Lecture 11 Flashcards
What is the third embryonic germ layer that arose after the origin of diploblastic animals?
The mesoderm (triploblastic)
What are the two clades of triploblastic animals called?
Protostomes and deuterostomes
Which of the two clades of triploblastic animals has more numbers of species and individuals?
Protostomes
When is the trait of the formation of the blastopore not universally shared?
No blastopore forms during early development of insects
What are the characteristics of protostomes?
Bilateral symmetry
Anterior brain that surrounds the entrance to the digestive tract
Ventral nervous system consisting of paired or fused longitudinal nerves
What type of coelom is found in protostomes?
Acoelomate- flatworms
Pusedocoelomate and coelomate
In what two clades has the coelom been secondarily modified?
- Arthropods
- Mollusks
How has the coelom been secondarily modified in arthropods?
Lost their ancestral coelom, internal cavity has become a hemoceol (blood chamber) where open circulatory fluid bathes internal organs
How has the coelom been secondarily modified in mollusks?
Open circulatory system
Have some hemocoel but have retained enclosed coelom around major organs
What are the two major clades of protostomes?
Lophotrochozoans
Ecdysozoans
What type of skeleton do lophotrochozoans have?
Internal skeletons
What type of larvae do many lophotrochozoans have?
Trochophore- free living larvae
How do many lophotochozoans move?
Cilia
What do several, distantly related groups of lophotrochozoans have?
A lophopore
What is a lophopore?
A circular or U shaped ridge around the mouth that bears one or two rows of ciliated, hollow tentacles
What is the purpose of a lophopore?
Food collection and gas exchange
How has the lophopore evolved?
Independently, at least twice, or else it was ancestral and has been lost
What is a characteristic of most individuals with a lophopore?
Sessile as adults
What do some lophotrochozoans, including flatworms, ribbon worms, annelids and mollusks, exhibit?
A form of radial cleavage known as spiral cleavage- these are a nonmonophyletic group called spiralians
What are members of several groups with radial cleavage like?
Worm-like
What is the purpose of a worm-like body?
To be able to burrow efficiently in muddy and sandy marine sediment or soil
Except mollusks
What do ecdysozoans have?
An exoskeleton
What is the external skeleton of ecdysozoans?
Non-living covering secreted by underlying epidermis
What does an exoskeleton provide?
Protection and support
How do ecdysozoans grow?
By shedding or moulting the exokeleton and replacing it with a new one
What recent evidence showed that molting evolved 500 million years ago?
Discovery of cambrian period soft-bodied arthropod
What evidence suggests that ecdysozoans have a common ancestor?
Molecular and genetic evidence, including a set of shared hox genes
What happens when an ecdysozoan molts?
The new exoskeleton has not yet hardened, the animal is vulnerable- slow moving and soft
What name is given to the exoskeleton of wormlike ecdysozoans that are thin and flexible?
Cuticle
What does a cuticle allow?
Some protection, little body support, gas, mineral and water exchange
What does a cuticle restrict?
Animals to a moist habitat
Where do most animals with a cuticle live?
Marine sediment
How do marine sediment worm-like cuticle covered ecdysozoans capture larger prey?
Using a toothed pharynx
What is a pharynx?
A muscular organ at the anterior end of the digestive tract
What type of eaters are many wormlike ecdysozoans?
Predators- eating protists and small animals
How is the exoskeleton of other ecdysozoans thickened?
Layers of protein and polysaccharide chitin
What does chitin do?
Impedes passage of oxygen and nutrients into the animal
How do animals with hard exoskeletons move rapidly?
Apendages- extensions of the body that can be manipulated by mucles
What did evolution of apendages during late precambrian period lead to?
Arthropod clade
What triploblastic animal was difficult to classify as protostome or deuterstome and why?
Arrow worms because they retained features that are ancestral to diploblastic animals
What is the body plan of arrow worms?
Coelom divided into three compartments: head, trunk, tail
Where are most arrow worms found?
Swimming in the open sea, some on sea floor
How do arrow worms exchange gas and waste?
