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How to Distinguish the Octopuses, Cuttlefishes and Squids?

    The difference among octopuses, cuttlefishes and squids in shape is first of all -- mantle. These three all belong to Cephalopoda with three parts as the whole: head, foot and body. The body part is so-called mantle which includes three shapes: ball shape (octopus), bag shape (cuttlefish), cone shape (squid). And squids we eat most in daily life, also called calamary, is a kind of Teuthida,Loliginidae Family and we can imagine their appearance as the name suggests. 

    Octopuses, cuttlefishes and squids of which body parts in below pictures are the most common fishing targets. The below pictures respectively respond to:  Octopus ochellatus & Octopus variabilis, two kinds octopuses in Octopoda; sea arrow & calamary two kinds squids in Teuthoidea of Decapodiformes and Sepia esculenta hoyle & Sepiella maindroni de Rochebrune in Sepiidae of Decapodiformes.
    The second obvious difference is arms. Octopuses have eight long arms, and that’s why they are often called “eight- arm fish”. Besides, fins are so different. Octopuses have degraded or medium-sized fins; squids have tail fins; cuttlefishes have body -around fins or medium-sized fins.

    Cuttlefishes and squids are both Decapodiformes with ten tentacles, so it is easier to distinguish them from octopuses. Ten tentacles of cuttlefishes and squids are left-right symmetrically arranged. First pair is on central back. Toward the ventral side is second to fifth pair, among which the fourth pair is much longer and its end is so expanded that is like tentacles.
    A squid has ten arms: eight with the same length and two extra long ones used in grabbing prey. These extra two arms are called tentacles. 

    What’s more, suction cups on the tentacles are also unlikely. Octopuses are characterized by their eight arms, usually bearing one or two lines of suction cups. Cuttlefishes have four lines of suction cups.
    All above are the differences in shape. However, if you have dissecting experience, you will find the inner differences. The most obvious difference between most cephalopods and other mollusks is the apparent lack of a shell. Octopuses do not have shells at all.  Almost entirely soft bodies with no internal skeleton enables them to squeeze through very narrow slits.
    In the art of camouflage, the protagonists are obviously octopuses and squids. They can use chromatophore cells (iridophore and leucophores) to change skin brightness and patterns to backgrounds.The Cephalopoda has a sensitive visual sense. In experiment, octopuses are able to identify the brightness, shape, size, and vertical & horizontal direction of the objects. But it’s very interesting that the most Cephalopoda is color blind. So far, only one type of Cephalopoda is proved to have colorful vision --- Watasenia scintillans once emerging on a large scale on Fuji seaside in Japan.
    From the way of lighting, luminous organ of Cephalopoda includes body and gland two kinds. The former is located on mantle, heads, eyes and wrists, producing radioactive complex by itself and emitting heatless light under the involvement of oxygen, magnesium ion and fluorescence enzyme while the later is located on viscus and gives light relying on bacterium in the glandular. Watasenia scintillans mentioned above is the representative of the former kind, possessing complex epidermal illuminator and eye illuminator. Several kinds of Sepiolinae have visceral illuminator.

    Although Octopuses, cuttlefishes and squids each has its own merits on disguising and shining, they are just pronouns of delicious seafood for most persons. Octopuses, cuttlefishes and squids are important fishing targets except rare Nautilus in Cephalopoda. The sharp decline of some specie resources has emerged since 1980s as the consequence of the unreasonable utilization and intensive fishing, such as the disappearance of Sepiella japonica in the fishing season. Chowhounds shall have a mercy heart to protect them when enjoying them.

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