The Slender Inshore Squid (Doryteuthis plei), also known as the Arrow Squid, is a medium-sized squid

Squid

Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...

 belonging to the family Loliginidae

Loliginidae

Loliginidae, commonly known as pencil squids, is an aquatic family of the order Teuthida .-Species:The following classification follows Vecchione et al. and the Tree of Life Web Project .*Genus Afrololigo...

. It occurs abundantly in coastal waters of the Atlantic Ocean

Atlantic Ocean

The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

, from Argentina

Argentina

Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...

 northward to North Carolina

North Carolina

North Carolina is a state located in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north. North Carolina contains 100 counties. Its capital is Raleigh, and its largest city is Charlotte...

.

Physical description

As both common names imply, these squid have elongate, cylindrical bodies with a length to width ratio of 7:1. The arms are in contrast short and weak; the two tentacle

Tentacle

A tentacle or bothrium is one of usually two or more elongated flexible organs present in animals, especially invertebrates. The term may also refer to the hairs of the leaves of some insectivorous plants. Usually, tentacles are used for feeding, feeling and grasping. Anatomically, they work like...

s are somewhat less than the mantle

Mantle (mollusc)

The mantle is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself.In many, but by no means all, species of molluscs, the epidermis of the mantle secretes...

 length. The rhombus

Rhombus

In Euclidean geometry, a rhombus or rhomb is a convex quadrilateral whose four sides all have the same length. The rhombus is often called a diamond, after the diamonds suit in playing cards, or a lozenge, though the latter sometimes refers specifically to a rhombus with a 45° angle.Every...

-shaped fins are large, up to about 50 percent of the mantle length. Running the ventral length of the mantle is a noticeable ridge. The squid are a reddish orange colour with a large complement of chromatophore

Chromatophore

Chromatophores are pigment-containing and light-reflecting cells found in amphibians, fish, reptiles, crustaceans, and cephalopods. They are largely responsible for generating skin and eye colour in cold-blooded animals and are generated in the neural crest during embryonic development...

s.

The suckers of the arms possess blunt teeth. On the meaty ends (clubs) of the tentacles, there are four rows of suckers; the inner two (mesial) rows are three times as large as the outer two (marginal) rows. The larger suckers have horny rings with up to 45 teeth.

These squid reach a maximum mantle length of 33 centimetres in males and 22 centimetres in females. Sexual dimorphism

Sexual dimorphism

Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...

 is apparent, with the left ventral arm in males modified into a hectocotylus

Hectocotylus

A hectocotylus is one of the arms of the male of most kinds of cephalopods that is modified in various ways to effect the fertilization of the female's eggs. It is a specialized, extended muscular hydrostat used to store spermatophores, the male gametophore...

; this is used to facilitate fertilization during mating. Males also have a number of purple stripes running lengthwise on the ventral side of the mantle; along with other visual cues produced by chromatophores, these stripes are used in elaborate courtship displays.

Ecology

Due to their abundance, Slender Inshore Squid are important to both commercial and subsistence fisheries. During the annual summer mating season, the squid congregate in large numbers near shore. During the austral summer in waters off Brazil

Brazil

Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

, annual catches may reach 763 metric tonnes.

While there may be safety in their numbers, the squid are an important prey item for large fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

 such as tuna

Tuna

Tuna is a salt water fish from the family Scombridae, mostly in the genus Thunnus. Tuna are fast swimmers, and some species are capable of speeds of . Unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red coloration derives from myoglobin, an...

 and shark

Shark

Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....

s and a number of cetaceans: Pygmy Killer Whale

Pygmy Killer Whale

The pygmy killer whale is a small, rarely seen cetacean of the oceanic dolphin family . It derives its common name from sharing some physical characteristics with the orca It is the smallest species that has "whale" in its common name. In fact, "killer" may be more apt in the case of the pygmy...

s, Orca

Orca

The killer whale , commonly referred to as the orca, and less commonly as the blackfish, is a toothed whale belonging to the oceanic dolphin family. Killer whales are found in all oceans, from the frigid Arctic and Antarctic regions to tropical seas...

s, Atlantic Spotted Dolphin

Atlantic Spotted Dolphin

The Atlantic Spotted Dolphin is a dolphin found in the Gulf Stream of the North Atlantic Ocean. Older members of the species have a very distinctive spotted coloration all over their body.-Taxonomy:...

s, Rough-toothed Dolphin

Rough-toothed Dolphin

The Rough-toothed dolphin is species of dolphin that can be found in deep warm and tropical waters around the world.The species was first described by Georges Cuvier in 1823...

s, and Bottlenose Dolphin

Bottlenose Dolphin

Bottlenose dolphins, the genus Tursiops, are the most common and well-known members of the family Delphinidae, the family of oceanic dolphins. Recent molecular studies show the genus contains two species, the common bottlenose dolphin and the Indo-Pacific bottlenose dolphin , instead of one...

s are all known predators of Slender Inshore Squid. Other predators include South African and Antarctic Fur Seal

Antarctic Fur Seal

The Antarctic fur seal is one of eight seals in the genus Arctocephalus, and one of nine fur seals in the subfamily Arctocephalinae. As its name suggests, the Antarctic fur seal is distributed in Antarctic waters. Around 95% of the world population breeds at the Island of South Georgia...

s.

The squid prey upon several species of estuarine fish, including: killifish

Killifish

A killifish is any of various oviparous cyprinodontiform fish . Altogether, there are some 1270 different species of killifish, the biggest family being Rivulidae, containing more than 320 species...

, mosquitofish

Mosquitofish

The mosquitofish is a species of freshwater fish, also commonly, if ambiguously, known by its generic name, gambusia. It is sometimes called the western mosquitofish, to distinguish it from the eastern mosquitofish . It is a member of the family Poeciliidae of order Cyprinodontiformes...

 and mollies

Poecilia

Poecilia is a genus of euryhaline brackish water fish in family Poeciliidae of order Cyprinodontiformes. The type species is P. vivipara. Live-bearers, the Poecilia species are collectively known as mollies, with the exception of Endler's livebearer and the famous guppy...

. Small crustacean

Crustacean

Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...

s such as grass shrimp are also taken.