Predators & defenses
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  Defenses of octopuses and their relatives can be divided into passive and active. Topics relating to passive defenses include colour change & camouflage, considered in this section, and HIDING AWAY, NOCTURNAL BEHAVIOUR and MAKE BODY SEEM LARGER, considered in other sections.

Active defenses include BEAKS & BITING and WITHDRAWAL & INKING
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Colour change & camouflage


Colours in cephalopods result from contraction and expansion of chromatophores, or colour cells, scattered within the skin. In cephalopods the chromatophores are under nervous control; hence, colour changes are virtually instantaneous. In comparison, chromatophores in fishes and crustaceans are under hormonal control and responses are slower - measured in minutes, hours, or days.

Colour change is considered here, while camouflage is dealt with in its own sub-section below.

Research study 1

photograph of an octopu model showing arm curling Abrupt colour changes including blanching are common responses to distubance or stress in octopuses, such as Enteroctopus dolfleini.  They may be accompanied by escape by crawling and jetting, and by ink release. photograph of octopus Enteroctopus dolfleini in its denAdditionally, when an octopus is in defensive attitude, the arms may curl around on themselves (see model on Right) while the chromatophores rapidly change colour. Mather 1998 J Comp Psychol 112: 306.

Enteroctopus dolfleini in
partially blanched mod

photograph of a hunched-up octopus Enteroctopus dolfleini taken from a video

CLICK HERE to see a short video of an octopus Enteroctopus dolfleini exhibiting quick colour change.

NOTE the video replays automatically

Research study 2

Eyebars, as a strategy for disguising the distinctiveness of eyes in both predator and prey alike, are common in many animals including birds and tropical fishes, and also in some west-coast cephalopods. However, as the photographs below show, of 5 common west-coast species only Enteroctopus dofleini and Octopus rubescens possesses distinctive eyebars. All photographs are taken in daytime. What the function of the eyebars could be is not known, but consider this: eyebars as "eye-disruptors" would be most effective against daytime predators but, of the octopod species shown, O. rubescens and O. bimaculoides are generally diurnally active, while E. dolfleini is generally nocturnally active. However, note that O. bimaculoides, although lacking eyebars, does sport a distinctive false eye on either side of its body. Photograph #2 in the series courtesy Roland Anderson & Seattle Aquarium, #4 courtesy Roger Hanlon, and #5 courtesy Kevin Lee diverKevin.

NOTE whether eyebars are present or not in octopuses, even in E. dolfleini, depends in large extent to the particular pattern and magnitude of activity of surrounding chromatophores. The photograph selected below for O. dolfleini (#1 in the series) shows off the eyebars particularly well

photograph of eye of octopus Enteroctopus dolfleini photograph of eye of octopus Octopus rubescens courtesy Roland Anderson photograph of eye of Humboldt squid Dosidicus gigas photograph of eye of octopus Octopus bimaculoides courtesy Roger Hanlon photograph of eye of squid Doryteuthis opalescens courtesy Kevin Lee
Eye and eyebar of octopus Enteroctopus dolfleini Octopus rubescens peers from its egg mass. Note shading on eye Eye of squid Dosidicus gigas. Body shading is dark above, light below Eye of Octopus bimaculoides. Note "ocellus" beneath eye Eye of squid Doryteuthis opalesc-ens. Note large tapetum area
Research study 3

photograph of octopus appearing to mimic worm tubes, courtesy Kevin Lee, Fullerton, CaliforniaCamouflage through mimicking has not been studied in west-coast octopuses, yet their ability to adjust body posture, skin texture, and colouring makes this subject worthy of research consideration.  Photograph courtesy Kevin Lee, Fullerton, California diverKevin.






An unidentified octopus, possibly O.
, appears to be mimicking
the worm tubes that it is perched amongst.
Alternatively, it may be attacking one of the
worms pulled down in its parchment tube 1X

Research study 4

Detailed studies of colours and patterning in Octopus bimaculoides in southern California disclose 8 general colour patterns.  These are:

Photograph of O. bimaculoides courtesy Roger Hanlon, Woods Hole Marine Biological Laboratory, Woods Hole, Massachusetts.1 & 2. UNIFORM LIGHT & GENERAL MOTTLED:  these common or "chronic" patterns are used for concealment and persist for a long time.  In comparison, the next 6 “acute” patterns last only seconds or minutes, and are used for localised encounters involving sex, aggression, and the like.
4. DISRUPTIVE: in hatchlings the body is divided into dark halves separated by a longitudinal whiteish central stripe.  Variations of pattern are used for concealment.
5. DEIMATIC ("god-like" L.): a mottled pattern accompanied by well-defined ocelli.
6. FLAMBOYANT: an uncommon behaviour seen in small swimming individuals; accompanied by raised skin papillae.
7. PASSING CLOUD: waves of chromatophore expansions radiating from arm bases to tips; seen in young animals. Forsythe & Hanlon 1988 Malacologia 29: 41.

Rapidly moving O. bimaculoides displaying No. 1 colour pattern


Other than general pattern disruption and camouflage, the function of colour patterns in O. bimaculoides and octopuses, in general, are not well understood. In addition, in adult O. bimaculoides there are 2 or more prominent white spots on the mantle, and 2 prominent eyespots or ocelli symmetrically placed on the upper arm web.  The spots are usually brilliant blue on a variable background, but colours vary depending upon age and behaviour. Their function is unknown, but could be defensive, social, or perhaps something else. The subject would certainly make a nice research topic for someone. Photograph of O. bimaculoides above and the eyspots below courtesy Roger Hanlon, Woods Hole Marine Biological Laboratory, Woods Hole, Massachusetts.

