Lecture 12: The protosome invertebrates

Question 1

Phylum Mollusca (Lophotrochozoa)

Answer 1

Molluscs (snails, clams, squid)

• 50,000 species
• appearances vary, but all share same body plan
• trochophore larval stage
• not segmented

Question 2

Classes of Mollusca

Answer 2

• Gastropoda
• Bivalvia
• Cephalopoda

Question 3

Mollusca: Class Gastropoda

Answer 3

• (snails, limpets, slugs)
• 40,000 spp
• similar to the basic body plan, usually with coiled shell
• in some snails the mantle cavity serves as a lung allowing adaptation to terrestrial environments

Question 4

Mollusca: Class Gastropoda during development

Answer 4

• visceral mass rotates 180 degrees moving mantle cavity over head = torsion
• torsion caused by earlier growth of retractor muscles on right side
• why torsion? predation? balance?

Question 5

Mollusca. Class Bivalvia:

Answer 5

• (clams, oysters) -7,000spp
• shell divided into two halves
• body and foot laterally compressed
• gills adapted for filter feeding
• head & radula lost
• sedentary lifestyle

Question 6

Mollusca: Class Cephalopoda

Answer 6

• (squid, octopus)
• 600spp
• Nautilus only shelled extant species
• beak-like jaws
• foot modified into a muscular siphon and tentacles
• mantle = propulsive bellows
• highly active predatory lifestyle
• closed circulatory system with 3 hearts
• complicated eye design, lens moves to and from retina
• Chromatophores provide camouflage
• well developed CNS and brain, capable of memory and learning

Question 7

Gastropod looks like

Answer 7

snail

Question 8

Bivalve looks like

Answer 8

squished snail

Question 9

Cephalopod looks like

Answer 9

squid more

Question 10

Ecdysozoa undergo

Answer 10

ecdysis (shedding of exoskeleton outgrown by the animal)

Question 11

3 types of protostome:

Answer 11

Lophotrochozoa

Ecdysozoa

Question 12

Several phyla of Ecdysozoa

Answer 12

• Nematoda

- Arthropoda

Question 13

Phylum Nematoda:

Ecdysozoa

Answer 13

• Roundworms -90,000 species (?)
• coelom not fully bounded by mesoderm
• once thought primitive due to lack of true coelom but DNA suggests closest to arthropods
• cylindrical unsegmented body tapers at tail
• cuticle shed during growth
• complete digestive tract with anus
• lacks circulatory system, nutrients transported in pseudocoel
• pseudocoel and cuticle act as hydrostatic skeleton
• moves by thrashing tail using longitudinal muscles

Question 14

Nematodes:

Answer 14

• free-living and parasitic types
• may be most abundant multicellular animal
• 1 m3 of muck from Holland yielded ~ 4,000,000 worms
• 1 acre UK farmland may contain 100,000,000,000
• Caenorhabditis elegans is one of the most important model organisms in developmental biology and genetics

Question 15

nematodes are extremely important..

Answer 15

agricultural (both plants and animals) and human pests (e.g. Trichinella in pork)

Question 16

Phylum Arthropods:

Answer 16

• Lobsters, spiders, insects -1,000,000 spp known
• body covered by jointed exoskeleton
• hard exoskeleton or cuticle made of chitin and protein
• cuticle strong and waterproof, enables exploitation of land
• cuticle inelastic, shed to allow growth
• segments fused in groups forming regions (tagma)
• appendages specialised
• well developed cephalisation and sensory organs

Question 17

Arthropods hace an __ circulatory system & do gas exchange through

Answer 17

• open circulatory system with haemolymph being pumped by tubular heart into sinuses that bathe the internal organs
• gas exchange through gills (aquatic) or tracheae (terrestrial)

Question 18

Arthropod subgroups:

Answer 18

• Trilobites
• Chelicerates
• Crustacea
• Uniramia

Question 19

Uniramia:

Answer 19

Class Insecta (Hexapoda)

• 3 tagmata (head, thorax, abdomen)
• one pair antennae
• efficient gas exchange through well developed tracheal system in which tubes lead to every cell in the body
• spiracles regulate air flow and water loss
• sophisticated sensory organs including complex eye
• well developed nervous system, allows complex behaviour
• one or two pairs of wings derived from cuticle out-folding

Question 20

Insect wings. Key feature enabling:

Answer 20

escape from predators, finding food, finding mates, dispersal

Question 21

Insect wings: Potential origins:

Answer 21

-heat absorption in terrestrial ancestor
-gliding from vegetation to ground
-gills in aquatic ancestor
swimming fins in aquatic ancestor

Question 22

Insect wings:

Answer 22

abundance of muscle tissue, lightweight jointed skeleton, small body size, waterproof covering, efficient gas & nutrient exchange, highly developed nervous & sensory systems for navigation