Intro to Annelids

Annelid Taxonomic Classes:
Class Polycheta
Class Clitellata
“Bristle worms” “oligochetes”
Phylum Annelida
I. General Characteristics
II. Class Polychaeta
A. Basic Body Plan, Swimming, Reproduction and Development
B. Polychaete Adaptive radiation
Class Echiura
“Leeches”
III. Other Marine Annelids
A. Family Siboglinida : Vent worms and whale worms
B. Echiura and Sipuncula
IV. Class Clitellata
A. Oligochaetes
B. Hirudinea
Despite apparent differences the polychetes
and oligochetes share fundamental features
oligochete
Segmented body
Metamerism
Hydrostatic skeleton by
a true coelom
Complete digestive tract
Closed circulatory system
Class Polycheta: marine bristle worms
Prototype Errant Nereis
(Fig 15.4)
Prostomium peristomium
segment
polychete
Leeches along with
oligochetes; both are in the
Class Clitellata
Clitellum
Coccoon
No parapodia
No head appendages
Metameric condition
Parapodia
bristles
acicula
Fig 15.1-3
Circulatory system
The excretory system consists
of metanephridia that work by
selective transport
(fig 15.2)
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Polychete Reproduction:
Gametes form from cells that line the coelom
Some copulate but most form Epitokes
• Hierarchical System of Controls
- Day length cues seasonal
reproduction
– Lunar Cycles synchronize local
spawning events
(Fig 17)
- Meteorological phenomena are
likely the final trigger to epitoky
In Fiji and Samoa, palolo worms swarm
on the 7th night after the full moon
that follows the autumnal equinox!!
Odontosyllis enopla
- Complex Sex Pheromones
synchronize nuptual dance and
spawning
Corresponding structures in a trochophore larva
and in an adult polychete.
Polychete Reproduction
(similarities to mollusca)
Fig 18
Adaptive Radiation in Polychaetes
-- metameric body plan of Nereis and other errants is
the basic condition
-- some are adapted to live in the plankton: swimming
polychaetes like Tomopteris
-- burrowing polycheates are “earthworm-like”
-- sedentary forms secrete tubes or dwell in burrows;
head has prominent tentacles for suspension or deposit
feeding.
-- some are highly specialized tube dwellers
Crawlers
• Head prominent
• Crawling parapods
• Eversible pharynx
some spp. with
poison glands.
Burrowers
• Move by peristalsis
• Head streamlined
• Parapods reduced
• Deposit Feeders
“earthworm-like”
Swimmers
• Large parapods
• Transparent body
• Enormous eyes
• Active predators
Tube dwellers
• Movement limited
• Head reduced but
with tentacles
• Parapods small
• Passive and Active
suspension feeders
• Filter Feeders
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Annelid Taxonomic Classes:
Polychaete
Family
Siboglinidae
F. Siboglinidae :
Perviates
< 1mm diameter
10 - 74 cm long
(spaghetti worms)
opisthosoma
Class Echiura
“
Fig 13.12-13.14
6-25 segments containing coelomic
compartments that are isolated
from each other by muscular septa;
each segment bears chitinous setae
Newest
Siboglinidae
F. Siboglinidae
Vestimentiferans
(vent worms)
plume
heart
V blood vessel
trophosome
Osedax
tube
Rouse, GW. et al. 2004
Fig 13.15-16
“... small but very intriguing group…”
Archea and other
bacteria abound!
• Live in the deepest parts of the ocean
• No digestive system
• Thrive in areas of high methane or sulfur
• Trophosome with bacteria
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No light yet a very rich community
of exotic marine organisms?
Experiment: Use of sulfur by trophosome bacteria
SO 3
-
SH -
S 2 O 3
--
No light yet a very rich community
of exotic marine organisms?
Bacterial Chemosynthesis
CO 2 + H 2 S + O 2 [CH 2 O] n + H 2 SO 4
Photosynthesis
Fig 17.5
But H 2 S usually inhibits
Cytochrome c oxidase activity (ETS enzyme)
Does vent worm Cyt c tolerate H 2 S?
Is sulfide somehow detoxified?
Expts. By M. Powell and George Somero
“The Echiura”
With Addition of
pogonophoran blood
Hemoglobin
Binds to sulfide
Molecules
With scoop-shaped proboscis
Main body is large coelom
Fig 13.26-13.29
Muco-ciliary deposit feeders
Live in sand, mud, crevices
“Fat inkeeper” worm is best known representative
“The Sipuncula”
Ecologically and functionally like Echiura
Instead of a proboscis a fully retractable
head region known (introvert) aids feeding
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The Sipuncula:
Some Annelid (Echiura) vs Sipuncula Characteristics
Annelid-like
Characteristic Echiura Sipuncula
Musculature outer circular and inner longitudinal
Setae Present Absent
Metamerism early juvenile Absent
- Fewer than 600 species; found primarily in shallow
marine habitats; deposit/detritus feeders
- Soft bodied, with very poor fossil record, but with
distinctly protostomous embryological characters
- Not as abundant or as ecologically important as annelids
Coelom form.
Cleavage
Larval form
All have schizocoelous formation
All with spiral determinate cleavage
The trochophore is the first larva
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