''Neopilina'' is a highly derived genus of modern monoplacophoran.Organisms, Genes and Evolution: Evolutionary Theory at the Crossroads ; Proceedings of the 7th International Senckenberg Conference. By Dieter Stefan Peters, Michael Weingarten. Contributor: Dieter Stefan Peters. Published by Franz Steiner Verlag, 2000. , 9783515076593. 243 pages.

Species

Four species are recognized: * '' Neopilina bruuni'' Menzies, 1968 * '' Neopilina galatheae'' Lemche, 1957 * '' Neopilina rebainsi'' Moskalev, Starobogatov & Filatova, 1983 * '' Neopilina starobogatovi'' Ivanov & Moskalev, 2007

Phylogeny

Some molecular results show that they fall within the polyplacophoran clade, although these results have been called into question. Fossil and morphological data show that they are rather derived and bear very little resemblance to an 'ancestral mollusc'.

Anatomy

Its anatomy led researchers to believe that the

cephalopod A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...

s evolved from the Monoplacophora. Its pair of preoral tentacles are considered homologous to those of gastropods; like

prosobranch Prosobranchia was a large Taxonomy (biology), taxonomic Class (biology), subclass of sea snails, land snails and freshwater snails. This taxon of gastropods dates back to the 1920s. It has however been proven to be polyphyly, polyphyletic (consis ...

gastropod tentacles, their nerves connect to the cerebral

ganglia A ganglion (: ganglia) is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system, this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system, there a ...

. The post-oral tentacles are equated with bivalves' labial flaps, cephalopods'

arms Arms or ARMS may refer to: *Arm or arms, the upper limbs of the body Arm, Arms, or ARMS may also refer to: People * Ida A. T. Arms (1856–1931), American missionary-educator, temperance leader Coat of arms or weapons *Armaments or weapons **Fi ...

, and

scaphopod Scaphopoda (plural scaphopods , from Ancient Greek σκᾰ́φης ''skáphē'' "boat" and πούς ''poús'' "foot"), whose members are also known as tusk shells or tooth shells, are a class (biology), class of shelled Marine life, marine inve ...

s' captacula. Cuticular hardenings around the mouth of the organism are considered to be jaw-like and not far removed from the beaks of cephalopods or the jaws of many gastropods. The presence of a single shell prompts comparisons to the cephalopod ''

Nautilus A nautilus (; ) is any of the various species within the cephalopod family Nautilidae. This is the sole extant family of the superfamily Nautilaceae and the suborder Nautilina. It comprises nine living species in two genera, the type genus, ty ...

'', but besides its bilateral symmetry and direction of coiling, there is not a clear equivalence; ''Nautilus shell is notably different in the possession of septa (and thus a

siphuncle The siphuncle is a strand of biological tissue, tissue passing longitudinally through the mollusc shell, shell of a cephalopod mollusc. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the li ...

). It bears a similar degree of similarity to most other mollusc groups, leading to speculation that it may reflect a relatively unchanged ancestral mollusc. The shell itself is aragonitic, consisting mainly of a prismatic layer, lined with

nacre Nacre ( , ), also known as mother-of-pearl, is an organicinorganic composite material produced by some molluscs as an inner shell layer. It is also the material of which pearls are composed. It is strong, resilient, and iridescent. Nacre is ...

. The organism bears five pairs of ctenidia (gills), unusually for molluscs; the rear two are homologous to the two pairs in ''Nautilus''. This is unlike the Polyplacophora (chitons), which have a number of pairs of ctenidia, but this number varies and is not related to the number of their body 'segments'. The foot and pallial groove are very difficult indeed to discriminate from the polyplacophora, supporting its placement in this group by molecular methods Its radula is not unlike that of the polyplacophora; notably, its fifth tooth is modified to be comb-like.

Ecology

''Neopilina'' is a bottom feeder, probably a deposit feeder; whilst alive, its shell is covered by a layer of mucus that might be involved in feeding or locomotion. In 2017, a deep-sea expedition by the '' Okeanos Explorer'' off the coast of

American Samoa American Samoa is an Territories of the United States, unincorporated and unorganized territory of the United States located in the Polynesia region of the Pacific Ocean, South Pacific Ocean. Centered on , it is southeast of the island count ...

filmed the first-ever high-resolution video of a monoplacophoran in its natural habitat. Two ''Neopilina'' sp. individuals were filmed on the ocean floor. The individuals may belong to an undescribed species, with five pairs of long gills clearly visible.

References

External links

Video of ''Neopilina'' sp.
Footage taken by ROV Deep Discoverer, NOAA 2017 American Samoa Expedition (EX-17-02), dive 08 at ‘Utu’ seamount, 3837 m depth. {{Taxonbar, from=Q865430 Monoplacophora Mollusc genera