The Bythograeidae are a small family of blind crabs which live around hydrothermal vents. The family contains 16 species in six genera. Their relationships to other crabs are unclear. They are believed to eat

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

and other vent organisms. Bythograeidae are a monophyletic,

sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

of the superfamily

Xanthoidea Xanthoidea is a superfamily of crabs, comprising the three families Xanthidae, Panopeidae and Pseudorhombilidae. Formerly, a number of other families were included in Xanthoidea, but many of these have since been removed to other superfamilies. ...

which split to inhabit hydrothermal vents around the

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...

Origins

Due to the lack of fossils found in this group the exact date of origin of Bythograeidae remains unknown. It has been suggested that bythograeidae do not originate from an ancient hydrothermal

bathyal The bathypelagic zone or bathyal zone (from Greek βαθύς (bathýs), deep) is the part of the open ocean that extends from a depth of below the ocean surface. It lies between the mesopelagic above, and the abyssopelagic below. The bathypelagi ...

groups but instead arose from brachyuran stock that was adapted to shallow hydrothermal vents and then transitioned to deep sea hydrothermal vents around the Eocene. Cyanagraea

Distribution

Bythograeidae are almost exclusively found in the

East Pacific Rise The East Pacific Rise is a mid-ocean rise (termed an oceanic rise and not a mid-ocean ridge due to its higher rate of spreading that results in less elevation increase and more regular terrain), a divergent tectonic plate boundary located alon ...

. Some exceptions include '' Austinograea alayseae'', '' Austinograea williamsi'' and the genus '' Gandalfus'' which are found in the western Pacific and '' Austinograea rodriguezensis'' which is found only in the Central Indian Ridge.

Ecology

The hydrothermal vents where these crabs live are typically short lived, lasting from 10 to 100 years. These are extreme environments, with high temperatures, high concentrations of

sulphides Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds lar ...

, heavy metals, carbon dioxide and an acidic environment. At this depth there is also limited access to light making photosynthesis nearly impossible. Instead, organisms rely on

Chemosynthetic In biochemistry, chemosynthesis is the biological conversion of one or more carbon-containing molecules (usually carbon dioxide or methane) and nutrients into organic matter using the oxidation of inorganic compounds (e.g., hydrogen gas, hydro ...

bacteria to sustain the vast amounts of life in

Chemotroph A Chemotroph is an organism that obtains energy by the oxidation of electron donors in their environments. These molecules can be organic (chemoorganotrophs) or inorganic ( chemolithotrophs). The chemotroph designation is in contrast to phototr ...

ic ecosystems. Bythograeidae are

omnivorous An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nut ...

scavengers, they are believed to eat

and other vent organisms however they can also be found far from active sites.

Species

* Genus ''Allograea'' Guinot, Hurtado & Vrijenhoek, 2002 ** '' Allograea tomentosa'' Guinot, Hurtado & Vrijenhoek, 2002 * Genus ''Austinograea'' Hessler & Martin, 1989 ** '' Austinograea alayseae'' Guinot, 1990 ** '' Austinograea hourdezi'' Guinot & Segonzac, 2018 ** '' Austinograea jolliveti'' Guinot & Segonzac, 2018 ** '' Austinograea rodriguezensis'' Tsuchida & Hashimoto, 2002 ** '' Austinograea williamsi'' Hessler & Martin, 1989 * Genus ''Bythograea'' Williams, 1980 ** '' Bythograea galapagensis'' Guinot & Hurtado, 2003 ** '' Bythograea intermedia'' Saint Laurent, 1988 ** '' Bythograea laubieri'' Guinot & Segonzac, 1997 ** '' Bythograea microps'' Saint Laurent, 1984 ** '' Bythograea thermydron'' Williams, 1980 ** '' Bythograea vrijenhoeki'' Guinot & Hurtado, 2003 * Genus ''Cyanagraea'' Saint Laurent, 1984 ** '' Cyanagraea praedator'' Saint Laurent, 1984 * Genus ''Gandalfus'' McLay, 2007 ** ''

Gandalfus puia ''Gandalfus puia'' is the only known New Zealand species of crab in the family Bythograeidae, commonly known as the blind vent crabs. Like other blind vent crabs, it only lives in hydrothermal vent waters. This species was first described in 200 ...

'' McLay, 2007 ** '' Gandalfus yunohana'' (Takeda, Hashimoto & Ohta, 2000) * ラウユノハナガニ

Genus ''Segonzacia'' Guinot, 1989 ** '' Segonzacia mesatlantica'' (Williams, 1988)

References

{{Taxonbar, from=Q902121 Crabs Animals living on hydrothermal vents Decapod families