arthropod groups insects 6 legs, 3 body parts crustaceans gills, 2 pairs antennae crab, lobster,...
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Arthropod groupsArthropod groups
insects6 legs, 3 body parts
crustaceansgills, 2 pairs antennaecrab, lobster, barnacles, shrmp
arachnids8 legs, 2 body partsspiders, ticks, scorpions
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ArthropodsArthropods
• Two out of every three known species of animals are arthropods
• Members of the phylum Arthropoda are found in nearly all habitats of the biosphere
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Arthropod OriginsArthropod Origins
• The arthropod body plan consists of a segmented body, hard exoskeleton, and jointed appendages, and dates to the Cambrian explosion (535–525 million years ago)
• Early arthropods show little variation from segment to segment
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Fig. 33-27Fig. 33-27
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• Arthropod evolution is characterized by a decrease in the number of segments and an increase in appendage specialization
• These changes may have been caused by changes in Hox gene sequence or regulation
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General Characteristics of ArthropodsGeneral Characteristics of Arthropods
• The appendages of some living arthropods are modified for many different functions
CephalothoraxAntennae(sensoryreception) Head
Thorax
Abdomen
Swimming appendages(one pair locatedunder eachabdominal segment)
Walking legs
Mouthparts (feeding)Pincer (defense)
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• The body of an arthropod is completely covered by the cuticle, an exoskeleton made of layers of protein and the polysaccharide chitin
• When an arthropod grows, it molts its exoskeleton
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• Arthropods have an open circulatory system in which fluid called hemolymph is circulated into the spaces surrounding the tissues and organs
• A variety of organs specialized for gas exchange have evolved in arthropods
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• Molecular evidence suggests that living arthropods consist of four major lineages that diverged early in the phylum’s evolution:– Cheliceriforms (sea spiders, horseshoe
crabs, scorpions, ticks, mites, and spiders)– Myriapods (centipedes and millipedes)– Hexapods (insects and relatives)– Crustaceans (crabs, lobsters, shrimps,
barnacles, and many others)
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Table 33-5Table 33-5
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CheliceriformsCheliceriforms
• Cheliceriforms, subphylum Cheliceriformes, are named for clawlike feeding appendages called chelicerae
• The earliest cheliceriforms were eurypterids (water scorpions)
• Most marine cheliceriforms (including eurypterids) are extinct, but some species survive today, including horseshoe crabs
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Fig. 33-30Fig. 33-30
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• Most modern cheliceriforms are arachnids, which include spiders, scorpions, ticks, and mites
Scorpion
Dust mite
Web-building spider
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• Arachnids have an abdomen and a cephalothorax, which has six pairs of appendages, the most anterior of which are the chelicerae
• Gas exchange in spiders occurs in respiratory organs called book lungs
• Many spiders produce silk, a liquid protein, from specialized abdominal glands
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Fig. 33-32Fig. 33-32
Intestine
HeartDigestivegland
Ovary
Anus
Spinnerets
Silk gland
Gonopore(exit for eggs) Sperm
receptacle
Book lung
Chelicera Pedipalp
Poisongland
Eyes
Brain
Stomach
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MyriapodsMyriapods
• Subphylum Myriapoda includes millipedes and centipedes– Myriapods are terrestrial, and have jaw-like mandibles
• Millipedes, class Diplopoda, have many legs– Each trunk segment has two pairs of legs
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Fig. 33-33Fig. 33-33
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• Centipedes, class Chilopoda, are carnivores – They have one pair of legs per trunk segment
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InsectsInsects
• Subphylum Hexapoda, insects and relatives, has more species than all other forms of life combined
• They live in almost every terrestrial habitat and in fresh water
• The internal anatomy of an insect includes several complex organ systems
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Fig. 33-35Fig. 33-35
Abdomen Thorax Head
Compound eye
Antennae
Heart
Dorsalartery Crop
Cerebral ganglion
Mouthparts
Nerve cords
Tracheal tubesOvary
Malpighiantubules
Vagina
Anus
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• Insects diversified several times following the evolution of flight, adaptation to feeding on gymnosperms, and the expansion of angiosperms
• Insect and plant diversity declined during the Cretaceous extinction, but have been increasing in the 65 million years since
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• Flight is one key to the great success of insects
