Loligo (Squid)
Systematic Position
Phylum: Mollusca
Class: Cephalopoda
Genus: Loligo
Habit and Habitat
Marine mollusc
Found in open seas and coastal waters
Free-swimming (nektonic)
Carnivorous predator
External Morphology
Body is elongated and spindle-shaped
Shell absent externally, present as an internal pen (gladius)
Body divided into:
Head
Mantle (long and muscular)
Visceral mass
Foot modified into 10 appendages:
8 arms (short)
2 long tentacles (for catching prey)
Arms and tentacles bear suckers
Fins
Pair of lateral fins on mantle
Help in slow swimming and balance
Mantle and Siphon
Mantle encloses visceral mass
Funnel (siphon) used for jet propulsion
Digestive System
Complete digestive system
Mouth has beak-like jaws
Radula present
Feeds on fish, prawns, and other molluscs
Respiration
Aquatic respiration
Respiration through two gills (ctenidia)
Circulatory System
Closed circulatory system
Three hearts:
2 branchial hearts
1 systemic heart
Excretory System
Pair of kidneys (metanephridia)
Nervous System
Highly developed
Large brain with cartilaginous protection
Sense Organs
Well-developed camera-type eyes
Statocysts for balance
Chemoreceptors on arms
Special Features
Ink sac for defence
Chromatophores for colour change
Jet propulsion for fast swimming
Reproduction
Dioecious
Internal fertilization
Male has hectocotylized arm to transfer spermatophores
Development
Direct development
No larval stage
Economic Importance
Important seafood
Used in biological and neurophysiological research
Identification Points (Exam ⭐)
Marine cephalopod
10 appendages (8 arms + 2 tentacles)
Internal shell (pen)
Closed circulatory system
Ink sac present
Quick Difference: Loligo vs Octopus
Feature
Loligo
Octopus
Arms
8 arms + 2 tentacles
8 arms only
Shell
Internal pen
Absent
Fins
Present
Absent
Shape
Elongated
Rounded
