Annelid Taxonomic Classes:
Over 9000 spp., mostly aquatic many live in tubes
Polycheta
“Bristle worms”
Clitellata
“Earthworms”
“Leeches”
Annelid Taxonomic Groups:
Previously considered sepearate phyla
Echiura
Sipuncula
Pogonophora
“
Annelida
I. General Characteristics
II.Class Polychaeta
A.
B.
Basic Body Plan, Swimming, Reproduction and Development
Polychaete Adaptive radiation
III. Other Marine Annelids (derived polychaetes)
A.
B.
Family Siboglinida : Vent worms and whale worms
Echiura and Sipuncula
IV. Class Clitellata
A. Oligochaetes
B. Hirudinea
Despite apparent differences the polychaetes and oligochetes
share fundamental features
oligochete
Segmented body
Metamerism
Hydrostatic skeleton by
a true coelom
Complete digestive tract
Closed circulatory system
Leeches along with
oligochetes; both are in the
Class Clitellata
polychete
Clitellum
Coccoon
No parapodia
No head appendages
Class Polychaeta: marine bristle worms
Prototype Errant (crawling-type) Nereis
(Fig 15.4)
Prostomium peristomium
segment
Metameric condition
Setae
or Chetae
Parapodia
acicula
Fig 15.1-3
(made of chitin)
Parapodia
capillaries
ganglia
nephridia
Circulatory system
Urine
The excretory system consists
of metanephridia that work by
selective transport
(fig 15.2)
Types of Skeletons in Animals
Endoskeleton
Exoskeleton
Hydrostatic skeleton
In what ways are these three types
of skeletons functionally similar?
Polychaete swimming simulation
Polychete Reproduction:
Gametes form from cells that line the coelom
Some copulate but most form Epitokes
(Fig 17)
In Fiji and Samoa, palolo worms swarm
on the 7th night after the full moon
that follows the autumnal equinox!!
(October usually….)
Odontosyllis enopla
• Hierarchical System of Controls
- Day length cues seasonal
reproduction
– Lunar Cycles synchronize local
spawning events
- Meteorological phenomena are
likely the final trigger to epitoky
- Complex Sex Pheromones
synchronize nuptual dance and
spawning
Polychete Reproduction
Is the trochophore a plesiomorphic
(ancestral) character shared by
molluscs, annelids and related phyla?
Metameric body plan of Nereis and
of other errants is the “basic” condition
• Head prominent
• Crawling parapods
• Eversible pharynx
some spp. with
poison glands.
fireworm
Swimming Polychete: Tomopteris
• Large parapods
• Transparent body
• Enormous eyes
• Active predators
Swim with paddle-like parapodia or for rapid
swimming by increasingly rapid undulations of the
body combined with parapodia
Burrowing Polychaete:
• Move by peristalsis
• Head streamlined
• Parapods reduced
• Deposit Feeders
“earthworm-like”
tube
dwellers
Feather duster
Xmas tree
Fan worms
etc.
--Tubes of
Mucus
Sand
Parchment
Calcite
tube
dwellers
•Movement limited
•Head reduced but
with tentacles
•Parapods small
•Passive and Active
suspension feeders
•Filter Feeders
Most specialized
Tube dweller is
Chaetopterus
Marine annelid diversity
Specialized Taxa
Annelid Diversity:
SubFamily
Vestimentifera
Polychaeta
Family Siboglinidae
SubFamily
Frenulata
Class EchiuraGenus Osedax
“
Annelid Family Siboglinidae
“... small but very intriguing group…”
• Live deep in the ocean
• No digestive system
• Thrive in areas of high
methane or sulfur
Includes
Frenulate “spaghetti worms” that
feed by absorbing nutrients
Whale carcass worms: root
system absorbs bacterial
nourishment from bone marrow;
& symbiotic bacteria
Vestimentiferan giant cold seep
and hot vent worms
Sub Family Frenulata
< 1mm diameter
10 - 74 cm long
(spaghetti-like worms)
opisthosoma
6-25 segments containing coelomic
compartments that are isolated from
each other by muscular septa; each
segment bears chitinous setae
Fig 13.12-13.14
Sub Family
Vestimentifera
vestimentum
Large thick bodies,
up to 2 m long
Whale fall time series
Hagfish
Sleeper sharks
Polychaete worms (free living, bacterial grazers)
Vigtorniella
(Polychete)
Whale carcass worms Osedax not considered
Vestimentiferans
A watercolor painting shows females and males from the new marine worm species. The female worms are
illustrated both in their tubes and with a whalebone “cutaway,” to reveal their large ovisacs and extensive roots
that invade the bone. The small males live in the tubes of the females and are shown as “blowups” with their
relative positions in the tubes indicated by the dark lines. Top left: male Osedax rubiplumus. Top right: female
Osedax rubiplumus. Bottom left: male Osedax frankpressi. Bottom right: female Osedax frankpressi.
F. Siboglinidae
Vestimentiferans
vent worm Riftia
plume
heart
V blood vessel
trophosome
tube
Fig 13.15-16
Read Research Focus 13.1
on Chemosynthesis
Microbiologically analogous to Archean
vent systems and may serve as models
for the origin and evolution of life in
Archean vents.
Baross ad Hoffman (1985) in
Origins of Life and Evolution of Biospheres
…deep-sea hydrothermal vents may
help advance the understanding of
how early microbial life forms gained
a foothold in hydrothermal systems
on early Earth and potentially on
other planetary bodies.
(McCliment et al., 2005, Environmental
Microbiology 8: 114-125)
An alternative proposal to the “pre-biotic soup” theory…chemical
conversions that involve “transition metal sulphide catalysts” create
favorable environments for abiogenic acetate production that release
energy… acetyl-coA is the most central carbon backbone in microbial
metabolism
Martin et al., 2008, Nature Reviews 6: 804-14
The Newest Annelids
Sipuncula
Annelids
(peanut worms)
Echiura
(inn keeper
worms)
The Sipuncula:
- 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
- Best known for having teleplanic larvae
The Sipuncula
Ecologically and functionally like Echiura
Instead of a proboscis a fully retractable
head region known (introvert) aids feeding
The Echiura
With scoop-shaped proboscis
Main body is large coelom
Muco-ciliary deposit feeders
Live in sand, mud, crevices
“Fat inkeeper” worm is best known representative
Some Annelid (Echiura) vs Sipuncula Characteristics
Annelid-like
Characteristic
Musculature
Setae
Metamerism
Coelom form.
Cleavage
Larval form
Echiura
Sipuncula
outer circular and inner longitudinal
Present
Absent
early juvenile
Absent
All have schizocoelous formation
All with spiral determinate cleavage
The trochophore is the first larva
Phylogeny of Annelida
Among the Eumetazoa, within
the lineage of Lophotrochozoa
that includes molluscs
Annelida monophyly is widely
accepted
Phylogeny within the Annelida
in turmoil over last 15 yr, but a
consensus is emerging
2007
Family Capitellidae
Nuclear genes and
rDNA sequence analyses
Whither
Polychaeta?
Evolution of
Clitellata?
Taxonomic Families
traditionally
considered to be
polychaetes
Family Terebellidae
Family Nerididae