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Appearance move to sidebar hide From Wikipedia, the free encyclopedia Organ in cephalopods used to squirt ink in defense

An ink sac is an anatomical feature that is found in many cephalopod mollusks used to produce the defensive cephalopod ink. With the exception of nocturnal and very deep water cephalopods, all Coleoidea (squid, octopus and cuttlefish) which dwell in light conditions have an ink sac, which can be used to expel a cloud of dark ink in order to confuse predators.[1]

The ink sac is a muscular bag which originated as an extension of the hind gut; it is a modified hypobranchial gland.[2] It lies beneath the gut and opens into the anus, into which its contents – almost pure melanin – can be squirted; its proximity to the base of the funnel means that the ink can be distributed by ejected water as the cephalopod uses its jet propulsion.[1] The ejected cloud of melanin is bound by mucus particles, so it forms a lump approximately the size and shape of the cephalopod, fixing the predator's attention while the mollusc itself makes a hasty escape.[1]

References

[edit]

1. ^ a b c Boyle, Peter; Rodhouse, Paul (2004). Cephalopods : ecology and fisheries. Ames, Iowa: Blackwell. doi:10.1002/9780470995310.ch2. ISBN 0-632-06048-4.
2. ^ Nair, J.R., D. Pillai, S.M. Joseph, P. Gomathi, P.V. Senan & P.M. Sherief (2011). "Cephalopod research and bioactive substances" (PDF). Indian Journal of Geo-Marine Sciences 40(1): 13–27.

v t e Cephalopod anatomy
Shell	Types External Ammonoid shell Argonautid eggcase Nautiloid shell Orthocone Internal Belemnoid guard Cirrate shell Cuttlebone Gladius (pen) Spirula shell Stylet Features External Aperture Apex Callus Lirae Periostracum Sculpture Spire Sutures Umbilicus Internal Body chamber Camerae Nacre Phragmocone Septa Siphuncle Whorls
Mantle & funnel	External anatomy Dermal structures Fins (wings) Flotation devices ("secondary fins") Funnel–mantle locking apparatus Tail Internal anatomy Branchial hearts Ctenidia (gills) Hepatopancreas (digestive gland) Ink sac and ink Needham's sac Nephridia ("kidneys") Nidamental glands Osphradium Pericardial glands
Head & limbs	Brachial crown Arms Hectocotylus Tentacles Carpus Dactylus Manus Suckers and hooks Buccal region Aptychus Beak Odontophore Radula Spadix and antispadix Occipital region Nuchal crest (occipital crest) Nuchal folds (occipital folds) Occipital membrane Olfactory organ Nuchal organ Other parts Eyes Statocysts
General	Chromatophores Photophores Nervous system Squid giant axon Squid giant synapse
Developmental stages: Spawn → Paralarva (Doratopsis stage) → Juvenile → Subadult → Adult • Egg fossils • Protoconch (embryonic shell)

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