Squilla

Squilla
Squilla mantis
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Malacostraca
Order:	Stomatopoda
Family:	Squillidae
Genus:	Squilla Fabricius, 1787
Type species
Cancer mantis Linnaeus, 1758

Squilla is a genus of mantis shrimp, whose first appearance in the fossil record came 145 million years ago. They are found in marine habitats in tropical and sub-tropical climates all over the world, though they exist in high concentrations around the Indian Ocean and Mediterranean sea. They are often caught unintentionally by fisheries in their climate, and they are not used for human food or fish meal, though valuable compounds such as chitin and chitosan can be extracted from their shells. This genus includes the following species:

• Squilla aculeata Bigelow, 1893
• Squilla biformis Bigelow, 1891
• Squilla bigelowi Schmitt, 1940
• Squilla brasiliensis Calman, 1917
• Squilla cadenati Manning, 1970
• Squilla caribaea Manning, 1969
• Squilla chydaea Manning, 1962
• Squilla deceptrix Manning, 1969
• Squilla discors Manning, 1962
• Squilla edentata (Lunz, 1937)
• Squilla empusa Say, 1818
• Squilla grenadensis Manning, 1969
• Squilla hancocki Schmitt, 1940
• Squilla intermedia Bigelow, 1893
• Squilla latreillei
• Squilla lijdingi Holthuis, 1959
• Squilla mantis (Linnaeus, 1758)
• Squilla mantoidea Bigelow, 1893
• Squilla obtusa Holthuis, 1959
• Squilla panamensis Bigelow, 1891
• Squilla parva Bigelow, 1891
• Squilla rugosa Bigelow, 1893
• Squilla surinamica Holthuis, 1959
• Squilla tiburonensis Schmitt, 1940

Physiology

A 1913 account of a species within the Squilla genus, found in the Indo-Pacific region of Calcutta.

Squilla are small marine organisms, with a size range of 40-70mm. The males and females tend to be the same size. All the different species possess a form that is typical of most other Stomatopods, consisting of extended eyestalks, a rostrum, carapace, and a raptorial claw used for hunting.

All Squilla posses a bilaterally symmetrical body Additionally, Squilla have developed a nauplius eye, which is an eye that is composed of three to four pigment ocelli. Likely, this eye only allows the organism to determine the location of a light source. This means species within the Squilla genus have poorer eyesight than their more famous counterparts of the Odontodactylus genus, which can see more colors than even humans.

Synapomorphies

Though the many species of the Squilla genus vary greatly in location, they are all defined by a few common shared traits. One of those notable ones is the number of teeth on their claw, which tends to be of a middling size. Because Squilla lack a calcified appendage like some of their fellow Stomatopods, they cannot break open hard shells, and thus catch largely soft bodies prey for food. The claw of the Squilla genus is known to have six teeth. Another defining trait is the lack of a raised ridge in the exoskeleton of Squilla-- or rather, the extension of the ridge over the entire exoskeleton, as such creating the appearance of the lack of a ridge. Often referred to as a "carina", this ridge can be used to differentiate Squilla from other similar Stomatopods.

Aside from these major features used to differentiate Squilla, other features include a tail plate with four to six spines, unlike the fused tail plates found in other Stomatopods, and shorter antennular peduncles, which are the structures at the base of the shrimp's antennae that attach them to their head.

Feeding strategy

Squilla are predatory benthic burrowers. They dig holes in the sand, hide, and await soft bodied prey that they are able to snatch up with their relatively weak claw. This means that, unlike other genuses of Stomatopods, Squilla cannot typically consume prey with hard shells. However, their burrowing strategy makes them a bio-diffuser, as they engage in ecosystem engineering that scatters organic and inorganic particles about the ocean floor. They tend to prey on other benthic organisms such as worms, krill, small fish, and even other species of Squilla when they are able. Despite their small size, Squilla has found great success with their strategy, as they have been around for over one hundred million years and have diversified into over a dozen different species.

Life Cycle and Reproduction

Squilla go through a five stage maturity cycle of immature, early maturation, maturation, ripe, and spent, with their life cycle ending shortly after they reproduce. Their life cycles are short, being only eighteen months at the longest, and their reproduction season begins in spring, with most females going from maturation to ripe in winter and ending their life cycle spent in summer. In the studies that determined this, the stage of a female's life cycle was determined by how much space her ovaries consumed in regards to her entire body mass. In spring and summer, females tend to hide in galleries and tend to their eggs, leading to fisheries to catch more males. But in autumn, the females will leave the galleries and become more vulnerable to being caught by humans.

Bioactive compounds extracted from Squilla

Squilla exoskeletons being harvested for chitosan production.

Though Squilla offers little nutritional value due to its very small size, the compounds chitin and chitosan are able to be extracted from Squilla exoskeletons, as is the case with many crustacean species. Chitosan, in particular, has been found to reduce blood plasma levels of HDL in humans, as well as protect against the growth of some microorganisms, most notably Candida, which is a genus of yeasts. New research has also demonstrated that chitosan produced from Squilla shells may also be beneficial in fighting fungus infections and cancerous growths.

These chemicals are extracted by first collecting large amounts of various Squilla species, which is often done unintentionally by fisheries who catch Squilla in their net while fishing for other larger species. These catches are then shelled, and the shells are put through multiple chemical treatments, including demineralization, decolorization, deproteinization, and deacetylation, before they can become finished commercial grade chitosan.