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Table of Contents
Marine cephalopods, squids in the superorder Decapodiformes, are distinguished for their elongated bodies, large eyes, eight arms, and two tentacles. Not only do they play an important role in the marine food chains, but squids also serve as a well-known source of food for humans.
See the fact file below for more information on the squids or alternatively, you can download our 22-page Squid worksheet pack to utilise within the classroom or home environment.
Key Facts & Information
TAXONOMY AND PHYLOGENY
- Squids are classified under the class Cephalopoda and subclass Coleoidea. Their orders Myopsida and Oegopsida are categorized in the superorder Decapodiformes, a Greek word for “ten-legged.”
- They are also under the order Teuthida, and two other orders of decapodiform cephalopods are also labelled squid, although they are taxonomically different from Teuthida and are recognized in their gross anatomical features. These include the bobtail squid of order Sephiolida and the ram’s horn squid of the single species order Spirulida.
- The vampire squid is more associated to the octopuses than to any of the squid species, and is classified in its own order, Vampryromorphida, in the superorder Octopodiformes.
- Squid are soft-bodied molluscs whose anatomy evolved to adjust and conform to an active predatory way of life. The head and foot of the squid are at one end of a slender body, and this endpoint is functionally anterior, guiding the shrimp as it travels through the water. A set of eight arms and two unique tentacles enclose the mouth; each appendage adapts the form of a muscular hydrostat and is versatile and prehensile, usually housing disc-like suckers.
- The suckers may lie straight on the arm or be stalked. Their rims are stabilized with chitin and may hold small, toothlike denticles. These traits, together with its strong musculature, and a small ganglion below each sucker to permit individual control, allow a very powerful adhesion to hold the prey. Hooks can also be seen on the arms and tentacles in some squid species, but their function is still unknown. The two tentacles are longer than the arms and are more retractile. Suckers are defined to the spatulate tip of the tentacle, called the manus.
- In an adult male, the external half of one of the left arms is hectocotylised, where it stores and transfers spermatophores to the female, and ends in a copulatory pad instead of suckers. A ventral region of the foot has also been turned into a funnel through which water leaves the mantle cavity.
- The main body mass is placed within the mantle, which has a swimming fin along each side, although these are not the primary source of movement in most species.
- The mantle wall is muscular and internal, and the visceral mass, which is surrounded by a thin, membranous epidermis, creates a cone-shaped posterior region called the “visceral hump.” The mollusc shell is decreased in size to an internal, longitudinal chitinous “pen” in the functionally dorsal area of the squid; the pen stiffens the animal and adds attachments for muscles.
- On the functionally ventral region of the squid’s body lies an opening to the mantle cavity, which houses the gills and openings from the excretory, digestive, and reproductive systems. An inhalant siphon at the back of the funnel lets water enter into the mantle cavity through a valve. The squid makes use of the funnel for movement through precise jet propulsion, where water is sucked into the mantle cavity and released out of the funnel in a fast, strong jet. The direction of movement depends on the orientation of the funnel.
- Squid apply a number of camouflage techniques, such as active camouflage for background matching in shallow water and counter-illumination. This protects them from their predators and lets them get close to their prey.
- The skin is coated in controllable chromatophores of various colors, allowing the squid to match its coloration to its location. The play of colors may also distract the prey as the squid’s tentacles approach it. Their skin also has light reflectors called iridophores and leucophores that, when triggered, in milliseconds form changeable skin patterns of polarized light. These skin camouflage acts as a mechanism for communication with nearby squid, prey detection, navigation, and orientation during looking for prey or finding shelter.
- Some mesopelagic squid, like the firefly squid (Watasenia scintillans) and the midwater squid (Abralia veranyi) practice counter-illumination camouflage, producing light to match the downwelling light reflected from the ocean surface, creating the effect of countershading, which makes the underside lighter than the upper side.
- Squid distract approaching predators by releasing a cloud of ink, giving themselves a chance to escape. The ink gland and its related ink sac empties into the rectum near the anus, letting the squid quickly eject black ink into the mantle cavity and surrounding water.
- The ink is a suspension of melanin particles and abruptly discharges to create a dark cloud that conceals the escape plan of the squid. Predatory fish may also be scared off by the alkaloid nature of the ink which may intervene with their chemoreceptors.
- They can also move in a number of ways. Slow locomotion happens when a gentle upward or downward movement of the muscular lateral fins on either side of the trunk which directs the squid forward. A more basic means of locomotion supplying maintained movement is done by jetting, during which contraction of the muscular wall of the mantle cavity produces jet propulsion.
- Fast jetting, on the other hand, is used for escape. Radial and circular muscles are involved, resulting in a hyper-inflated mantle cavity with a larger volume of water compared to slow jetting.
- Although a squid can attack a large prey, their mouth is quite small, and the food must be broken down into pieces by the chitinous beak with its powerful muscles prior to being eaten. Their diet consists of large zooplankton and small nekton, krill, amphipods, small crustaceans, and large arrow worms. Fish are also occasionally eaten, and some squid are cannibalistic.
- Squid are carnivores, with the help of their strong tentacles and suckers. Their prey is distinguished by sight or touch, grabbed by their arms which can be done with extreme rapidity, brought back to within the reach of the tentacles, and grasped by the hooks and suckers on their surface. In some species, their saliva has toxins which can subdue the prey. These are implanted into its bloodstream when the prey is bitten, together with vasodilators and chemicals to pump the heart, and instantly circulate to all parts of its body.
- They are also one of the most intelligent invertebrates. For instance, groups of Humboldt squid forage cooperatively, spiralling up through the water at night and harmonizing their vertical and horizontal movements while searching for food.
- Giant squid has been widely known as a monster of the deep since the classical era. They were initially mentioned by Aristotle in his History of Animals and Pliny the Elder in his Natural History.
- Squid create a major food resource and are used in cuisines around the world. In Japan, they are eaten as Ika Sōmen, sliced into vermicelli-like strips, as sashimi, and as tempura.
- In Western countries, squid as food is sometimes called calamari, adopted from Italian into English in the 17th century.
This is a fantastic bundle which includes everything you need to know about the squids across 22 in-depth pages. These are ready-to-use Squid worksheets that are perfect for teaching students about the squids which are, in the superorder Decapodiformes, distinguished for their elongated bodies, large eyes, eight arms, and two tentacles. Not only do they play an important role in the marine food chains, but squids also serve as a well-known source of food for humans.
Complete List Of Included Worksheets
- Squid Facts
- Getting to Know a Squid
- Squid Anatomy
- Two Cephalopods
- Squid Recipe
- Other Members
- The More You Know
- Squid Wiki
- Tale of the Giant Squid
- Fill in the Jar
- Squids All Over the World
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Link will appear as Squid Facts & Worksheets: https://kidskonnect.com - KidsKonnect, January 3, 2021
Use With Any Curriculum
These worksheets have been specifically designed for use with any international curriculum. You can use these worksheets as-is, or edit them using Google Slides to make them more specific to your own student ability levels and curriculum standards.