Model Answer
0 min readIntroduction
Animal classification is a hierarchical system used to organize the vast diversity of life. Phyla represent the major groupings within the animal kingdom, based on fundamental body plans. However, not all phyla are equally represented in terms of species diversity. While a few phyla, termed ‘major phyla’, encompass the majority of animal species, numerous others, known as ‘minor phyla’, contain relatively few species and often exhibit unique or primitive characteristics. Understanding the distinction between these groups is crucial for comprehending the evolutionary history and biodiversity of the animal kingdom.
Differentiating Major and Minor Phyla
The distinction between major and minor phyla is primarily based on the number of species they contain, their ecological dominance, and the complexity of their body organization.
| Feature | Major Phyla | Minor Phyla |
|---|---|---|
| Number of Species | Large (thousands to millions) | Small (few to hundreds) |
| Ecological Dominance | Often ecologically dominant in various habitats | Typically restricted to specific or marginal habitats |
| Body Plan Complexity | Generally exhibit complex body plans with well-developed organ systems | Often possess simpler body plans, sometimes exhibiting primitive characteristics |
| Examples | Chordata, Arthropoda, Mollusca | Onychophora, Hemichordata, Pogonophora |
Salient Features of Phylum Chaetognatha (Arrow Worms) – A Minor Phylum
Phylum Chaetognatha, commonly known as arrow worms, represents a small but ecologically significant group of marine predators. They are transparent, gelatinous, and bilaterally symmetrical.
Key Characteristics:
- Body Plan: Elongated, transparent body divided into head, trunk, and tail. Lack true body segmentation.
- Locomotion: Move by lateral undulation of the body, aided by chaetae (bristles) on the lateral surfaces.
- Feeding: Predatory, feeding on copepods and other small planktonic organisms. Possess a grasping apparatus with tooth-like hooks.
- Digestive System: Complete digestive system with a mouth, esophagus, intestine, and anus.
- Nervous System: Relatively simple nervous system with a cerebral ganglion and a ventral nerve cord.
- Reproduction: Hermaphroditic, with both male and female reproductive organs. Exhibit both sexual and asexual reproduction.
- Habitat: Exclusively marine, found in all oceans, typically in planktonic communities.
Ecological Role:
Arrow worms play a crucial role in regulating planktonic populations, acting as important predators in marine food webs. They are particularly abundant in areas of high plankton concentration.
Evolutionary Significance:
Chaetognaths are considered to be relatively primitive deuterostomes, and their phylogenetic position has been debated. Some studies suggest a close relationship with the Chordata, while others place them closer to the Echinodermata.
Conclusion
In conclusion, the distinction between major and minor phyla highlights the uneven distribution of biodiversity within the animal kingdom. Major phyla dominate in terms of species numbers and ecological impact, while minor phyla often represent evolutionary relics or occupy specialized niches. Studying these minor phyla, like Chaetognatha, provides valuable insights into the early evolution of animal life and the diversity of body plans that have arisen over millions of years. Further research is needed to fully understand their phylogenetic relationships and ecological roles.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.