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Coelomate Invertebrates

Chapter 33

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Coelomates

• Coelomates have a new body design that allows for the development of complex tissues and organs.

– allows wider array of body architectures and increased body size

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Mollusks

• Mollusks (Mollusca)– extremely diverse– characterized by a coelom

great economic significancepearlsmother of pearl

economic / environmental costszebra mussel invasion intermediate hosts for parasites

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Body Plan of the Mollusks

• Distinct bilateral symmetry• Digestive, excretory, and reproductive organs

are all concentrated in a visceral mass and a muscular foot.

• May have differentiated head• Folds constituting a mantle

– gills - increased surface area for gas exchange

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Body Plan of the Mollusks

• Shells serve primarily for protection• Radula - rasping tongue-like organ used for

feeding• Circulatory system (except cephalopods)

consists of a heart and an open circulatory system.

• Nitrogenous wasted removed by nephridia– nephrostome lined with cilia

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Mollusk Body Plans

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Body Plan of the Mollusks

• Reproduction in mollusks– most have distinct male and female

individuals– most engage in external fertilization– many have free-swimming larvae

(trochophores) which closely resemble larval stage of many marine annelids

veliger stage follows trochophore stage

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Classes of Mollusks

• Polyplacophora: chitons– oval bodies with eight overlapping

calcareous plates• Gastropoda: snails and slugs

– heads of most have pair of tentacles with eyes at the ends

– undergo torsion during embryological development.

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Classes of Mollusks

• Bivalvia: bivalves– clams, scallops, mussels and oysters– two lateral shells hinged together dorsally– mantle secretes shell and ligaments– most are sessile filter-feeders

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Classes of Mollusks

• Cephalopoda: octopuses, squids, nautilus– most intelligent of the invertebrates– active marine predators– foot evolved into a series of tentacles

equipped with structures to capture prey– highly developed nervous systems

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Segmented Animals

• Building of body from series of similar segments

– small change in existing segment can produce new kind of segment with different function

• Annelids– three characteristics:

repeated segments specialized segments connections

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Segmented Animals

• Body plan of the annelid– tube within a tube– internal digestive tract within the coelom

specialized for different functions– hydrostatic skeleton for locomotion– each segment typically possesses setae,

that help anchor during locomotion– most have closed circulatory system– nephridia collect and transport wastes

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Classes of Annelids

• Polychaeta: polychaetes– well developed head with specialized

sense organs– parapodia on most segments– usually lack permanent gonads

• Oligochaeta: earthworms– hermaphroditic

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Classes of Annelids

• Hirudinea: leeches– occur mostly in fresh water– hermaphroditic– develop clitellum during breeding season– unable to self-fertilize– secrete anticoagulant into wounds

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Lophophorates

• Lophophore - circular or U-shaped ridge around the mouth bearing one or two rows of ciliated, hollow tentacles

– functions as surface for gas exchange and as food-collection organs

– use cilia to capture food

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Jointed Appendages and Exoskeleton

• All arthropods have jointed appendages.• Rigid external skeleton (exoskeleton)

– protects animal and provides sites for muscle attachment

brittle, thus arthropod body size limited due to exoskeleton thickness

– estimates of a quintillion insects alive at any one time

1,000,000 species

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Arthropod Body Plan

• Exoskeleton– tough outer covering that also serves to

anchor muscles• Molting (ecdysis)

– shedding of outer cuticular layer

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Arthropod Body Plan

• Compound eye– composed of many ommatidia

each covered with a lens and linked to a complex of eight retinal cells and a light sensitive core rhabdom

– Simple eyes (ocelli) have single lenses. function in distinguishing light from

darkness

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The Compound Eye

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General Characteristics of Arthropods

• Circulatory system– greatly reduced coelom– open circulatory system

• Nervous system– double chain of segmented ganglia

running along the animal’s ventral surface brain appears to be inhibitor rather than

stimulator

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General Characteristics of Arthropods

• Respiratory system– no single major respiratory organ– small branched air ducts - tracheae

branch into tracheolesair passes into trachea through

spiracles• Excretory system

– Malpighian tubules

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Crustaceans

• Most crustaceans have two pairs of antennae, three types of chewing appendages, and various numbers of leg pairs.

– all pass through nauplius larval stage– mandibles likely originated from a pair of

limbs that took on chewing function during course of evolution

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Crustaceans

• Decapod crustaceans– “ten footed”

exoskeleton usually reinforced with calcium carbonate

most body segments are fused into cephalothorax covered by carapace

Lobsters and crayfish have swimmerets and uropods to aid in swimming, and may have a telson (tail spine).

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Decapod Crustacean

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Crustaceans

• Terrestrial and freshwater crustaceans– about half of estimated 4,500 species are

terrestrial and live in moist habitats pillbugs sowbugs isopods

• Sessile crustaceans– barnacles

free-swimming larvae

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Class Arachnida

• Largest of three classes– have a pair of chelicerae, a pair of

pedipalps, and four pairs of walking legs– most are carnivorous, except for mites– many spiders have book lungs

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Class Arachnida

• Order Araneae: spiders– about 35,000 named species of spiders

many do not spin webs, but actively hunt

have poison glands leading through their chelicerae

used to bite and paralyze prey

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Class Arachnida

• Order Acari: mites and ticks– largest in terms of number of species and

most diverse of arachnids about 30,000 named species diverse in structure and habitat

found in virtually every habitat known ticks can carry many diseases

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Class Chilopoda and Diplopoda

• Centipedes and millipedes– both have bodies that consist of a head

region followed by numerous segments centipedes have 30+ legs

carnivorous millipedes have 60+ legs

herbivorous

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Class Insecta

• Largest group of organisms on earth– More than half of all named species on

earth are insects. hectare of lowland tropical rainforest is

estimated to be inhabited by as many as 41,000 insect species

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Class Insecta

• External features– three body segments

head, thorax, and abdomen– three pairs of legs– one pair of antennae– modified mouthparts– solid wings

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Class Insecta

• Internal organization– tubular digestive system

dilute digestive enzymes– trachea extends throughout body– fat body for food storage

• Sense receptors– sensory hairs - linked to nerve cells– tympanum - found with tracheal air sacs– pheromones – communication signals

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Insect Life Histories

• Metamorphosis– simple

immature stages– complete

larvae pupa (chrysalis)

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Deuterostome Development

• Echinoderms– ancient group of marine animals

consisting of about 6,000 living species name refers to hard, calcium-rich

endoskeleton beneath the skin unique water-vascular system is a fluid-

filled system used to aid in movement and feeding

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Echinoderm Body Plan

• Secondary radial symmetry– bilaterally symmetrical during larval

development, but become radially symmetrical as adults.

• Five part body plan• Nervous system - nerve ring

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Echinoderm Body Plan

• Endoskeleton– delicate epidermis containing thousands of

neurosensory cells– continuous growth– body plates often pierced to allow tube

foot extension

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Echinoderm Body Plan

• Water vascular system– radiated from a ring canal that encircles

esophagus five radial canals extend into each of the

five body partswater enters through madreporite radial canals extend into the hollow

tube feet ampulla located at base

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Echinoderm Water-Vascular System

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Echinoderm Body Plan

• Body cavity– coelom connects with tubular systems and

helps provide circulation and respiration• Reproduction

– many echinoderms have the ability to regenerate

– most reproduction is sexual and external

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Class Asteroidea

• Sea stars– abundant in intertidal zone– important marine predators– body composed of central disc that

merges gradually with the arms