Fascinating Creatures of the World - Squids
Where do squids come from?
From the past to the present, squids have evolved into a complex organism capable of living in a variety of environments. Although there are three hundred known species of squid in the world today, each species contains similar structures and organs that help it survive and reproduce (information).
Squids belong to the phylum mollusca, which includes:
- many others
Whereas these other creatures evolved to different classes like gastropoda for snails and bivalvia for clams, squids and octopi are part of the class cephalopoda. The prefix cephalo means "head" and the suffix poda means "foot", but these organisms do not have feet at all.
How do Squids Move?
Instead of using a foot like their relatives, squids move by jet propulsion via their long, powerful tentacles. Let's explore this more closely:
- Water is taken in as the mantle, which is everything visible behind the head, opens. The outer body wall and all fins, head, etc are part of the mantle.
- As it closes, water is expelled through the siphon, which is a nozzle like structure right below the eyes. The squid can swim in any direction by bending the siphon, but it usually swims backwards (Animal Planet). Some squid can propel themselves up to twenty-five body lengths per second, which helps it stay away from predators or attack and capture its prey.
- The expulsion of water propels the squid in the direction it desires.
What and How do Squids Eat?
Speaking of prey, what common foods might be tasty and exciting for the squid?
Most squids tend to feed on small fish, crabs, and shrimp. Sometimes when food is scarce, squids will eat other squids that are smaller or weaker than them, but this is not very common. However, squid cannibalism is not unheard of in the event of a food shortage.
Using a small beak that serves the same function as a mouth, squid can easily pierce their prey and shred it into small pieces that are easier to digest. They initially capture their prey using their tentacles. These long tentacles have small circular rings that hold the prey still and capture them using suction so the squid's meal cannot escape.
What were to happen to a population of squid if a species or predator were to be introduced?
Today's squid are a primary meal for predators like sharks (blue shark), but what would happen to squids if a new predator - one that relied on speed and eyesight - were to inhabit a squid's environment? Natural selection would take its course, where some squid with certain traits would be more likely to survive than others, but what traits would be valuable in these circumstances?
Say that a species of squid inhabits a shallow, rocky portion of the ocean. A lot of sunlight comes through the water, making the squid rely on the plants and rocks for protection against predators that live out in the open water. Originally this species of squid range from a muddy brown color to a cool grey, with the rocks it lives next to also a cool grey. These squid are naturally brown to grey, and the rocks it lives near are also grey.
What new predator would shape the future evolution of squids?
The predator is a new species of shark that are not native to this area. The shark can easily see squid that cannot blend in with their environment, therefore...
- They are more likely to attack the brown squids instead of the grey ones.
- Over time, the grey squids become a large majority because of the lack of the brown gene present in this species due to predation.
- Grey squids have a better sense of camouflage by making it more difficult for the sharks to see them against their environment.
- This species would likely become more grey over a long period of time.
Could size be an advantage or disadvantage?
Smaller squids could also have an advantage over larger squids.
Squids with long tentacles could be easier to capture than squids with short tentacles.
However, short tentacles make it more difficult for a squid to capture its prey. If the squids have a stable food source or something easy to capture, then shorter tentacles would have an advantage. If the squid were easily preyed upon and had trouble finding food, then the species would likely not survive in the shallow, rocky area unless it could fit in the rocks to hide from the sharks.
What about beaks?
Squids already have sharp beaks that capture and shred prey, but what would happen when a squid must change from a primarily offensive to a primarily defensive organism? Squids with larger beaks would have a higher chance of survival because larger beaks can do more damage to prey and predators. If the size is not a factor, then a squid with a serrated beak or a sharper one would outlive a squid with a smaller, ordinary beak. These squid would survive and reproduce, allowing more squid with well equipped beaks into the population.