NOTE  the brilliant colour is created by blue wavelengths scattering from fine granules of purine contained within cells positioned above a layer of black chromosomes (melanophores).  The octopus apparently can regulate the colour and conspicuousness of the blue ring by varying the expansion or contraction of pigment within the melanophores.  Parker 2000 J Opt A: Pure Appl Opt 2 (6): R15

NOTE the obvious function, that of mimicking an eye, is hard to reconcile. In tropical fishes, purported defensive eyespots are located towards the tail, thus potentially deflecting attacks of predators to that part of the body and leading to ready escape by fast swimming in a forwards direction. The eyespots in O. bimaculoides are located below and just to the front of the head region. Could the spots in this case be functioning for warning?

photograph showing close view of the eyespot of Octopus bimaculoides photograph showing close view of the eyespot of Octopus bimaculoides <empty>photograph showing close view of the eyespot of Octopus bimaculoides photograph of 4-eye butterflyfish Chaetodon capistratus showing eyespot photograph of juvenile rock beauty Holocanthus tricolor showing eyespot
Eyespot coloration in juvenile O. bimaculoides Eyespot coloration in a dark-coloured adult Eyespot coloration in a light-coloured adult Eyespot location in a 4-eye butterflyfish. Note also the vertical eyebar 0.5X Eyespot location in a juvenile rock beauty Holocanthus tricolor. Note blue eyebar 1X
photograph of a stranded and moribund Humboldt squid Dosidicus gigas exhibiting chromatophore changes taken from a video

CLICK HERE to see a video of chromatophore activity in a Humboldt squid Dosidicus gigas. This individual has been stranded on the beach for several hours and is nearly dead. What you see is a rapid flickering as chromatophores in the mantle skin expand and contract.

NOTE the video replays automatically

  Research study 5

images of chromatophore expansion in Octopus bimaculoidesWhat controls pattern camouflaging in octopuses and other cephalopods?  The simplest explanation is that the eyes collect information about colour and pattern in the environment and communicate this information via direct motor neurons to individual chromatophores.  However, based on past reports that chromatophores in isolated skin samples of both octopuses and squids react to light being shined on them, researchers at the University of California, Santa Barbara thought there must be more to it.  Indeed, exposure of isolated skin tissue from octopuses Octopus bimaculoides to different wavelengths of light elicits variable degrees of chromatophore expansion (see photographs on Left), with greatest responses to blue wavelengths (480nm).  This wavelength closely matches the known spectral sensitivity of opsin found in octopus eyes, and analyses of the skin by the authors indicate expression of these same opsins in sensory neurons in the skin (see photo series on Right).  While the investigations are still preliminary, the authors’ work suggests that octopus skin is intrinsically light sensitive, and may operate outside of the eyes and central nervous system to control colour expression and patterning. Ramirez et al. 2015 J Exp Biol 218: 1513. Photograph of hatchling courtesy Markos Alexandrou.

photographs of fluorescing ciliary bundles associated with sensory nerves in the skin of Octopus bimaculoidesNOTE  opsins are light-sensitive proteins found in photoreceptor cells of the retina that convert light photons into electrochemical signals that fire off sensory nerves.  In vertebrates with colour vision, there are 4 main types of opsins: rhodopsin or “visual purple” expressed in rod cells for night vision (maximally sensitive to green/blue light), “red” opsin (560nm), “green” opsin (530nm), and “blue” opsin (430nm).  Cephalopods lack colour vision and appear to have only one type of opsin that absorbs maximally in the blue region of the light spectrum at 480nm.  This wavelength is one that transmits well through seawater

Hatchling Octopus bimaculoides with a line of fluorescing
sensory neurons in the head region (see vertical array).  The
fluorescence originates from opsins expressed along
the lengths of ciliary bundles that extend from the
neuronal cell bodies out onto the skin surface (see inset)


Textural camouflaging

Research study 6

diagram showing different musculatures involved in papilla raising and retracting in octopuses Octopus bimaculoidesA nice study on the comparative morphology of skin papillae is provided by a consortium of east-coast researchers who use ordinary and scanning microscopy to determine mode of operation of papillae in several species of cuttlefish and photographs of octopuses Octopus bimaculoides comparing smooth and papillate skin conditionsoctopus, including the west-coast Octopus bimaculoides. Papillae in most species, including the last, are hydrostatic organs and use 2 sets of muscles for extension, and a third set for retraction. The first 2 are circular erector muscles arranged concentrically to raise the papilla and horizontal erector muscles differentially pulling inwards to determine its shape (see diagram). The third set, or retractors, pull the papilla down and stretch out its base to flatten it. Mucopolysaccharide-rich connective tissue packed around the muscular core provides the structural support, yet is deformed easily by the various muscles. Elasticity of collagen fibres in the deeper regions provide passive retractive power when the erector muscles relax. Although function is not discussed specifically by the authors in this mainly morphological treatise, the presence of reflective elements (iridophores and leucophores) in the papillae just beneath the chromatophore layer of the skin suggests a signalling role in addition to a camouflaging one. Allen et al. 2014 J Morph 275: 371.

NOTE “papilla” or “papula”? While both have been used to describe the epithelial bumps and extensions on octopuses and cuttlefishes, most cephalopodologists seem to prefer the former

Smooth and papillate skin states of Octopus bimaculoides. Arm
papillae in this species are small, simple, and conical; mantle
papillae may be small or large in size; dorsal eye papillae have
more complex musculature and are capable of greater distortio

cross-section of skin papilla of Octopus bimaculoides showing structure
cross-section of complex papilla type of octopus Octopus bimaculoides

Partially raised papilla showing epidermis and dermal erector muscles embedded within connective tissue

Erect complex type of papilla showing chromatophores beneath the epidermis and elastic collagen-connective tissue forming body of papilla