1. Define and explain these terms: eucoelomate,
prostomia, deuterostomia, schizocoelous, enterocoelous and trochophore.
2. Explain the etymology of Annelida and compare
the general complexity of the body sustems of the annelids with previously
studied phyla.
3. Explain metamerism. Highlight the two different
forms of segmentation displayed by the remaining phyla to be studied.
4. State the three classes within the phylum
Annelida and give examples of each.
5. Discuss the ecological impact of members
of the phylum, citing the earthworm specifically and its role in maintaining
good soils.
6. List several general phylum characteristics
concentrating on new developments.
7. Identify members of the class Hirudinea
and discuss differences between members of this class and the other two of
the phylum.
8. Cite differences between polychaete worms
and others in the phylum.
9. Discribe the reproductive patterns of the
South Pacific Palolo worm.
10. Discribe the digestive tract of the Oligocheata,
tracing the passage of materials from mouth to anus.
11. List and briefly describe the organs and
systems which are introduced for the first time with the annelids, or which
are more highly developed in the annelids than in previously studied groups.
12. Describe how reproduction occurs in the
earthworm, a representative of the class Oligochaeta.
Resources: Text: Animal Diversity, Chapter
11
Internet Resources:
http://gnv.fdt.net/~windle
http://dmoz.org/Science/Biology/Zoology/
http://www.il-st-acad-sci.org/health/wormlink.html
http://www.mhhe.com/hickmanad4e
Metamerism
- segmentation, linear series of essentially similar units called segments,
somites or metameres
-metamerism evolved twice in Animal Kingdom
1. annelid/arthropod line: locomotion ---> burrowing
2. chordate line: locomotion ---> swimming
homonomous segmentation
- metameres structurally and functionally similar,
each acts as semi-independent
unit, however, cannot function independently
(ex. Annelida)
heteronomous segmentation-
metameres in different regions of body
dissimilar, not always obvious
(ex. Arthropods, chordates)
*Metamerism allowed development of greater complexity of structure and function;
-made possible independent
and seperate movements by seperate segments,
the need for fine control
led to evolution of more sophisticated nervous system
-repetition of body parts
gave organism built in redundancy, safety factor, if one
segment fails, others can
still function, thus injury to one part not necessarily fatal.
-evolutionary significance evident in great success of arthropods and vertebrates.
Phylum Annelida
- segmented worms(bristle worms) ~9000 species
-inhabit virtually all marine environments,
have successfully invaded freshwater and
moist terrestrial
CLASS OLIGOCHAETA- most familiar, earthworms, nearly all F.W. and Terr.
CLASS HIRUDINEA- carnivorous, bloodsucking, leeches
CLASS POLYCHAETA- largest class ~5000 species, marine, Nereis
Ecology/Economics
-predators, ciliary filter feeders, saprophytes
-burrow, build tubes, free swimming
-Earthworms and leeches directly influence
human welfare
Charles Darwin- one m2 of ground
may contain 20 earthworms, castings
scattered over soil surface.
-can equate to 4.5 Kg (~10lb) of
soil carried to surface/year, over 20 years
a layer 8cm thick would be transformed.
*in addition to soil turnover:
1. makes soil porous, better
penetration of water and air
2. accelerates bacterial decomposition
of organic matter.
Aristotle- "intestines of soil"
Leech used in medicine- bad blood/blood letting
-red stripe on barbers pole indicated
that barber was also blood letter (white
stripe signified bandage)
-salivary gland produces HIRUDIN, anticoaggulant
*making medical comeback, microsurgury, reattachment, leeches relieve congestion
General Phylum Characteristics:
-segmented body, metamerism, bilateral symmetry
-antagonizing muscle groups
-setae, chitinous bristles (except
in leeches), polychaetes have setea on fleshy
parapodia, setae used to anchor worm
and aid in locomotion
-coelom divided by septa (except leeches)
-closed circulatory system;
hemoglobin present in some amoebocytes present
in blood (similar to WBC's)
-digestive tract complete but not segmented
-Respiratory system absent or reduced
to gills, gas exchange by diffusion through skin
(moisture necessary)
-excretory by nephridia; one pair per segment (why?)
