolved a lophophore
-A circular or U-shaped ridge around the mouth with 1-2 rows of ciliated tentacles
-Functions in gas exchange and feeding
Most members undergo radial cleavage
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Phylum Bryozoa
Bryozoans are small and live in colonies
-Their anus opens near their mouth
-Phylum also called Ectoprocta
-Individuals secrete a tiny chitinous chamber called a zoecium
-Used for attachment
-Asexual reproduction occurs frequently by budding
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Phylum Bryozoa
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Phylum Bryozoa (Cont.)
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Phylum Brachiopoda
Brachiopods have two calcified shells
-Valves are dorsal and ventral (not lateral as in bivalves)
-Solitary lophophorates
Phoronids were once a separate phylum
-Each individual secretes a chitinous tube and lives out its life within it
-Develop as protostomes (unlike brachiopods)
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Phylum Arthropoda
Arthropods are the most successful animals
-1,000,000 species (2/3rd of all species)
-About 80% are insects
-For each human, 200 million insects are alive at any one time
Athropods affect all aspects of human life
Are divided into four major classes:
-Arachnids, myriapods, crustaceans and insects
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Arthropod Morphology
All arthropods have jointed appendages
-Modifications: antennae, mouthparts, legs
Arthropods also have an exoskeleton made of secreted chitin and protein
-Functions: protection & muscle attachment
-Its thickness limits arthropod body size
Arthropod bodies are segmented
-Some segments are specialized into functional groups, or tagmata
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Arthropod Morphology
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Arthropod Morphology
Arthropods have an open circulatory system
Compound eyes are found in many arthropods
-Composed of independent visual units called ommatidia
Other arthropods have simple eyes, or ocelli
-Have single lenses
-Distinguish light from darkness
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Arthropod Morphology
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Arthropod Morphology
Nervous system consists of a double chain of segmented ganglia on ventral surface
-Brain seems to be an inhibitor, rather than as a stimulator, as it is in vertebrates
Respiratory system consists of tracheae and tracheoles
-Connected to the exterior by spiracles
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Arthropod Morphology
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Arthropod Morphology
Arthropods have a unique excretory system consisting of Malpighian tubules
-Eliminates nitrogenous wastes as concentrated uric acid or guanine
Arthropods periodically undergo ecdysis or molting
-Shedding the outer cuticular layer
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Arthropod Morphology
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Class Arachnida
Arachnids are largely terrestrial organisms
-Spiders, ticks, mites, scorpions, and others
The most anterior appendages, chelicerae, often function as fangs or pincers
Body is divided into two main tagmata
-Prosoma (anterior): Bears all appendages
-Opisthosoma (posterior): Contains the reproductive organs
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Class Arachnida
Pedipalps (palps) are posterior to chelicerae
-Resemble legs, but have one less segment
-Used as copulatory organs, pincers, or sensors
Most arachnids are carnivorous
-Mites are largely herbivorous
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Class Arachnida
Order Araneae (spiders)
-About 35,000 species
-Many spiders catch their prey in silk webs
-Silk protein forced out of spinnerets found on the posterior of the abdomen
-Other spiders actively hunt their prey
-All spiders have poison glands leading through their chelicerae
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Class Arachnida
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Class Arachnida
Order Acari (mites and ticks)
-Largest and most diverse arachnid order
-Most mites are small
-Cephalothorax and abdomen are fused into an unsegmented ovoid body
-Ticks are larger than mites
-Are blood-eating parasites
-Can carry many diseases (spotted fevers, Lyme disease)
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Centipedes and Millipedes
Centipedes (class Chilopoda) and Millipedes (class Diplopoda) have bodies with a head followed by numerous segments
Centipedes are all carnivores (eat insects)
Millipedes are largely herbivores
In both fertilization is internal
-The sexes are separate
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Centipedes and Millipedes
Centipedes have fewer legs than millipedes
-Centipedes: one leg pair on each segment
-Millipedes: two on some or all segments
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Class Crustacea
Crustaceans are primarily aquatic organisms
-Crabs, shrimps, lobsters, barnacles, others
Have three tagmata
-The two most anterior fuse to form a cephalothorax
Have two pairs of antennae, three pairs of appendages, and various pairs of legs
Most appendages are biramous
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Class Crustacea
Mandibles (biting jaws) likely evolved from a pair of limbs that took on a chewing function
Most crustaceans have separate sexes
Majority develop through a nauplius stage
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Class Crustacea
Decapod crustaceans include shrimps, lobsters, crabs and crayfish
-Have ten feet
-Exoskeleton usually enforced with CaCO3
-Most body segments are fused into a cephalothorax
-Lobsters and crayfish have appendages that aid in swimming
-Swimmerets and uropods
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Class Crustacea
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Class Crustacea
Order Cirripedia
-Barnacles are crustaceans that are sessile as adults
-Free-swimming larvae
-Are hermaphroditic
-Some have stalks
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Class Hexapoda
Insects are by far the largest group of animals
-More than half of all named animal species
Insects are primarily a terrestrial group
Approximately one billion billion (1018) insects are alive at any one time
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Class Hexapoda
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Class Hexapoda (Cont.)