Diffusion through body surface (due to size between 3mm and 12cm)
What type of circulatory system do arrow worms have?
None- waste/nutrients are moved by coelomic fluid propelled by cilia lining the coelom
What type of development do arrow worms have?
Direct development
How are arrow worm eggs fertilized?
Internally following elaborate courtship between two hermaphroditic individuals
How are arrow worms stabalised in water?
By two pairs of lateral fins and a tail
What do arrow worms eat?
They are predators of planktonic organisms in the open ocean
How do arrow worms capture prey?
They are motionless, movement signals approach of prey, they dart forward and grasp prey with stiff spines adjacent to mouth
How many species of ectoprocts are there?
4500
What do ectoprocts live in?
colonies in a house made of material secreted by the external body wall
Where do all ectoprocts live?
Marine- a few in fresh or brackish water
What is the structure of an ectoproct colony?
Small individuals connected by strands of tissue along which nutrients can be moved.
How are ectoproct colonies founded?
Asexual reproduction of founding member- 2 million individuals
Where can ectoprocts be found?
Rocks in coastal regions in many parts of the world
How do individual ectoprocts increase their contact with prey?
By oscillating and rotating their lophophore which can also be retracted
How are eggs fertilized in ectoprocts?
Internally, developing embryos are brooded before exit as larvae
What diverse group is found below ectoprocts?
Flatworms, rotifers and ribbon worms
What type of coelom do flatworms, rotifers and ribbon worms have?
Flatworms- acoelomate
Rotifers- Psuedocoelomate
Ribbon worms- coelomate
How do flatworms keep each cell near their body surface for gas exchange?
Dorsoventrally flattened body form
What type of gut does a flatworm have:
A mouth opening into a blind sac
What is the structure of a flatworms blind sac?
Highly branched
What are some free-living flat worms
Cephalized- head bears chemoreceptor organs, two eyes and a brain
How do free-living flatworms move?
Glide over surfaces powered by broad bands of cilia
What type of feeding do flatworms have?
Most are internal parasites
Other feed externally on living or dead animal tissues
Some are free-living
What are the two groups of most species of living flatworm?
Tapeworm and flukes- internal parasites particularly of vertebrates
What disease do some tapeworms and flukes cause in humans?
Schistosomiasis
What group of flatworms are external parasites of fishes and other aquatic vertebrates?
Monogeneans
What group includes most free-living species of flatworm?
Turbellarians
How big are rotifers?
50-500 micrometers long
What type of gut do rotifers have?
A complete gut as well as specialized internal organs
What type of body cavity do rotifers have?
A psuedooel
What is the function of the psuedocoel in rotifers?
Hydrostatic skeleton
How do rotifers move?
Rapdily beating cilia
What is the most distinctive organ of rotifers?
Ciliated corona (surmounts head)
Coordinated beating of cilia sweep particles of organic matter down through the mouth into what complicated structure?
The mastax- which grinds food
What species of rotifers has only females?
bdelloid rotifers
Where do most rotifers live?
Freshwater
Where do some other rotifers live?
Surfaces of mosses or lichens in a desiccated, inactive state until it trains
What are ribbon worms also called?
Nemerteans
What type of excretory system do ribbon worms have?
Simple nervous and excretory systems
Complete digestive tract
How do ribbon worms move?
Small by beating cilia
Large by using waves of muscle contraction to move over or burrow into sediment
What is the fluid filled cavity of ribbon worms?
Rhynchocoel
What lies within the fluid filled rhynchocoel?
Hollow, muscular proboscis (feeding organ)
How does the proboscis work?
Contraction of muscles around rhynchocoel cause proboscis to exit explosively through anterior pore
What might line the proboscis?
Sharp stylets that pierce prey and discharge paralysis causing toxins
Where do ribbon worms live?
Largely marine, some live in freshwater or on land
What other groups of animals use a lophophore to feed?
Brachiopods and phoronids
How did the lophophore evolve?
Independently, or was lost in other groups
When were brachiopods most abundant?
