The main difference between cuttlefish and squids is that cuttlefish have internal shells called cuttlebones, while squids don’t. Cuttlefish are also generally smaller, weigh less, and live shorter lives than squids. Both animals have similar limbs, diets, and sexual and social lives. Both die after mating.
At first glance, some might not notice any differences between a squid and a cuttlefish. After all, both are cephalopods with similar body structures.
But there are many key differences between the two mollusks. Upon further investigation, we might find that the lives of cuttlefish and squids differ in many ways.
In this article, we take a look at the differences between squids and cuttlefish. Apart from these, we detail the many similarities between the two animals as well.
Cuttlefish vs. Squid: An Overview
Cuttlefish are lighter, smaller, and live shorter lives than squids. They also have an internal structure called a cuttlebone, which squids lack. Cuttlefish eggs are circular, while squid eggs are elongated. The two animals are similar in their limbs, diet, social lives, and mating habits. They both die due to senescence.
Squids and cuttlefish are both mollusks and cephalopods. It is natural that they are mistaken for each other at a first glance, as their body structures are similar. But further observations reveal how different these marine beasts are.
Cuttlefish vs. Squid: Differences
Squids are bigger than cuttlefish growing up to 43 feet, while cuttlefish are merely 3.2 feet long. Cuttlefish are also lighter, live shorter lives, and lay different types of eggs. The main difference is their internal structures. Squids have gladii, while cuttlefish have cuttlebones.
| Differences | Squids | Cuttlefish |
| Internal Structure | Have gladius | Have cuttlebone |
| Size | Up to 43 feet | Up to 3.2 feet |
| Weight | Up to 1,500 pounds | Up to 23 pounds |
| Lifespan | Between 1–3 years (rarely up to 5 years) | Between 1–2 years |
| Eggs | Elongated, up to 0.055 inches long | Circular, up to 1 inch long |
Although both animals are related, they are extremely diverse. As such, there are five key differences between squids and cuttlefish:[1]
- Internal structure
- Size
- Weight
- Lifespan
- Eggs
1. Internal Structure
Although both squids and cuttlefish present a hardened internal structure, they are different in many ways.
Squids have a sole hardened internal structure called “gladius”. It is a chitinous, long, narrow bone-like structure in the squid’s upper mantle. Gladii support squids’ bodies and maintain the mantles’ elongated shape. Another name for the gladius is “pen”, as it looks like a long plastic pen.[2]
Cuttlebones are also in the mantles, but they look different. They are composed of aragonite, a carbonate mineral. They are filled with gas and their main function is to control buoyancy. As they need to be hollow and spacious for the gas, cuttlebones aren’t narrow. Their shape resembles a sunflower seed.[3]
2. Size
Squids and cuttlefish come in all shapes and sizes, but the biggest squids are exponentially larger than the biggest cuttlefish.[4]
The longest of all squids is the giant squid. They grow to a maximum length of 43 feet. Although the brunt of their body length is made up of their tentacles, even their mantles are bigger than a whole cuttlefish.
The giant cuttlefish (the largest cuttlefish species) grows up to about 3.2 feet long. This is half the size of an average giant squid mantle (6.6 feet). For further illustration, giant cuttlefish have mantles up to 20 inches long. These are only slightly bigger than the diameter of the colossal squid’s eyes (12–16 inches in diameter).[5]
3. Weight
As with size, the upper end of a squid’s weight is far greater than the heaviest cuttlefish.
The heaviest squid species is the elusive colossal squid. Weighing at least 1,000 pounds, the largest individuals may reach an estimated 1,500 pounds of weight. In comparison, the giant cuttlefish reach a maximum of 23 pounds.[6]
Theoretically, cuttlefish can grow as big as squids. They are indeterminate growers, meaning they grow rapidly at a young age and slower after reaching adulthood. Cuttlefish’s growth is only halted by their deaths. As cuttlefish have a short lifespan, they never outgrow the largest squids.
4. Lifespan
Squids are thought to live a few years longer than cuttlefish.
Claims that there have been individuals living up to 15 years exist. Most squids live for one to three years, and scientists suggest the maximum life expectancy is about five years, but it is yet to be confirmed.
