The Nihoa trapdoor spider (''Nihoa mahina'') is a species of trapdoor spider in the family of

Barychelidae Barychelidae, also known as brushed trapdoor spiders, is a spider family with about 300 species in 39 genera. Behaviour Most spiders in this family build trapdoor burrows. For example, the long '' Sipalolasma'' builds its burrow in rotted wood, ...

that occurs on the island of

Nihoa Nihoa (; or ), also known as Bird Island or Moku Manu, is the tallest of ten islands and atolls in the uninhabited Northwestern Hawaiian Islands (NWHI). The island is located at the southern end of the NWHI chain, southeast of Necker ...

Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

in the northwestern area of the Hawaiian island chain. Its scientific name can be broken up into two parts, ''Nihoa'' which is not only its place of origin but the name of its genus, and ''mahina'', which means 'moon' in the

Hawaiian language Hawaiian (', ) is a critically endangered Polynesian language of the Austronesian language family, originating in and native to the Hawaiian Islands. It is the native language of the Hawaiian people. Hawaiian, along with English, is an offi ...

. This could tie back to the fact that the species was discovered not only in the moonlight but also has fine silver hair, resembling its namesake. The species can also be distinguished by a pattern found on its dorsal and the absence of a second row of teeth. Burrows of trapdoor spiders can commonly be found by mangrove roots or near loose coral rubble. Before the 1980s, trapdoor spiders were not thought to exist in Hawaii. Upon their discovery, the genus was given the name ''

'', because it was assumed not to exist elsewhere.

Taxonomy and classifications

''Nihoa mahina'' is an

arachnids Arachnids are arthropods in the class Arachnida () of the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegaroons. Adult arachnids ...

belonging to the subphylum

Chelicerata The subphylum Chelicerata (from Neo-Latin, , ) constitutes one of the major subdivisions of the phylum Arthropoda. Chelicerates include the sea spiders, horseshoe crabs, and arachnids (including harvestmen, scorpions, spiders, solifuges, tic ...

and the family

. Before the 1980s, trapdoor spiders were not thought to exist in Hawaii. Upon discovery, the species was originally classified as part of the genus '' Idioctis''. However, upon further research by Tracey Churchill and

Robert Raven Robert John Raven is an Australian arachnologist, being the Head of Terrestrial Biodiversity and the Senior Curator (Arachnida) at the Queensland Museum. Dr Raven has described over 450 species of spider in Australia and elsewhere, and is spider ...

, they were moved to a new genus due to their differing physical attributes, given the name ''

'', because it was thought to exist nowhere else. Eventually, over 23 species across the Pacific were found throughout the southwestern Pacific. The species' conservation status has also been accepted by the science community as a vulnerable species.

Description and anatomy

The spider itself is a species of intertidal trapdoor spider. The species was discovered in moonlight but also has fine silver hair. Its furrow promargin has eight thick teeth and three smaller teeth which act as a multi-purpose tool for spiders within the

subphylum. These spiders are hunters that dig a hole near rocks and cover it with a concealed trapdoor. These burrows are excavated completely with the spider's jaw. When prey approaches or falls in, the spider pounces on it. Then its abnormally large

pedipalps Pedipalps (commonly shortened to palps or palpi) are the secondary pair of forward appendages among Chelicerata, chelicerates – a group of arthropods including spiders, scorpions, horseshoe crabs, and sea spiders. The pedipalps are lateral to ...

are used to take food into the mouth. Nihoan trapdoor spiders can be distinguished by their wider

sternum The sternum (: sternums or sterna) or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major bl ...

, the medially located teeth paired claws of the males, and the absence of a second row of teeth on the claws of the females. Male Nihoan trapdoor spiders grow to almost long, including their

chelicerae The chelicerae () are the arthropod mouthparts, mouthparts of the subphylum Chelicerata, an arthropod group that includes arachnids, horseshoe crabs, and sea spiders. Commonly referred to as "jaws", chelicerae may be shaped as either articulated ...

. The females are larger, reaching up to . Females also carry a dissimilarity to their vulva which is crucial to the identification of the species.

Distribution and habitat

This species is

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

to the island of Nihoa,

. They inhabit the area of the coastline that is exposed during low tide and submerged during high tide, and are commonly found by mangrove roots or near loose coral rubble.

References

Barychelidae Endemic fauna of Nihoa Spiders of Hawaii {{barychelidae-stub