Download Topic 11b: Lophotrochozoans (Ch. 33)

BIOL 1030 – TOPIC 11b LECTURE NOTES
Topic 11b: Lophotrochozoans (Ch. 33)
I.
Lophotrochozoa clade includes the following phyla that we will cover:
1. Ectoprocta (or Bryozoa; clade)
2. Platyhelminthes (clade?)
3. Rotifera (clade)
4. Annelida (clade)
5. Nemertea (clade)
6. Brachiopoda (clade?)
7. Phoronida (clade)
8. Mollusca (clade)
II.
Phylum Ectoprocta (bryozoans, or moss animals)
A. ~4500 living species
B. coelomate
C. aquatic, mostly marine
D. use lophophore for feeding
E. secrete and live in a chitinous chamber (zoecium); also may be reinforced with calcium carbonate
F. adults are sessile and colonial; communicate chemically through pores in zoecia
G. some non-protostome characteristics: radial cleavage, secondary mouth, deuterostome-style coelom
H. appear to be a sister group to rest of the lophotrochozoans
III.
Phylum Platyhelminthes – the flatworms (must exclude Acoelomorpha to have any hope of having a grade or clade;
acoelomorphs are interesting though, feel free to look up information about them on your own)
A. ~20,000 living species
B. acoelomate
C. ribbon-shaped, soft-bodied, flattened
D. most are parasitic, some are scavengers and carnivores
E. non-parasitic forms far more active than cnidarians or ctenophores
F. those with a digestive cavity have an incomplete gut (only one opening)
G. excretory system - small tubules lined with ciliated flame cells (move water and waste into tubules and out of body)
H. no circulatory system – oxygen and food must diffuse to all cells
I. some have nerve cords and simple central nervous system
J. reproduction
1. most are hermaphroditic
2. most have internal fertilization: each partner deposits sperm in the other’s copulatory sac
3. asexual regeneration also possible in many
K. three classes to learn (we’ll leave out the 4th class, Monogenea)
L. Class Turbellaria (grade)
1. only free-living flatworms
2. use ciliated epithelial cells for movement
3. have eyespots; usually move away from light
4. have sensory pits or tentacles for detecting food, chemicals, and nearby movement
5. use pharynx (muscular throat) in feeding
6. abundant in many aqueous environments
7. some occur in moist terrestrial areas
8. include planaria
M. Class Trematoda (clade) – flukes
1. all parasitic; resistant to digestive enzymes and host immune responses
2. use mouth to feed
3. 1 mm to 8 cm long
4. attach via suckers, anchors or hooks
5. usually have two or more hosts (larvae almost always in snails, final host almost always a vertebrate)
6. important pathogens of humans:
 human liver fluke
 inhabit bile passages in the liver of humans, cats, dogs, and pigs
 can get them from eating raw fish
 can cause cirrhosis and death in high infestations
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BIOL 1030 – TOPIC 11b LECTURE NOTES

blood flukes of genus Schistosoma afflict 5% of world’s human population and cause schistosomiasis (kills
~800,000 each year)
N. Class Cestoda (clade) – tapeworms
1. all parasitic; resistant to digestive enzymes and host immune responses
2. absorb food through skin (no mouth, no digestive tract or digestive enzymes)
3. scolex - attachment organ with several suckers and possibly also hooks
4. neck – unsegmented; connects scolex to proglottids
5. proglottids - complete hermaphroditic units, making sperm and eggs
 older ones further from neck have mature, fertilized eggs,
 embryos develop and fill proglottid
 proglottids shed through feces and deposited for some other animal to pickup
6. human pathogen – beef tapeworm
 juvenile intermuscular parasite on cows
 frequent parasite of humans, can get from eating rare beef
 adult in intestines of humans - to 10 m+!
 1% of cattle in U.S. are infected - don't eat rare beef!
IV.
Phylum Rotifera – rotifers
A. ~1800 species;
B. pseudocoelmate
C. common, small (most <1 mm), mainly aquatic animals
D. mostly free-living and found in freshwater environments; some are parasites; some terrestrial
E. corona - ciliated, food-gathering organ at tip of head (filter-feeders)
F. sometimes called “wheel animals” because of appearance of beating cilia
G. true digestive tract with separate mouth and anus
H. jaws in pharynx
I. hydrostatic skeleton with rudimentary circulatory system
J. separate sexes; some species with parthenogensis – development of unfertilized eggs
K. appear to group with true Platyhelminthes and others in a clade called Platyzoa
V.
