Idiosepius pygmaeus

{{Short description|Species of mollusc}}

{{Speciesbox

| image2_caption = Tropical Pigmy squid

| status = DD

| status_system = IUCN3.1

| status_ref = {{cite iucn |author=Barratt, I. |author2=Allcock, L. |date=2012 |title=Idiosepius pygmaeus |volume=2012 |page=e.T162604A926579 |doi=10.2305/IUCN.UK.2012-1.RLTS.T162604A926579.en |access-date=19 November 2021}}

| image = Idiosepius pygmaeus.png

| image_caption = Hatchlings of Idiosepius pygmaeus (ca. 2 mm long) stained with phosphotungstic acid (left) and Lugol's iodine (right)

| image2 = Tropical Pygmy Squid (Idiosepius pygmaeus) (25377304317).jpg

| taxon = Idiosepius pygmaeus

| authority = Steenstrup, 1881

{{Cite web|title=WoRMS - World Register of Marine Species - Idiosepius pygmaeus Steenstrup, 1881|url=https://www.marinespecies.org/aphia.php?p=taxdetails&id=342345|access-date=2022-02-25|website=www.marinespecies.org|language=en}}

}}

Idiosepius pygmaeus, also known as the two-toned pygmy squid or tropical pygmy squid, is a species of bobtail squid native to the Indo-Pacific. It occurs in waters of the South China Sea, Japan, Philippines, Palau, Indonesia, Northern Mariana Islands, as well as northern and northeastern Australia. It inhabits shallow, inshore waters.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.{{Cite web |url=http://www.cephbase.utmb.edu/biogeo/eez.cfm?CephID=180 |title=Countries' Exclusive Economic Zones with Idiosepius pygmaeus |access-date=2007-02-26 |archive-url=https://web.archive.org/web/20030523053957/http://www.cephbase.utmb.edu/biogeo/eez.cfm?CephID=180 |archive-date=2003-05-23 |url-status=dead }}

I. pygmaeus weighs 0.00033 g upon hatching and increases in weight to 0.175 g as it reaches maturity in 50 days (1260 degree days). It inhabits waters at a temperature of 25.2 °C. Growth rate has been calculated as 12.55 and physiological growth rate as 0.498.Wood, J.B. & R.K. O'Dor 2000. {{cite web|url=http://www.cephbase.utmb.edu/refdb/pdf/6374.pdf |title=Do larger cephalopods live longer? Effects of temperature and phylogeny on interspecific comparisons of age and size at maturity. |url-status=dead |archive-url=https://web.archive.org/web/20041214235304/http://www.cephbase.utmb.edu/refdb/pdf/6374.pdf |archive-date=2004-12-14 |df= }} {{small|(134 KiB)}} Marine Biology 136(1): 91–99.

I. pygmaeus grows to 20 mm in mantle length.

This species has been reared on a diet of glass shrimp (Acetes sibogae australis) in the laboratory.Jackson, G.D. 1988. The Use of Statolith Microstructures to Analyze Life-history Events in the Small Tropical Cephalopod Idiosepius pygmaeus. Fishery Bulletin (U.S.) 87: 265-272.

The type specimen was collected in the South China Sea ({{coord|04|20|N|107|20|E|scale:250000}}) and is deposited at the Zoologisk Museum of Kobenhavns Universitet in Copenhagen.[http://www.mnh.si.edu/cephs/newclass.pdf Current Classification of Recent Cephalopoda]

The Idiosepius pygmaeus is heavily concentrated in seagrass meadows. They are known to attach onto seagrass using a special organ that supports adhesion. However, due to environmental changes caused by human activities, seagrass meadows have been disturbed. This habitat used for shelter by organisms such as the Idiosepius are being threatened.