Lecture 5 Diversity And Adaptation 2 Flashcards
Protostome features
Mouth forms from blastopore(Cambrian)
Bilateral symmetry
Anterior brain surrounding entrance to digestive tract
Ventral nervous system - paired/fused longitudinal nerve cords
Highly variable other features e.g. no circulatory system (flatworms) closed (earthworms) open - bathing organs (anthropods
Protostome clade Lophotrochozoa
Most have lophopores ( structure for feeding/gas exchange) tentacle bearing loop surrounding mouth.
And/or have a trocophore lava w/distinct ciliated band w/internal hydrostatic skeleton
Protostome clade Ecdysozoa
Have non living exoskeleton and grow by ecdysis (moulting)
Molecular and genetic evidence including a single set of hox genes (for body development control) suggests single common ancestor.
Most well known Ecdysozoa is the group: arthropods - creatures with joined limbs including insects (hexapods) crustaceans, spiders and centipedes but there are many other groups
Deuterostomes
Vertebrates evolved from this group
Marine evolutionary, Cambrian
Common ancestor bilateral but return to radial symmetry in adult echinoderms like starfish
Phylum Annelida (segmented worms)
“true” worms, classic shape
metamerically segmented suited to burrowing (earthworms)
~16500 spp
over half are class polychaetes (many bristles + setae) mostly marine, live in/on sediments or in tubes attached to rocks
Class oligochaeta fresh water/terrestrial includes earthworms
Class Hirudinea includes leaches
Phylum annelida (2nd card)
Metameric (similar repeated segmentation)
Earliest mid Cambrian
Closed circulatory system
Nerve bundles (ganglia) control segments, nerve cord connects between segments
Most lack rigid external covering though some have chitin plates
At risk of dessication
Marine groups have planktonic larvae freshwater and terrestrial groups do not
Gaseous exchange through body surface and many polychaete species have gills
Segmentation + longitudinal/radial muscle allow extension of parts of worm by hydrostatic pressure (pressure exerted by fluid due to gravity) while another part is anchored
Phylum annelida: typical body of polychaete worm
Most marine and bottom dwelling
May be mobile (predatory) or sedentary (deposit/filter feeders)
Long paired parapodia - fleshy extensions from segments act as gills and chaetae (bristles) assist movement
Pharynx may be protrusible (extendable) with or without jaws
Phylum mollusca
Adaptive radiation of body plan
Originate in Cambrian
Polyplacophora (chitons) & monophacophora most ancient mollusc lineage
Gastrapoda - snails, whelks, sea slugs slugs, abalone etc.
Bivalvia - clams, oysters, mussels etc
Cephlapoda - Nautilus, squid, octopus and cuttlefish
One of the most diverse protostome phyla
Flexible 3 component body plan: muscular foot, visceral mass and mantle
Mantle is a fold of tissue covering organs of the visceral mass that secretes a calcerous protective shell
Molluscs have larvae, usually trocophore, free swimming that develop into vetiger larvae with shells and foot that settle on the bottom to develop into adult form
Phylum mollusca (card 2)
In most molluscs mantle extends beyond visceral mass forming a mantle cavity for gas exchange. It contains gills for aquatic molluscs and a lung in terrestrial groups (land snails and slugs)
Torsion (twisting) of body is common in mollusc development
Blood vessels an open circulatory system - blood empties into large haemocoel and slowly circulates bathing organs - it is moved by a heart which is more advanced in cephlapods
Phylum mollusca - bivalves
Head reduced and body enclosed between two calcerous valves
Many specialised for filter feeding
Use an inhalant and exhalant siphon to create water flow trapping food in mantle to pass to mouth
Foot may be used for digging
Cephlapoda
Marine, from Cambrian period
Top predators
Exhalant siphon controls water flow out of mantle cavity providing jet propulsion
V. Well developed sensory/ nervous system, complex behaviour
Single gender and develop from egg
Changeable colour patterns under neural control
Subdue prey with tentacles
Vertebrate top predators
Probably outcompeted megacephalopods
Evolved from marine bilateral filter feeding deuterostome chordate
Skeletal support by vertebral column replaced notochord
Endoskeleton of bone/cartilage enhanced mobility & jaws evolved - see cooption last lecture
Anthropods
Successful > 1.1million spp
Possible due to highly adaptable body plan, segmentation, appendages modified for purpose + exoskeleton
Most ancient arthropod group is chelicerata e.g. horseshoe crabs followed by myriapods, crustaceans and hexapods
Arthropod body plan
Exoskeleton protects internal organs and supports internal muscle w/flexible joints for movement
Each section has two sets of appendages which are specialised e.g. for olfaction, vision, food handling, food grinding, defence, walking, swimming or gill ventilation
Exoskeleton supports whole body for walking and is moulted for growth
Jointed appendages allow complex movement
Form chitin in special layers (waxy epicuticle in land insects reduces water loss dramatically)
Arthropods on land
~400 MYA arrived on land
Crucial problems to solve: dessication risk, gas exchange in air, reproduction and locomotion
Low permeable integuments high SA/vol
Gas exchange as tracheal plumbing systems
Early development of young inside cases eggs
Efficient water/ solute regulatory system in place ( N stored as Uric acid)
Insects have evolved flight. Wings are modified appendages, the pdm gene leads to appendage development in crayfishes and wings in drosophila
