Transcript newannelidappnotesx - Spring

Christmas Tree worm
Phylum Annelida
Segmented
Worms
Bristleworm
General Characteristics
• Phylum contains over
15,000 species
• Closed circulatory
system
• Spiral cleavage
• Bilateral symmetry
• True coelomates
– Contain a coelom that
is completely lined with
peritoneum
(mesodermal
epithelium)
General Characteristics
• Most (not leeches) have tiny chitinous bristles
called setae
• Function
–
–
–
–
Anchor somites during locomotion
Prevent slipping
Aid in swimming
Prevent them from being pulled out of home
Segmentation
• Exhibits metamerism
– Division of the body into succession of segments
• Segments called metameres or somites
– Arranged linearly
– Marked by circular grooves called annuli (outside)
• Each segment contains representatives of all major
organs and is separated by septa (inside)
Role of Segmentation
• Each segment filled with fluid that forms the
hydrostatic skeleton around which muscles
can act
• Increases efficiency because contraction in
one part of the body is not felt through the
entire body
• Force of the muscle is localized to one area
• Allows for greater body control
Body Plan
Anterior End: Prostomium
Segmented Body
Posterior End: Pygidium
* During development new somites differentiate in front of the pygidium thus the oldest
segments are at the anterior end and the youngest are at the posterior end
Organization of the Body Plan
Outer covering: non-chitinous cuticle (collagen) secreted by epidermis
Epidermis
Longitudinal muscle
Circular muscle
Dorsal mesentery
Septum
Muscular Layer
Ventral mesentary
 Longitudinal and circular muscles
 Run length of body, but divided into partitions in between somites
 Allows the organism to swim, crawl, and burrow
Body Cavity
• Coelom is found as a pair of compartments on
either side of the gut
– Completely lined with peritoneum (mesodermal
epithelium)
• Peritoneum lines body wall and all organs
– Forms dorsal and ventral mesenteries (divisions)
– Mesenteries provide support above and below gut
• Septa is the intersection of adjacent segments
– Partitions the anterior and posterior walls of the
coelomic sacs between segments
– Perforated by the gut and blood vessels
Function of the Coelom
1. Filled with fluid to form hydrostatic skeleton
2. Separates the body wall from the digestive
tract
3. Surrounds all the organs
4. Supplements the role of the circulatory
system
5. Plays a role in the excretory and
reproductive process
Burrowing Annelids
• Annelids can burrow because of a concerted
effort of the:
– Circular and longitudinal muscles
– Fluid filled coelom
– Segments
Class: Polychaeta
• Largest class with over 10,000 species
• Location
– Most are marine
– Some are eurythaline (tolerate range of salinity)
– Fresh water in warmer regions
Feather duster
General Characteristics
• Well differentiated head region with
specialized sense organs
• Paired appendages, parapodia, on most
segments
– Used in crawling, swimming, and as a respiratory
organ
• Contain many setae arranged as bundles on
parapodia
• Some somites are differentiated
Significance of Polychaeta
• Play vital role in marine food chains
• Source of food for fish, crustaceans, and
hydroids
Divided into 2 groups
• Free moving
– Leave home to feed or burrow (can be predators
of scavengers)
• Sedentary
– Located in tubes or burrows (feed on suspended
particles)
Structure of Polychaete
• Prostomium
– Head region with eyes,
tentacles, sensory structures
(palps)
• Peristomium (first segment)
– Surrounds the mouth
– May have setae and palps
– In predators, may have jaw
• Trunk-body
– Segmented with setae or
other structures
– Most segments have
parapodia
Notopodium
Setae
Neuropodium
Epidermis
Nutrition
Free moving polychaetes are predators and scavengers
Sedentary Polychaetes feed on suspended particles in sediment
Digestive System
• Foregut
– Contains the pharynx and
anterior esophagus
– Lined with cuticle
• Midgut
– Comes from the endoderm
– Anterior portion secretes
enzymes
– Posterior portion aids in
absorption
• Hindgut
– Derives from the ectoderm
– Connects the midgut to the
exterior (anus) on the
pygidium
Circulation and Respiration
• Some species use parapodia or gills for gas
exchange
• Others gas exchange occurs across the body
surface
Excretion
• Varies across species
• Most have metanephridia (one pair per somite)
– Type of tubular nephridium with the inner open
end draining the coelom and outer end
discharging to the exterior
Notopodium
Setae
Neuropodium
Epidermis
Nervous System
• Contain a dorsal cerebral ganglia connecting
to a sub-pharyngeal ganglia via the
circumpharyngeal commissure
• Contain a double nerve cord that runs the
length with ganglia arranged in each somite
Dorsal cerebral ganglia
Circumpharyngeal
commissure
Sub-pharyngeal ganglia
Nerve cord
Ganglia
Sense Organs
• Eyes
– Vary in complexity
– Some species have lenses
• Statocysts
– Help with body orientation
• Nuchal organs
– Ciliated sensory slits that function as
chemoreceptors for obtaining food
Reproduction and Development
• No permanent sex organs
• Usually have separate sex
organs
• Fertilization is external
• Most of the year that are
sexually immature, during the
breeding season a portion of
the body becomes sexually
mature (epitoke)
.
