Myopsida is one of the four

orders Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

squid True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting t ...

. It consists of two

families Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideall ...

: 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 "unispec ...

Australiteuthis ''A. aldrichi'' is a small species of squid found in northern Australian waters. The species was described by Chung Cheng Lu in 2005 based on specimens collected in the inshore waters of Northern Australia. The largest known individual of this ...

'' 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 follows V ...

(~50 species). Some taxonomists 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 Oegopsida is one of the two orders of squid in the superorder Decapodiformes, in the class Cephalopoda. Together with the Myopsina, it was formerly considered to be a suborder of the order Teuthida, in which case it was known as Oegopsina. T ...

not being demonstrated to form a

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

. A number of morphological features distinguish members of Myopsida from those of its sister group,

Oegopsida Oegopsida is one of the two orders of squid in the superorder Decapodiformes, in the class Cephalopoda. Together with the Myopsina, it was formerly considered to be a suborder of the order Teuthida, in which case it was known as Oegopsina. This ...

. Some of the most obvious differences are found in the structure of the eyes: 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 beaks. These appendages, which function as muscular hydrostats, have been variously termed arms, legs or tentacles. Description In the scientific li ...

lacks a locking apparatus, and a

tentacle pocket In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work main ...

is present on the head. The funnel has no lateral

adductor muscles The adductor muscles of the hip are a group of muscles mostly used for bringing the thighs together (called adduction). Structure The adductor group is made up of: *Adductor brevis *Adductor longus *Adductor magnus * Adductor minimus This is o ...

. An internalised shell is present in the form of a well-developed

gladius ''Gladius'' () is a Latin word meaning "sword" (of any type), but in its narrow sense it refers to the sword of ancient Roman foot soldiers. Early ancient Roman swords were similar to those of the Greeks, called '' xiphe'' (plural; singular ''xi ...

, which is located dorsally within the

mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...

and extends for almost its entire length. In contrast to oegopsids, females possess

accessory nidamental gland Nidamental glands are internal organs found in some elasmobranchs and certain molluscs, including cephalopods (specifically Decapodiformes and nautiluses) and gastropods.Young, R.E., M. Vecchione & K.M. Mangold (1999)Cephalopoda Glossary Tree of Li ...

s 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 gastropods.Young, R.E., M. Vecchione & K.M. Mangold (1999)Cephalopoda Glossary Tree of Li ...

s. They however lack a right oviduct.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. Myopsids are found in

coastal waters The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in n ...

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 of ...

, generally feeding on or near the bottom. Adult sizes range from the dwarf ''

'' and '' Pickfordiateuthis'', whose males mature at less than in mantle length (ML), to the large ''

Loligo forbesii ''Loligo forbesii'' (sometimes erroneouslyBouchet, P. and S. Gofas. (2013)''Loligo forbesi'' Steenstrup, 1856.World Register of Marine Species. Accessed 5 June 2013. spelled ''forbesi''), known commonly as the veined squid and long-finned squid, ...

'', which can exceed ML.

References

Squid {{squid-stub