Sepioteuthis sepioidea

Geographic Range

Sepioteuthis sepioidea lives in the ocean waters of Flordia and Bermuda through the West Indian islands and from Venezuela to Cozumel along the Caribbean shores of Central America and the northeast of South America. It lives in waters that are relatively clear and shallow to approximately 100 meters, with average salinity. It finds success and dominance in many localized areas of its range. (Moynihan and Rodaniche 1982)


The habitat of S. sepiodea changes according to the squid's stage of life and size. For ease of understanding, they will be divided into four size categories to help explain habitat preferences: very small (newly hatched), small, nonbreeding large, and large (breeding adult). The new hatchlings tend to reside in a very narrow range close to or between islands. Their habitat primarily includes areas from 0.2-1.0m below the surface on or under vegetation and 1-10m from the ocean bottom. These smallest individuals are found primarily during the day.

The small squid typically congregate in shallow turtle grass near islands and remain several centimeters to two meters from the surface to avoid bird predators. They also do not dwell on the ocean floor because of possible snapper predation. At night however, they often will swim to deeper waters and hunt with older, larger squid.

Nonbreeding adult S. sepioidea avoid the turtle grass flats of their younger years because of insufficient room to maneuver in these shallow waters. Most of the waters in the San Blas are home for these, including all varieties of ocean bottoms. They venture to depths of 100m and prefer open waters at night opposed to their shoreline home of their days.

Breeding and courting adults spend their days upon coral reefs of 1.5-8m depths. These large squid avoid all or most other habitats during this period. (Moynihan and Rodaniche, 1982)

Physical Description

The youngest individuals are semiplanktonic and swim rather passively due to their small, short fins. Their dorsal mantle is typically 8-9mm in length when they emerge from their eggs.

Adults of the species Sepioteuthis sepioidea resemble their close relative, the cuttlefish. They are less elongated, streamlined, and arrow-shaped than many other squids. Their triangular fins extend nearly the entire length of the body, which is a wide flattened viseral mass. Adult females' dorsal mantles reach lengths of at least 120 mm and males' reach at least 114 mm.

Their coloring is typically finely mottled, medium brown on the dorsal side and clear, light brown, or whitish on the ventral side. A distinct white line runs longitudinally on the dorsal side. Prominent brow ridges are above their large eyes. At night, individuals appear to be completely colorless because their pigment cells do not expand. It is not certain if this change in color at night has any significant purpose. (Moynihan and Rodaniche 1982)


The mating rituals of S. sepioidea are ambiguous and complex. Large adults typically form pairs of one female and one male before they disengage from the squid school to head for the reefs to mate. Most cephalopods, including the Caribbean reef squid, are semelparous; that is, individuals die after reproducing for the first and only time. Females lay eggs in clutches and die immediately after. However, males can copulate many times in a concentrated short period of time before they die. Females lay the eggs in well protected areas, scatterering them within the reefs, but do not care for the young in any direct way. It is advantageous for the male partner to escort the egg-bearing female to the reef in order for him to protect his investment from large carnivorous fish. (Hanlon and Messenger 1996)


Sepioteuthis sepioidea are gregarious, social creatures who use diverse signals to interact amongst one another. Individuals have to swim constantly to avoid sinking but not rapidly since they have long broad fins. They have many behaviors which are either ritualistic or loosely performed.

To express alarm, their brow ridges will turn a remarkable shade of gold and the central arms turn pale white. This is a common reaction to the approach of large, non-aggressive fish. Paling of the entire body to an opaque tone often accompanies the squids' retreats from predators. Under the strongest of alarm situations, S. sepioidea will eject a blob of ink to distract predators when they are in open water. This, and a practice of rapidly flashing false eyespots on their rear quarters, is common among many cephalopoda species. When adults are near a substrate and feel alarmed, their entire body may also turn chocolate-brown or red, and their white stripe will disappear as they retreat. This coloration is also common while they are at rest during the day. Bars characterized by transverse, dark stripes across the mantle or body are common when these squid are seen under ships at night. The maximum number of bars seems to be four and are accompanied by dark smudges or marks. The bars cause them to look more like vegetation and are therefore more common in the younger squid floating higher in the water column.

Numerous postures are also a distinctive quality of Sepioteuthis sepioidea. These include upward pointing preceeding a strike on a fish of prey, upward curls during territorial disputes and under hostile situations, head-down postures (a counterpart of upward pointing) when approached by a predator in open water, and V-shaped arms (arms are in one bundle during normal swimming) performed most by young individuals to mislead predators.

(Gilbert, et al 1990, Moynihan and Rodaniche 1982)

Food Habits

The diet primarily inculdes fishes (most of which are schooling sardines) and arthropods (usually shrimp floating near the surface at night). Squid eat on fish proportional to their own size. Very few fish larger than 12 cm are ever eaten; most are only a few centimeters in length. Presumably, S. sepioidea eat many planktonic animals that have not been recorded because they cannot be seen with the human eye. No available list of their prey is all inclusive since feeding patterns are derived entirely from observations made in the field.

S. sepioidea track food entirely by sight, which limits their feeding. They use body color changes to express emotion as well as to confuse or distract potential prey. Their tentacles remain hidden except during strikes when they extend the tentacles to bend upward and produce a hooklike effect.

It is not known upon what the semiplanktonic, newly-hatched squid feed. (Moynihan and Rodaniche 1982)

Economic Importance for Humans: Positive

All types of squid, including the species S. sepioidea, are particularly important to humans as a food source. Squid have little other significant economic importance for humans. (New 1995)

Economic Importance for Humans: Negative

Sepioteuthis sepioidea does not compete with humans for food or for habitat and consequently do not affect humans negatively in any respect. (New 1995)

Conservation Status

Other 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. Sepioteuthis sepioidea is among the species being studied. (Hanlon and Messenger 1996, New 1995)


Stephanie Ritter (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.


Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

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bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


the nearshore aquatic habitats near a coast, or shoreline.


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature


union of egg and spermatozoan

internal fertilization

fertilization takes place within the female's body

native range

the area in which the animal is naturally found, the region in which it is endemic.


reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.


An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).


structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season


offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.


reproduction that includes combining the genetic contribution of two individuals, a male and a female


Gilbert, D., W. Adelman, J. Arnold. 1990. Squid as Experimental Animals. New York and London: Plenum Press.

Hanlon, R., J. Messenger. 1996. Cephalopod Behaviour. New York: Cambridge University.

Moynihan, M., A. Rodaniche. 1982. The Behavior and Natural History of the Caribbean Reef Squid. Berlin and Hamburg: Verlag Paul Parey.

New, T. 1995. An Introduction to Invertebrate Conservation Biology. Oxford: Oxford University.