chapter 33 Flashcards
Porifera
Parazoa
Animals lacking tissues (and therefore organs) and a definite symmetry
7000 marine species; 150 freshwater species
Among the most abundant animals in the deep ocean
Most members lack symmetry Various growth forms Larval sponges free-swimming Adults remain attached – sessile Cell types Truly multicellular 3 functional layers in “vase”
Level of cellular specialization
Cells can disassemble and reassemble
Cells can change from one type to another
Activities of cells are loosely coordinated
3 layers -Outer epithelium Water comes in ostia, exits osculum -Mesohyl Middle layer – gelatinous matrix Spicules – needles of calcium carbonate Spongin – reinforcing tough protein fibers -Choanocytes Collar cells Flagellated – contributes to water circulation Face internal cavity Engulf and digest food from passing water
Sponge reproduction
Asexual
Fragmentation
Sexual
Choanocytes transform into sperm that are released into the water—go to another sponge
Sperm captured and passed to egg cell in mesohyl
Development may occur within mother or in open water
Larva is planktonic; will settle and transform into adult
Eumetazoa
Animals with distinct tissues Embryos have distinct layers Inner endoderm forms the gastrodermis Outer ectoderm forms the epidermis and nervous system Middle mesoderm (only in bilateral animals) forms the muscles True body symmetry Radial symmetry Bilateral symmetry
Phylum Cnidaria
Most marine, few fresh water species
Diploblastic
Bodies have distinct tissues but no organs
No reproductive, circulatory, or excretory systems
No concentrated nervous system
Latticework of nerve cells
Touch, gravity, and light receptors
Cnidarians use nematocysts to capture prey
Secreted within nematocyte–cnidocyte
Mechanism of discharge unknown
Some carry venom
2 basic body forms
Polyps – cylindrical and sessile
Medusa – umbrella-shaped and free-living
Body plan has single opening leading to gastrovascular cavity Site of digestion Most gas exchange Waste discharge Formation of gametes in many 2 layers to body wall Epidermis Gastrodermis Mesoglea between layers—acellular in polyps but cellular in medusae
Gastrovascular space also serves as hydrostatic skeleton—fluid under pressure
Provides a rigid structure against which muscles can operate
Gives the animal shape
Many polyp species build an exoskeleton of chitin or calcium carbonate around themselves—in colonial species, exoskeleton links members of the colony
Some build an internal skeleton
Cnidarian life cycle
Some cnidarians occur only as polyps, and others exist only as medusae, but many alternate between these two phases
Both phases consist of diploid individuals
In general, in species having both polyp and medusa in the life cycle, the medusa forms gametes
Sexes separate
Gonochorism – individual is either male or female
Zygote develops into planktonic planula
Metamorphosis into polyp
Polyp produces medusae or other polyps asexually
–dividing, budding or breaking off bits
Major evolutionary innovation in cnidarians is extracellular digestion of food inside the animal
Digestion takes place partly in gastrovascular cavity
Cells then engulf fragments by phagocytosis
Nematocyst—stinging capsules secreted by
nematocyte or cnidocyte
Nematocysts are barbed and some have toxins
The mechanism of discharge is one of the fastest
cellular processes in nature
4 or 5 classes
Anthozoa
Sea anemones, most corals, sea fans
Solitary and colonial polyps
Symbiotic dinoflagellates (zooxanthellae) photosynthesize and provide nutrients to reef coral
Coral reefs economically important
Gatrovascular cavity is compartmentalized; tentacles are hollow
-Cubozoa Box jellies Strong swimmers, voracious fish predators Stings may be fatal to humans -Hydrozoa Hydroids, Hydra, Portuguese man-of-war Both polyp and medusa stages Only class with freshwater members
-Scyphozoa
Jellyfish
Medusa more conspicuous and complex
Ring of muscle cells allows for rhythmic contractions for propulsion
-Staurozoa
Star jellies
Resembles a medusa in most ways but is attached to the substratum by a sort of stalk that emerges from the side opposite the mouth
Phylum Ctenophora
Known as comb jellies, sea walnuts, or sea gooseberries
8 rows of comblike plates of fused cilia that beat in a coordinated fashion
Many bioluminescent
2 tentacles covered with colloblasts (cells)
Discharge strong adhesive used to capture prey
Phylogenetic position unclear
Muscle cells—triploblastic?
Radial or bilateral?
