Phylum Annelida
 segmented worms ~15,000 sp
 C. Oligochaeta . freshwater terr. worms.
few setae - 3000 sp.
 C. Polychaeta . numerous setae – 10,000
sp.
 C. Hirudinea . freshwater, marine or terr.- 500
sp.
General characteristics
1) triploblastic, bilaterally symmetric, protostome
2) metamerism  body is compartmentalized w/each segment having own excretory,
nervous & circulatory structures.
 segments is separated by septa. circular & longitidinual muscles
found in each segment.
Advantage of metamerism
a)
b) coelom spaces in segments provide:
c) if one segment is damaged,
3)
- specialization of certain body regions,
better developed in arthropods, but seen in some annelid sp.
4) closed circulatory system
5) dorsal suprapharyngeal ganglia (
) & ventral nerve cord
6) metanephridia or protonephridia
Reproduction
 Asexual  Sexual  1-2 testes & 1 ovary found in certain anterior segments

for sperm storage & maturation prior to
release

after copulation
 ovisacs  copulation - worms align themselves in opposite direction, genital
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segments of one worm adjacent to clitellum in other worm

secretes mucus which holds worms in place
& aids in sperm transfer
 sperm travel from vesicles  receptacles via grooves




after copulation, clitellum forms cocoon w/food reserve eggs & sperm are released in cocoon where fertilization takes place
worm backs out of cocoon & cocoon is sealed
direct development after 1-few weeks in egg
Ecological, medical & economic importance
 filter feeders, predatory, detritivore –
 some ectoparasites
 also serve as prey for birds, fish and other sp.
 only a few eaten by humans – Samoan palolo worm
 earthworms help aerate & mix soils
 medicinal leech used to help stimulate vein regeneration
 no native earthworms in Minnesota

non-native species

are causing harm in native forests
Phylum Arthropoda (373-376)
 largest animal phylum –
 has colonized most habitats, including aerial habs.
 closely related to annelids
General characteristics
1) triploblastic, bilaterally symmetric, protostome
2) paired,
 uniramous  biramous -
3)
 mostly external, e.g. arrangement of appendages
 no internal septa prob. because of exoskeleton
 3 tagmata (
) in many
4)
 has inner processes for muscle attachment
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 flexible membrane at joints
5)
 molts when exoskeleton is too small
 organism vulnerable during hardening process
 controlled by nervous & endocrine systems
6)
- ventral nerve cord
w/segmental ganglia & paired lateral nerves
7) coelom reduced to cavities surrounding gonads & sometimes excretory
system
8)
- blood released into hemocoel
9)
- radical change in body form &
physiology btwn immature stages (larvae) and adults.
Success of arthropods
1) versatile exoskeleton – flexible yet still protects against water exchange
& damage to soft tissue
2) serial homology - flexibility in modifying jointed appendages for feeding,
locomotion, sensory & reproduction
3) development of tracheal system – helped invade land – insects, spiders,
etc.
4) highly developed sensory organs – compound eyes, highly sensitive
chemoreceptors & touch, hearing in some
5) complex behavior patterns – highly developed innate patterns as well as
some learned behavior
6) reduced intraspecific competition btwn larval & adult forms because of
metamorphosis
Arthropod taxonomy
 Subphylum Trilobita - trilobites, marine, biramous, extinct at end of
Permian
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Chelicerata – spider silk
 mostly:
 by weight stronger than steel
 various uses – webs, traveling around env. wrapping prey, egg sacs,
transferring sperm
 up to:
 released as a liquid from silk gland then polymerized & hardened in
spinnerets
 spiders often eat silk to recycle material
Crustacean - Ecdysis
 cuticle – non-cellular
 epicuticle -






exocuticle -

endocuticle –
epidermis –
cuticle separates from epidermis & epidermis begins to form outer layers
of cuticle
enzymes digest endocuticle & finally old cuticle is shed – soft shell stage
new endocuticle develops & exoskeleton hardens
hormonally-controlled, but env. influences
Subphylum Hexapoda – insect flight
 most insects have two pairs, diptera 1 pr. only, others are lacking
 not homologous w/bat or bird wings
 forewings provide most of lift
 hindwings (
in Diptera) responsible for equilibrium
Wing movements
 wing attached to thoracic dorsum (
 direct flight muscles –
)
 indirect flight muscles –

acts as fulcrum which wings rest on
Synchronous flight (dragonflies & grasshoppers)
 upstroke –
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 downstroke –
Asynchronous flight (bees & flies)
 upstroke  downstroke  resilience of tergum when one set of muscles contracts causes other
muscles to stretch – that stimulates them to contract
 faster wingbeats b/c fewer messages from brain
 midges can beat up to 1000 beats/sec
Ecological, Economic & Medical Importance of Arthropods
 majority are herbivorous, but all types of feeding occur among arthropods
 considered pests in agricultural & silvicultural habitats
 prey food for many species, including humans
 many insects pollinate flowers
 damage to wooden structure –
 carry disease –
 poisonous sp. –
 used for biological control of pest species –
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