..
Clam worms
• Sand worms
• Errant, live in mucus lined burrows in or near
low tide
• Active at night searching for food
– Feed on small animals, other worms, and larvae
– Evert their pharynx and their jaw protrudes
through their mouth to capture food
– Withdraw pharynx to swallow food
Clam worms continued
• Prostomium
– Palps sensitive to touch and taste
– Sensory tentacles
– Pair of small dorsal eyes
• Peristomium
– Ventral mouth with chitinous jaw
– 4 pairs of sensory tentacles
• Parapodium (Crawling and swimming)
– Have setae and blood vessels
– 2 lobes supported by chitinous spines
• Notopodium (dorsal)
• Neuropodium (ventral)
Scale worms
•
•
•
•
Flattened bodies
Lined with scales
Carnivorous
Live commensally with other polychaetes,
cnidarians, mollusks, or echinoderms
Fire worms
• Feed on corals and cnidarians
• Setae are hollow and brittle
– Contain poisonous secretion
– When touched setae break off in
wound and cause irritation
Class Oligochaeta
• ~3000 species
• Commonly known as Earthworms
• Location
– Terrestrial or fresh water
– Few marine or brackish water
• Contain Setae (4 pairs/segment)
– Not as numerous as polychaets
Earthworm
• Significance of earthworms
– Bring subsoil to surface to mix with
topsoil
– Permits air to get into soil
– Improves drainage
• Location
– Wet weather they are found near the surface
– Dry weather they are underground
Form and Function
Anterior End
Segments contain 4 pairs of setae
Posterior end
*Setae help in locomotion, burrowing, and anchoring the body into the ground
Earthworm movement
• Occurs by peristaltic movement
– Contractions of circular muscles in anterior end
lengthen the body pushing the anterior end
forward
– Contractions of the longitudinal muscles shorten
the body pulling the posterior end forward
Nutrition
• Scavengers
– Feed on decaying organic matter, leaves,
vegetation, refuse, and animal matter
Pathway of food
Intestine
Mouth
Gizzard
(moistens food)
(grind food)
(absorption of nutrients,
has increased blood
vessels)
Typhlosole
Muscular pharynx
Crop (temporary storage)
Esophagus
Calciferous glands (along
the esophagus, regulate
acid-base balance and
calcium ion levels)
(longitudinal fold into
intestine to increase
absorptive surface)
Anus
Chloragogen tissue:
surrounds intestine, acts as liver. Makes glycogen for fat storage, aids in excretion,
And Nitrogen metabolism
Circulation
• Double transport system
– Coelomic fluid
– Circulatory system
• Circulatory system
– Closed
– Includes vessels and capillary system in tissues
– 5 blood trunks run lengthwise through the body
Circulation continued
• Dorsal vessel
– Main collecting vessel
– Runs above the alimentary canal from pharynx to anus
– Pumping organ (true heart)
• Aortic arches (5 pairs)
– Maintain steady pressure of blood
• Capillary beds
– Found in every segment
– Allows blood to flow from dorsal to ventral
– Allow for exchange of dissolved food, nitrogen waste, and gases
• Ventral vessel
– Serves as the aorta
Blood flow
Aortic Arches
Dorsal Vessel
Ventral Vessel
Vessels of the body
wall and digestive
tract
Brain and vessels of
the rest of the
body
Capillary beds
Composition of blood:
Colorless amoeboid cells and hemoglobin
Respiration
•
•
•
•
No special respiratory organs
Gas exchange occurs across the skin
Cuticle is thin to allow exchange
Must be kept moist to allow diffusion
Excretion
• Most segments contain a pair of
metanephridia
– Each pair occupies 2 successive segments
• Coelomic fluid passes through the
metanephridia
• Useful substances are reabsorbed while
waste products are extracted from the blood
and secreted from the body
Metanephridium
Nephrostome
Ciliated funnel open
to the anterior
segment
Outside the body
near the ventral
surface
Septum
Connects to main
part of the
nephridium
Nephridiopore
Nephridial duct
Other excretory organs
• Calciferous gland
• Nitrogen secreted by choloragagen cells in
mucous
Pair of cerebral ganglia (brain)
Location: above the pharynx
Function: directs movement of the body
In response to light and touch
Nervous System
Pair of connectives
Location: Pass around the pharynx
Function: connects the brain with the first pair of
Ganglia in the nerve cord
Ventral Nerve cord
Location: runs to posterior
Function: composed of
ventral ganglion
First Ventral Ganglion
Location: first ganglion segment
after connectives
Function: if removed earthworm
cannot eat or burrow
Nervous System continued
• Each segment has a double segmental ganglion
• 3 pairs of segmental nerve branches that control
body structure
Nervous System continued
• Giant Axons
–
–
–
–
–
Serve in rapid escape movements
1 or more per worm
Located in the ventral nerve cord
Large in diameter and have a quick conduction
Make simultaneous contractions in many segments
• Neurosecretory cells
– Located in brain and ganglia
