Biodiversity 3: The protostomes

Question 1

What are the key features of the protostomes?

Answer 1

Spiral cell division
Early cell determination
Body cavity forms from mesoderm
Mouth forms first
Divided into lophotrochozoa (feeding cilia) / Ecdysozoa (shed exoskeleton)

Question 2

What is the common name for the phylum platyhelminthes?

Answer 2

Flatworm

Question 3

Describe the platyhelminthes

Answer 3

Simple body plan (no separate anus, no body cavity)
Mesoderm with digestive system and reproductive organs, but no circulatory organs
Simple brain and sensory/motor development and muscles allow active lifestyle

Question 4

Describe free living marine flatworms

Answer 4

Predators or scavengers
Blind gastrovascular cavity with complex folding
Ganglia and eyespots
Regenerate or reproduce sexually as hermaphrodites

Question 5

Describe parasitic flukes

Answer 5

Primary host is usually a vertebrate
Secondary host is usually an invertebrate
Can have multiple life stages, some asexual, others sexual
Schistosoma causes schistosomiasis in humans = liver failure and death

Question 6

Describe parasitic tape worms

Answer 6

Pork tapeworms
Head with hooks for attachments inside the hosts gut
Sacks of eggs (proglottids) break off and are transferred to other hosts through the host’s faeces
Self fertilising hermaphrodite
No sensory organs

Question 7

What is the phylum Annelida’s common name?

Answer 7

Segmented worms

Question 8

Describe the Annelida

Answer 8

Body linear and segmented
Body cavity divided by septa
Circular and longitudinal muscles in body wall
- Can move forward
Digestive tract has specialised regions
- Mouth, pharynx (sucks food in), crop (stores food, adds moisture), gizzard (grinding food), intestine (absorption), anus (waste)
Simple brain = can process tactile stimuli and react

Question 9

Describe Earthworms

Answer 9

Terrestrial and freshwater segmented worms
No head and no legs
Hugely important in soil formation, aeration and releasing nutrients for use by plants (all ecosystem services)

Question 10

Marine flatworms, Parasitic flukes and parasitic tape worms belong to which phylum?

Answer 10

Platyhelminthes (flatworms)

Question 11

Earthworms, polychaete worms and leeches belong to which phylum?

Answer 11

Annelida

Question 12

Describe polychaete worms

Answer 12

Marine segmented worms
Developed head and feet

Question 13

Describe leeches

Answer 13

Many are specialised blood sucking parasites
Dorsally flattened, segmented
Outwardly resemble flatworms

Question 14

What are some important evolutionary features of segmented worms?

Answer 14

Well developed body cavity:
Hydrostatic skeleton
Body space for storage and organ development
Cushion for internal organs
Buffers the actions of body wall muscles form the action of muscles in the digestive tract (allows movement while digesting

Question 15

What does the segmentation of segmented worms allow for?

Answer 15

Specialisation of regions in the body

Question 16

Name 4 classes that belong to the phylum mollusca

Answer 16

Gastropods, bivalves, cephalopods

Question 17

Describe molluscs

Answer 17

Not segmented
Diverse, but all share same basic body plan:
Foot = fleshy muscular pad, often used for locomotion
Visceral mass = lump of tissue containing most of the internal organs
Mantle = fold of tissue that covers visceral mass
Often uses calcium carbonate to secrete a shell e.g snails
A lot but not all have a radula = scrapes up food from substrate

Question 18

Describe the gastropods

Answer 18

snails, slugs, limpets
Similar to the basic body plan
Some hve a spiralled shells (snails), others have flattered shells (limpets)
In some snails the mantle cavity acts as a lung allowing them to breathe and inhabit terrestrial environs
Sense organs in head = active lifestyle

Question 19

Describe the bivalves

Answer 19

oysters, mussels, clams
Shell in 2 halves, body and foot compressed inside
Strong muscles hold 2 halves together and protect inside
Gills adapted for filter feeding
Head & Radula lost due to being filter feeders with sedentary lifestyle

Question 20

Describe the Cephalopods

Answer 20

squid, octopuses
External shell reduced / absent in most - mantle still present (only shelled Cephalopod today is the nautilus)
Beak-like jaws
Foot modified into muscular syphon and tentacles (attacking and feeding)
Mantle = propulsive bellows to drive water out of bellows (Humboldt squid up to 10 m/s)
Highly active predatory lifestyle

Question 21

Describe an octopuses circulatory system

Answer 21

Closed circulatory system with 3 hearts
2 small hearts pump blood to gills, 1 large heart pumps to body
Blue blood → haemocyanin (contains copper)

Question 22

Describe an octopuses eye

Answer 22

Efficient eye, lens moves to and from retina
Similar to vertebrate eye, due to convergent evolution
In many ways, their eye is superior to ours:
Our eyes change shape in order to focus = muscles get tired, why old people need glasses
In their eye, lens moves towards/ away from the retina
Photoreceptors point forwards, blood supply and nerves lead out the back of the retina (unlike ours) = can see much more clearly as no blind spot in the fovea

Question 23

What type of organs do many Cephalopods have for signalling and camouflage

Answer 23

Chromatophores in the skin

Question 24

What is the brain of an octopus like?

