Dive Dry with Dr. Bill

#543: The Cuddlefish... er, Cuttlefish

There were many species I looked forward to filming while in the Philippines and one was the cuddlefish... er, cuttlefish. I would have loved to have filmed the former, but all the ones I saw were previously "mated" so I was out of luck. Before this trip I only knew these mollusc relatives of the squid and octopus from the hard internal bone-like structure my great grandmother kept in her parakeet Tweetie Pie's cage as a source of calcium. The ancient Greeks and Romans used the brown ink they release when frightened as a dye.

The cuttlebone used by parakeet lovers is not a true bone but is made out of a calcium-based mineral known as aragonite. Each species has a unique shape and pattern, but I was not about the kill and dissect mine just to identify it. As an ardent conservationist, it wouldn't be prudent! I was surprised to find in my research that this cuttlebone is also used by jewelers and silversmiths to create molds for casting.

I'm no expert, but I believe the species I filmed was the broadclub cuttlefish (Sepia latimanus). Note the genus name sepia which is still used today for certain shades of brown, especially those found in old photographs. I assume no one will need a politically correct name for these molluscs since they are obviously not "fish" just as starfish and jellyfish are not finny vertebrates. This cuttlefish species is known from Indonesia to Australia and north to Japan.

Most of my readers are familiar with the ability of squid and octopuses to change color. If you are not, you haven't been paying attention! Cuttlefish are also masters at this and will change color to camouflage with their surroundings, communicate with other cuttlefish or warn off potential predators. They do so with pigment structures known as chromatophores that utilize red, yellow, brown and black pigments. There may be as many as 130,000 of these per square inch in their skin!

The chromatophores are actually sacs of different pigments that are coupled with a "large" membrane. They are controlled by sets of muscles surrounding the sac. Beneath the chromatophores are structures known as iridiphores which are made of protein and reflect blue and green light from the surrounding environment. They are also responsible for gold or silver coloration. Like a painter, the cuttlefish can mix the different chromatophores and iridiphores to create a wide palette of different colors. I'm partially color blind so I'm hopeless at painting anything but my walls. That probably also explains why I have difficulty identifying many of the species from the Philippines that I filmed.

Cuttlefish can sense their surroundings using eyes that are quite sophisticated for an invertebrate. Although they do not possess color vision, they can assess their surroundings and create a pattern that matches it in terms of contrast. Their eyes are fundamentally different from those of humans and other vertebrates... and I've never seen one wearing glasses.

Cuttlefish feed on crabs, fish and small shrimp. The hunt using their eyes and creep up on prey thanks to their camouflage. They shoot out streams of water to uncover munchies buried in the soft bottom, capture it with the sucker discs on their eight arms and two long feeding tentacles and pull it towards their beak. Like many cephalopods, their saliva contains neurotoxins produced by bacteria that paralyze the prey and allow them to easily eat it. Potential predators are defended against using the camouflage, as well as the ink which may be released to confuse them.

That covers munching, now on to mating. The boys may greatly out number the girls (sounds familiar from my nights at the Chi Chi Club). Males use threat displays to establish their dominance, but do not resort to physical contact and fisticuffs (tentacle-cuffs?) unless their competitor fails to back down. They may even use their toxic saliva to paralyze the challenger. The winner grabs a female using his tentacles and turns her so she faces him. Then a specialized tentacle is used to insert the sperm sac into an opening near her mouth.

Now despite all this combat and the rough treatment they give their ladies, don't get the idea that cuttlefish have no heart. In fact, they have three of them to pump their bluish-green, copper-based blood throughout the body. Two of them serve the gills with which the cuttlefish extracts oxygen from the water while the third serves the rest of the body. Because their blood holds less oxygen than that of animals which use red hemoglobin, cuttlefish must circulate blood more rapidly through their bodies. I guess they really get their hearts pumping just like mine will when I finally see that "cuddlefish" I've been seeking.

© 2013 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. You can also watch these episodes in iPod format on YouTube through my channel there (drbillbushing). Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

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The same broad club cuttlefish in lighter shades (top) and darker shades (bottom)

This document maintained by Dr. Bill Bushing.
Material and images © 2013 Star Thrower Educational Multimedia