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Phylum AnnelidaChapter 13
At the time of the November full moon on islands near Samoa in the South Pacific, people rush about preparing for one of their biggest yearly feast. In just one week, the sea will yield a harvest that can be scooped up in nets and buckets. Worms by the millions transform the ocean into what one writer called “vermicelli soup!” Celebrants gorge themselves on worms that have been cooked or wrapped in breadfruit leaves.
Samoan Palolo worm
Stock photo of hunters with powerful lights used to attract more palolo worm, Palola siciliensis, American Samoa, Pacific
Samoan Palolo worm
Image of palolo worms, Palola siciliensi, in water column after emerging from their burrows on night of the spawning, Tutuila Island, American Samoa, Pacific Ocean
Phylum Annelida• Class Polychaeta
•Marine worms
• Class Clitellata–Subclass Oligochaeta-
•Soiling building worms–Subclass Hirudinea-
•Predatory leeches
Phylum AnnelidaCharacteristics
–Metamerism - segmented body
–Bilateral–Protostome–Wormlike–Epidermal Setae–Closed Circulatory System–Dorsal ganglia and ventral nerve cord
–Metanephridia or protonephridia
Metamerism and Tagmatization
Metamerism – segmental arrangment of body parts.
Each segment has:excretory, nervous, and circulatory structures
Advantages of Metamerism:
• 1. Hydrostatic compartments- allows variety of locomotor and supportive functions like swimming, crawling, and burrowing.
Advantages of Metamerism:
• 2. Lessens the impact of injury- if few segments injured others can perform normal functions which increases the likelihood that the worm will survive.
Advantages of Metamerism:
• 3. Tagmatization- The specialization of body regions in a metameric animal
• permits the modification of certain regions of the body for specialized functions like feeding, locomotion, and reproduction.
Advantages of Metamerism:
Advantages of Metamerism:
Class Polychaeta
Class PolychaetaCharacteristics
• Marine• 5 – 10 cm in length
• 5,300 species• Largest of the annelid classes
Class Polychaeta
Live:• On the ocean floor• Under rocks and
shells• Within crevices of
coral reefs• Some can burrow
External Structure and Locomotion
Parapodia – lateral extensions supported by chitin
Setae – bristles secreted from the distal ends of the parapodia• Important for locomotion/ digging
Parapodium
Parapodia and Setae
Parapodia and Setae
Parapodia and SetaeSee them work in action
External Structure and Locomotion
Prostomium- lobe that projects dorsally and anterior to mouth
contains: eyes, antennae, palps and nuchal organs
Nuchal organs: ciliated sensory pits which are chemoreceptors for food detection
External Structure and Locomotion
Peristomium- first body segment; surrounds the mouth
Annelids also secrete a nonliving cuticle from the epidermis for protection
Prostomium and Peristomium
Prostomium and Peristomium
The prostomium (right) has two antennae and two large, two-segmented palps. The peristomium (segment behind the prostomium) has 4 pairs of tentacular cirri. This photo is a 3d composite made from a series of photos using a Keyence digital microscope. Photo by Dave Cowles, July 2009
Feeding and the Digestive System
Digestive tract is a straight tube:Pharynx- when everted can form a
proboscis (See it)Crop- storage sacGizzard- grindingIntestine-long and straight
Feeding and the Digestive System
• Polychaeta can be:–Predatory-usually burrow or live in coral crevices; some can have poison glands
–Herbivores–Scavangers–Filter feeders- tube dwelling (see them feed)
Examples of different worms and how they feed
Selective deposit feeders with tentacles.Filter feeders with radioles.
Feeding and the Digestive System
Elimination of waste for tube dwellers:If open ends: wastes carried away by water circulating in tube.
If closed end: then the worms either turns around in tube OR uses ciliary tracts along body wall to carry feces out.
Feeding and the Digestive System
• Polychaetes that inhabit substrates rich in dissolved organic molecules can absorb as much as 20% to 40% of their food across their body walls (very unusual among animals)
Gas Exchange and Circulation
• Respiratory gases diffuse across body wall and parapodia (increase surface area)
• Closed circulatory system• Oxygen is carried by molecules called
respiratory pigments- blood colorless, green or red
Gas Exchange and Circulation
• Dosal aorta- propels blood from rear (posterior) to front
• Ventral aorta- propels blood from front to rear
• With Capillaries between the two aortas
Nervous and Sensory• A pair of Suprapharyngeal ganglia-controls motor and sensory functions; feeding and forward movement.
Connects to
• A pair of Subpharyngeal ganglia- mediates locomotor functions required for coordination of distant segments.
By
• Circumpharyngeal connectives-run dorsoventrally along the pharynx
Nervous and Sensory
• Ventral nerve cord with paired segmental ganglia in each segment; allows escape response of segments
• Segmental ganglia- coordinate swimming and crawling movements in isolated segments.
• 2–4 pairs of eyes
Suprapharyngeal ganglia
Circumpharyngeal connectives
Subpharyngeal ganglia
Segmental ganglia
Excretion
• Excrete ammonia• Most of the excretory organs
in annelids are active in regulating water and ion balances
• Nephridia – excretory organs in annelids
Two types of Nephridia
• Protonephridia- tubule with a closed bulb at one end and a connection to the outside of the body at the other end.
• Metanephridia- open ciliated funnel (nephrostome) that projects through an anterior septum into the coelom of an adjacent segment
Excretion
Osmoregulation and waste removal
Metanephridia with nephrostomes open to coelomic fluid.
Lead to nephridioducts which reabsorb wanted materials.
Waste released through nephridiopore.
