Mollusca
Mollusks are a phylum that consists of predominantly marine animals as it takes up 23% of the animals in the water. Animals in this phylum include squid, cuttlefish, octopus, snails, slugs, etc. The molluscan nervous system consists of a pair of ganglia and nerve cords, with statocysts (balance organs) and eyes as major sense organs. Mollusks include the largest invertebrates and the smartest invertebrates (the octopus). They have two pairs of main nerve cords: the visceral cords - the internal organs and the pedal ones serving the foot and the ganglia. Most mollusks have a head with eyes, and all have a pair of sensor-containing tentacles.
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