-nervous system, ventral nerve cord w/
lateral nerves in each segment (due to
metamerism) dorsal cerebral ganglion
(paired brain)
BODY PLAN
*head (prostomium); segmented body,
terminal anus
-growth at posterior end just in
front of last segment
*muscle system for locomotion/burrowing
although coelomic fluid does serve as
hydrostatic skeleton (presence of
septa allows greater efficiency because muscle
contractions are not whole body) widening
and elongation can occur in localized areas
*as segments widened (by longitudinal
contraction) and body anchored to burrow wall,
setae aid in anchoring, anterior stretches
(circular muscles contract); locomotion
*coelom- schizocoel w/ peritoneum that forms mesentaries; covers all organs
*segments seperated by septa
CLASS HIRUDINEA ~520 SPECIES; leeches
-mainly freshwater but few marine and
terrestrial
-fixed # of segments, usually 34 (similar
to eutely)
-posterior and anterior suckers
-no parapodia; no setae (main
reason for grouping)
-no internal segmentation (coelom filled
w/fluid and connective tissue
-carnivores as well as external parasites.
-feeding:
mouth opens for muscular proboscis or
muscular pharynx w/ 3 jaws and teeth
blood suckers, take large quantities
digest slowly mainly w/aid of gut bacteria
CLASS POLYCHAETA ~5000 species, largest class Nereis and feather dusters
-exclusively marine, inhabit every possible niche, significant part of marine food chain
-polychaetes have well developed head
Prostomium (head)- often has
eyes, statocysts. eyes range from eyespot to well
developed organs.
Peristomium- surrounds
mouth, in Nereis bears chitinous jaws, in tube worms
bears fans for filter feeding
(tentacular crown)
-food attracted to arms (radioles), cilia move food to mouth
-no clitella, no permanent sex
organs, no permanent ducts for sex cells, dioecious,
fertilization is external
Palolo worm of South Pacific:
Posterior epitokes (gamete sacs)
Anterior atoke (non-reproductive)
-lives in burrows among
coral reefs
-during reproductive cycle
epitoke becomes swollen w/gametes
-swarming occurs during
last quarter of October/November moon
-epitokes break off and
swim to surface
-at surface epitoke segments
burst releasing gametes
-atoke regenerates posterior
epitoke
CLASS OLIGOCHAETA (few setae) ~3000 species, most F.W. and terrestrial ***earthworm
-no parapodia but do possess several varieties of setae
-peristaltic movement, waves of contraction along length of body, setae anchor segments.
DIGESTION- unsegmented tract
food into mouth (buccal cavity) by contractions
of muscular pharynx, then to esophagus
-3pr calciferous glands by esophagus (excrete excess Ca+ andCO3- ions from blood)
-in pharynx, saliva begins digestion
-from esophagus to crop, storage organ
-crop to gizzard, grinds food
into minute particles by geing squeezed and rolled about.
Injested grains of sand aid process
-food then to intestine:
Enzymes: amylase (carbos),
cellulase; pepsin and trypsin (protein); lipase (fats)
TYPHLOSOLE- folded area of intestine, why??????
CHLOROGOGUE TISSUE- surrounds
tract and dorsal blood vessel, intermediary
metabolism, synthesize and store
glycogen and fats, synthesize urea.
CIRCULATORY SYSTEM (coelomic fluid serves as accessory system)
-nutrients absorbed through intestine into coelom as well as blood vessels
-5pr. of aortic arches ("hearts")
at anterior end, dorsal blood vessel receives blood
from lateral vessels, dorsal blood
moves from post. to ant.; ventral takes blood
form ant. to post.
-blood contains hemoglobin and amoeboid cells
EXCRETION- nephridia, pr. in each segment;
nephridium occupies two successive
segments; nephridium in segment 5 drains
segment 4;
Nephrostome funnels wastes from preceeding segment, cilia conduct liquids.
-nitrogenous wastes eliminated through nephridiopores
NERVOUS- cerebral ganglia (bilobed
"brain") located dorsan to pharynx in 3rd segment
-connected to ventral nerve cord by
connective nerve tissue around pharynx
-ventral nerve cord extends length of body, lateral nerves branch into each segment.
Brain + nerve cord = Central nervous
system
Lateral nerves = peripheral nervous
system
REPRODUCTION
-hermaphroditic organisms that practice
cross fert.
-during copulation worms joined by
mucus secretion from clitellum and by specialized
setae
-sperm discharged and travels via seminal grooves to receptical of other worm
-after cop. (sometimes days later)
cocoon formed from clitellum, as cocoon moved
along body toward head, eggs, sperm
and albumin are deposited in cocoon.
Fertilization occurs in cocoon.
-clitellum develops when worm sexually mature