• Nephridia
Reproduction and Regeneration
•All polychaetes can regenerate lost segments
•May have natural break points if grabbed by predators (process called autotomy)
•Some reproduce by fission or budding
Reproduction and Regeneration
• Most sexually reproduce• Most are dioecious • External fertilization and
trochophore larvae• Swarming occurs in some
species, where large numbers of individuals join together to release sperm and/or eggs
Reproduction and Regeneration
• Very few species copulate (most external fertilization)
• A unique, weird, kinky copulatory habit has been reported in Platynereis megalops from Woods Hole, Massachusetts. Read page 216 for the details. . .
Reproduction and Regeneration
• Epitoky- formation of a reproductive individual (an epitoke) that differs from the nonreproductive form of the species (an atoke).
• Epitoke- body modified into 2 body regions; anterior segments-normal maintenance; posterior segments-enlarged & filled with gametes
• Example: Samoan palolo worm swarm
In some species the epitoke breaks free from the atoke, which stays in the burrow
The common clam worm Nereis succineain its atoke form (above) and epitoke form (below). Especially note the enlarged parapodia on the epitoke; it uses these to swim and release eggs or sperm.
In others, the epitoke is formed as part of the body, and the whole animal leaves
to mate
Epitoke on the left, atoke on the right
3 Advantages of Swarming Epitokes
1. Nonreproductive individuals remain safe below the surface waters; predators cannot devastate an entire population.
3 Advantages of Swarming Epitokes
2. External fertilization requires individuals to be ready at the same time. Swarming ensures large numbers of individuals are in the right place at the right time.
3 Advantages of Swarming Epitokes
3. Swarming of vast numbers of individuals for brief periods provide a banquet for predators. But because it is such a BREIF period, predators can only eat so much with respect to the limits of their normal diets. Predators can dine gluttonously and still leave epitokes that will yield the next generation of animals.
Class Clitellata
Giant Blue EarthwormTerriswalkeris terraereginae
mucin it releases is luminescent Lives in rainforest in Australia
Earthworms and Leeches
Class Clitellata Earthworms and Leeches
•Have a clitellumused in cocoon formation
•All are monoecious
•Have few or no setae
Class Clitellata
Subclass Oligochaeta-
Soiling building worms(earthworms)
Subclass Hirudinea-Predatory leeches
Subclass Oligochaeta
• 3,000 species• Freshwater and terrestrial
habitats throughout the world (some marine)
• Aquatic species live in shallow water; burrow in mud and debris
• Terrestrial species live in soils with high organic content
So you want to see the biggest earthworm in
the world? Go to Australia or sit back and
watch this. . .
Giant Gippsland Earthworm
Subclass Oligochaeta
External Features• Have setae but fewer• Lack parapodia- get in the way
because of burrowing
• Prostomium- lacks sensory appendages
External Features
• Clitellum- secretes mucus during copulation and forms a cocoon (girdle-like structure)
Locomotion• Have both circular and longitudinal muscles• Move by antagonistic contractions of these
muscles• Bulging and elongating body segments in
waves cause the worm to move forward• Small setae help anchor the worm• Small conical prostomium acts like a wedge
while burrowing, and soil is swallowed (important for decomposition)
Feeding and Digestive System
• Scavengers-fallen and decaying vegetation
• Mouth->muscular pharynx->esophagus• Esophagus expanded form of stomach,
crop ( thin-walled storage structure), gizzard (muscular grinding structure).
• Calciferous glands-evaginations of esophagus wall that rids the body of excess calcium absorbed by food; regulates pH
Feeding and Digestive System
• Intestine-principle site of digestion and absorption
• Anus
Subclass Oligochaeta
• Gas Exchange and Circulation: same as polychaetes
• Nervous and Sensory: same as polychaetes but lack well-developed eyes
Excretion
• Oligochaetes use metanephridia for excretion of ammonia and urea and for ion and water regulation.
• Chloragogen tissue- acts like a liver for amino acid metabolism (deaminates amino acids into ammonia and urea); excess carbohydrates converts into glycogen and water
Reproduction
•Monoecious•Reproduce sexually via reciprocal fertilization-both worms exchange sperm (can last 2-3 hours!)•Cocoon of mucous and chitinous materials produced by clitellum•Eggs, sperm, and food (albumen) deposited in cocoon where fertilization takes place•Young worms hatch from cocoon (no larvae)
Reproduction
Eggs
Figure 17.17
Reproduction
• Freshwater oligochaetes can reproduce asexually which is usually followed by the regeneration of missing segements.
Subclass Hirudinea• 500 species• Mostly freshwater but some marine
and terrestrial• Prey on small invertebrates or feed
on the body fluids of vertebrates.
External Structures• Lack parapodia and head
appendages• Leeches are dorsoventrally
flattened and tapered anteriorly
• Anterior and posterior segments have suckers
External Structures
• Have 34 segments
Locomotion• Have lost metameric partitioning,
resulting in single body cavity• Coelomic sinuses replace blood
vessels in most leeches • Complex musculature (four types
of muscles)• Move in looping motion or swim with
undulations
Locomotion• Inchworm-like
crawling.• Relatively few
but large neurons.
• Extremely sensitive to temperature and vibration.
Feeding
• Feed on body fluids, blood of vertebrates, or entire bodies of invertebrates
• Ectoparasites
Feeding• Mouth with sucker-3 chitinous jawsor proboscis
Feeding
• Have an anticoagulant and an anesthetic in saliva
• Anticoagulant: Hirudin- prevents blood from clotting
Feeding
• Pharynx-> esophagus-> large stomach with lateral cecea (increase body mass 2-10 times)-> short intestine-> anus
Figure 17.20
Subclass Hirudinea•Nervous System
Temperature senses
•Excretion10 to 17 nephridia
•ReproductionMonoeciousReproduce sexually ONLYClitellum present only in the spring
Subclass Hirudinea