Transcript Megan Van Der Plank - University of the Western Cape

Annelids: The first segmented
bodies
Megan Van Der Bank
Department of Biodiversity and Conservation
Biology, University of the Western Cape
[email protected]
Available at http://planet.uwc.ac.za/nisl/Eco_people/Presentations/
Contents
1 The major groups of annelids living today
2 Conservation status of annelids
3 Why are annelids so successful
4 Medicinal use of Hirudo medicinalis
5 The ecological role of earthworms
6 The first appearance of annelids
7 The environmental conditions during periods of diversification
8 Evolutionary advantage of segmentation
9 Myzostomida as the link between flatworms and polychaetes
10 The relationship between annelids and arthropods
Major annelid groups living today
 Three major classes can be distinguished, namely
Polychaeta, Hirudinea, Oligochaeta (Branch and Branch,
1981)
 These groups vary significantly in the habitat and niche
that they occupy
 The annelids are highly successful and ubiquitous,
occupying mostly moist environments
 All members show true segmentation and have chaeta,
are protostome and triploblastic (Hickman et al, 2004)
Class: Polychaeta
 Also known as bristle worms
 The largest annelid group, containing as many as
10 000 species (Hickman et al, 2004)
 Traditionally, free living forms (planktonic) are
called Errantaria, while sedentary forms (tubedwelling) are called Sedentaria (Branch and
Branch, 1981)
 Paddle-like parapodia with chaeta, trochophore
larval stage, definite head (Hickman et al, 2004)
http://images.google.co.za/imgres?im
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Fig 2. Free living polychaete
with parapodia
Fig 1. Ciliated trochophore larval
stage
http://www.ucmp.berkeley.edu/phyl
a/trochophore.gif
http://www.reefseekers.com/PIXPAGES/Bristle_worm.jpg
Fig 3. Free living polychaete with bristle containing parapodia
Class: Oligochaeta
 Earthworms are predominantly detritus feeders that are
mainly terrestrial, but can be freshwater or occupy the
interstices of marine sediments (Branch and Branch,
1981).
 They are hermaphroditic and secretes a cocoon into
which eggs and sperm are deposited, namely a clitellum
(http://en.wikipedia.org/wiki/Clitella).
 Oligochaetes lack the cilliated trochophore larvae
present in polychaetes (Hickman et al, 2004).
http://www.geocraft.com/WVFossils/Carboniferous_climate.html
Fig 4.The morphology and anatomy of the oligochaete
Class: Hirudinea
 Also known as leeches
 The organisms contain a posterior and anterior
sucker used to attach to the exterior surface of
vertebrates such as amphibians and even humans.
 However most are free-living, preying on small
invertebrates and tend to lack appendages such as
parapodia and chaeta.
 Species such as Hirudo medicinalis supply heparin,
a natural anticoagulant
(http://en.wikipedia.org/wiki/Clitella/Hirudinea).
Fig 6. The leech
Zeldia.cap.ed.ac.uk/teacheng/
odl/odl6/leech.gif
http://faculty.clintoncc.suny.edu/faculty/Michael.Gregory/f
iles/Bio%20102/Bio%20102%20lectures/animal%20diver
sity/protostomes/leech_showing_suckers.jpg
Fig 5. The leech with visible anterior and posterior
suckers
Conservation status of the annelids
 The annelids are highly successful, however some
vulnerable species such as Driloleirus americanus have
been identified
(http://www.redlist.org/search/detail.php?species=6828).
 Extinction can mainly be contributed to habitat loss due
to development and industrialization.
 Hypolimnus pedderensis as an example of an extinct
annelid species
(http://www.redlist.org/search/details.php?species=4125
4).
Why are the annelids so successful?
 The success of the annelids can mainly be contributed to
their mode of reproduction.
 Sexual reproduction allows better adaptation to the
environment.
 Asexual reproduction via fission and regeneration allows
a fast rate of reproduction
(http://en.wikipedia.org/wiki/Annelids#Reproduction)
 Segments have their own autonomy but unite to form a
common body function.
 Coelomic compartments serve as a supportive
hydrostatic skeleton.
 Annelids have a wide range of adaptive features.
Medical use of Hirudo medicinalis
 The therapeutic use Hirudo medicinalis dates back to
ancient Egypt where it was used in bloodletting.
 The medical use of leeches lost its popularity by the end
of the 19th century.
 In 1884 it was discovered that the leech saliva contains a
natural anticoagulant, heparin.
 With the advent of genetic engineering in 1986 heparin
could be produced in relatively large quantities.
 Recently it has been used to relieve blood congestion in
compromised tissue
 Researchers are currently developing a mechanical
leech (Whitaker et al, 2004)
Ecological role of earthworms
 Increases soil fertility
 Plays an important role in the cycling of soil organic
matter
 Plays a role in soil mixing, porosity, aeration and water
holding capacity
 Affects the overall soil structure (Edwards and Lofty,
1972)
The fossil record: When did
annelids first appear?
