Tridacna (Giant Clam)
Systematic Position
Phylum: Mollusca
Class: Bivalvia (Pelecypoda)
Genus: Tridacna
Habit and Habitat
Marine mollusc
Found in tropical coral reefs of the Indo-Pacific region
Lives fixed on coral rocks in shallow waters
Sedentary in habit
External Morphology
Body enclosed in two very large, thick shell valves
Shell valves are:
Heavy
Strongly ribbed
Unequal in outline
Head absent
Body consists of:
Mantle
Visceral mass
Reduced foot
Special Feature – Giant Size
One of the largest living bivalves
Shell may reach 1–1.5 meters in length
Weight can exceed 200 kg
Mantle
Mantle is large, colorful, and fleshy
Mantle lobes extend outside the shell
Mantle contains symbiotic algae (Zooxanthellae)
Digestive System
Complete digestive system
Radula absent
Filter feeder
Also obtains nutrition from photosynthesis by symbiotic algae
Respiration
Aquatic respiration
Respiration through large gills
Circulatory System
Open circulatory system
Heart is three-chambered
2 auricles
1 ventricle
Excretory System
One pair of kidneys (metanephridia)
Nervous System
Poorly developed
Ganglionic type nervous system
Sense Organs
Sense organs poorly developed
Numerous simple eyes (ocelli) on mantle margins
Osphradium present
Reproduction
Usually hermaphrodite
Fertilization external
Gametes released into seawater
Development
Indirect development
Larval stages:
Trochophore
Veliger
Economic Importance
Edible in some regions
Shells used for ornaments and lime
Important in coral reef ecosystems
Identification Points (Exam)
Largest bivalve mollusc
Very heavy ribbed shells
Symbiotic algae in mantle
Marine, sedentary
Radula absent
One-Line Memory Trick
“Tridacna = Titanic clam” 😄
