''Paraganitus ellynnae'' 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), ...

sea slug Sea slug is a common name for some Marine biology, marine invertebrates with varying levels of resemblance to terrestrial Slug, slugs. Most creatures known as sea slugs are gastropods, i.e. they are Sea snail, sea snails (marine gastropod moll ...

, an

acochlidian Acochlidiacea, common name acochlidians, are a taxonomic clade of very unusual sea snails and sea and freshwater slugs, aquatic gastropod mollusks within the large clade Heterobranchia. Acochlidia is a variant spelling. Description These ar ...

, a shell-less marine

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

mollusc Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

in the family

Parhedylidae Parhedylidae are a taxonomic family of sea slugs, marine gastropod mollusks in the superfamily Parhedyloidea.MolluscaBase eds. (2021). MolluscaBase. Parhedylidae Thiele, 1931. Accessed through: World Register of Marine Species at: http://www.m ...

. ''Paraganitus ellynnae'' is the only species in the genus ''Paraganitus''.

Description

''Paraganitus ellynnae'' is smaller than 5 mm and is externally symmetric. It has no shell in adults, and no operculum in adults. It has also no head shield and no posterior shield. It is able to partially retract parts of its anterior body into a temporal visceral cavity. The visceral sac is largely separated from the rest of the body. The mantle is robust. The visceral hump is conical. The tail is short and pointed. The foot is narrow, the anterior foot edge is rounded and it can crawl on the whole foot. It has no mantle cavity. It has elongated/pointed

rhinophore A rhinophore is one of a pair of Chemoreceptor, chemosensory club-shaped, rod-shaped or ear-like structures which are the most prominent part of the external head anatomy in sea slugs, Marine (ocean), marine gastropod opisthobranch mollusks suc ...

s. Like all acochlidians, it has oral (= labial)

tentacles In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work main ...

. ''Paraganitus ellynnae'' has long and slightly recurved oral tentacles. Oral tentacle nerves have been present in all examined acochlidians to date, but those nerves were not examined in this species. Like all acochlidians, it lacks plicate

gills A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...

. The position of the anus is unknown. It has no calcareous spicules, but it has integumental concrements. It has no

keel The keel is the bottom-most longitudinal structural element of a watercraft, important for stability. On some sailboats, it may have a fluid dynamics, hydrodynamic and counterbalancing purpose as well. The keel laying, laying of the keel is often ...

on the visceral hump. It has aggregations of precerebral ‘accessory ganglia’. It has no eyes. The presence or absence of

Hancock's organ Hancock's organ is a lateral concealed sensory organ of gastropods,Hancock, A., (1852). Observations on the Olfactory Apparatus in the Bullidae. The Annals and Magazine of Natural History Vol.IX – Series 2 188-190. a chemo-sensory sense organ f ...

is unknown. It has prepharyngeal CNS as is the case in all other acochlidians.

Ecology

''Paraganitus ellynnae'' is marine and is a mesopsammic species, in other words, these very small slugs live in the interstitial spaces of marine sands.

References

{{Taxonbar, from=Q7134571 Microhedylidae Gastropods described in 1968