Phylum
- Highest unit of classification after ‘Kingdom’
- Animals grouped into phyla based on shared characteristics
- Animals are heterotrophs, with no cell wall
Nematodes
- Round worms
- Many species, around 25,000 described
- Most abundant animals in Antarctica
- Moult (like arthropods)
- Eutelic (fixed number of cells/species)
Tardigrades (‘Water bears’ or ‘Moss Piglets’)
- Live in fresh water, moss and undergrowth
- Capable of surviving extremes (10 years without water)
- On final flight of space shuttle Endeavor
- Also eutelic (species specific number of cells)
Eutelic
Eutelic organisms have a fixed number of somatic cells when they reach maturity, the exact number being constant for any species
Development proceeds by cell division until maturity; further growth occurs via cell enlargement only.
Phylum: Onychophora
- Velvet worms or Claw bearers
- Terrestrial
- Have antennae (unique for worms)
- Capture prey by throwing out sticky threads
Eumetozoa
- Subkingdom
- Eumetozoa divided into:
- radially symmetrical animals e.g. cnidiaria, ctenophora
- bilaterally symmetrical animals e.g. bilateria
- Bilateria divided into:
- protostomes e.g. flatworms, segemented worms, molluscs, arthropods
- deterostomes e.g. echinoderms, chordates
Symmetry
- Bilateral Symmetry
- have one plane along which they are symmetrical
- can talk about anterior/posterior, dorsal/ventral, left/right
- Radial symmetry
- have several planes along which they are symmetrical
Germ layers
- later of embryonic cells that develops into body features
- ecto, meso, endo
- Diploblastic = two layers, no mesoderm, no gut cavity
- Tripoblastic = three layers
Blastula
- blastula = early developmental stage when cells begin to differentiate
- morula = ball of cells
Tripoblast
- 3 germ layers
- if the organism has a gut, must be a triploblast but a triploblast may not have a gut
- acoelomate = coelom absent
- coelomate = coelom present
The importance of the coelom
- Fluid-filled so can be used as internal support
- separates internal processes from gut
- allows transport of fluids (circulatory and excretory systems)
- provides space for development of internal organs
- enables increased body size
Fate of the Blastopore
- Protostome = ‘mouth first’
- blastopore becomes the mouth
- spiral cleavage, determinate development
- Deuterostome = ‘anus first’
- blastopore becomes the anus
- echinoderms and chordates
e. g. in humans, needs to get rid of wastes first in the uterus, does not eat via the mouth but gets nutrients via the umbilical cord
Segmentation
- Segmentation affects mesoderm and ectoderm
- series of repetitive segments
- Advantages: efficient movement, detect prey (mouth, head, sensory organs), specialisation, better adaptation (allow body organ to grow differentially, suited for a specific purpose)
Other important ways of distinguishing animals
- Moulting - Ecdysozoa (arthropods)
- Feeding mechanisms
- Larval biology - trophocore larvae (e.g. annelids, molluscs)
- Reproduction - sexual/asexual (most species sexaul; some asexual; some sexual and asexual)
Subgkindom: Parazoa
Phylum: Porifera - Sponges
- Simplest animals
- Aquatic, mainly marine
- No mouth or gut
- Layers of cells with protein matrix; no tissues or organs
- No nervous system
- Mainly filter feeds
- Have specialised cells - pinoctyes - can engulf larger prey
- Sexual and asexual reproduction
Subkingdom: Eumetozoa
Phylum: Cnidaria
- Split into three classes
- Hydras (Hydrazoa)
- Jellyfish (Scyphozoa)
- Corals and Anemones (Anthozoa)
- Radia symmetry (mostly)
- Diploblastic: two body layers are separated by a gelatinous layer called the mesoglea
- Aceolomate
- Unsegmented
- Nerve net, in the mesoglea, simple nervous system
- Reproduction - usually sexual and asexual
- Use nematocysts to catch prey, barbed wire within specialised cell, cnidoctye
Typical Cnidarian life cycle
- asexual polyp stage
- sexual medusae stage
- Medusa, free to swim, Jellyfiish
- Sessile, fixed onto ocean floor
Reproduction begins when the females catch sperm released by the males to fertilize the eggs she has produced and holds it in her mouth. These fertilized eggs remain attached to her oral arms, and there they grow into flat bean-shaped planula. Once they grow into flower-shaped polyps, they are released into the ocean where they attach themselves to a solid surface and undergo budding.
Polyps reproduce asexually, producing medusae that then release gametes. The male and female gametes unite under water to form the zygote that then develops into larva and later produces another polyp.
The form that reproduces asexually is the polyp. Polyps produce medusae via budding in Obelia and via strobilation in Aurelia.
Phylum: Cnidaria
Class: Hydrozoa (Hydra)
- Freshwater polyp
- Long tentacles for prey capture with stinging nettles
- Anchored by ‘foot’
Phylum: Cnidaria
Class: Schyphozoa (Jellyfish)
- Marine, free-swimming
- Also have stinging tentacles (sometimes enormously poisonous)
- One of the world’s longest animals is the lion’s mane jellyfish (200ft long)
Phylum: Cnidaria
Class: Anthozoa (Corals and anemones)
- marine polyps
- often colonial
- many have symbiotic algae living intra-cellularly, coral provies algae with nutrients and protection, algae provides coral with N2 and organic C compounds
Subkingdom: Eumetozoa
Phylym: Platyhelminthes
- Flatworms
- two modes of living: free-living or parasitic
- four classes:
- Turberllaria: aquatic flatworm, free-living
- Monogenea: external flukes, parasitic
- Trematoda: internal flukes, parasitic
- Cestoda: tapeworms, parasitic
- bilateral
- triploblastic
- acoelomate
- protostome - simple gut with mouth only
- unsegmented
- bottom surface may be covered in cilia - aids movement
eye > brain > ventral nerve cord > pharynx > mouth/anus
Tapeworms
- vertebrate gut parasites
- attach to intestinal lining via head structure (scolex)
- feed by absorption through epidermis (very thin/flat)
- reproduce by breaking off body segments (proglottids)
- can grow very long…3 metres plus
- famously used as a diet aid