Cuttlefish have about one to two years to live. Their deaths are often caused by senescence, a common biological process in cephalopods.
5. Eggs
Here are three differences between cuttlefish eggs and squid eggs:
- Size
- Shape
- Number
Squids lay between 2,000 and 20,000 eggs. The Humboldt squids lay the most eggs, around 20 million. The eggs are extremely small, being up to 0.05 inches long. They are long, strained together, and placed in further clusters containing hundreds of eggs.
Cuttlefish lay a few hundred eggs at a time. These eggs can be an inch in diameter and are often circular. They may be transparent, but some cuttlefish lay black eggs.
Cuttlefish vs. Squid: Similarities
Cuttlefish and squids have two tentacles and eight arms. They are both carnivorous and feed on similar animals. Their social lives and mating habits are similar as well. Both animals mate once in their lives and die after.
| Similarities | Description |
| Limbs | Ten limbs (two tentacles and eight arms) |
| Diet | Carnivorous. Diet includes mollusks, crustaceans, and fish. |
| Social Lives | Mostly solitary, they may group up. |
| Mating | Mate once per life, color changing, and swimming in circles during mating. The sperm sac is transferred into the female’s mantle cavity. |
| Senescence | Death after mating is imminent and the process is irreversible. |
Apart from the many differences, there are five essential aspects that are similar in both animals:
- Limbs
- Diet
- Social life
- Mating
- Senescence
1. Limbs
Both cuttlefish and squids have ten limbs altogether. They have eight shorter arms with suckers throughout their length. The arms are wide at the base and get gradually narrower near the tip.
The two tentacles are longer and wide at the tips. Suckers are only found on the wider ends. Tentacles are used for grabbing prey, while arms are for swimming and handling prey.
2. Diet
Squids and cuttlefish are carnivorous. They both have beaks with venom in their saliva. The beaks are used for breaking open exoskeletons, while the venom is strong enough to paralyze smaller animals for a hassle-free meal.
Squids and cuttlefish eat the following animals:
- Crustaceans
- Mollusks
- Small fish
3. Social Life
As most mollusks, squids and cuttlefish are solitary. They both exhibit grouping tendencies. While cuttlefish are more social, they mostly live alone.
Generally, the two animals only meet another individual of their species when they search for a mate.
4. Mating
Elaborate courtships are exhibited by both cephalopods. Swimming in circles and color-changing are involved while courting. Cuttlefish embrace each other while mating and squids may engage in jaw-locking.
Cuttlefish and squid males have specialized “sex arms” called “hectocotylus”. They use these arms to transfer sperm sacs into females’ mantle cavities. Females may store these sacs or instantly fertilize their eggs after mating.
5. Senescence
Cephalopods go through a process called senescence. This is a life stage in which they deteriorate after mating. The process is caused by an overproduction of hormones in the optic glands (organs behind squids and cuttlefish eyes).
Senescence is irreversible. It is characterized by a lack of appetite, erratic behavior, and self-mutilation. The males are the first to perish, and the females die around the time the eggs hatch.
Conclusion
The difference between cuttlefish and squids is that cuttlefish are smaller, lighter, and live shorter lives than squids. Squids have an internal structure called gladius, while cuttlefish have cuttlebones. Cuttlefish lay fewer, more circular, and larger eggs than squids.
Both animals have the same amount and type of limbs. They eat similar animals and have similar social lives. The mating process is almost identical for both cephalopods. Cuttlefish and squids go through a process called senescence after mating.
FAQs
Cuttlefish vs. Squid: Who Would Win in a Fight?
Squids would undoubtedly win in a fight between them and cuttlefish. The largest cuttlefish are only 3.2 feet long and weigh 23 pounds, while squids can be 43 feet long and weigh 1,500 pounds. Squids are much stronger than cuttlefish.
What Is a Sepia Squid?
A Sepia squid is a misnomer for cuttlefish. Cuttlefish are taxonomically referred to as Sepiida, which derives from the Greek and Latin word sepia. They are called as such as the Greeks and Romans extracted reddish-brown color called sepia from cuttlefish.
