Idiosepius

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. Pygmy squid brain structures and nervous system are comparable to other squids and octopuses but they have a more developed optical tract. The beaks of Idiosepius show small toothlike structures, a genus specific feature which can be useful in distinguishing Idiosepius species. ==Species==

The following species are recognised in the genus Idiosepius: • Idiosepius hallami Reid & Strugnell, 2018 • Idiosepius kijimuna Reid, Sato, Jolly & Strugnell, 2023 • Idiosepius minimus (d'Orbigny in Férussac & d'Orbigny, 1835) • Idiosepius paradoxus (Ortmann, 1888) • Idiosepius picteti (Joubin, 1894) • Idiosepius pygmaeus Steenstrup, 1881 == Phylogeny ==

The major morphological characteristic that separates Idiosepius from other cephalopods is its adhesive organ. Molecular analysis has separated Idiosepius species into 4 clades 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, however, I. biserialis and I. macrocheir are now considered junior synonyms of Idiosepius minimus. == Reproduction ==

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. 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. There is less variation in spawning patterns among species, females either adhere upside down to a substrate to lay eggs, or float near a substrate and swim closer to lay eggs. == Growth and development ==

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 All species of Idiosepius, except I. thailandicus and I. minimus, hatch with tentacles. Temperate Idiosepius species mature slower, grow larger, and have less generations a year compared to tropical species. Sexual dimorphism in Idiosepius is common and generally females are larger than males. == Behaviour ==

Adhesion strategy Pygmy squids adhere to substrates using secretions from the adhesive organ, Once the buccal mass has been inserted, the squid releases cephalotoxin to paralyze the prey, and enzymes to externally digest the flesh. == References ==