• An animal that can fly can escape predators, find food, and disperse to new habitats much faster than organisms that can only crawl
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• Many insects undergo metamorphosis during their development
• In incomplete metamorphosis, the young, called nymphs, resemble adults but are smaller and go through a series of molts until they reach full size
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• Insects with complete metamorphosis have larval stages known by such names as maggot, grub, or caterpillar
• The larval stage looks entirely different from the adult stage
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Fig. 33-36Fig. 33-36
(a) Larva (caterpillar)(b) Pupa
(c) Later-stage pupa (d) Emerging
adult
(e) Adult
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• Most insects have separate males and females and reproduce sexually
• Individuals find and recognize members of their own species by bright colors, sound, or odors
• Some insects are beneficial as pollinators, while others are harmful as carriers of diseases, or pests of crops
• Insects are classified into more than 30 orders
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Fig. 33-37aFig. 33-37a
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Fig. 33-37bFig. 33-37b
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Fig. 33-37cFig. 33-37c
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Fig. 33-37dFig. 33-37d
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Fig. 33-37eFig. 33-37e
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CrustaceansCrustaceans• While arachnids and insects thrive on
land, crustaceans, for the most part, have remained in marine and freshwater environments
• Crustaceans, subphylum Crustacea, typically have branched appendages that are extensively specialized for feeding and locomotion
• Most crustaceans have separate males and females
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• Isopods include terrestrial, freshwater, and marine species– Pill bugs are a well known group of terrestrial
isopods
• Decapods are all relatively large crustaceans and include lobsters, crabs, crayfish, and shrimp
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Fig. 33-38Fig. 33-38
(a) Ghost crab
(b) Krill (c) Barnacles
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• Planktonic crustaceans include many species of copepods, which are among the most numerous of all animals
(b) Krill
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• Barnacles are a group of mostly sessile crustaceans
• They have a cuticle that is hardened into a shell
(c) Barnacles
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Echinoderms and chordates are Echinoderms and chordates are deuterostomesdeuterostomes
• Sea stars and other echinoderms, phylum Echinodermata, may seem to have little in common with phylum Chordata, which includes the vertebrates
• Shared characteristics define deuterostomes (Chordates and Echinoderms)– Radial cleavage– Formation of the mouth at the end of the
embryo opposite the blastopore
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Invertebrate: Invertebrate: EchinodermataEchinodermata
• Starfish, sea urchins, sea cucumber– radially symmetrical as adults– spiny endoskeleton– deuterostome loss of bilateral symmetry?
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EchinodermsEchinoderms• Sea stars and most other echinoderms
are slow-moving or sessile marine animals
• A thin epidermis covers an endoskeleton of hard calcareous plates
• Echinoderms have a unique water vascular system, a network of hydraulic canals branching into tube feet that function in locomotion, feeding, and gas exchange
• Males and females are usually separate, and sexual reproduction is external
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Fig. 33-39Fig. 33-39
AnusStomach
Spine
Gills
Madreporite
Radialnerve
Gonads
Ampulla
Podium
Tubefeet
Radial canal
Ringcanal
Central disk
Digestive glands
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• Living echinoderms are divided into six classes:– Asteroidia (sea stars)
– Ophiuroidea (brittle stars)
– Echinoidea (sea urchins and sand dollars)
– Crinoidea (sea lilies and feather stars)
– Holothuroidea (sea cucumbers)
– Concentricycloidea (sea daisies)
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Table 33-6Table 33-6
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Sea StarsSea Stars
• Sea stars, class Asteroidea, have multiple arms radiating from a central disk
• The undersurfaces of the arms bear tube feet, each of which can act like a suction disk
• Sea stars can regrow lost arms
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Fig. 33-40Fig. 33-40
(a) A sea star (class Asteroidea)
(c) A sea urchin (class Echinoidea)
(e) A sea cucumber (class Holothuroidea)
(b) A brittle star (class Ophiuroidea)
(d) A feather star (class Crinoidea)
(f) A sea daisy (class Concentricycloidea)
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ChordatesChordates
• Phylum Chordata consists of two subphyla of invertebrates as well as hagfishes and vertebrates
• Chordates share many features of embryonic development with echinoderms, but have evolved separately for at least 500 million years
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