Zoology Test 2d Flashcards
adaptive radiation
describes the evolution of many new species from common ancestor
mollusc origins
- originated in ocean, but now in almost every freshwater and terrestrial habitat
- very large phylum
- 50,000 extant species
- 35,000 extinct species
symmetry of mollusc
- bilaterally symmetrical
- some have secondarily derived asymmetry
- contains eucoelomate
general characteristics of mollusc
- muscular foot for crawling, burrowing and grasping
- visceral mass which contains internal organs
- mantle which secretes calcium carbonate shell
- soft unsegmented body
reproduction in mollusc
- most dioecious, some monoecious
- some have direct and some have indirect development
Development in mollusc
- mostly direct development
- larvae stage though is trocophore larvae
nervous system in mollusc
- several pairs of ganglia
- cerebral, pedal and visceral
- generally simpler than that found in anthropoids
- system of cephalopods is most advanced in any vertebrate
trocophore larvae
- found in annelids, platyhelminthes
- homology; indicate genetic relationship
cephalization in molluscs
- cephalopods and gastropods
- most others are grazers, scavengers or filter-feeders with little need for external cephalization
- usually have “foot”
excretory system in molluscs
- contain two nephridia
circulatory system in molluscs
- open system with pumping heart, blood vessels and blood sinuses whereby blood returns to heart
- cephalopods have closed system of arteries, capillaries and veins, complex with three hearts
respiratory system in molluscs
- most have gills derived from mantle tissue to increase efficiency of gas exchange
- incurrent and excurrent siphons present in bivalves
molluscs
- Monoplaophora
- Polyplacophora
- Scaphopoda
- Bivalvia
- Gastropod
- Cephalopod
Monoplaophora
- primitive mollusc
- found on ocean bottom known only as fossil
- exhibit pseudometamerism (segmentation)
Polyplacophora
- characterized by 8 dorsal plates
- found in intertidal zone of seacoasts
- feed by grazing on algae on rocks
Scaphopoda
commonly referred to as “tooth shells” or “tusk shells”
Bivalvia
- large, economically important class of mollusks
- highly adapted for burrowing
- filter-feeding
- clams, oysters, mussels, limpets, periwinkles, scallops
- restricted to aquatic environments
- most diverse in marine systems, but many freshwater
anatomy of bivalvia
- two shells connected by hinge ligament
- shell grows outward in “rings” from umbo
- foot extends anteriorly from shell to put animal forward
- adductor muscles pull shells together
respiration in bivalvia
- gills suspended from dorsal, interior surface of mantle cavity
- posterior incurrent and excurrent siphons create respiratory water flow
digestion in bivalvia
- gills also used for filter feeding
- mucus on gills traps food particles
reproduction in freshwater bivalve
- freshwater bivalve eggs fertilized internally in suprabrachial chamber above the gill
- eggs develop into glochidia larvae that parasitize a particular species of fish
reproduction in marine bivalve
- fertilization is external
- 2 larval stages
- one larval stage being the trochophore larvae
endangered bivalves
- dams and locks prevent fish migration so some can’t reproduce because their host fish aren’t present
- siltation and other forms of water pollution foul filter-feeding apparatus
- being overwhelmed by introduced mussels, which filter food
- poaching for pearl industry
- 184 of 300 native species are extinct, endangered or soon to be endangered
invasive bivalves
- zebra mussel (Dreissena polymorpha)
- Asian clam (Corbicula fluminea)
Is there a symbiotic relationship in certain bivalves? And if yes, what?
yes, mantle tissue contains photosynthetic zooxanthellae that provide much of clam’s nutrients and color
pearls
produced by secreted fluid from the mantle called nacre that smooths out irritations (sand)
Gastropoda
- largest by far in terms of number of recognized species
- 70,000 living species
gastropod body plan
- torsion
- coiling
- lost organs, doesn’t seem to bother them that they have lost organs
- radula
torsion
- is responsible for moving mantle cavity from back to front of body
- occurs before hatching
- space available in mantle cavity allows animals head to be withdrawn into shell for protection, foot forms barrier to outside
coiling
- spiral winding of visceral mass and shell
- original symmetrical arrangement gave way to conispiral shape, with shell to one side, which resulted in loss of gill on right side
- advantage: wastes expelled from right side of mantle instead of over head
radula
- rasping/grasping organ in mouth
- “teeth”
- modified for feeding, shell prying, harpooning and envenomating prey, chewing
reproduction in gastropod
- monoecious
- sperm exchange with internal fertilization
- some use dart to puncture mate
- eggs laid singly or attached to substrate
- larval stages occur before hatching
- hatchlings are miniature adults (direct development)
gastropod diversity
- nudibranchs
- sea hare
- conus (cone shell)
sea hare
marine gastropod squirts copious purple secretion from purple gland in mantle cavity when provoked
nudibranch
- nudibranchs feed on cnidarians and reuse undischarged nematocysts
- elaborate papillae covering their dorsal surfaces contain reused nematocysts
conus
- marine gastropod stings its prey to paralyze before consuming
- can kill other cone shells or humans
Cephalopods general characteristics
- nautilus
- octopus
- squid
- cuttlefish
- very derived molluscs but very ancient too
- most extinct forms had exterior shells
- active predators
advancements of cephalopods
- well-developed external cephalization and foot modified into series of tentacles and suckers
- completely closed circulatory system
- complex reproductive behavior
Cephalopod reproduction
- very sophisticated
- males undergo color displays directed against rival males
- sperm encased in spermatophores
- one modified tentacle used to pluck spermatophore from own mantle cavity and insert into mantle cavity of female
Cephalopod nervous system
- sophisticated nervous system
- sophisticated sensory organs
- tentacles with tactile and chemosensory cells
- mantle with chromatophores or bioluminescence for camouflage and communication
- intelligent with sophisticated behavior
- complex communication abilities
- contain eyes
