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Terms in this set (60)
Phylum Annelida: common names
The segmented worms; marine polychaetes, earthworms, leeches, and marine "beardworms"
Level of Organization
What types of environments do they live in
terrestrial, freshwater and marine environments
Why are annelids important in marine ecosystems?
They are involved in nutrient redistribution through burrowing: they convert organic debris into CO2 to be used by marine phytoplankton for photosynthesis, releasing O2
Why are annelids important in terrestrial ecosystems?
Earthworms redistribute nutrients and help soil drainage and aeration
Protosomes and/or lophotrochozoans
Annelids are the first major group of what type of body?
Type of coelom formation; coelom is not derived from the gut
division of the body into distinct, serially repeated coelomic segments or "compartments"
each individual segment in a metameric organism
external circular rings that separate the metameres
internally separate the metameres
What systems are usually repeated in each metamere?
excretory, circulatory, reproductive, and nervous; the gut runs all the way through the segments
What is the evolutionary significance of metamerism?
permits greater flexibility, complexity, and larger size, leading to greater species diversity
What is the problem with metamerism? And what does this give rise to?
coelomic fluid in non-metameric phyla can be used to transport nutrients and wastes, but there are now septa acting as barriers; so there is a greater need to have a system to transport materials, i.e. a closed circulatory system that can transverse the segments
What are the two vessels in the closed circulatory system called?
the dorsal vessel and the ventral vessel; capillary beds connect the two major blood vessels in the body wall and in the gut wall
Which way does blood flow in the dorsal vessel?
anteriorly, or forward
Which way does blood flow in the ventral vessel?
posteriorly, or backward
What happens in the capillary beds in the body wall?
blood gets oxygenated by diffusion
What happens in the capillary beds in the gut wall?
blood picks up nutrients
tiny chitinous bristles; short stiff setae anchor a segment in an earthworm and prevent slippage backward; long setae help aquatic annelids swim
coelom still serves as a hydrostatic skeleton; circular and longitudinal muscles in body wall allow metameres to move independently, resulting in more complex and variable forms of locomotion
includes a pair of cephalic ganglia ("brain") attached to a double ventral nerve cord that runs the length of the animal with additional ganglia and nerve branches repeated in each segment; some combination of tactile organs, chemoreceptors, balance receptors, and photoreceptors; some swimming and predatory forms have fairly well developed eyes, including lenses
increased activity and movement increases metabolism; metanephridia tubules in almost all segments collect and filter coelomic fluid, removing nitrogenous wastes (urea in terrestrial species; ammonia in aquatic species) to outside through nephridiopores - so not just for osmoregulation and ion balance but true excretory (N-waster) function
occurs by diffusion across the body wall, modified into "gills" in some species; large annelids may use respiratory pigments to increase the oxygen-carrying capacity of blood
complete digestive tract; the gut is often modified into regions specialized for different tasks
U-shaped intestine increases surface area for absorption
many modes: filter feeders, carnivores, herbivores, deposit feeders, blood-sucking parasites
a long and muscular pharynx found in carnivores and herbivores
What do surface deposit and filter feeders use to eat?
Ciliated tentacles coated with mucus to trap and transport food particles to mouth
oligochaetes (e.g. earthworms) and leeches are monoecious; development is either direct (young adult emerges) or indirect with a ciliated trochophore larval stage
fertilized egg undergoes spiral cleavage and the blastula develops into a ciliated trochophore larva with three body parts: a prototroch, a metatroch, and a telotroch; as the larva grows, segments are added between the metatroch and telotroch
Growth and development (protosomes)
adult develops as segments added to larva; the anterior "head" of adult is comprised of a prostomium and peristomium; the terminal "tip" bearing the anus is the pygidium
Where do new metameres form?
In front of the pygidium; the newest segments are at the posterior end
What are the three classes in the the phylum annelida?
Polychaeta, Oligochaeta, and Hirudinea
mainly marine and usually benthic (in or on substrate) - now also include beardworms
terrestrial; include earthworms; sometimes combined with Hirudinea in a new Class Clitellata
blood-sucking and predatory leeches; generally freshwater; sometimes combined with Oligochaeta in a new Class Clitellata
mostly marine; metameric with bilobed parapodia and setae on each segment; some exhibit epitoky; some are dioecious
no permanent gonads; gonads form only during the breeding season, and usually in posterior segments
non-sexual form or part of polychaete
sexual part or form of polychaete
filter-feeding tube worms; beating of cilia on the pinnulles of the radioles produces a current that flows upwards and out; particles are trapped on the pinnules and are driven by cilia into a ciliated groove running the length of each radiole; the largest particles are rejected and fine material is carried into the mouth
some in marine sediments, others found in the deep sea associated with geothermal/hydrothermal vents at 2600 meters depth; 10 cm to 2 m
beardworms: digestive tract
no digestive tract; two different feeding strategies: if small, tentacles and body wall might create a sufficiently large surface to directly absorb dissolved organic matter; if large species at geothermal vents, a trophosome is loaded with symbiotic mutualistic chemosynthetic bacteria that use sulfur oxidation, methane, and sulfide to supply their annelid host with organic nutrients
dioecious: gonads are the only other organ system that occupies the trunk; eggs are brooded
primarily deposit or substrate feeders; a few aquatic forms are predators; terrestrial forms are important nutrient recyclers and soil aerators;
Oligochaeta: digestive tract
the gut is divided into specialized regions: pharynx (includes teeth in leeches), crop, gizzard, and intestine
hermaphrodites exchange sperm; slime tube is secreted from clitellum that slides forward and collects eggs and sperm
monoecious worms that cross-fertilize; like oligochaetas, have a clitellum but it is evident only during reproduction; embryos develop inside cocoons where they develop directly into small worms
Hirudinea: digestive tract
pharynx can include teeth or a protrusible proboscis; crop (no gizzard needed: bloodsuckers); intestine is short in leeches; leech salivary glands secrete aneasthetics, antibiotics, and anticoagulants of medical importance
Hirudinea: additional characteristics
the coelomic body cavity has been filled with tissue, and all that remains is a system of lacuna and sinuses surrounding internal organs; lack setae; species have a fixed number of segments (usually about 34), although the annuli are had to see externally and no internal septa; primarily carnivorous ectoparasites with a posterior sucker that attaches to host; use anterior sucker to suck host's blood/body fluids
Phylum Echiura: segmentation?
no sign of segmentation, but molecular (DNA) data suggests echiutans are descended from polychaete annelids and evolutionarily "lost" their segmentation - something that happened with leeches as well
Echiura: body set-up
commonly called spoonworms because of their constantly extended, spoon-shaped proboscis (which can be over a meter long); mouth at the base of the proboscis; complete gut; oval or sausage-shaped trunk;
the proboscis traps food in mucus and uses cilia to propel it along the food groove to the mouth
many are marine burrowers (live in U-shaped burrows); others live in rock and coral crevices; found at all ocean depths
dioecious; external fertilization; trochophore larva
closed circulatory system of contractile vessels (no heart)
ventral nerve cord and nerve ring (no brain)
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