Cuttlefish


Cuttlefish, or cuttles, are marine molluscs of the family Sepiidae. They belong to the class Cephalopoda which also includes squid, octopuses, and nautiluses. Cuttlefish have a unique internal shell, the cuttlebone, which is used for control of buoyancy.
Cuttlefish have large, W-shaped pupils, eight arms, and two tentacles furnished with denticulated suckers, with which they secure their prey. They generally range in size from, with the largest species, the giant cuttlefish, reaching in mantle length and over in mass.
Cuttlefish eat small molluscs, crabs, shrimp, fish, octopuses, worms, and other cuttlefish. Their predators include dolphins, larger fish, seals, seabirds, and other cuttlefish. The typical life expectancy of a cuttlefish is about 1–2 years. Studies are said to indicate cuttlefish to be among the most intelligent invertebrates. Cuttlefish also have one of the largest brain-to-body size ratios of all invertebrates.
The Greco-Roman world valued the cuttlefish as a source of the unique brown pigment the creature releases from its siphon when it is alarmed. The word for the cuttlefish in both Greek and Latin, sepia, now refers to the reddish-brown color sepia in English.

Nomenclature

The "cuttle" in "cuttlefish", which is itself sometimes used to refer to these animals, is derived from the Old English name for the group, cudele. The word may be cognate with the Old Norse koddi and the Middle Low German Kudel.

Taxonomy

116 species of cuttlefish are currently recognized; for decades, the classification of this family relied on just three genera: Metasepia, Sepia, and Sepiella, with Sepia containing most of the species and several subgenera. A 2023 paper shifted this perception by having recovered Sepia as containing several monophyletic groups or clades. The authors subsequently revived several synonymized genera and elevated some subgenera of Sepia to full genus level, reassigning many species of Sepia to these revived genera. Conversely, Metasepia was found to nest within one of these revived genera, and as it was named after Ascarosepion it became a junior synonym of that genus.
The genera and species of Sepiidae is as follows:
  • Order Sepiida
  • *Suborder Sepiina
  • **Superfamily Vasseurioidea
  • **Superfamily Sepioidea
  • ***Family Anomalosaepiidae Yancey & Garvie, 2011
  • ***Family Belosaepiidae Dixon, 1850
  • ***Family Sepiidae
  • ****Genus Acanthosepion
  • *****Acanthosepion aculeata, needle cuttlefish
  • *****Acanthosepion elliptica, ovalbone cuttlefish
  • *****Sepia esculenta, golden cuttlefish
  • *****Sepia lycidas, kisslip cuttlefish
  • *****Acanthosepion pharaonis, Pharaoh cuttlefish
  • *****Acanthosepion ramani
  • *****Acanthosepion recurvirostra, curvespine cuttlefish
  • *****Sepia smithi, Smith's cuttlefish
  • *****Sepia stellifera
  • ****Genus Ascarosepion
  • *****Ascarosepion apama, giant Australian cuttlefish
  • *****Ascarosepion bandense, stumpy-spined cuttlefish
  • *****Ascarosepion cultratum, knifebone cuttlefish
  • *****Ascarosepion filibrachia
  • *****Ascarosepion latimanus, broadclub cuttlefish
  • *****Ascarosepion mestus, reaper cuttlefish
  • *****Ascarosepion novaehollandiae, New Holland cuttlefish
  • *****Ascarosepion opipara
  • *****Ascarosepion papuensis, Papuan cuttlefish
  • *****Ascarosepion pfefferi, flamboyant cuttlefish
  • *****Ascarosepion plangon, mourning cuttlefish
  • *****Ascarosepion rozella, rosecone cuttlefish
  • *****Ascarosepion tullbergi, paintpot cuttlefish
  • ****Genus Aurosepina
  • *****Aurosepina arabica, Arabian cuttlefish
  • ****Genus Decorisepia
  • *****Sepia australis, southern cuttlefish
  • *****Sepia hedleyi, Hedley's cuttlefish
  • *****Decorisepia madokai, Madokai's cuttlefish
  • ****Genus Digitosepia
  • *****Digitosepia barosei
  • *****Sepia dubia
  • *****Sepia faurei
  • *****Sepia robsoni
  • *****Digitosepia shazaei
  • *****Digitosepia roeleveldi
  • ****Genus Doratosepion
  • *****Doratosepion andreana, Andrea cuttlefish
  • *****Sepia braggi, slender cuttlefish
  • *****Sepia erostrata
  • *****Sepia foliopeza
  • *****Doratosepion kobiensis, Kobi cuttlefish
  • *****Sepia limata
  • *****Sepia longipes, longarm cuttlefish
  • *****Sepia lorigera, spider cuttlefish
  • *****Sepia pardex
  • *****Sepia peterseni
  • *****Sepia tenuipes
  • *****Sepia tokioensis
  • ****Genus Erythalassa
  • *****Erythalassa trygonina, trident cuttlefish
  • ****Genus Hemisepius
  • *****Hemisepius typicus
  • ****Genus Lusepia
  • *****Lusepia hieronis
  • ****Genus Rhombosepion
  • *****Sepia elegans, elegant cuttlefish
  • *****Rhombosepion omani, Oman cuttlefish
  • *****Sepia orbignyana, pink cuttlefish
  • *****Sepia prashadi, hooded cuttlefish
  • ****Genus Sepia
  • *****Sepia hierredda
  • *****Sepia officinalis, common cuttlefish
  • *****Sepia vermiculata
  • ****Genus Sepiella
  • *****Sepiella inermis, spineless cuttlefish
  • *****Sepiella japonica, Japanese spineless cuttlefish
  • *****Sepiella ornata, ornate cuttlefish
  • ****Genus Spathidosepion
  • *****Sepia angulata
  • *****Sepia papillata
  • *****Sepia tuberculata
The subsequent species are in need of taxonomic review, as they were not examined in the 2023 study.
  • ? Sepia bartletti
  • ? Sepia baxteri *
  • ? Sepia dannevigi *
  • ? Sepia whitleyana
  • Sepia acuminata
  • Sepia adami
  • Sepia appellofi
  • Sepia aureomaculata
  • Sepia bathyalis
  • Sepia bertheloti, African cuttlefish
  • Sepia bidhaia
  • Sepia brevimana, shortclub cuttlefish
  • Sepia burnupi
  • Sepia carinata
  • Sepia chirotrema
  • Sepia confusa
  • Sepia cottoni
  • Sepia dollfusi
  • Sepia elongata
  • Sepia elobyana, Guinean cuttlefish
  • Sepia filibrachia
  • Sepia gibba
  • Sepia incerta
  • Sepia insignis
  • Sepia irvingi
  • Sepia ivanovi
  • Sepia joubini
  • Sepia kiensis *
  • Sepia koilados
  • Sepia mascarensis
  • Sepia mira
  • Sepia mirabilis
  • Sepia murrayi, frog cuttlefish
  • Sepia plana
  • Sepia plathyconchalis
  • Sepia pulchra
  • Sepia reesi
  • Sepia rex
  • Sepia rhoda
  • Sepia savignyi, broadback cuttlefish
  • Sepia saya
  • Sepia senta
  • Sepia sewelli
  • Sepia simoniana
  • Sepia sokotriensis
  • Sepia subplana
  • Sepia subtenuipes
  • Sepia sulcata, grooved cuttlefish
  • Sepia tala
  • Sepia tanybracheia
  • Sepia thurstoni
  • Sepia vecchioni
  • Sepia vercoi
  • Sepia vietnamica
  • Sepia vossi
  • Sepiella weberi
  • Sepia zanzibarica
  • Sepiella cyanea
  • Sepiella mangkangunga
  • Sepiella ocellata
The species listed above with an asterisk are questionable and need further study to determine if they are a valid species or a synonym. The question mark indicates questionable placement within the genus.
File:Trachyteuthis hastiformis 3243.JPG|thumb|Trachyteuthis hastiformis; Museum of Nature and Archaeology

