Idiosepius
Template:Short description Template:Automatic taxobox
Idiosepius is a genus of squids in the family Idiosepiidae.<ref name=WoRMS/> Most well known for their incredibly tiny size, these squids range from 10 to 18 mm (0.39 to 0.75 in) in adult specimens.<ref>Template:Citation</ref> Members of this genus are of no interest to commercial fisheries.<ref name=Reid>Reid, A. 2005. Family Idiosepiidae. In: P. Jereb & C.F.E. Roper, eds. Cephalopods of the world. An annotated and illustrated catalogue of species known to date. Volume 1. Chambered nautiluses and sepioids (Nautilidae, Sepiidae, Sepiolidae, Sepiadariidae, Idiosepiidae and Spirulidae). FAO Species Catalogue for Fishery Purposes. No. 4, Vol. 1. Rome, FAO. pp. 208–210.</ref> Idiosepius are found primarily in tropical and temperate waters throughout the Indo-Pacific, often found in association with seagrass and mangrove roots.<ref name="Reid & Strugnell 2018"/>
AnatomyEdit
Idiosepius have 8 tentacles and 2 arms and have an adhesive organ located on the dorsal mantle side at the posterior end between the fins.<ref name=":2">Template:Cite journal</ref> Pygmy squid brain structures and nervous system are comparable to other squids and octopuses but they have a more developed optical tract.<ref name=":1">Template:Cite journal</ref> The beaks of Idiosepius show small toothlike structures, a genus specific feature which can be useful in distinguishing Idiosepius species.<ref name=":1" />
SpeciesEdit
The following species are recognised in the genus Idiosepius:<ref name=WoRMS>Template:WoRMS</ref>
- Idiosepius hallami Reid & Strugnell, 2018<ref name="Reid & Strugnell 2018">Template:Cite journal</ref>
- Idiosepius kijimuna Reid, Sato, Jolly & Strugnell, 2023<ref>Template:Cite journal</ref>
- Idiosepius minimus (d'Orbigny in Férussac & d'Orbigny, 1835)<ref name=III>Férussac, A. & d'Orbigny, A. (1835). Histoire naturelle générale et particulière des Céphalopodes acétabulifères vivants et fossiles. Paris: Baillière.</ref>
- Idiosepius paradoxus (Ortmann, 1888)<ref name=IV>Ortmann, A. (1888). Japanische Cephalopoden. Zoologische Jahrbücher, Systematik, 3, 639–670</ref>
- Idiosepius picteti (Joubin, 1894)<ref name=V>Joubin, L. (1894). Céphalopodes d'Amboine. Revue suisse de Zoologie et Annales du Musée d'Historie Naturelle le Genèva, 2, 23–64.</ref>
- Idiosepius pygmaeus Steenstrup, 1881<ref name=I/>
- Idiosepius thailandicus Chotiyaputta, Okutani & Chaitiamvong, 1991<ref name=VI>Template:Cite journal</ref>
PhylogenyEdit
The major morphological characteristic that separates Idiosepius from other cephalopods is its adhesive organ.<ref name=":1" /> Idiosepius phylogenetic placement is disputed with early analysis placing Idiosepius as sister taxa to Teuthida and recent analysis placing Idiosepius in Order Sepiolida.<ref name=":1" /> Species within Idiosepius have been morphologically categorized by the shape of the male hectocotylus and arrangement of tentacle suckers.<ref name=":3">Template:Cite journal</ref> Molecular analysis has separated Idiosepius species into 4 clades<ref name=":3" /> although there has been debate about the number of species of Idiosepius. Molecular and morphological analysis supported the hypotheses that I. thailandicus and I. macrocheir were junior synonyms of I. biserialis,<ref name=":1" /><ref name=":3" /> however, I. biserialis and I. macrocheir are now considered junior synonyms of Idiosepius minimus.<ref name="WoRMS" />
ReproductionEdit
Most reproductive research has been on female pygmy squids. They are able to spawn multiple batches of eggs without a decrease in quality as they are deposited, and have a preference for spawning in no or low light.<ref name=":1" /><ref name=":4">Template:Cite journal</ref> A female has the ability to allocate more or less energy to reproductive tissues and the development of eggs depending on the season, which causes slower body growth but larger gonads during colder temperature spawning periods.<ref name=":1" /> Cross mating has been observed in I. minimus and I. thailandicus.<ref name=":4" /> Male and female Idiosepius reproductive structures and organs are the same or similar to most other types of squids.<ref name=":1" />
Reproductive behavioursEdit
