Topic 14 Flashcards
What is the clade bilateria?
bilateral symmetry
vary degrees of cephalization (differentiation of a head region)
anterior concentration of neural ganglia (brain)
reduced in sedentary animals
triploblastic: endo-, ecto-, and mesoderm
What are the benefits of a bilateral plan?
muscles have superior pull using solid mesoderm versus mesoglea
What are the issues of a bilateral plan?
organs cannot move freely
difficult to move nutrients from gut to body wall
What are the solutions to the bilateral plan?
some sort of body cavity = coelom
organs bathed in fluid
movement doesn’t squeeze organs
organs can grow within space
diffusion of nutrients/wastes is easier
What are the advantages of coelom?
- Hydrostatic skeleton: more effective skeletal support, fluid filled cavity provides more rigid structure than mesoderm for muscles to pull against
- Circulatory system: absorbed nutrients can be circulated around body, wastes can be carried to body surface more easily
What is the clade lophotrochozoa?
includes ~18 phyla
range from morphologically very simple (eg. flatworms) to morphologically and behaviorally very complex
some have lophophore larval stage and others have trochophore larvae
relationships among lophotrochozoan phyla unclear
What is the phylum platyhelminthes?
flatworms
acoelomate: triploblastic, but no fluid-filled body cavity, basically solid tissue
no special circulatory or gas-exchange system
do not have a complete digestive system (have a mouth and a gut lumen, but no anus, some parasitic ones lack mouths and guts)
What are the three classes of the phylum platyhelminthes?
Class Turbellaria
Class Cestoidea
Class Trematoda
What is the class turbellaria?
free-living flatworms
mostly marine, mostly predatory
epidermis of turbellarians covered by cilia
have a pair of ventral nerve cords
a pair of ganglia (brain) at front of the body
no anal opening: undigested food ejected from mouth
What is the class cestoidea?
tapeworms
entirely endoparasitic in digestive systems of other animals, most vertebrates, but invertebrates can act as intermediate hosts
lack digestive system, absorb nutrients through thin body wall
modified body
scolex: head with sucker and/or hooks for holding on to host’s gut
posterior to scolex: long chain of units devoted to reproduction = proglottids
What is the phylum Annelida?
segmented: many repeated units with similar internal and external anatomy (divided by septa)
eucoelomate: body cavity completely lined with mesodermally derived tissues, hydrostatic skeleton
closed circulatory system: blood contained in vessels
gas exchange via skin
complete digestive system with anus (applies to subsequent taxa)
excretory system, nervous system
What are characteristics of the class oligochaeta?
simultaneous hermaphrodites: transfer sperm by copulation, each worm in a pair acts both as male and female, temporarily deposits sperm in partner’s seminal receptacle, produces gelatinous cocoon with secretions from clitellum, deposits egg in cocoon, slides cocoon forwards, deposits stored sperm, fertilization is external
direct development (no larval stage)
What are the characteristics of the phyum mollusca?
mantle: thin layer of tissue that secretes shell
muscular ventral foot used for movement
organ contained in visceral mass above foot
mouthparts a strap-like rasping organ called a radula
What is the class gastropoda?
75% of extant mollusc species
snails and their relatives
glide along using muscular contractions of large foot
single, coiled, tubular shell
torsion: visceral mass twists during development so that anal opening over head
What is the class bivalia?
clams, oysters, mussels, scallops
mostly marine, but many freshwater
have two hinged shells
feed by filtering water through gills
no radula (do not really have a head)
some are sessile
most sedentary