Answer 24

Very well developed - capable of memory and learning

Question 25

Describe the mimic octopus

Answer 25

Habitat is shallow open waters, off the coasts of Indonesia and Malaysia Due to daytime foraging and unprotected habitat = would be v open to predators Mimics other creatures: Using its chromatophores and tucking 6 legs into a hole in the sand = mimics a poisonous banded sea snake Only mimic this snake when predatory Damselfish are pursuing them, because sea snakes feed on Damselfish! When danger is passed it undulates away mimicking a Flounder Biologists think they’ve witnessed up to 13 different species imitations!

Question 26

What is the common name for the phylum Nematoda

Answer 26

Roundworms

Question 27

Describe the roundworms

Answer 27

Tough outer cuticle is shed as it grows Unsegmented, tapers at tail Complete digestive tract with anus Moved by thrashing tail using only longitudinal muscles (not circular like segmented worms) = Movement is not directional May be most abundant multicellular animal on Earth

Question 28

Give an example of a roundworm

Answer 28

C. Elegans (free living)

Question 29

Describe the Arthropoda

Answer 29

Highly diverse e.g spiders, lobsters, insects Vertebrates Body covered by jointed exoskeleton (cuticle) Thick in some places = armour Thin in other places = joints between sections Cuticle strong and waterproof, made of chitin and protein = enables exploitation of dry terrestrial habitats Segments fused in groups forming regions Appendages specialised (walking, flying, feeding etc.) Well developed brain and sensory organs at anterior end = active lifestyle

Question 30

Describe the basic body plan of the arthropods

Answer 30

Brain, ventral nerve cord Simple gut 3 regions (foregut,midgut, hindgut) Dorsal heart Open circulatory system Hemolymph pumped by tubular heart into sinuses that bathe organs Gas exchange through gills (aquatic) or trachea (terrestrial) Well developed musculature

Question 31

Give some examples of arthropods

Answer 31

spiders, lobsters, insects

Question 32

Describe the Chelicerates

Answer 32

Cephalothorax and abdomen Head and thorax fused together Cephalothorax lack antennae First appendages are chelicerae for feeding, then pedipalps (sensing or feeding) and 4 pairs of legs Abdomen usually lacks legs

Question 33

Give some examples of the subphylum Chelicerates

Answer 33

Spiders, horseshoe crabs, ticks

Question 34

Which phylum does the subphylum Chelicerates belong to?

Answer 34

Arthropoda

Question 35

Give some examples of crustaceans

Answer 35

Lobsters, crabs

Question 36

Which phylum does the subphylum Crustaceans belong to?

Answer 36

Arthropoda

Question 37

Describe the crustaceans

Answer 37

2 pairs of antennae 3+ pairs of mouthpart appendages Thorax has legs for walking Head and thorax not segmented Abdominal segments have swimming appendages

Question 38

Describe centipedes and millipedes

Answer 38

Head and rest of body is highly segmented Paired segments are fused in millipedes so there are 2 legs per segment Centipedes have 1 per segment

Question 39

Describe the key features of insects

Answer 39

3 specialised regions (head, thorax, abdomen) = tagma 1 pair of antennae 3 legs on thorax, none on abdomen Unbranched appendages Efficient gas exchange through a well developed tracheal system leading to every cell in the body Spiracles regulate air flow and water loss Sophisticated sensory organs, e.g complex compound eye Well developed brain allows complex behaviours 1 / 2 pairs of wings commonly on thorax

Question 40

Describe an insects compound eye

Answer 40

Sophisticated Made up of light sensors called ommatidia (10 - 10,000s) Compound eyes have poor image resolution, but can detect fast movement and in some cases the polarisation of light (e.g bees)

Question 41

What were the potential evolutionary origins of insect wings?

Answer 41

Gliding from vegetation to ground Heat absorption in terrestrial ancestor Gills in aquatic ancestor Swimming fins in aquatic ancestor

Question 42

What features made the evolution of insect wings possible?

Answer 42

Abundance of muscle tissue Lightweight jointed skeleton Small body side Efficient gas and nutrient exchange Highly developed nervous & sensory systems for navigation

Question 43

What are the benefits of insect wings?

Answer 43

Escape predators, finding food, finding mates, dispersal