Animal Kingdom - Salient features and classification of Non-chordates (Phyla Porifera to Echinodermata)
Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Basis of Classification: Animals are classified based on levels of organization (cellular, tissue, organ, organ-system), body symmetry (radial or bilateral), germ layers (diploblastic or triploblastic), and the presence or absence of a coelom (body cavity).
Phylum Porifera: Commonly known as sponges. They have a cellular level of organization and a unique 'Water Canal System'. Water enters through minute pores called ostia into a central cavity, the spongocoel, and exits through the osculum. Choanocytes (collar cells) line the spongocoel.
Phylum Cnidaria (Coelenterata): They exhibit tissue-level organization and are diploblastic. They possess cnidoblasts or cnidocytes containing stinging capsules called nematocysts. Some, like Obelia, show 'Metagenesis' (alternation of generation between Polyp and Medusa).
Phylum Platyhelminthes: Known as flatworms due to dorso-ventrally flattened bodies. They are triploblastic, acoelomate, and exhibit bilateral symmetry. Specialized cells called flame cells (protonephridia) help in osmoregulation and excretion.
Phylum Aschelminthes: Roundworms with a circular cross-section. They are unique for being 'Pseudocoelomates', where the mesoderm is present as scattered pouches between the ectoderm and endoderm.
Phylum Annelida: Characterized by metameric segmentation (body divided into metameres). They possess longitudinal and circular muscles for locomotion. Excretion is carried out by .
Phylum Arthropoda: The largest phylum of Animalia. They have jointed appendages and a chitinous exoskeleton. Respiratory organs include gills, book gills, book lungs, or tracheal systems.
Phylum Mollusca: The second largest phylum. Body is covered by a calcareous shell () and is unsegmented with a distinct head, muscular foot, and visceral hump. They possess a rasping organ for feeding called the radula.
Phylum Echinodermata: Spiny-bodied organisms with an endoskeleton of calcareous ossicles. A distinctive feature is the 'Water Vascular System' used for locomotion and food capture. Adults show radial symmetry, while larvae show bilateral symmetry.
📐Formulae
💡Examples
Problem 1:
Identify the phylum of an animal that possesses bilateral symmetry, is triploblastic, pseudocoelomate, and has a complete alimentary canal.
Solution:
Phylum Aschelminthes
Explanation:
Aschelminthes (roundworms) are the only group characterized specifically by a pseudocoelom (false body cavity). They are triploblastic ( germ layers) and were the first to develop a complete digestive tract with a muscular pharynx.
Problem 2:
A student observes an aquatic animal with a soft body, a calcareous shell, and a rasping organ. Name the organ and the phylum.
Solution:
Organ: Radula; Phylum: Mollusca
Explanation:
The presence of a (calcareous) shell and a file-like rasping organ for feeding, known as the radula, are definitive characteristics of Phylum Mollusca.
Problem 3:
Explain the significance of the water vascular system in Asterias (Starfish).
Solution:
Locomotion, capture and transport of food, and respiration.
Explanation:
In Echinoderms, the water vascular system is a modified part of the coelom. It operates via hydraulic pressure to extend tube feet for movement and feeding.