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Class Hexapoda (Cont.)
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Class Hexapoda
External features-Three body regions1. Head = Has pair of antennae and modified mouthparts2. Thorax = Has three segments, each with a pair of legs
-May have one or two pairs of wings 3. Abdomen
Most insects have compound eyes
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Class Hexapoda
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Class Hexapoda
Internal organization
-The digestive tract is a coiled tube
-Lined with cuticle on anterior and posterior regions
-Digestion takes place in stomach (midgut)
-Excretion tales place through Malpighian tubules
-Tracheae permeate all tissues
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Class Hexapoda
Sensory receptors
-Sensory setae are hair-like structures
-Detect chemical and mechanical signals
-Tympanal organs are composed of a thin membrane, the tympanum
-Detect sound
-In addition, insects can communicate by means of pheromones
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Class Hexapoda
Insect life histories
-Many insects undergo metamorphosis
-Simple metamorphosis (grasshopers)
-Immature stages similar to adults
-Complete metamorphosis (butterflies)
-Immature larva are wormlike
-A resting stage, pupa or chrysalis, precedes the final molt into adult form
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Phylum Echinodermata
Echinoderms are an ancient group of marine animals, with about 6000 living species
-Characterized by deuterostome development and an endoskeleton
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Echinoderm Body Plan
The echinoderm body plan undergoes a fundamental shift during development
-Larvae = bilateral symmetry
-Adults = pentaradial symmetry
Body structure is discussed in reference to their mouths, which define the oral surface
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Echinoderm Body Plan
Endoskeleton -Found internal to a delicate epidermis which contains thousands of neurosensory cells-Composed of either movable or fixed calcium-rich (calcite) plates called ossicles
-Perforated by pores to allow extension of tube feet
-Contains mutable collagenous tissue-Provides ability to autotomize body
parts
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Echinoderm Body Plan
Water-vascular system
-A hydraulic system that aids in movement and feeding
-Composed of a central ring canal from which five radial canals extend into each of the body’s five parts
-Madreporite = Opening for water entry
-Ampulla = Muscular sac for tube feet control
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Echinoderm Body Plan
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Echinoderm Body Plan
Echinoderms have a large coelom which connects with a complicated tub system
-Helps provide circulation and respiration through extensions called papulae
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Echinoderm Body Plan
Reproduction
-In some echinoderms, asexual reproduction takes place by splitting
-Broken parts can regenerate the whole animal
-Most reproduction in the phylum is sexual and external
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Classes of Echinoderms
There are more than 20 extinct classes
In addition, there are five extant classes
1. Asteroidea (sea stars and sea daisies)
2. Crinoidea (sea lilies and feather stars)
3. Echinoidea (sea urchins & sand dollars)
4. Holothuroidea (sea cucumbers)
5. Ophiuroidea (brittle stars)
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Classes of Echinoderms
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Classes of Echinoderms (Cont.)
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Classes of Echinoderms (Cont.)