Lecture 16 Flashcards
Evolutionary innovation across animal groups: (6)
- Multicellularity
- Tissues
- Gut
- Mesoderm
- Head
- Segmentation
These differ btwn protostomes and deuterostomes (5)
- Nervous system
- Hard skeleton
- Coelom
- Anus
- Circulatory system
Protostomes
Blastopore develops into mouth
Ex. Rotifers, Flatworms, Annelid, Molluscs, Nematodes, Arthropods
Deuterostomes
Blastopore develops into anus
Ex. Echinoderms, Chordates
Who are Deuterostomes?
Echinodermata (starfish), Hemichordatata, exenoturbellida, Chordata (us)
What is the initial way to distinguish protostome and deuterostomes? What is wrong with it?
- Embryonic Development (gastrulation)
- Priapulid worms are protostomes but their blastopore develops into anus (a protostome with deuterostome development, exception)
- Priapulids (penis worm): been around since Cambrian
Protostomes and Deuterostomes (4)
- Significance? When? Monophyly (2)?
- Two major evolutionary lineages of Bilateria
- Split around the Cambrian (500 MYA)
- Monophyly of protostomes is confirmed by genetic similarities (everything in protostomes group is most closely related to others in that group than anything else. Everything radiated from protostomes descended from one common ancestor)
- Deuterostomes are also monophyletic
How to distinguish Deuterostomes from protostomes?
- Circulatory system has ventral heart
- Central nervous system is dorsal
- Hard skeleton is internal
Echinoderms “spiny skins”
- 7000 species
- strictly marine
- benthic (bottom dweller)
- Diverse modes of nutrition
- Ex. Sea stars, sea urchins, sand dollars
Echinoderms - Hard endoskeleton
- CaCO3 plates
- Continuous growth (plates enlarge and new ones are added)
- covered by thin layer of skin and muscle
Echinoderms - Bilateria
Some characteristic go away when larvae becomes adults (Echinoderms larvae is bilateral, then pentaradial)
How do echinoderms change their symmetry?
Metamorphosis
- intermediate larval stage grows 3 adhesive arms and suckers
- Original mouth and anus disappear and new mouth reappears on left side
- Transformation from egg to newly formed starfish takes about 2 months
Water Vascular system
- System of water-filled tubes - hydrostatic skeleton
- end in “tube feet” (podia) - extend through pores in endoskeleton
Closed system - except for madreporite (opening of hydrostatic skeleton) that let water in and out
Podia
used to locomotion, gas exchange, feeding, excretion
secretes an adhesive material when you pull it off
Sexual Reproduction - Echinoderms
- separate sexes
- external fertilization
- Broadcast spawning - at a certain time of year, all eggs and sperm (gametes) are released into water and they come into contact and develop into larvae
- Larvae (planktonic, ciliated arms)
Asexual Reproduction - Echinoderms
Regeneration
Arms may be dropped and regenerated to:
- Escape predation
- decrease change of infection spreading, reproduce
Parthenogenesis
- does not occur normally; induced
- development of unfertilized egg
- can be induced artificially in sea urchin with salt solution
Echinoderm Diversity
- Echinoids, Ophiuroids, Holothuroids, crinoids, asteroids
Crinoidea
- Sea lilies and feather stars
- Filter feeders
- Can swim if they are detached from water
Ophiuroidea
- Brittle stars (many arm spines, filter-feeders, predators, detritivores)
- Basket stars (branched arms, filter-feeders)
Asteroidea: Sea stars
- predatory
- fairly mobile
- evert stomach, secrete enzymes to digest prey and then engulf partially digested prey
Echinoidea: sea urchins and sand dollars
Sea urchins
- have many spines, locomotion, defense
- Pincers - defense, cleaning (echinoids and asteroids)
- have aristotle’s lantern for scraping algae off rocks
Holothuroidea
- Sea cucumber
- detritivores, scavengers, filter-feeders
- reduced endoskeleton
- give rows of tube feet
- respire by drawing water into anus
- feeding tentacles
- Commensal relationship with pearlfish, pearlfish hides in anus of sea cucumber to escape predators
Chordates
- 65000 species
- broad, deep phylogeny of chordates
- include the vertebrates
- deuterostomes (pharyngeal slits)
- Coelomates
- Bilateral symmetry
Characteristics unique to Chordates
- Dorsal Hollow nerve cord
- Notochord
- Post-and-tail
Pharyngeal slits are an ancestral trait of deuterostomes
Characteristics common to Chordates
- Ventral heart
- Reduced segmentation
- Segmented musculature (Myomeres - important for being able to generate thrust)
Chordates (3)
- Cephalochordates
- Urochordates
- Vertebrates
Cephalochordates
- Lancelets
- 30 species
- fish like bodies
- live in sediments as adults
- tropical, shallow marine water
- 1-5 cm
- filter feeders
- adults retain all 3 unique chordates characteristics
Urochordates
- 3000 species, 90% tunicates (sea squirts)
- Marine
- Do not retain all 3 unique chordates characteristics as adults
- As adults: 1mm to 60 cm
- Solitary or colonial
- Benthic, sessile
- Filter-feeders
As larvae: Planktonic, resemble tadpoles
Urochordates Life History
- Planktonic Larvae
- Larve settles on its head
- Pharynx enlarges
- head and tail degenerate
- becomes sessile adult (no notochord)
Urochordates larvae
all three unique chordates characteristics
Urochordates adults
no notochord, enlarge pharyngeal gill slits, no dorsal hollow nerve cord