– Secrete neurohormone for reproduction, regulation,
and sex characteristics
How muscles work
• Each ganglion
receives impulses
from sensory cells Longitudinal muscle
Circular muscle
• Ganglia coordinate Dorsal mesentary
the impulses so that
the longitudinal
Septum
muscles relax while
the circulatory
Ventral mesentary
muscles contract
Sense Organs
• Located all over the body
• No eyes but have many photoreceptors in
the epidermis
• Earthworms stay away from bright lights but
move towards low light
General Behaviors
• Chemical
– Aid in food choices
– Earthworm senses its texture, acidity, and calcium
• Light
– Avoid light unless very weak
• Mechanical stimulation
– Positive to moderate stimuli
– Negative to strong vibrations
• Burrow quickly
Reproduction
• Monoecious = hermaphroditic
– Have both male and female reproductive organs
• Keep eggs and sperm separate (protandry) to
avoid self-fertilization
Male reproductive system
• 2 pairs of small testes
• 2 pairs of sperm funnels surrounded by 3 pairs
of large seminal vesicles
Pathway of sperm
Testes
Seminal vesicles
(immature sperm)
(mature sperm)
Sperm Ducts
Male genital pore
Seminal receptacles
(receive and store
sperm from the mate)
Funnels
Expelled during
copulation
Pathway of the egg
Ovaries
(eggs are discharged
into coelom)
Genital pore
Oviducts
(egg carried via
ciliated funnels)
Reproduction Process
• Can occur during any season
• Usually takes place at night during warm moist
weather
• Clitellium
– Thickened saddle like portion of mid body segments
– Secrete mucus that holds the earthworms together
• Position
– Worms extend their anterior ends from their burrows
and bring their ventral surfaces together
Steps of Reproduction
1. Sperm is discharged and travels to the seminal receptors of the other worm
2. Each worm secretes a mucous tube and then a band forms a cocoon
around the clitellum
3. As the cocoon passes forward eggs from the oviducts, albumin from the skin
glands, and sperm from the mate (stored in the receptacles) pass into the
cocoon
4. Fertilization of the eggs takes place in the cocoon
5. When the cocoon slips past the anterior end of the worm its end closes
producing a sealed cocoon
6. Development take place in the cocoon and the form that is hatched from
the egg is a young worm similar to the adult
*Juveniles do not develop a clitellum until they are sexually mature
Clitellum
Slime tube
Seminal
Receptacle
With sperm
Class Hirudinea
• Leeches
– (~500 species)
• Location
– Freshwater
– Few marine and terrestrial
– Found mainly in tropical countries
Different to earthworms
•
•
•
•
Highly specialized
Lost setae that are used for locomotion
Developed suckers for attachment
Gut specialized for storage of large quantities of
blood
Similar to earthworms
• Hermaphroditic
• Presence of a clitellum ( only during mating season)
Movement
• Creeping with looping
movement
• Attach first sucker and
then the other…pulling the
body along the surface
Form and Function
•
•
•
•
Fixed number of somites (~34)
Lack distinct coelomic compartments
In most species the septa have disappeared
Coelomic cavity is filled with connective tissue
and a system of spaces called lacunae
– Coelomic lacunae form a regular system of
channels filled with fluid that serve as circulatory
system
Eyes
Segment
Anus
Posterior sucker
Nutrition
• Many are predators
• Some are parasitic (true blood
suckers)
– Do not stay on host for long
• Terrestrial leeches
– Feed on insects, earthworms,
and slugs
– Some climb trees to reach birds
and other warm blooded animals
• Freshwater leeches
– mainly predators or scavengers
– Some blood suckers feed on
cattle, horses, humans, and
others
Medicinal leeches
• Blood suckers have jaws for cutting tissue
Respiration and Excretion
• Occurs through the skin
• Some leeches have gills
Nervous System
• 2 brains
– Anterior brain
• Composed of 6 pairs of fused ganglia forming a ring
around the pharynx
– Posterior brain
• Composed of 7 pairs of fused ganglia
– Additionally, 21 pairs of segmental ganglia occur
along the double nerve cord
Sensory System
• Have free sensory nerve endings
• In epidermis have photoreceptor cells
• Row of sensory organs called sensillae ocelli
also present
Reproduction
• Have both male and female sex organs
(hermaphroditic)
• Practice cross-fertilization
Reproductive process
Penis or hypodermic
impregnation
(expels sperm)
Sperm penetrates
integument of other
worm
Clitellum secrets a
cocoon
Bury cocoon in mud
or damp soil
Cocoon gathers egg
and sperm
Circulatory System
In leeches the coelom has been decreased by appearance
of connective tissue
Some orders have a
typical circulatory
system same as the
earthworm
Some orders: blood vessels are
lacking and system of coelomic
sinuses forms the only blood
vascular system
Contractions of longitudinal
channels provides propulsion of
blood