Phylum Annelida – segmented worms
A. ~16,500 species in marine, freshwater and terrestrial systems
B. coelomate
C. includes polychaetes, earthworms, and leeches
D. unquestionably segmented
1. repeated segments visible as rings
2. segments separated by partitions called septa
3. each segment has its own coelom
4. fluid inside coelom of each acts as a hydrostatic skeleton
5. muscles push against the fluid, expanding and contracting (each segment acts independently)
6. anterior segments often modified as heads, with sense organs, a brain, and even some with eyes
7. some segments modified as copulatory organs
8. connections between segments
 nervous system via ventral nerve cord
 circulatory system blood vessels (closed circulatory system)
 digestive tract with separate mouth and anus
E. most have setae – bristles of chitin used to anchor the worm to a substrate (“bristleworms”)
F. closed circulatory system has some enlarged vessels that serve as hearts
G. gases are exchanged at skin (no gills or lungs)
H. excretory system includes nephridia (like in mollusks)
1. 2 per segment
2. transport waste out of coelom by excretory tubules
I. 3 classes: Polychaeta (polychaetes), Oligochaeta (earthworms), and Hirudinea (leeches)
J. Class Polychaeta (grade) – polychaetes
1. many unusual and colorful forms; include plumed worms, peacock worms, fan worms, and many others
2. ~10,000 living species, mostly marine
3. often live in burrows
4. usually filter-feeders, sometimes carnivores or parasites
5. distinctive characteristics:
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BIOL 1030 – TOPIC 11b LECTURE NOTES
 typically more cephalized than other annelids
 parapodia - paired, fleshy, paddle-like flaps on most segments- used for moving and gas exchange
6. sexes separate, but usually lack permanent gonads (sex organs); instead, make gametes from cells lining coelom or septa
7. external fertilization
8. trochophore larvae – similar to that of mollusks (ciliated)
K. Class (or subclass) Oligochaeta (grade) – earthworms
1. mostly terrestrial (in moist soil); a few aquatic species
2. eat their way through soil (usually eat own weight in soil each day; most soil has passed many times through worm guts)
3. 100-175 segments, with mouth on first one and anus on last one
4. no eyes, but some light-sensitive organs near end of body
5. reproduction
 hermaphroditic
 join in opposite directions at the clitellum (obvious thickened band), which secretes mucus that holds the pair
together during copulation
 exchange sperm, and then each lays eggs in mucous cocoon surrounded by chitin that is secreted by the clitellum
(this cocoon protects the fertilized eggs)
L. Class (or subclass) Hirudinea (clade) – leeches
1. mostly freshwater species; some marine, some terrestrial
2. hermaphroditic with clitellum (only during breeding season)
3. reduced segmentation (34 segments), and coelom is reduced and continuous (septae lost)
4. usually dorsoventrally flattened (resemble flatworms)
5. all but one species have no setae
6. have suckers at one or both ends of body
7. includes parasites, predators, and scavengers
8. many suck blood (external blood-sucking parasites)
 chitinous jaws used to rasp through skin
 produce an anticoagulant to keep blood flowing
 once again being used by doctors to drain blood
9. form a clade with Oligochaeta that is sometimes called class (or superclass) Clitellata
VI.
Phylum Nemertea – the ribbon worms or proboscis worms
A. ~ 900 living species; mostly marine
B. partially coelomate/partially acoelomate
C. similar to free-living flatworms
D. often large (up to many meters)
E. proboscis – long muscular tube covered by a sheath, thrust out quickly to capture prey
F. excretory and nervous systems similar to flatworms
G. complete digestive system (two openings, mouth and anus)
H. closed circulatory system (blood vessels)
VII. Phylum Phoronida – horseshoe worms
A. 20 living species
B. coelomate
C. marine; many burrow into sea bed
D. use lophophore for feeding
E. U-shaped gut; secrete and live within a chitinous tube
VIII. Phylum Brachiopoda
A. 335 living species
B. brachiopod “clams” – have two calcified shells, superficial resemblance to clams
C. use lophophore for feeding
D. most are anchored via a unique stalk
E. were very common and diverse in the Paleozoic
F. decimated in the “Great Dying” (end Permian mass extinction event ~250 mya)
G. form a clade with Phoronida
IX.
Phylum Mollusca (clade) – mollusks
A. very successful phylum: over 93,000 named, living species
B. largest number of living species for animals after Arthropoda
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C.
D.
E.
F.
mostly aquatic, but over 35,000 terrestrial species (more than all terrestrial vertebrates)
includes snails, slugs, clams, oysters, chitons, cuttlefish, octopi, etc.
from microscopic to 21 m (giant squid – largest invertebrate)
economically important (food, ornamentation, currency, pests)
X.
defining characteristics of mollusks
A. bilateral symmetry with true coelom; usually have a differentiated head
B. unsegmented (some argument as to whether lost during evolution or never present in phylum)
C. three main body parts: muscular foot, visceral mass, and mantle
D. muscular foot – used for locomotion, food capture, attachment
1. may be solid or have tentacles or may be a “wing” or fin in pelagic forms
2. covered with soft epithelium
3. may secrete mucus to glide on
E. visceral mass – contains most of the internal organs, including these systems:
1. digestive system – more complicated than in phyla to this point (true coelom)
 complete (separate mouth and anus)
 mouth, stomach, intestine
 radula – rasping “tongue” with rows of microscopic, chitinous “teeth” used to scrape or drill for food
2. excretory system – simplest animals with efficient excretory system
 nephridia – tubular structures that gather wastes from coelom
 walls of nephridia reabsorb useful compounds (sugars, salts, water, etc.)