Paleozoic and mesozoic eras
How big are the 20 known species of phoronids?
5-25cm
What are characteristics of phoronids?
Sessile worms living in muddy or sandy sediments or attached to rock substrate
Where are phoronids found?
Marine waters, from intertidal zone to about 400 m deep
What do phoronids secrete?
Tubes of chitin in which they live
How do phoronids capture food?
Cilia drive water on top of the lophophore tentacles, water moves through, particles are caught and transported to mouth by ciliary action
How do phoronids reproduce?
Eggs are released into water to be fertilized, but some eggs are retained in certain species to be brooded until hatching
What are brachiopods?
Solitary marine animals with a rigid shell dividing them into two parts connected by a ligament
What do brachiopods superficially resemble?
Bivalve mollusks- shells evolved independently
How are brachipods shells different to mollusk shells?
Brachiopod shells are dorsal and ventral- bivalves have lateral shells.
Where are brachiopods lophophores located?
Within their shells
How big are brachiopods?
4-6cm long, up to 9
How do brachiopods live?
Attached by short, flexible stalk to solid substratum or embedded in soft sediment
How are gasses exchanged in brachiopods?
Across body surfaces
How are annelids and mollusks related?
They are sister groups
How are annelids different to other worm groups?
They are clearly segmented
What is the name given to the unique body plan of mollusks?
Tripartite body plan
What were the earliest segmented worms?
Preserved in fossils from the late cambrian, they were burrowing marine worms
In most annelids, how is the coelom arranged?
Each coelom in a segment is isolated from the other segments
What is the name given to the nerve centre that controls the coelom of each segment of an annelid?
Ganglion
How are ganglions function coordinated?
Nerve cords connect ganglion
What is the surface of most annelids?
A thin, permeable body wall for gas exchange- thus most are restricted to moist environments
Where do annelids live?
Marine, freshwater, moist terrestrial environments
What are two major groups of annelids?
Polychaetes
Clitellates
Where do most polychaetes live?
Marine, burrowing in soft sediments
How many eyes do polychaetes have?
One or more pairs
How many tentacles do polycheates have?
One or more pairs
Where are polychaetes tentacles and what do they do?
At the anterior end
Filter prey from surrounding water
In polychaetes, how are segments arranged?
Body wall of most segments extends laterally in a series of thin outgrowths called parapodia
What are parapodia in polychaetes?
Paired bristle appendages used for locomotion, sensation or respiration
What protrudes from parapodia?
Setae- stiff bristles
What do setae do on polychaetes parapodia?
Form temporary attachments to the substratum
What is the name of the clade of polycheates that lost their digestive tract?
pogonophorans
What are pogonophorans?
Burrowing animals with a crown of tentacles through which gas exchange occurs
What do pogonophorans live in?
A tube of chitin and other substances which they secreted
What does the pogonophoran coelom consist of?
An anterior compartment into which tentacles can be withdrawn and a long, subdivided cavity the length of most of the body
What end of the pogonophoran body is segmented?
The posterior end
What do pogonophorans eat?
Dissolved organic matter in the sediment in which they live or surrounding water
How is uptake of nutrients by pogonophorans facilitated by? In which organ does this occur?
Endosymbiotic bacteria
Trophosome
Where do most clitellates live?
Freshwater or terrestial environments
What are the two major groups of clitellates?
Leeches and oligochaetes
What are some characteristics of oligochaetes?
No parapodia, no eyes, no anterior tentacles, few setae.
What is a familiar oligochaete?
Earth worms
What is a common feature of all oligochaetes?
They are hermaphroditic (each individual is born male and female)
How is egg and sperm exchanged between oligochaetes?
Simultaneously between two copulating individuals
What do oligochaetes do with their eggs?
Lay them in a cocoon outside of the adults body
What happens to the eggs laid in a cocoon by oligochaetes?
The cocoon is shed when development is complete and miniature, independent worms emerge
What are some features of leeches?
They lack parapodia and tentacles, undivided coelom, filled with undifferentiated tissue
What are groups of segments at each end of a leeches body modified into?
