Sepioteuthis sepioidea
Reef Squid [+]

Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Order: Teuthida
Family: Loliginidae
Genus: Sepioteuthis
species: sepioidea
+ITIS +WoRMS

Description & Behavior

Squid are abundant in all oceans of the world. Approximately 40 species are known to live along the west coast of North America alone. A few live in shallow water close to shore, but most live in the open ocean far from land, often at great depths.

Squids are mollusks: they are closely related to the cuttlefish and octopus and more distantly to the snails, clams, oysters, and sea slugs.

The reef squid, Sepioteuthis sepioidea (Blainville, 1823), aka Caribbean reef squid, are members of the 10 arm cephalopods (decabrachia) with torpedo-shaped bodies (with the hood-like part above the head called the mantle which contains the stomach, gills, ink sac, pen, reproductive organs, and digestive organs), two large complex eyes, 8 short arms near the mouth and 2 longer tentacles, tucked inside, armed with suckers to capture prey. Their fins extend nearly the entire length of the body and undulate rapidly as they swim. All 10 appendages of the squid are "fixed to its head", and are arranged in a circle around the mouth.

The Caribbean reef squid is one our favorite cephalopods. It is often encountered among shallow reefs and is usually unafraid of divers, if not curious about them. The mantles of newly hatched squid are about 8-9 mm in length and the mantles in adult males and females reach 12-20 cm in length. Adult reef squid closely resemble their cousins, the cuttlefish, in that their bodies are broad and less streamlined than many other squids. Reef squid can also move using jet propulsion by pressing water from the pallial cavity (in the mantle) through their funnel to move through the water.

The basic coloring of a Caribbean reef squid is a mottled medium green to brown on the dorsal side with lighter coloring on the ventral side for camouflage from predators swimming below. These animals are social creatures often found in small groups that communicate through a variety of complex signals. Both cuttlefish and squid communicate by controlling the pigment in their skin. Messages such as readiness to mate, sexual identification, and alarm are flashed through various colorful spots, blotches, and background color. To signal slight alarm, their brow ridges turn bright gold and the central arms turn white. The entire body will pale if the squid retreats from its potential predator and in open water when faced with an extremely aggressive predator, reef squid will obstruct themselves and confuse the predator by ejecting a cloud of black ink. Retreating squid near the protection of the reef will often turn dark brown or reddish in color to match their surroundings.

In addition to their colorful signaling behavior, S. sepioidea display unique behaviors such as pointing their bodies upward prior to striking a fish or prey, curling upward during territorial disputes and in hostile situations, and pointing head-down when approached by a predator in open water. The main adult squid predators include the yellowfin grouper as well as other large predatory fishes.

Compared to the overall body, squid's eyes are strikingly large. The have the largest eye to body ratio in the entire animal kingdom.

World Range & Habitat

Found throughout the Caribbean sea as well as off the coast of Florida, commonly in small schools (4-30) in the shallows associated with reefs. The habitat of reef squid changes according to the squid's stage of life and size. New hatchlings tend to reside close to the shore in areas from 0.2-1 m below the surface on or under vegetation. Young small squid typically congregate in shallow turtle grass near islands and remain several centimeters to two meters from the surface to avoid bird predators. Adult reef squid venture out into open water and can be found in depths up to 100 m. When mating, adults are found near coral reefs in depths of 1.5-8 m.

» GBIF occurrence data in Google Earth [Tips] | Ocean Biogeographic Information System (OBIS) (World Distribution) [about]

Feeding Behavior (Ecology)

Squid are voracious eaters typically consuming 30-60% of their body weight daily. Prey is caught using the club-like end of the long tentacles which are then pulled towards the mouth supported by the shorter arms. Like other cephalopods, they have a strong beak used to cut the prey into parts so that the raspy tongue, or radula, can be used to further process the food. They consume small fish, other mollusks and crustaceans.

Life History

The mating rituals of S. sepioidea are ambiguous and complex. Like other cephalopods, Caribbean reef squid, are semelparous; that is, they die after reproducing. Females lay their eggs then die immediately after. The males, however, can fertilize many females in a short period of time before they die. Females lay the eggs in well-protected areas scattered around the reefs. After competing with 2-5 other males, the largest male approaches the female and gently strokes her with his tentacles. At first she may indicate her alarm by flashing a distinct pattern, but the male soon calms her by blowing water at her and jetting gently away. He returns repeatedly until the female accepts him, however the pair may continue this dance or courting for up to an hour. The male then attaches a sticky packet of sperm to the female's body.

Reef squid, Sepioteuthis sepioidea

Caribbean reef squid

As he reaches out with the sperm packet, he displays a pulsating pattern. The female places the packet in her seminal receptacle, finds appropriate places to lay her eggs in small clusters, and then dies having completed her role in evolution.

Conservation Status/Additional Comments

Scientists are studying cephalopods' large brains, elaborate sense organs, and complex behavior in order to understand more about learning and behavior patterns in all species. S. sepioidea is among the species being studied.

"Before my eyes was a horrible monster, worthy to figure in the legends of the marvelous. It was an immense cuttle-fish, being eight yards long. It swam cross-ways in the direction of the Nautilus with great speed, watching us with its enormous staring green eyes. Its eight arms, or rather feet, fixed to its head, that have given the name of cephalopod to these animals, were twice as long as its body, and were twisted like the furies' hair.... The monster's mouth, a horned beak like a parrot's, opened and shut vertically.... What a freak of nature, a bird's beak on a mollusk! Its spindle-like body formed a fleshy mass that might weigh 4,000 to 5,000 lbs.; the varying color changing with great rapidity, according to the irritation of the animal, passed successively from livid gray to reddish brown." - Jules Verne, Twenty Thousand Leagues Under the Sea (1870)