12. Feb, 2016

The amazing cuttlefish

 Body plan of a cuttlefish

1: gonad; 2: stomach; 3: shell (cuttlebone); 4: mantle; 5: eye; 6a: long tentacles; 6b: short tentacles; 7: heart; 8: kidney; 9: mantle cavity (pallial cavity); 10: ink gland; 11: anus; 12: funnel (siphon); 13: radula; 14: beak; B: internal shell (cuttlebone). ***

Cuttlefish are considered to be highly intelligent invertebrates.  With the squid, octopus and nautilus they belong to class of cephalopods (derived from the Greek κεφαλόποδα  meaning head-footers) 1).  They are not fish but molluscs with large, W-shaped pupils. Most cuttlefish are around 10-20 cm, but some species like Sepia Apama become  much larger like 50 cm-1 meter (not be confused with the larger squids  that can grow to 5 meters).* Cuttlefish are amazingly versatile creatures that can change appearance at will  from mimicking floating vegetation or rocks on the seafloor to its own shape or a member of the opposite  sex (see also  https://www.youtube.com/watch?v=L-cxg8mF_Lw).

Just like  the octopus, the cuttlefish is equipped with eight arms and an ink sac. The ink  is most often used  as a ‘smoke screen’.  But some species can use the ink to  produce "pseudomorphs":  black shapes that have roughly the size and form of the cuttlefish. Cuttlefish have excellent (back-white) vision and they ‘hear’ with their lateral line, like many fishes do. Surprisingly, cuttlefish  also have a  beak  that looks like a parrot's beak and that can be used to bite its enemy or prey.  

The eight arms of  the cuttlefish are mainly used to grasp  its prey after it has captured it with its two elongated tentacles, that  shoot rapidly from a pocket at the base of the arms to grab the prey.**  To jet away from a predator  the cuttlefish sucks water into the cavity of its mantle  and then uses its strong mantle muscles to expel the liquid with great force, driving the cuttlefish in the opposite direction. Its fins, looking like short fluttering skirts are used for mobility in all directions, up and down forward and backward.  

The  cuttlebone  is an unique internal shell with an interesting construction. The shell has both gas-filled forward chambers and water-filled rear chambers. The porous shell serves to control its buoyancy, although it can take hours for the cuttlefish to change its density. The cuttlebone is rich in calcium and is often sold in pet stores as a nutritional supplement for birds.

During mating the male grabs the females tentacles, turns her so that  they are face to face. He then uses a specialized arm to insert sperm (called  spermatophores) into an opening in a sac near the female's mouth. When the  female has found a safe place to put her eggs, she also empties the sac with the spermatophores.  She then uses her arms to wipe the stored spermatophores over the eggs. The male must often fight off male rivals  before he can consider the female as his ‘own’.  But he also can use camouflage and disguise himself as a female cuttlefish, either to approach a female or to fool a larger competitive male**

Probably the most fascinating quality of the  cuttlefish is its ability to change colour. The reason why they are often called chameleons of the sea*.  It has in its skin around 200 chromatophores per square millimeter: elastic sacs containing different pigments  like  red, yellow, brown, and black. Bands of muscles radiate from each chromatophore and are controlled by neurons in the motor centres in the brain. The muscles can also be used to change the texture of the skin (e.g.  from smooth to rough). When seeking for a mate, a male cuttlefish will  sometime show contrasting zebra displays. Colour patterns are also used to communicate with another, to warn  of potential predators and competitors and as camouflage. Swimming  in groups  cuttlefish often change colours in rapid succession, perhaps as a way to communicate with other members of the group.

1) Cuttlefish beong to the order of Sepiida.  Squids belongto a different order of cephalopods caled Teuthida.  Squid as food is also kown as calamare. Squid are found abundantly in certain areas, and provide large catches  for fisheries. The often grow larger than cuttlefish

Sources:

*https://en.wikipedia.org/wiki/Cuttlefish

**http://www.pbs.org/wgbh/nova/camo/anat-nf.html

*** http://vetnetwork.net/ext_clients/chastain/pca.php?article_id=521