''Elpidia minutissima'' is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of deep-sea swimming

sea cucumber Sea cucumbers are echinoderms from the class (biology), class Holothuroidea ( ). They are benthic marine animals found on the sea floor worldwide, and the number of known holothuroid species worldwide is about 1,786, with the greatest number be ...

in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Elpidiidae Elpidiidae is a family of deep-sea sea cucumbers. They have a translucent body with long and stout podia acting like legs. The mouth is surrounded by thick and short oral tentacles, and the dorsal part often shows pairs of elongated podia as wel ...

. It is a

detritivore Detritivores (also known as detrivores, detritophages, detritus feeders or detritus eaters) are heterotrophs that obtain nutrients by consuming detritus (decomposing plant and animal parts as well as feces). There are many kinds of invertebrates, ...

and is found in the northern Pacific Ocean.

Description

Specimens collected from the

Aleutian Trench The Aleutian Trench (or Aleutian Trough) is an oceanic trench along a convergent plate boundary which runs along the southern coastline of Alaska and the Aleutian islands. The trench extends for from a triple junction in the west with the Ula ...

averaged in length and had three pairs of dorsal podia whereas specimens collected from Station M in the northeastern Pacific Ocean at a depth of about had four pairs, two pairs on the dorsal surface and two pairs on the ventral surface, the hindermost of the ventral podia being shorter than the others. At times of low abundance, the average length of these sea cucumbers was similar to the specimens from the Aleutian Trench but at times of high abundance it increased to . It is possible that these two populations are not in fact the same species.

Ecology

''Elpidia minutissima'' feeds on

detritus In biology, detritus ( or ) is organic matter made up of the decomposition, decomposing remains of organisms and plants, and also of feces. Detritus usually hosts communities of microorganisms that colonize and decomposition, decompose (Reminera ...

on the

seabed The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as seabeds. The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...

, the result of "

marine snow In the deep ocean, marine snow (also known as "ocean dandruff") is a continuous shower of mostly organic detritus falling from the upper layers of the water column. It is a significant means of exporting energy from the light-rich photic zone to ...

" consisting of mucus, faeces and organic debris, that sink into the depths from surface waters. It plays an important part in the processing, utilization and redistribution of particles of organic material that has fallen to the sea bed. ''Elpidia minutissima'' is one of a number of echinoderm species that show great variations in population density. Researchers in one study found that, over a sixteen-year period, two deep sea holothurians, ''E. minutissima'' and '' Peniagone vitrea'', underwent a decline in density of the order of one to two magnitudes. It has been hypothesized that two factors that increase the likelihood of large swings in population are broadcast spawning and the possession of planktotrophic larvae. These factors provide a

positive feedback Positive feedback (exacerbating feedback, self-reinforcing feedback) is a process that occurs in a feedback loop where the outcome of a process reinforces the inciting process to build momentum. As such, these forces can exacerbate the effects ...

loop so that once populations decline, recovery is very slow. When individual organisms are further apart, broadcast spawning is less likely to result in fertilisation and this means fewer larvae available for recruitment.

References

Elpidiidae Animals described in 1971 {{Holothuroidea-stub