Suckers, used for temporary anchoring to aid movement
How does a leech move along the substratum?
The posterior sucker attaches, the leech extends its body by contracting circular muscles, leech shortens by contracting longitudinal muscles, etc.
Where do leeches live?
Freshwater or terrestrial habitats
How do leeches suck blood?
Makes an incision in the host.
Secretes an anticoagulant to keep blood flowing
What is the name of the medicinal leech?
Hirudo medicinalis
What is Hirudo medicinalis used for?
Reduce fluid pressure and prevent blood clotting in damaged tissues, to eliminate pools of coagulated blood and to prevent scaring
What are the anticoagulants of other leeches being studied for possible medical uses for?
contain anesthetics and blood vessel dilators
What were the probable features of the ancestors of modern mollusks?
Unsegmented, wormlike animals
What have mollusks undergone?
A dramatic evolutionary radiation
The evolution of what feature set the stage for the dramatic animal evolutionary evolution of mollusks?
Tripartite (three parts) body organization
What are the three major components of the mollusk body plan?
A foot, visceral mass, mantle
What is the foot of a mollusk?
A large, muscular structure
What was the mollusk foot originally used for?
Locomotion and support of internal organs
What happened to the mollusk foot in squids and octopuses?
It was modified to form arms and tentacles
What is the foot used for in clams?
A burrowing organ
What is the visceral mass of mollusks?
Where the heart, digestive tract, excretory and reproductive organs are concentrated
What is the mantle of mollusks?
A fold of tissue that covers the organs of the visceral mass, secretes a hard calcareous shell typical of many mollusks
What happens with the mantle in most mollusks?
It extends beyond the visceral mass to form a mantle cavity
What is within the mantle cavity in mollusks?
vascularized gills for gas exchange
How is a current of water generated to move over mollusks gills?
Cilia beat
How do mollusks feed?
Gills can be used as a filter feeder,
Others used a rasping structure called a radula to scrape algae from rocks
Where has the radula been modified and what into?
Marine cone snails
Into a drill or poison dart
What circulatory system do mollusks have?
Not a closed system
Fluid empties into large hemocoel
What are 5 major groups of mollusks?
Monoplacophorans Chitons Bivalves Gastropods Cephalopods
How are monoplacophorans different to all other living mollusks?
Gas exchange organs, muscles and excretory pores are repeated over the length of the body
What characterizes chitons?
Multiple gills and shell plates, bilateral symmetry, simple internal organs
What do most marine chitons eat?
They are marine herbivores
Scrape algae from rocks with radulae
How do chitons move?
Slowly by rippling waves of muscular contraction in the foot
Where does fertilization of chitons take place?
In the water
Sometimes internally and then brooded
What are some familiar examples of bivalves?
Clams, oysters, scallops, mussels
Where are bivalves found?
Marine and freshwater
What is the body plan of bivalves?
Small heads, hinged two-part shells
What do most bivalves use their foot for?
To burrow into mud and sand
How do bivalves feed?
By taking water in through an incurrent siphon and filtering out food using their gills
How does water and gametes exit bivalves?
Through their excurrent siphon
Where does fertilization of bivalves take place?
In open water
Give some examples of gastropods.
Snails, whelks, limpets, slugs, naudibranchs, abalones
How do gastopods move?
Gliding on their muscular foot,
Swimming using foot (sea butterflies, heteropods)
What are two features of naudibranchs?
Lost their protective shell
Aposematic or camouflaged coloring
How many parts make up the shell of shelled gastropods?
one
In terrestrial species of mollusks (gastropods only) what is the mantle tissue modified into?
Highly vascularized lung
Name some cephalopods.
Squids, octopuses, nautiluses
How is the excurrent siphon modified in cephalopods?
To allow the animal to control water content in mantle cavity- move by jet propulsion
What did jet propulsion of cephalopods allow
Them to become major predators
How do cephalopods capture and subdue prey/
With their tentacles
What cephalopods still have chambered shells to control their buoyancy?
Nautiloids
