Octopus
Systematic Position
Phylum: Mollusca
Class: Cephalopoda
Genus: Octopus
Habit and Habitat
Marine mollusc
Found in seas and oceans, usually near rocky shores
Lives in crevices and burrows
Carnivorous predator
External Morphology
Body is soft, unsegmented, and bilaterally symmetrical
Shell absent
Body divided into:
Head
Visceral mass
Foot modified into 8 long arms
Arms bear suckers for attachment and capturing prey
Mantle
Thick and muscular
Encloses visceral mass
Mantle cavity contains gills
Digestive System
Complete digestive system
Mouth has a strong beak-like jaw
Radula present
Feeds on crabs, fish, and molluscs
Respiration
Aquatic respiration
Respiration through two gills (ctenidia)
Circulatory System
Closed circulatory system (important feature)
Three hearts:
2 branchial hearts (pump blood to gills)
1 systemic heart (pumps blood to body)
Excretory System
Pair of kidneys (metanephridia)
Nervous System
Highly developed nervous system
Large brain protected by cartilage
Shows learning ability and intelligence
Sense Organs
Well-developed eyes (camera-type)
Statocysts for balance
Chemoreceptors on suckers
Special Features
Ink gland → releases ink for defence
Chromatophores → change body colour (camouflage)
Jet propulsion → fast movement by expelling water through siphon
Reproduction
Dioecious (sexes separate)
Internal fertilization
Male arm modified into hectocotylus for sperm transfer
Development
Direct development
No larval stage
Economic Importance
Used as seafood
Important in marine food chains
Used in scientific research
Identification Points (Exam ⭐)
Marine cephalopod
Shell absent
8 arms with suckers
Closed circulatory system
Ink gland and chromatophores present
One-Line Memory Trick
“Octopus = 8 arms + no shell + closed blood system”