The Bilaterian Acoelomates
Characterized by bilateral symmetry Allowed for high levels of specialization Bilaterians are traditionally classified by the condition of their coelom triploblastic Acoelomates Pseudocoelomates Coelomates Acoelomates and pseudo- coelomates have evolved multiple times--homoplastic
Phylum Platyhelminthes
Flatworms are ciliated, soft-bodied animals
Bodies are solid aside from an incomplete digestive cavity
Many species are parasitic
Others are free-living
Marine, freshwater, moist terrestrial
Only one opening to digestive cavity
Muscular contractions in the pharynx allows food to be ingested and torn into small bits
Lack circulatory system
Diffusion for gas transport
Gut functions in digestion and food distribution
Some particles digested extracellularly
Cells engulf particles by phagocytosis
Tapeworms (parasitic flatworms) lack digestive systems – absorb food directly through body walls
-Have an excretory and osmoregulatory system
Network of fine tubules runs through body
Flame cells located on the side branches
Flagella move water and excretory substances into the tubules and then to pores located between the epidermal cells through which the liquid is expelled
Metabolic wastes are excreted into the gut and eliminated through the mouth
Simple nervous system
Anterior cerebral ganglion and nerve cords
Eyespot can distinguish light from dark
Reproduction
Most are hermaphroditic
Undergo sexual reproduction
Also have capacity for asexual regeneration
2 major groups Free-living Turbellaria Probably not monophyletic Dugesia – common planarian in bio labs Parasitic Neodermata Trematoda – flukes Attach within host body by suckers, anchors, or hooks Life cycle may have 2 or more hosts Clonorchis sinensis, oriental liver fluke No eyespots Cercomeromorpha – tapeworms
One of most important trematodes to human health are blood flukes Schistosoma
Afflict 5% of world’s population
About 800,000 people die each year from schistosomiasis or bilharzia
Adults are in blood vessels in the intestinal or bladder wall. Fertilized egg must break through the wall of the blood vessels in intestine or the urinary bladder to get out
Cercomeromorpha – tapeworms
Adult hangs onto inner wall of host intestine using scolex
12 species in humans
Most of tapeworm body is proglottids Complete hermaphroditic unit, containing both male and female reproductive organs Formed continuously at neck region Beef tapeworm, Taenia saginata Frequent human parasite From eating uninspected rare beef
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Phylum Acoelomorpha
Acoel flatworms were once considered basal members of the phylum Platyhelminthes
Have a primitive nervous system and lack a digestive cavity
Based on molecular evidence, similarities are convergent
Phylum Cycliophora
Discovery reported in 1995
Size of a period
Striking circular mouth surrounded by a ring of cilia
Anatomy and life cycle are very unusual
Live on the mouthparts of claw lobsters on both sides of the North Atlantic
Pseudocoelomates
Pseudocoelom – cavity that lies between tissues derived from the mesoderm and those derived from the endoderm
Pseudocoelomic fluid performs the functions carried out by a circulatory system in most coelomate animals and as a hydrostatic skeleton—more efficient movement thanacoelomates
Not monophyletic
Phylum Nematoda
Vinegar eels, eelworms, and other roundworms
Members of this phylum are found everywhere – abundant and diverse
Marine, freshwater, parasites, free-living
Bilaterally symmetrical and unsegmented Covered by a flexible, thick cuticle that is molted as they grow Gas exchange through cuticle Only longitudinal muscles Digestive system well developed--complete Stylets – piercing organs near mouth Pharynx – creates sucking action Anus
Sexual reproduction
Most gonochoric (dioecious, separate sexes)
Sexual dimorphism – male smaller with hooked end
Internal fertilization
Indirect development – egg, larva, adult
Eutely
Adults consist of a fixed number of cells
Caenorhabditis elegans has only 959 cells
Important in genetic and developmental studies
Lifestyles
Many are active hunters, preying on protists and other small animals
Others are parasites of plants
Still others live within the bodies of larger animals
Largest known nematode, which can attain a length of 9 m, parasitizes the placenta of sperm whales
About 50 species cause human diseases Hookworms Common in southern U.S. Produce anemia Trichinella causes trichinosis Forms cysts in muscles Infection from eating undercooked meat
Pinworms, Enterobius vermicularis Infects 30% of children in U.S. Causes itching of the anus Ascaris lumbricoides – intestinal roundworm Infects 1 in 6 worldwide Adult female can be 30 cm long Rare in areas with modern plumbing Serious tropical nematode diseases Filariasis—nemaodes live in circulatory sys. Elephantiasis—live in lymph ducts
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Phylum Rotifera
Spiralian Platyzoan
Bilaterally symmetrical, unsegmented pseudocoelomates
Highly developed internal organs
Corona – “wheel animals”
Conspicuous ring of cilia at anterior end
Used for locomotion and sweeping food into the mouth
