| Bobtail squid | |
|---|---|
 | |
| Sepiola atlantica | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Cephalopoda |
| Superorder: | Decapodiformes |
| Order: | Sepiolida Fioroni, 1981 |
| Families | |
Bobtail squid (order Sepiolida)[1] are a group ofcephalopods closely related tocuttlefish. Bobtail squid tend to have a roundermantle than cuttlefish and have nocuttlebone. They have eight suckered arms and two tentacles and are generally quite small (typical male mantle length being between 1 and 8 cm (0.39 and 3.15 in)).[2]
Sepiolids live in shallowcoastal waters of thePacific Ocean and some parts of theIndian Ocean andAtlantic Ocean as well as in shallow waters on the west coast of theCape Peninsula off South Africa. Like cuttlefish, they can swim by either using thefins on their mantle or by jet propulsion. They are also known as "dumpling squid" (owing to their rounded mantle) or "stubby squid".
Bobtail squid have asymbiotic relationship withbioluminescentbacteria (Aliivibrio fischeri), which inhabit a special light organ in the squid's mantle. The luminescent properties of the bacteria regulate gene expression in the light organ.[3] The bacteria are fed a sugar and amino acid solution by the squid and in return hide the squid'ssilhouette when viewed from below by matching the amount of light hitting the top of the mantle. This method ofcounter-illumination is an example of animalcamouflage.
The organ contains filters which may alter thewavelength of luminescence closer to that of downwellingmoonlight andstarlight; alens withbiochemical similarities to the squid's eye to diffuse the bacterial luminescence; and areflector which directs the lightventrally.[2]
Sepiolida areiteroparous and a female might lay several clutches, each of 1–400 eggs (dependent onspecies), over her estimated one-year-long lifetime.[2] The eggs are covered with sand and left without parental care.[2] Symbiosis withA. fischeri from the surrounding seawater is initiated immediately upon hatching, and the bacteria'scolonisation of thejuvenile light-organ inducesmorphological changes in the squid that lead tomaturity.[2]
About seventy species are known. Sepiolid taxonomy within thecoleoid cephalopods is currently controversial, thus their position is subject to future change.[2]