Protostomes and Deuterostomes
Overview of Animal Development Stages
- Three main stages of life:
Body Organization and Directional Terms
- Body Directions:
- Importance of understanding anatomical directions for various parts of the body rather than specific locations.
- Examples include tail and anus.
Major Differences Between Protostomes and Deuterostomes
- Cleavage Patterns:
- Protostomes: Spiral cleavage.
- Deuterostomes: Radial cleavage.
- Development:
- Protostomes: Determinate development.
- Deuterostomes: Indeterminate development.
- Symmetry:
- Protostomes and deuterostomes exhibit bilateral symmetry, unlike sponges and cnidarians.
Basal Taxa in Phylogenetic Trees
- Basal Organisms:
- All trees include sponges as the basal organisms.
- Cnidarians: First derived group after sponges known for radial symmetry, highlighted as the only radially symmetric animals.
- Cnidarians lack a defined head, employing a nerve net for sensory capabilities across their body.
Characteristics of Bilateral Animals
- Head Development:
- Bilateral animals generally have a head (anterior end) for sensory and nerve information accumulation.
- The head may not resemble traditional heads (e.g., no classic brain) but is characterized by sensory processing at the anterior.
Lophotrochozoans and Their Unique Features
- Lophophores:
- Hair-like structures on the body surface (could be cilia or larger finger-like structures) typically used at some stage of life for feeding.
- Trochophore Larvae:
- A larval stage equipped with a crown of cilia aiding movement and feeding.
- Ectoprocts:
- Possess a cuticle that is shed, although not an exoskeleton (only arthropods have true exoskeletons).
Diversity in Animal Adaptations
- Survival Adaptations:
- All animal diversity reflects variations in reproduction, development, nutrition, locomotion, and defense mechanisms.
Phylogenetic Trees as Hypotheses
- Importance of recognizing that phylogenetic trees represent hypotheses and not definitive classifications.
- Ability to label characteristics like lophophores on given trees.
Groups of Interest
Lophophorates
- Description of lophophorates:
- Unique feeding methodology using lophophores to funnel food.
- Body Structure:
- Mouth, anus, and reproductive openings are combined into a single ventral opening referred to humorously as the "mouth hole."
Flatworms
- Notable absence of a circulatory system; rely on surface area to volume ratio for gas exchange.
Lampshells (Brachiopods)
- Distinct from clams, they utilize a strong anchoring foot and lophophores for trapping food.
Debates in Animal Evolution
- Noteworthy discovery of deuterostomic development in certain organisms, challenging earlier interpretations of phylogenetic relationships.
Annelida (Segmented Worms)
- Segmented Worm Characteristics:
- Segmentation allows high customization of body plans, enabling evolutionary flexibility.
- Gas Exchange:
- Annelids utilize skin for gas exchange rather than a circulatory system with a central heart.
Calcifiers and Environmental Impact
- Importance of calcifiers in marine environments, facing risks due to climate change; their evolutionary significance outlined.
Mollusks
- Structure:
- Typical mollusk body includes a muscular foot and a radula for feeding (like a band saw).
- Vulnerabilities of trochophore larvae as calcifiers linked to environmental changes.
- Discussion of intelligence in cephalopods (e.g., octopi) and their capabilities in sensory processing.
Ecdysozoa and their Characteristics
- Diverse group of bilateral animals, characterized by molting protective coverings.
- Benefits and Costs of Molting:
- Protection vs. vulnerability during shedding process.
Specific Groups in Ecdysozoa
- Loriciferans:
- Do not create a structure for protection but use sticky surfaces.
- Velvet Worms:
- Possess a soft cuticle with minimal protection.
- Tardigrades:
- Known as water bears, capable of surviving extreme conditions (dry, wet, hot, etc.).