Myopsida is one of the four

orders Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * H ...

squid A squid (: squid) is a mollusc with an elongated soft body, large eyes, eight cephalopod limb, arms, and two tentacles in the orders Myopsida, Oegopsida, and Bathyteuthida (though many other molluscs within the broader Neocoleoidea are also ...

. It consists of two

families Family (from ) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictability, structure, and safety as ...

: the

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...

'' Australiteuthis'' and the diverse and commercially important

Loliginidae Loliginidae, commonly known as pencil squids, is an aquatic family of squid classified in the order Myopsida. Taxonomy The family Loliginidae was formerly classified in the order Teuthida. Taxonomic list The classification below (includi ...

(~50 species). Some

taxonomist In biology, taxonomy () is the science, scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxon, taxa (si ...

s classify this taxon as a suborder of the order Teuthida, in which case it is known as Myopsina. This reclassification is due to Myopsina and Oegopsina not being demonstrated to form a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

. A number of morphological features distinguish members of Myopsida from those of its sister group, Oegopsida. Some of the most obvious differences are found in the structure of the

eyes An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...

: those of myopsid squids lack a secondary eyelid and are instead covered by a transparent corneal membrane, the opening of which is reduced to a microscopic anterior pore in most species. The arms and tentacles are ornamented with simple suckers (hooks are never present), with additional suckers usually borne on the buccal lappets. The carpal ("wrist") portion of the

tentacular club All cephalopods possess flexible limbs extending from their heads and surrounding their cephalopod beak, beaks. These appendages, which function as muscular hydrostats, have been variously termed arms, legs or tentacles. Description In ...

lacks a locking apparatus, and a tentacle pocket is present on the head. The

funnel A funnel is a tube or pipe that is wide at the top and narrow at the bottom, used for guiding liquid or powder into a small opening. Funnels are usually made of stainless steel, aluminium, glass, or plastic. The material used in its constructi ...

has no lateral adductor muscles. An internalised shell is present in the form of a well-developed

gladius ''Gladius'' () is a Latin word properly referring to the type of sword that was used by Ancient Rome, ancient Roman foot soldiers starting from the 3rd century BC and until the 3rd century AD. Linguistically, within Latin, the word also came t ...

, which is located dorsally within the mantle and extends for almost its entire length. In contrast to oegopsids, females possess accessory nidamental glands in addition to the main

nidamental gland Nidamental glands are internal organs found in some elasmobranchs and certain molluscs, including cephalopods (specifically Decapodiformes and nautiluses) and gastropod Gastropods (), commonly known as slugs and snails, belong to a large Ta ...

s. They however lack a right

oviduct The oviduct in vertebrates is the passageway from an ovary. In human females, this is more usually known as the fallopian tube. The eggs travel along the oviduct. These eggs will either be fertilized by spermatozoa to become a zygote, or will dege ...

.Jereb, P. & C.F.E. Roper (2010). Squids. In: P. Jereb & C.F.E. Roper (eds.)
Cephalopods of the world. An annotated and illustrated catalogue of species known to date. Volume 2. Myopsid and Oegopsid Squids
'. FAO Species Catalogue for Fishery Purposes No. 4, Vol. 2. FAO, Rome. pp. 34–35.Vecchione, M. & R.E. Young (2008)
Myopsida Naef, 1916

Tree of Life Web Project The Tree of Life Web Project (ToL) is an Internet project providing information about the diversity and phylogeny of life on Earth. This collaborative peer reviewed project began in 1995, and is written by biologists from around the world. The s ...

. Myopsids are found in coastal waters worldwide. They are

demersal The demersal zone is the part of the sea or ocean (or deep lake) consisting of the part of the water column near to (and significantly affected by) the seabed and the benthos. The demersal zone is just above the benthic zone and forms a layer o ...

, generally feeding on or near the bottom. In turn, they are considered prey items by virtually all marine predators, including birds. Adult sizes range from the dwarf '' Australiteuthis'' and '' Pickfordiateuthis'', whose males mature at less than in mantle length (ML), to the largest species '' Loligo forbesii'', which has been measured to ML.Body size and fin length as determinants in the geographic distribution of Loliginid squids
/ref> The earliest fossils of this group are ''

Loligo ''Loligo'' is a genus of squid and one of the most representative and widely distributed groups of myopsid squid. The genus was first described by Jean Baptiste Lamarck in 1798. However, the name had been used earlier than Lamarck ( Schneider, ...

'' statoliths from the early

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

. In addition, a pyritized ''Loligo'' fossil is known from the

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...

, marking the earliest true squid known from a complete body fossil.

References

Decapodiformes Squid {{squid-stub