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These notes cover everything from Parazoa to Chordata, explained clearly with cleavage types and body cavities.
1. BODY PLAN & SYMMETRY
| Type | Definition | Examples |
|---|---|---|
| Asymmetry | No symmetry | Sponges (Porifera) |
| Radial Symmetry | Body parts around central axis | Cnidaria, Ctenophora |
| Bilateral Symmetry | Mirror-image halves | Platyhelminthes to Chordata |
2. LEVELS OF ORGANIZATION
| Level | Description | Phyla Examples |
|---|---|---|
| Cellular | Loose aggregation of cells | Porifera |
| Tissue | Cells form tissues | Cnidaria, Ctenophora |
| Organ | Tissues form organs | Platyhelminthes |
| Organ System | Organs form systems | Annelida to Chordata |
3. PARAZOA & METAZOA
| Group | Definition | Example |
|---|---|---|
| Parazoa | No true tissues | Sponges |
| Metazoa | Multicellular with tissues | All other animals |
4. BODY PLAN PATTERNS
| Type | Description | Examples |
|---|---|---|
| Blind Sac | One opening serves as mouth & anus | Cnidaria, Platyhelminthes |
| Tube within Tube | Separate mouth and anus | Annelida to Chordata |
5. PROTOSTOME vs. DEUTEROSTOME
| Feature | Protostome | Deuterostome |
|---|---|---|
| Blastopore | Mouth | Anus |
| Cleavage | Spiral, Determinate | Radial, Indeterminate |
| Coelom formation | Schizocoelous | Enterocoelous |
| Examples | Annelida, Arthropoda | Echinodermata, Chordata |
6. BODY CAVITY (COELOM)
Types of Coelom
| Type | Description | Examples |
|---|---|---|
| Acoelomate | No body cavity | Platyhelminthes |
| Pseudocoelomate | Not fully lined by mesoderm | Nematoda |
| Eucoelomate | True coelom | Annelida to Chordata |
Coelom Development
| Type | Description | Examples |
|---|---|---|
| Schizocoelomate | Splitting mesoderm | Annelida, Arthropoda |
| Enterocoelomate | From gut pouches | Echinodermata, Chordata |
7. GERM LAYERS
| Layer | Forms |
|---|---|
| Ectoderm | Skin, nervous system |
| Mesoderm | Muscles, skeleton, circulatory system |
| Endoderm | Lining of gut, lungs, liver |
8. CLEAVAGE PATTERNS
Types of Cleavage
| Type | Description | Egg Type |
|---|---|---|
| Holoblastic Equal | Complete and equal | Isolecithal (Amphioxus) |
| Holoblastic Unequal | Complete but unequal | Moderately telolecithal (Amphibians) |
| Meroblastic | Incomplete cleavage | Heavily telolecithal (Birds) |
Based on Fate
| Cleavage | Description | Phyla |
|---|---|---|
| Radial & Indeterminate | Totipotent cells | Deuterostomes |
| Spiral & Determinate | Fixed fate early | Protostomes |
Cleavage in Humans
- Holoblastic unequal cleavage
- Radial and indeterminate
- Microlecithal eggs
- Stages: 2-cell → 4-cell → 8-cell → Morula → Blastocyst
9. BODY CAVITIES IN HUMANS
| Cavity | Organs | Mesothelium |
|---|---|---|
| Cranial | Brain | Meninges |
| Thoracic | Lungs, Heart | Pleura, Pericardium |
| Abdominal | Stomach, Liver, Intestines | Peritoneum |
| Pelvic | Bladder, Reproductive organs | Peritoneum |
Mesothelium secretes lubricating fluid & protects organs for smooth movement.
10. PHYLA-SPECIFIC FEATURES
| Phylum | Symmetry | Coelom | Development | Cleavage |
|---|---|---|---|---|
| Porifera | Asymmetrical | Acoelomate | Cellular | – |
| Cnidaria | Radial | Acoelomate | Tissue | – |
| Ctenophora | Biradial | Acoelomate | Tissue | – |
| Platyhelminthes | Bilateral | Acoelomate | Organ | Spiral, Determinate |
| Nematoda | Bilateral | Pseudocoelomate | Organ system | Spiral, Determinate |
| Annelida | Bilateral | Schizocoelomate | Organ system | Spiral, Determinate |
| Arthropoda | Bilateral | Schizocoelomate | Organ system | Spiral, Determinate |
| Mollusca | Bilateral | Schizocoelomate | Organ system | Spiral, Determinate |
| Echinodermata | Larvae-bilateral, Adult-radial | Enterocoelomate | Organ system | Radial, Indeterminate |
| Chordata | Bilateral | Enterocoelomate | Organ system | Radial, Indeterminate |
Body Plan & Symmetry
Symmetry Types:
- Asymmetry: No symmetry (Sponges – Porifera)
- Radial Symmetry: Body parts arranged around a central axis (Cnidaria, Ctenophora)
- Bilateral Symmetry: Body divided into two mirror-image halves (Platyhelminthes to Chordata)
Levels of Organization
| Level | Description | Example Phyla |
|---|---|---|
| Cellular Level | Loose aggregation of cells | Porifera |
| Tissue Level | Cells form tissues | Cnidaria, Ctenophora |
| Organ Level | Tissues form organs | Platyhelminthes |
| Organ System Level | Organs work together as systems | Annelida to Chordata |
Parazoa & Metazoa
Parazoa: No true tissues (Sponges – Porifera)
Metazoa: Multicellular animals with true tissues (All other animals)
Protostome vs. Deuterostome
| Feature | Protostome | Deuterostome |
|---|---|---|
| Blastopore | Becomes mouth | Becomes anus |
| Cleavage | Spiral, determinate | Radial, indeterminate |
| Coelom Formation | Schizocoelous | Enterocoelous |
| Examples | Annelida, Arthropoda, Mollusca | Echinodermata, Chordata |
Body Cavity Types
- Acoelomates: No body cavity (Platyhelminthes)
- Pseudocoelomates: False body cavity (Nematoda)
- Coelomates: True body cavity (Annelida to Chordata)
Germ Layers
Ectoderm: Forms the outer layer, gives rise to skin, nervous system (e.g., invertebrates, vertebrates).
Mesoderm: Forms muscles, circulatory system, and other internal structures (e.g., Arthropods, Vertebrates).
Endoderm: Forms the digestive system, lungs (e.g., Vertebrates, Mollusks).
Cleavage Patterns
Radial Cleavage: The planes of division are parallel or perpendicular to the main axis (Deuterostomes, e.g., Echinoderms, Chordates).
Spiral Cleavage: The planes of division are at an angle to the main axis (Protostomes, e.g., Annelids, Molluscs).
Cleavage Types
Determinate Cleavage: The fate of the cells is fixed early on (Protostomes).
Indeterminate Cleavage: The fate of the cells is not fixed early on (Deuterostomes, allowing for identical twins).
Phylum-wise Features
Porifera: Asymmetrical, no true tissues, filter feeders.
Cnidaria: Radial symmetry, true tissues, cnidocytes (stinging cells).
Platyhelminthes: Bilateral symmetry, acoelomates, flat body.
Chordata: Bilateral symmetry, notochord, dorsal hollow nerve cord.