Silver spinyfin
Encyclopedia
The silver spinyfin, Diretmus argenteus, is a spinyfin
Spinyfin
Spinyfins are a family, Diretmidae, of beryciform fishes. The name is from Greek, di meaning "two" and eretmos meaning "oar". They are found worldwide in deep waters, down to as much as ....

 of the genus Diretmus, found around the world except the Mediterranean, at depths down to 2,000 m. It belongs to the monotypic
Monotypic
In biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...

 genus Diretmus. Their length is between 30 and 40 cm.

The silver spinyfin is a widely distributed but rare species with a flattened disc-shaped body with a sharp scute
Scute
A scute or scutum is a bony external plate or scale, as on the shell of a turtle, the skin of crocodilians, the feet of some birds or the anterior portion of the mesonotum in insects.-Properties:...

-covered edge on the belly. A large upturned mouth and huge eye
Eye
Eyes are organs that detect light and convert it into electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement...

 dominate the front half of the disc and a small forked tail projects from the other. They are oviparous and the larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

e spend time in the plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...

.

It has small spiny scale
Scale (zoology)
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...

s but no lateral line and is a uniform silvery colour, the top of the back being black.
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