Pygmy squids do not display monogamous behaviors such as pairing up or protecting a mate. Instead, they will copulate with many other pygmy squids.<ref name=":4" /> Mating patterns vary between species and involve the orientation of the male and female squid (with one or both partners floating above a substrate or one or both partners adhering to a substrate), the posture of each partner (either vertical or horizontal), and the colour patterns of each partner.<ref name=":1" /><ref name=":4" /> 4 unique patterns have been observed in I. thailandicus and 3 have been observed in I. minimus.<ref name=":4" /> Idiosepius species differ in how males hold onto females and with which appendages they use to pass spermatophores during copulation.<ref name=":1" /><ref name=":4" /> Females also have the ability to remove spermatophores received from males and exhibit a preference for smaller, faster copulating males for reproduction.<ref name=":1" /><ref name=":0">Template:Cite journal</ref> There is less variation in spawning patterns among species, females either adhere upside down to a substrate to lay eggs,<ref name=":1" /> or float near a substrate and swim closer to lay eggs.<ref name=":4" />
Growth and developmentEdit
Idiosepius eggs range from 0.87 to 0.91 mm (0.032 to 0.036 in) in length and 0.67 to 0.72 mm (0.026 to 0.028 in) in width<ref name=":1" /> and the amount of egg layers varies among species.<ref name=":4" /> Embryo development typically take less than a month depending on the species<ref name=":1" /> and their mortality and gestation period depend on water temperature. Warm temperatures of 30°C (86°F) had no mortalities and the shortest gestation periods, whereas colder temperatures of 20°C (68°F) and lower had higher mortality rates and the longest gestation periods.<ref name=":1" /> I. paradoxus has been found to survive at temperatures as low as 4.5°C (39.74°F).<ref name=":52">Template:Cite journal</ref> All species of Idiosepius, except I. thailandicus and I. minimus, hatch with tentacles.<ref name=":1" /> Temperate Idiosepius species mature slower, grow larger, and have less generations a year compared to tropical species.<ref name=":1" /> Sexual dimorphism in Idiosepius is common and generally females are larger than males.<ref name=":1" />
BehaviourEdit
Adhesion strategyEdit
Pygmy squids adhere to substrates using secretions from the adhesive organ,<ref name=":1" /> not using suckers on their appendages. They are thought to temporarily attach to substrates in a similar fashion to gastropods, however the mechanism involved with detaching from a substrate is currently unknown.<ref name=":1" /> Adhesion is important during mating,<ref name=":4" /> egg deposition, and is a mechanism for avoiding predation.<ref name=":1" />
Habitat preferenceEdit
Idiosepius are all neritic marine species.<ref name=":1" /> They have been found in the Indo-Pacific region, specifically South Africa, Tasmania, Mozambique, Japan, China, Australia, Indonesia, and Thailand.<ref name=":1" /><ref name=":3" /><ref name=":52" /> Pygmy squids like to adhere to substrates in seagrass beds, mangroves, seashores, and estuaries.<ref name=":1" /> Individuals and eggs are assumed to migrate as the substrate they are adhered to is moved and may also disperse passively as they are caught in sea currents.<ref name=":1" /><ref name=":52" />
Predatory behaviourEdit
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Most research into Idiosepius feeding behaviour has mainly been studied in I. paradoxus and has been categorized into attacking and eating phases.<ref name=":1" /> Pygmy squids attack prey in a similar fashion to cuttlefish, and once their prey has been captured, the squid inserts the buccal mass into the exoskeleton or skin.<ref name=":1" /><ref name=":6">Template:Cite journal</ref> Once the buccal mass has been inserted, the squid releases cephalotoxin to paralyze the prey, and enzymes to externally digest the flesh.<ref name=":6" /> Pygmy squids typically only predate on smaller prey like shrimp, as larger prey can not be paralyzed and are only partially digested.<ref name=":6" /> These squids are able to digest so much of the flesh of a shrimp, that what remains often resembles what is left after a moult.<ref name=":6" /> I. paradoxus has been observed to sometimes ink during predation, which may function as a type of smoke screen or distraction when catching active prey.<ref name=":7">Template:Cite journal</ref>
ReferencesEdit
Further readingEdit
- von Boletzky, S., et al. 2005. {{#invoke:citation/CS1|citation
|CitationClass=web }} Template:Small Phuket mar. biol. Cent. Res. Bull. 66: 11–22.