''Ipnops meadi'', also known as the grideye fish, is a highly specialized species of Placodithyran abyssal fish found in the Clarion-Clipperton Zone of the Indo-Pacific Ocean. The species was named after Giles W. Mead of the Harvard Museum of Comparative Zoology, a biology professor at Harvard, deep sea explorer, and ichthyologist.

History

''Ipnops'' were first discovered and named in 1878 by Dr. Albert Günther during the expedition of . ''Ipnops'' was originally classified as a broad species of abyssal flat-headed fish with either very small eyes or membranes covering their eyes. Due to recent scientific advancements and increased deep-sea expeditions, the ''Ipnops'' genus now divided into three species (''I.agassizi'', ''I.meadi'', ''I.murrayi'') based on geographic location. Most information on ''Ipnops'' species has been collected via deep-sea expeditions, the most prominent being HMS ''Challenger'' (1878), “

Galathea ''Galathea'' is a genus of squat lobsters in the family Galatheidae. It is one of the largest genera of squat lobsters that in 2008 contained 73 species (17 in the Atlantic Ocean, 25 in the Indian Ocean and 43 in the Pacific Ocean The ...

”(1950–52), and “Okeanos” (2017). Since ''Ipnops'' are rather difficult to locate and photograph at high resolution, very little is known about any of the three species.

Habitat

Due to their rarity, and lack of photos, the three species of ''Ipnops'' (''I. agassizi'', ''I. meadi'' and ''I. murrayi'') are distinguished by the depth and location of which they reside. ''I. meadi'' and ''I. agassizi'' are found in the Indo-Pacific Ocean, and ''I. murrayi'' are found in the Atlantic and Caribbean Sea. ''Ipnops agassizi'', ''meadi'', and ''murrayi'' also differ by which the depths they occupy. ''I. agassizi'' and ''murrayi'' are found at depths 3,000 meters and above, while ''I. meadi'' are found from 3,300-5,000 meters.

Diet

Stomach dissections of ''I. meadi'' indicate the species primarily feed on small crustaceans.

Physiology

Since all three species of ''Ipnops'' are primarily distinguished by their geography, all three species have roughly the same physiology. All ''Ipnops'' are generally characterized as long and slender fish lacking traditional ocular lenses found on most marine organisms. In place of eyes, grideye fish have flat bony membranes on top of their skull which act as photosensitive plates. ''Ipnops'' also have large mouths, given their size, and sharp, pointed teeth on both the

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and

vomer The vomer (; ) is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones. The vomer forms ...

regions of the mouth. Based on the dissection of multiple samples, all species have roughly 13-15 anal rays, 13-15 pectoral fin rays, and 54-58 vertebrae. However, due to the species similarity, some scientists have suggested the ''Ipnops'' are hybrids and not reproductively isolated, or that ''Ipnops'' should just be a single species. From collections and dissections of ''Ipnops'' species, there are a few characteristics specific to ''I. meadi'', compared to the other two species, including: *Higher average number of lateral line scaleshttp://www.fishbase.org/glossary/Glossary.php?q=lateral+line+scales *Higher average number of vertebrae *Higher average number of gill rakes on the anterior arch *Absence of

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Size

*Average standard length of juvenile and adult ''Ipnops meadi'' ranges from 55-121mm. *Larval ''Ipnops'' measured a standard length of 14mm.

Photosensitive plates

The photosensitive plates of the ''Ipnops'' are theorized to be sensors that exclusively detect the presence or absence of light. Some scientists hypothesized that the plates serve as an adaptive protection mechanism, helping the ''Ipnops'' detect bioluminescence from predators.

Reproduction

Dissections of ''Ipnops'' species’ gonads indicate that these fish are hermaphroditic and lay an average of 900 eggs per clutch.

Larval stages and development

Currently, there is only one study of larval ''Ipnops''. This study found the larva in shallower depths (1600m) which suggest larvae move to the surface during their development and return to the depths once they are adults The larva also had very large eyes and no presence of the membrane which covers adult ''Ipnops'' eyes. This indicates that as larva develop, they lose their sense of sight and their eyeballs transition into the photosensitive plates. However, this is purely hypothetical and more studies need to be conducted before the scientific community can be certain.

References

{{Taxonbar, from=Q6413313 Ipnopidae Taxa named by Jørgen G. Nielsen Fish described in 1966