 The annelids, like many other soft bodied animals, are
sparsely represented in the fossil record.
 Some polychaetes leave a calcareous cement to their
tube walls allowing these tubes to be preserved in
marine sediment
(http://www.palaeos.com/Mesozoic/Cretaceous/AptianAl
ban.htm#Annelida)
 The polychaete Canadia is the oldest fossil found in
Burgess shale, dating back as far as the Late
Precambrian, Early Cambrian
(http://tolweb.org/Annelida).
Fig 8. Ichnofossil of a segmented worm found during the late Cambrian
http://gpc.edu/~pgore/geology/geo102/cambrian.htm#camb.
http://www.palaeos.com/Mesozoic/Cretaceous/Im
ages/SerpulaHamulus.jpg
Fig 7. Calcareous tube fossils of polychaetes
 Members of the Sepulidae, Spionidae, and Eunicida
were recovered, dating back to the Ordovician
(http://tolweb.org/Annelida).
 By the end of the Carboniferous most polychaete
lineages had appeared.
 Archarenicola, a member of the group Scolecida dates
back to the Triassic.
 Oligochaetes evolved during the Jurassic and diversified
during the Cretaceous
Conditions during periods of
diversification.
 Cambrian 542 million years ago
(http://en.wiki.org/wiki/Cambrian_explosion.htm)
 Explosive adaptive radiation of most metazoan phyla
 Warmer climate and higher oxygen levels.
 Four major continents, Laurentia, West Eurasia, East
Eurasia and Gondwanaland were concentrated around
the equator
(http://www.ucmp.berkeley.edu/cambrian/camblife.html).
http://www.ucmp.berkeley.edu/cambrian/camblife.html
Fig 9. The major four continents around the equator during the
cambrain period
http://www.geocraft.com/WVFossils/Carboniferous_climate.html
Fig 10. Global temperatures and CO2 over geologic time
 Mesozoic Cretaceous 142-65 million years ago
 Period of extensive sea floor spreading along the
oceanic ridges and Gondwana fragmentation
 Increased carbon dioxide levels leading to increased
global temperatures caused by the greenhouse effect
 Rise in sea levels
 Early Cretaceous was dominated with conifers, ferns and
cycads
 Appearance of the first angiosperms leads to
diversification of oligochaetes (Hickman et al, 2004).
The evolutionary significance of
segmentation.
 True metamerism is shared by annelids, arthropods and
chordates (Davis et al, 1999)
 The advent of segmentation allowed the development of
greater complexity in structure of function.
 Segments are a repetition of body units and are able to
function independently.
 Segmentation allow better flexibility and increased the
efficiency of burrowing in annelids (Hickman et al, 2004).
Myzostomida as the link between
polychaetes and flatworms.
 Myzostomida is frequently classified within annelida but
are actually more closely related to flatworms.
 Ultrastructural evidence suggests that the segmentation,
chaeta and trochophore larvae of Myzostomida are
homologous to those of annelids.
 The ancestor of myzostomids, flatworms and
trochozoans is segmented, worm-like with chaeta and a
trochophore larval stage (Eeckhaut et al, 2000)
The relationship between annelids
and arthropods
 Arthropods and annelids evolved segmentation
separately.
 The last common ancestor of arthropods and annelids
was unsegmented but possibly had repeating organ
systems resembling that of some large flatworms or
nemerteans.
 The arthropods became segmented and evolved jointed
appendages while annelids evolved segmentation and
retained their flexible epidermal cuticle (Valentine, 1990).
References
 Branch G, Branch M (1981) Living Shores of Southern Africa. Struik
Publishers, Cape Town.ISBN 0869771159, pp272.
 Davis G and Patel N (1999) The origin and evolution of segmentation.
Trends in Genetics 15(12)M68-M72
 Edwards C, Lofty J (1972) Biology of earthworms. Chapman and Hall
LTD, London. ISBN 412110601,pp 283
 Eeckhaut I, McHugh D, Mardulyn P, Tiedemann R, Monteyne D,
Jangoux M, Milinkovitch C (2000) Myzostomida: A link between
Trochozoans and Flatworms. Biological Sciences 267(1451)1383-1392
 Hickman C, Roberts L, Larson A, I’Anson H (2004) Integrated principles
of Zoology. McGraw Hill, New York. ISBN 0072439408, pp 872
 Valentine J (1990) Molecules and the Early Fossil Record. Paleobiology
16(1)94-95
 Whitaker J (2004) Historical Article:Hirudo medicinalis : ancient origins
of, and trends in the use of medicinal leeches throughout history. British
Journal of Oral and Maxiillofacial surgery 42(2)133-137