Squid Dissection

Last Friday our Biology class dissected a mollusk, one that is abundant in most marine environments, and is even one of the main characters on the popular kid's show, Spongebob Squarepants. We dissected Squidward, or at least someone related to him; a fifth cousin perhaps?

A squid is a cephalopod. In Latin this means "head foot". It sounds a little strange, but the name is actually quite logical. A squid really is just a head attached to some feet! Octopi are another well known species of this phylum. The two other types of mollusks that can be seen are known as Gastropods and Bivalves. One of the most common Gastropods in existence is the garden snail. Gastropods are "stomach feet", as their stomach is literally just above their feet inside their bodies. The next species in the phylum Molluska are the Bivalves. Their name means "two shell" as they possess two shells that can be tightly closed with strong muscles. Many of our most delectable seafood items, like clams and oysters are bivalves. It is interesting to note that although these forms are radically different from each other phenotypically, they all share specially evolved shells and feet. In fact, this is how they are classified. The squid, for example, has hardly any shell externally, but has a small plastic-like tube inside of it called the pen which is what is left of the squid's shell after evolution.

The squid has a most interesting internal make-up. Its insides are quite jelly like, save for the hard pen, and its ink sac looks quite a bit like a small minnow that has not yet been digested by the squid. It has a closed circulatory system rather than an open one like the bivalves as an open system is not conducive to free swimming and active animals such as squids. They possess advanced vision and brains and will secrete an ink cloud when threatened. It is difficult to explain the various features of the squid,  and how its internal organs function. Dissecting the squid allows us a first hand look inside its body, a real life explanation of its complex inner workings. Squids are fascinating   creatures and there is so much more to them than one sees as they glance into the plastic case at the T and T supermarket, and that is why dissection is so helpful to one's understanding of internal biology.

Our squid had 8 arms and 2 tentacles.

 The squid uses arms and tentacles for different purposes. Tentacles serve to help the squid grab prey and hold on to it and also play a role in mating whereas the arms are used to aid in feeding and grasping prey once it is in close proximity to the beak. Suckers on the arms are bigger than those on the tentacles.

 Forgot to take a picture for this one. To move, the squid draws water up into its mantle cavity and then expels it through the funnel creating jet propulsion. The squid can move either forward or backward.

Our squid's eye. Its eyes and tentacles are both adaptations for its predatory life. Its light-sensitive eyes allow it to see prey even in the darkness of the depths of the ocean, and its tentacles allow it to catch prey by surprise, snatching it at high speeds from far away.

Two traits that the squid shares with other mollusks are the presence of a mantle and of a visceral mass. Although all mollusks also have a foot, it is highly specialized and evolved to each mollusk's needs and thus looks different for every species.

The squid has 2 pairs of gills, one on each side.

The ink sac empties into the siphon and out of the squid's body into the surrounding water. Its function is to allow the squid camouflage in a dangerous situation so that it can quickly swim away from a predator.

This is the pen of our squid. The function of the pen is to give the squid structural support. It is considered a vestigial structure, so the squid's functions would most likely not be impaired were it not to have a pen.

As squids do possess a full digestive system, wastes exit the squid through the anus.