Essay on 1 POSTED Animals Invertebrates

Submitted By Eward11E
Words: 679
Pages: 3


Learning Objectives: (These apply to both animal lectures (vertebrates/invertebrates)

1) List the traits that distinguish the major animal groups; identify the trait and groups on a phylogeny
2) Explain what a coelom is and explain its function(s)
3) Explain the value of cephalization, a central nervous system, and segmentation to diversification in animals
4) Explain the pros and cons of endoskeletons vs exoskeletons and provide examples of each from the animal group
5) Distinguish between a protostome and a deuterostome
6) List the four features of chordates and explain how vertebrates are different from chordates and how they are different from tetrapods
7) Explain examples of modification of existing parts to create new structures
8) Explain an example of homology and convergent evolution in the animal group


Animals…followed plants onto the land

1.4 million named species - includes 1.2 million arthropods, 1 million insects

Animals are defined as being/having:
- multicellular
- lack cell walls
- heterotrophic
- mobile/motile
- nerves and muscles (except for sponges) (enabled rapid response to external stimuli)
- sexual reproduction (production/fusion of haploid gametes)

There are: 30-35 Phyla (depending on who you talk to)
...all of which seem to have emerged in the Cambrian – and none since

- Animals at the “Phylum” level have shared traits based on “body plan” stemming from a common ancestry.
- Animals are monophyletic (have a single common ancestor)

Key synapomorphies in the animal lineage:
- multicellularity
- cell-to-cell adhesion

Clear evolutionary trend toward increasing complexity:
- Sponge has no true tissue
- Cnidarians: tissues but no organs
- Flatworms and above: organ and organ systems

1) Radial vs Bilateral symmetry:
- hypothesis: origin of Central Nervous System (CNS) is linked to evolution/origin of bilateral symmetry
- along with cephalization, this enabled more efficient hunting and capturing prey

2) Origin of coelom – a “tube within a tube” with: - inner tube of gut and anus - outer tube of nerves and skin - middle tube of muscle and organs

- a fluid-filled cavity that provides space for circulation of oxygen and nutrients
- allows organs to move independently of each other
- Primitive animals: no cavity; solid tissue
- True coelom: space for organs to develop; organism can operate independent of body wall

Protostomes and Deuterstomes
- Protostomes: mouth develops first and blocks of mesoderm hollow out to form coelom
- Deuterostomes: anus develops first and pockets of mesoderm pinch off to form coelom
…end result appears the same; adaptive significance of either one is uncertain

Major groups in the protostomes: mollusks, annelids, flatworms, rotifers

Major groups in the deuterostomes:

3) Segmentation: hypothesis is that segmentation enables specialization

Protostome phylogeny is confusing because…although they are monophyletic…
- some traits evolved independently in different lineages
- some traits that were synapomorphies were lost in some lineages

Major Phyla:
1) Phylum Porifera – sponges - ancient and primitive - flagella move water -…