Fossil record

The earliest fossils of cuttlefish are from the end of the Cretaceous period, represented by Ceratisepia from the Late Maastrichtian Maastricht Formation of the Netherlands. Although the Jurassic Trachyteuthis was historically considered possibly related to cuttlefish, later studies considered it to be more closely related to octopuses and vampire squids.

Description

Cuttlebone

Unlike other cephalopods, cuttlefish possess a unique internal structure called the cuttlebone, a highly modified internal shell, which is porous and is made of aragonite. Except for Spirula, they are the only coleoid cephalopods with a shell with a phragmocone divided into chambers separated by septa. The pores provide it with buoyancy, which the cuttlefish regulates by changing the gas-to-liquid ratio in the chambered cuttlebone via the ventral siphuncle. Each species' cuttlebone has a distinct shape, size, and pattern of ridges or texture. The cuttlebone is unique to cuttlefish, and is one of the features that distinguish them from their squid relatives.

Visual system

Cuttlefish, like other cephalopods, have sophisticated eyes. The organogenesis and the final structure of the cephalopod eye fundamentally differ from those of vertebrates, such as humans.
Superficial similarities between cephalopod and vertebrate eyes are thought to be examples of convergent evolution. The cuttlefish pupil is a smoothly curving W-shape. Although cuttlefish cannot see color, they can perceive the polarization of light, which enhances their perception of contrast. They have two spots of concentrated sensor cells on their retinas, one to look more forward, and one to look more backward. The eye changes focus by shifting the position of the entire lens with respect to the retina, instead of reshaping the lens as in mammals. Unlike the vertebrate eye, no blind spot exists, because the optic nerve is positioned behind the retina. They are capable of using stereopsis, enabling them to discern depth/distance because their brain calculates the input from both eyes.
The cuttlefish's eyes are thought to be fully developed before birth, and they start observing their surroundings while still in the egg. In consequence, they may prefer to hunt the prey they saw before hatching.