Govt. Exams
Entrance Exams
Cnidocytes contain nematocysts (stinging cells) that fire to capture, paralyze, and kill prey. This is a defining characteristic of the phylum Cnidaria.
The correct hierarchical order of biological classification follows the sequence: Kingdom, Phylum, Class, Order, Family, Genus, and Species from largest to smallest taxonomic units.
# Sponge Cell Layers: Identifying the Choanoderm
Understanding sponge anatomy requires recognizing the specialized cell layers that form the body wall and line the internal cavity.
Step 1: Identify the Spongocoel
The spongocoel is the central cavity within a sponge where water circulates. The cells that form the inner lining of this cavity are specialized for water movement and feeding.
Step 2: Recognize Choanocytes (Collar Cells)
Choanocytes are flagellated cells with a distinctive collar-like structure around the base of their flagellum. These cells line the spongocoel and are responsible for:
- Creating water currents through flagellar movement
- Filtering food particles from water
- Maintaining the sponge's water circulation system
Step 3: Define the Choanoderm Layer
The choanoderm is the tissue layer composed entirely of choanocytes that directly surrounds and lines the spongocoel. This is the innermost epithelial layer of the sponge.
Step 4: Eliminate Other Options
- (A) Epidermis — outer protective layer, not the inner lining
- (B) Gastrodermis — occurs in cnidarians, not sponges
- (C) Mesenchyme — gel-like middle layer containing amoebocytes, not the spongocoel lining
Answer: The layer of cells surrounding the spongocoel is the Choanoderm (choanocytes/collar cells) (Option D)
Feathers are unique to birds and are not found in any other vertebrate group. While other animals lay eggs or have hollow bones, only birds possess true feathers.
Gills are specialized respiratory organs that extract dissolved oxygen from water for gas exchange, which is their primary function.
Echinoderms possess a unique water vascular system (hydraulic system) used for locomotion and feeding, not found in other phyla.
During embryonic development, the notochord is replaced by the vertebral column (spine) in vertebrates, forming the axial skeleton.
Starfish (Echinodermata) exhibits radial symmetry in adults, while earthworms show bilateral symmetry. Butterflies and fish are bilaterally symmetric.
Birds (Aves) uniquely possess feathers for insulation and flight, along with air sacs for efficient respiration.
Echinoderms (starfish, sea urchins) possess a characteristic water vascular system used for locomotion and feeding.