 ability to reabsorb is why the system is considered efficient
 wastes discharged into mantle cavity; gills pump wastes out of animal
3. circulatory system
 some have closed system, most have open system
 if open, coelom is generally confined to a small area around the heart
 heart may have three chambers
 some fast cephalopods have auxiliary hearts to speed blood movement
4. reproductive system and life cycle
 most have separate sexes; however, many snails are hermaphrodites
 trochophore – ciliated free-swimming larva of many marine mollusks
 veliger – second stage in development of most marine snails and bivalves; has beginnings of foot and mantle
F. mantle
1. folds (often 2) from dorsal body wall
2. enclose a cavity between mantle and visceral mass (the mantle cavity)
3. mantle cavity - may act as lung or enclose gills
 gills are filamentous projections of mantle
 gills are rich in blood vessels
 gills have a large surface area for gas exchange
 continuous pumping keeps flow of water into and out of mantle cavity
 may have siphons to move water in (incurrent) and out (excurrent) of mantle cavity
 bring in oxygenated water and send out deoxygenated water
 may be used to bring in food (in bivalves)
 may be used for jet propulsion (in cephalopods)
4. shell (if present) – secreted by mantle, usually on outside, but on inside in some snails, squid, and cuttlefish, and lost in
slugs, nudibranchs, and octopi
 provides protection
 one or two valves (shells)
 outer layer - horny protein layer; protects inner layers from eroding
 middle layer - densely packed crystals of calcium carbonate (calcite or aragonite)
 inner layer - pearly - increases in thickness throughout life of mollusk
 pearls form between the inner layer and mantle in bivalves
XI.
Mollusk taxonomy
A. 7 or 8 classes; we will cover 4, all of which appear to be clades
B. Class Polyplacophora (clade) – chitons
1. ~1000 living species
2. marine; shell is segmented with 8 overlapping, calcareous plates
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BIOL 1030 – TOPIC 11b LECTURE NOTES
3. body beneath shell is not segmented
4. head is greatly reduced
5. foot used for locomotion and for holding onto substrates
C. Class Gastropoda (clade) – snails and slugs
1. name means “stomach foot”
2. ~70,000 living species
3. mostly marine, but abundant in freshwater, and many are terrestrial
4. most have a shell
 single shell, if present
 operculum found in most marine gastropods – a horny plate that forms a covering “door” when the snail withdraws
into its shell
 coiling (spiral twisting) of shell due to one side of larva growing faster than the other side
 shell has been lost in the course of evolution for slugs and nudibranchs (sea slugs)
5. body clearly divisible into head, foot, and visceral mass
 head of most has a pair of tentacles with eyes (tentacles lost in more advanced species)
 torsion of visceral mass in development leads to asymmetry of visceral mass; anus ends up practically over the head
 terrestrial forms may have mantle cavity serve essentially as a lung – area very rich in blood vessels, allowing
efficient gas exchange
6. feeding – diversity in feeding habits; many are herbivorous (some major agricultural pests); some are active predators
D. Class Bivalvia (clade) – the bivalves
1. includes clams, oysters, scallops, and mussels
2. ~20,000 living species
3. 2 shells (valves) hinged together
4. strong adductor muscles used to pull shells together
5. typically with siphons - most are filter feeders (food trapped on mucus on gills)
6. complex folded, ciliated gills
7. no distinct head or radula
8. most have a strong muscular foot (many different adaptations)
9. some can move by clapping their shells together (scallops); however, most bivalves are sessile for most of their adult
lives, tethered to some substrate by strong threads they secrete or using their foot as an anchor
10. scallops have many eyes on soft body parts next to the edges of their shells
11. freshwater mussels the most endangered group in North America, and Alabama has the highest diversity of freshwater
mussels in the world
E. Class Cephalopoda (clade) – the cephalopods (“head foot”)
1. includes octopi, squids, cuttlefish, and nautilus
2. ~800 living species
3. 0-1 shells, internal or external
 octopi – no shell
 squid and cuttlefish – internal shell remnant used for support
 nautilus – chambered shell, superficially resembling snails
4. highly developed nervous system
 giant axons –great for research
 elaborate eyes (some up to 40 cm across – largest known eyes)
 most intelligent invertebrates; complex behavior
 many are skillful hunters
5. foot modified into grasping tentacles with suckers
6. built for speed – jet propulsion using siphons (they are fast-moving predators)
7. most have a closed circulatory system (only mollusks with this)
8. strong beak for biting; radula used to pull prey in
9. squid and octopi can release a dark “ink” to cloud water for escaping predators or even for trapping prey
10. cuttlefish are famous for changing color to match background or for messaging, using chromatophore pigment pouches;
most octopi and squid can do this as well
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