The Squid

Jul 27, 2008 Features / Columnists, Interesting Creatures in Guyana

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Squids can be described as a large, diverse group of marine creatures called cephalopods. It is said that all cephalopods and specifically squids are distinguished by having a distinct head, bilateral symmetry, a mantle and arms.

These creatures, which have a close resemblance to the octopus or cuttlefish, have eight arms and two tentacles that are arranged in pairs.

Reports are that the main body mass of the squid is enclosed in the mantle which has a swimming fin along each side.

It should also be noted that these fins, unlike in other marine organisms, are not the main source of ambulation in most species.

Reports are that the skin of the squid is covered in chromatophores, which enables it to change colour to suit its surrounding.

Their underside is also reportedly found to be lighter than the topside in order to provide camouflage from both prey and predator.

Researchers have also deduced that the under body of the squid has openings to their mantle cavity which contains the gills and openings to the excretory and reproductive systems.

At the front of the mantle cavity lies the siphon which the squid uses for locomotion via precise jet propulsion.

The majority of squids are no more than 60 centimetres long although the giant squid may reach 13 metres in length.

A part of the squid called the giant axon can grow to about one millimetre in diameter, and is able to control part of the jet propulsion system.

According to reports, this is done by sucking water into the mantle cavity and quickly expelling it out of the siphon in a fast, strong jet-like motion. The direction of the siphon can be changed in order to suit the route of travel.

It must be noted that inside the mantle cavity, beyond the siphon, lies the visceral mass of the squid which is covered by a thin membranous epidermis under which all the major internal organs can be found.

Researchers have found that with their intriguing designs squids have differentiated from their ancestral molluscs in such a way that their body plan has been condensed and extended into a complex set of tentacles and highly developed sense organs, including advanced eyes similar to those of vertebrates.

A squid’s tentacles do not grow back if severed. In mature male squid, one basal half of the left ventral tentacle is hectocotylised and ends in a copulatory pad rather than suckers. It is used for intercourse between mature males and females.

The mouth of the squid is equipped with a sharp horny beak mainly made of chitin and cross-linked proteins, and is used to kill and tear into manageable pieces.

The beak is very robust but does not contain any minerals unlike the teeth and jaws of many other organisms, including marine species.

Captured whales often have squid beaks in their stomachs, the beak being the only indigestible part of the squid. The eyes of the squid are found on either side of the head, each containing a hard lens.

The lens, according to reports, is focused by moving much like the lens of a camera or telescope rather than changing shape as the lens in the human eye does.

The female of this marine creature has an ink sac which is hidden from view by a pair of white glands called nidamental that lie anterior to the gills. They also have what are called red-spotted accessory nidamental glands.

Reports are that both of these organs are associated with the manufacture of food supplies and shells for the eggs.

Females are also said to have a large translucent ovary situated towards the posterior of the visceral mass.
Male squid on the other hand do not possess these organs but instead have a large testis in place of the ovary and a spermatophoric gland and sac.

In mature males this sac may contain spermatophores which are placed inside the mantle of the female during mating.

And squids like all cephalopods have complex digestive systems, thus their food is transported into a muscular stomach, found roughly in the midpoint of the visceral mass.

The bolus is then transported into the caecum for digestion. The caecum is a long white organ that can be found next to the ovary or testis.

In mature squids more priority is given to reproduction and so the stomach and caecum often shrivel up during the later stages of life.

An interesting fact about these intriguing creatures is that they have three hearts, two of which are used to feed the gills. These hearts surround the larger systemic heart that pumps blood around the body.

The hearts have a faint greenish appearance and are surrounded by the renal sacs – the main excretory system of the squid.

Their kidneys are faint and difficult to identify and stretch from the hearts to the liver. The systemic heart is made of three chambers, a lower ventricle and two upper auricles.

Squids possess edible meat which humans hunt regularly and eat as a delicacy. In fact, fishermen right here in Guyana frequently snare this species of marine life which locals consume with much satisfaction.

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