Pinctada (Pearl Oyster)
Systematic Position
Phylum: Mollusca
Class: Bivalvia (Pelecypoda)
Genus: Pinctada
Habit and Habitat
Marine mollusc
Found in shallow tropical seas
Lives attached to rocks or coral reefs
Common in pearl fisheries
External Morphology
Body is soft and laterally compressed
Enclosed in two equal shell valves
Shell:
Smooth outside
Inner surface lined with nacre (mother-of-pearl)
Head absent
Body consists of:
Mantle
Visceral mass
Small foot
Shell
Two valves joined by a hinge ligament
Shell layers:
Periostracum (outer)
Prismatic layer (middle)
Nacreous layer (inner) → important for pearl formation
Mantle and Mantle Cavity
Mantle lobes secrete the shell and nacre
Mantle cavity contains:
Gills (ctenidia)
Labial palps
Incurrent and excurrent siphons present
Digestive System
Complete digestive system
Radula absent
Filter feeder
Food particles collected by gills
Respiration
Aquatic respiration
Respiration through 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
Cerebral, pedal, and visceral ganglia present
Sense Organs
Sense organs poorly developed
Osphradium present
Eyes absent
Reproduction
Dioecious (sexes separate)
External fertilization
Development
Indirect development
Larval stages:
Trochophore
Veliger
Pearl Formation (Very Important for Exams ⭐)
A foreign particle (sand, parasite) enters mantle cavity
Mantle secretes nacre around it
Layer-by-layer deposition forms a pearl
Pearl composed of calcium carbonate + conchiolin
Economic Importance
Source of natural pearls
Important in pearl industry
Shell produces mother-of-pearl used in ornaments
Identification Points (Exam)
Marine bivalve
Nacreous shell lining
Pearl formation
Radula absent
Filter feeder
One-Line Memory Trick
“Pinctada = Pearl producer”
