Biodiversity 3: The protostomes Flashcards
What are the key features of the protostomes?
Spiral cell division
Early cell determination
Body cavity forms from mesoderm
Mouth forms first
Divided into lophotrochozoa (feeding cilia) / Ecdysozoa (shed exoskeleton)
What is the common name for the phylum platyhelminthes?
Flatworm
Describe the platyhelminthes
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
Describe free living marine flatworms
Predators or scavengers
Blind gastrovascular cavity with complex folding
Ganglia and eyespots
Regenerate or reproduce sexually as hermaphrodites
Describe parasitic flukes
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
Describe parasitic tape worms
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
What is the phylum Annelida’s common name?
Segmented worms
Describe the Annelida
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
Describe Earthworms
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)
Marine flatworms, Parasitic flukes and parasitic tape worms belong to which phylum?
Platyhelminthes (flatworms)
Earthworms, polychaete worms and leeches belong to which phylum?
Annelida
Describe polychaete worms
Marine segmented worms
Developed head and feet
Describe leeches
Many are specialised blood sucking parasites
Dorsally flattened, segmented
Outwardly resemble flatworms
What are some important evolutionary features of segmented worms?
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
What does the segmentation of segmented worms allow for?
Specialisation of regions in the body
Name 4 classes that belong to the phylum mollusca
Gastropods, bivalves, cephalopods
Describe molluscs
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
Describe the gastropods
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
Describe the bivalves
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
Describe the Cephalopods
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
Describe an octopuses circulatory system
Closed circulatory system with 3 hearts
2 small hearts pump blood to gills, 1 large heart pumps to body
Blue blood → haemocyanin (contains copper)
Describe an octopuses eye
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
What type of organs do many Cephalopods have for signalling and camouflage
Chromatophores in the skin
What is the brain of an octopus like?
Very well developed - capable of memory and learning
Describe the mimic octopus
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!
What is the common name for the phylum Nematoda
Roundworms
Describe the roundworms
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
Give an example of a roundworm
C. Elegans (free living)
Describe the Arthropoda
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
Describe the basic body plan of the arthropods
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
Give some examples of arthropods
spiders, lobsters, insects
Describe the Chelicerates
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
Give some examples of the subphylum Chelicerates
Spiders, horseshoe crabs, ticks
Which phylum does the subphylum Chelicerates belong to?
Arthropoda
Give some examples of crustaceans
Lobsters, crabs
Which phylum does the subphylum Crustaceans belong to?
Arthropoda
Describe the crustaceans
2 pairs of antennae
3+ pairs of mouthpart appendages
Thorax has legs for walking
Head and thorax not segmented
Abdominal segments have swimming appendages
Describe centipedes and millipedes
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
Describe the key features of insects
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
Describe an insects compound eye
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)
What were the potential evolutionary origins of insect wings?
Gliding from vegetation to ground
Heat absorption in terrestrial ancestor
Gills in aquatic ancestor
Swimming fins in aquatic ancestor
What features made the evolution of insect wings possible?
Abundance of muscle tissue
Lightweight jointed skeleton
Small body side
Efficient gas and nutrient exchange
Highly developed nervous & sensory systems for navigation
What are the benefits of insect wings?
Escape predators, finding food, finding mates, dispersal
