Download Annelida

Phylum Annelida
Adapted from Lesser Known Protostome
Phyla. SICB 2001. J.R. Garey.
Possess trochophore larvae
Mollusca and Annelida are closely allied phyla
Porifera
Cnidaria
Ctenophora
Platyhelminthes
Gastrotricha
Gnathostomulida
Cycliophora
Rotifera
Annelida
Mollusca
Sipuncula
Nemertea
Bryozoa
Brachiopoda
Phoronida
Arthropoda
Onychophora
Tardigrada
Nematomorpha
Nematoda
Priapulida
Kinorhyncha
Loricifera
Echinodermata
Hemichordata
Chordata
Arthropoda
Mollusca
Chordata
Platyhelminthes
Nematoda
Annelida
Porifera
Echinodermata
Other
Sarcomastigophora
Apicomplex
Ciliophora
Phylum Annelida: 12,500 spp: 3 classes =
Class Polychaeta (8000 spp)
Class Clitellata;
subclass Oligochaeta (3500 spp)
subclass Hirudinea (630 spp)
Annelid characteristics
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Trochophore larvae
Closed circulatory system
True coelom
Annuli refer to segmented, metameric body plan
– Each segment has metanephridia, branches of nerves and
blood vessels, chitinous setae / chaetae
– Segments partially divided by septa
→ efficient hydrostatic skeleton
→ Pre-adapted for regional specialization and tagmatization
Metamerism
Septa provide regional control
over hydrostatic skeleton
Circular musc.
Longitudinal musc.
setae
From this pic, know: metameric repetition of body segments (septa, metanephridia,
nerves, blood vessels), modest cephalization, limited regional specialization
Polychaeta
• Mostly marine
• Errant and
sedentary spp
Possess parapodia:
Capillaries for gas exchange
Swimming
Crawling
Burrowing
setae
acicula = chitinous rods for support
Cephalization
Jaws
Ocelli (photoreceptors)
Tentacles:
Mechanoreceptors
Chemoreceptors
Tube worms:
The sedentary polychaetes
Parapodia reduced (no
acicula, vascularization)
Feathery appendages at
anterior end for feeding, gas
exchange
Giant tube worms
• Discovered in 1977
• Ocean floor 8000 ft
deep
• 4 ft tall
• No mouth. Get food
from endosymbiotic
bacteria that feed on
sulphur released at
deep sea vents
Polychaete reproduction
Separate sexes
1. Conventional sexual reproduction:
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Sperm + egg released into water →
trochophore larva
2. Epitoky:
– Epitokous individual forms an
epitoke by
a. Transformation of posterior portion
b. Asexual budding
– Mature indiv = atoke
– Gamete-bearing part = epitoke
capable of swimming about in
search of mates (timed w lunar
cycle)
atoke
epitoke
Class Clitellata
• Possess cylindrical ring used in reproduction
– Formation of a cocoon for the embryos
• Permanent gonads
• Two subclasses:
1. Oligochaeta
2. Hirudinea
Oligochaeta
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Mostly fossorial, some aquatic
little cephalization
No specialized organs for gas exchange
Feed on detritus, organic debris
Hermaphroditic
– Sperm exchanged between two mating
individuals
Sperm exchange between mating earthworms:
• Sperm from testis stored in, and later released
from, seminal vesicles
• Sperm from other worm stored in seminal
receptacles
• After separation, sperm from other worm used to
fertilize eggs from the ovary
• Eggs and sperm from
other worm released
into forming cocoon
• Many terrestrial forms
can be parthenogenic
Hirudinea
• Occur in freshwater or moist terrestrial habitats
• Highly streamlined
• No special organs for gas exchange, sensory
except ocelli
• Have 2 suckers for feeding, locomotion
– 3-toothed jaws
• Ectoparasitic, but many
are predaceous or scavenge
Leech reproduction
• Reproduction similar to oligochaetes (use
of clitellum to form cocoons)
Class(?) Echiura: spoon worms
• Have trochophore larva but lack segments
or any indication of metamerism as adults
• Briefly segmented period as embryos
• Molecular data links Echiura to Annelida
• Reproduction similar to polychaeta
-140 spp
-Marine
-Burrow in sand, mud