The Japanese pygmy seahorse (Hippocampus japapigu) is a Japanese species of seahorse in the family Syngnathidae.^[2] It is also sometimes known as the Japan pig.^[3]

Quick Facts Conservation status, Scientific classification ...

Japanese pygmy seahorse
A is the male; B is the female.
Conservation status
CITES Appendix II (CITES)[1]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Syngnathiformes
Family:	Syngnathidae
Genus:	Hippocampus
Species:	H. japapigu
Binomial name
Hippocampus japapigu Short, R. Smith, Motomura, Harasti & H. Hamilton, 2018

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It lives in Northwestern Pacific near Japan, and lives at depths from 5 to 22 meters, but its usually found at 10 to 13 meters,^[2] but does not live with any specific species to host, and instead clings onto algal turfs in subtropical reefs.^[4]

As of 2018^[update], H. japapigu is only known to be found in Japan, including Kashiwa-jima Island, Sukumo Bay; Kushimoto, Kii Peninsula; Osezaki, Izu Peninsula; the Izu Islands of Miyake and Hachijo; Sagami Bay; and Chichi-jima, Ogasawara Islands.^[5]: 44

The type locality was collected off Imasaki, Okago, Hachijo-jima Island, Izu Islands at a depth of 10 m (33 ft).^[5]: 30

It reaches a length of 1.6 cm, and contains 28 tail rings, 14 dorsal fin rays, 9 pectoral fin rays, and 4 subdorsal rings.^[2] It is the size of a jellybean, and its coloration is made for hiding in algae-covered reefs, clinging to soft corals while feeding on plankton. It has a pair of wing-like protrusions on its neck; unlike other species, it contains only one pair instead of two, and is the only seahorse in the world known to have a bony ridge running down its back.^[3]

The broad pouch of the pygmy seahorse is present within the body cavity and located on the trunk, in contrast to tail-brooding non-pygmy seahorses.^[6]

In 2013, after completing his PhD on the biology of the Bargibant's and Denise's pygmy seahorses, Richard Smith went to a fish biology conference in Okinawa in 2013, after which he photographed the Japanese pygmy seahorse on several dives off of Hachijo-jima, one of the Izu Islands about 180 miles from Tokyo. There he found about a dozen specimens.^[7]

The species description was published by Short and colleagues in a 2018 issue of ZooKeys; it was based on one female holotype, a male and a female paratype, and two photographs of additional specimens. The holotype and one paratype were deposited at the Burke Museum at the University of Washington; the other paratype was deposited at the Kagoshima University Museum.^[5]: 30

Short and colleagues proposed Japanese pygmy seahorse as the English and Japanese common names for the species. The specific epithet comes from its colloquial Japanese name: Japan Pig or Japapigu.^[5]: 45