Chiton
Systematic Position
Phylum: Mollusca
Class: Polyplacophora
Genus: Chiton
Habit and Habitat
Marine mollusc
Found on rocky sea shores, especially in intertidal zones
Lives attached to rocks
Herbivorous, feeds on algae
External Morphology
Body is elongated, oval, and dorsoventrally flattened
Covered by eight overlapping calcareous shell plates arranged in a row
Body divided into:
Head (poorly developed)
Visceral mass
Muscular foot
Shell (Special Feature ⭐)
Shell consists of 8 dorsal plates (valves)
Plates embedded in a tough girdle called perinotum
Allows flexibility and firm attachment to rocks
Foot
Broad, flat, and muscular
Used for creeping and strong adhesion to rocks
Mantle and Mantle Cavity
Mantle forms a girdle around the body
Mantle cavity present on both sides of the foot
Contains many pairs of gills
Digestive System
Complete digestive system
Mouth contains a radula
Radula well developed and used to scrape algae from rocks
Respiration
Aquatic respiration
Respiration through numerous gills in mantle groove
Circulatory System
Open circulatory system
Heart is three-chambered:
2 auricles
1 ventricle
Excretory System
One pair of kidneys (metanephridia)
Nervous System
Simple nervous system
No true ganglia
Nerve cords connected by commissures
Sense Organs
Eyes and tentacles absent
Shell plates may contain aesthetes (light-sensitive organs)
Reproduction
Dioecious
External fertilization
Development
Indirect development
Larval stage:
Trochophore larva
Economic Importance
Minor food value
Important for marine ecosystem balance
Identification Points (Exam ⭐)
Marine mollusc with 8 shell plates
Belongs to Polyplacophora
Broad creeping foot
Radula present
Many gills in mantle groove
One-Line Memory Trick
“Chiton = eight-plated living tank” 😄
