Annelida: the metameric and tagmatization of animals

The slide about metamerism

1. 1
Metameric 分节的

2. uBody metameric, bilaterally
symmetrical, and worm-like
uSpiral cleavage(旋裂), trochophore
larvae, and schizocoelous coelom (
分裂体腔)formation
uPaired, epidermal setae（刚毛）
uClosed circulatory system
uDorsal suprapharyngeal ganglia and
ventral nerve cord(s) with ganglia
u Metanephridia (usually) or
protonephridia
12.1 Relationships to Other Animals
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3. Metamerism and Tagmatization
分节和标记化
背部肠系膜
腹部肠系膜
隔膜
oMetamerism
nSegmental arrangement of body parts including
many internal organ systems
nCoelomic compartments develop segmentally
nAdvantages
oHydrostatic compartments function in locomotion.
oLessened(减少的) impact of injury
oTagmatization possible
nSpecialization of body regions for specific functions such
as feeding, locomotion, and reproduction
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4. 10.2 Annelid Structure and functions
-
oMostly marine
oVariety of habitats
nOcean floor, under rocks & shells, crevices of coral reefs, burrows.
oExternal structure and locomotion
nParapodia（疣足） - paired lateral extensions of body wall in each segment
oErrantia（游走亚纲） – chitinous rods support parapodia
oSedentaria（隐居亚纲） – reduced or absent parapodia
nSetae（刚毛） – bristles secreted from invaginations of parapodia
oAid in locomotion by digging (Errantia)
oHold worms in their burrows (Sedentaria)
nProstomium（口前叶）
oLobe projecting dorsally and anteriorly from the mouth
oContains many sensory structures
nPeristomium（围口节）
oFirst body segment, surrounds the mouth, sensory tentacles
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Clade Errantia

5. Figure 12.5 Annelid locomotion.
(a)Dorsal view of a primitive errantian
annelid, showing the antagonism of
longitudinal muscles on opposite sides
of the body and the resultant protrusion
and movement of parapodia.
(a)Both the period and amplitude of
locomotor waves increase as the
annelid changes from a “slow walk” to
a swimming mode.
Locomotion
The propulsive force is the result of parapodia
and setae acting against the substrate or water.
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6. Feeding and the Digestive System
oStraight tube suspended within body cavity by mesenteries and septa（
隔膜）
oAnterior proboscis may be everted （鼻子外翻）
oFeeding strategies are varied:
nPredators
nHerbivores
nScavengers
nDeposit feeders （食碎屑）
nFilter feeders
oCrop, gizzard（砂囊）,
intestine
Clade Sedentaria. Filter feedersChaetopterus
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7. Figure 12.6 Circulatory System of a Polychaete.
[,pærə'pəʊdɪəm]
伪足，疣足
伪足的毛细血
管
Gas Exchange and Circulation
oGas exchange
nDiffusion across body wall
nParapodia increase surface area
for exchange
oCirculation
nClosed circulatory system
nBlood with respiratory
pigments（呼吸色素）
nDorsal aorta and ventral aorta
are contractile
nSegmental vessels and
capillaries serve intestine, body
wall, and parapodia.
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8. Nervous and Sensory Functions
oSuprapharyngeal and subpharyngeal ganglia,
connected by circumpharyngeal connectives
oVentral nerve cord (double) with segmental
ganglia
oSegmental ganglia coordinate movements in
isolated segments
oSubpharyngeal ganglia coordinate distant
segments
oSuprapharyngeal ganglia control sensory and
motor functions involved with feeding and
locomotion
oGiant fibers mediate escape responses
Figure 12.7 Annelid Nervous System.
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9. Excretion
oAmmonia
nNitrogenous waste
nFreely diffusible
oExcretory organs active in water and ion
balance regulation
nProtonephridia present in some primitive
annelids
oFlagella drives fluids to nephridiopore
nMetanephridia present in most annelids
oNephrostome, bladder, tubule
oActive transport of ions between blood and
nephridium
Figure 12.8 Annelid Nephridia.
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10. Regeneration, Reproduction, and Development
10Figure 12.9 Polychaete development.
Trochophore
A later planktonic larva
(c) Juvenile worm
oRegeneration abilities well developed
oAsexual reproduction
nBudding or transverse fission
oSexual reproduction more coomon
nMost are dioecious
nGametes shed into coelom to mature.
nGametes released using various strategies:
oNephridium and nephridiopore
oRupture of body wall
oGonoducts present in a few species
nExternal fertilization
nEpitoky (formation of a reproductive
individual that differs from the non-
reproductive form) common
oDevelopment
nSpiral cleavage with trochophore larva that
bud segments anterior to the anus
nDirect development in some

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12. Figure 12.17 Earthworm structure.
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凹入成盲道
oFeeding and the digestive system
nScavengers
nFallen and decaying vegetation
nPathway of food:
oMouth leads to pharynx
oPharynx to esophagus
oEsophagus to stomach/crop/gizzard
nDigestive system structure (figures
12.17)
Maintenance Functions
nClosed circulatory system

13. Maintenance Functions continued
oGas exchange
nDiffusion across body wall
oCirculation
nClosed circulatory system (figure 12.17)
nDorsal aorta and ventral aorta are
contractile
nSegmental vessels and capillaries serve
intestine and body wall
oSome contractile and propel blood
between dorsal and ventral blood vessels
oEarthworm “hearts”
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14. Reproduction and Development
nMonoecious
nMutual sperm exchange between
copulating individuals (figure 12.19)
oSeminal vesicles store sperm prior to
copulation
oSeminal receptacles receive sperm
during copulation
nFertilization within mucous sheath
secreted by clitellum
nForms cocoon that is deposited in soil
nSpiral cleavage and direct
development
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Figure 12.19 Earthworm Reproduction.

15. Summary
1. Explain how metamerism influences the biology of
annelid worms.
2. Compare the closed circulatory system of an annelid
worm to the open circulatory system of a bivalve mollusc
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