Transcript (PPTX, 3.12MB)

Annelid Classes
Disclaimer: These classifications are somewhat
out of date and are mostly correct. There is
some research helping to reconstruct the
classification more accurately!
Class Polychaeta
(poly = many, chaeta = bristles)
Probably the most diverse of the three groups!
Have various ecological niches such as…
• Active predators
• Burrowers
• Swimmers
• Tube worms
• Symbiotic
Mostly marine.
Big parapods, (those flattened extensions on the
body wall that also act as gills).
• Paired on each segment.
Parapods have bundles of bristles.
• Give the class its name. (chaeta)
Parapodia
Sexes are usually separate. (Gonochoristic)
• Gametes exit via metanephridia or special
ducts.
Some worms have a special stage that releases
gametes into water called epitokes.
• Epitokes asexually bud of rear of worms.
Have larvae called trochophore larvae.
Epitokes
Trochophore larva
Where have we seen this alternation of lifecycles
before?
CNIDARIANS!
Class Oligochaeta
(oligo = a few, chaeta = bristles)
These guys you know mostly as earthworms.
Not as diverse in terms of lifestyle and body
form.
The bodies are streamlined for burrowing.
• No parapodia.
• Fewer chetae.
– Retractable into pits!
Mostly terrestrial or freshwater.
Pump-like pharynx for their detritus feeding
lifestyle.
They are mostly hermaphroditic.
Some reproduce asexually via fragmentation or
parthenogenesis.
No larval stages!
Earthworms have a clitellum, a thickened
section of surface tissue.
• Secretes a mucus ring which collects
exchanged sperm and eggs as it moves down
earthworms tail.
• Falls off at the end and forms a cocoon where
young worms develop and hatch.
Class Hirudinea, “Leeches”
Mostly freshwater and tropical.
Mostly tropical species.
They are ectoparasites.
• They are parasites but not internal ones.
• They attach to their hosts externally and suck
their blood.
A sucker at each end of the body. (anterior, and
posterior)
• The posterior sucker usually attaches to the
host.
• The anterior sucker penetrates the skin with
razor sharp jaws or by a penetrating
proboscis.
• Anticoagulant released.
• Some species use an anesthetic to avoid
detection.
No segmentation. No chetae. No septa.
Hermaphroditic.
No asexual reproduction.
No larval stages.
Again have a pump-like pharynx which sucks
up the blood of their host.
Class Pogonophora
Bizarre worms that live at the bottom of the ocean
by hydrothermal vents.
No mouth. No anus.
Get their food and energy from symbiotic bacteria
that live inside of them.
Symbiotic bacteria feed on H2S from the
hydrothermal vents to make energy/food.
• Share it with the worms.