Oxygyrus

{{Use dmy dates|date=March 2023}} {{Cleanup taxon|date=Jan 2019|concern=unaccepted}} {{Speciesbox | name = ''Oxygyrus keraudrenii'' | fossil_range = Pliocene-Recent<ref name="Janssen 2007"/> | image = Oxygyrus keraudrenii.png | image_caption = Apical view of the shell of ''Oxygyrus keraudrenii'' from the Pliocene Epoch | display_parents = 2 | parent_authority = Benson, 1835<ref>Benson W. H. (1835). "Account of ''Oxygyrus''; a new genus of pelagian shells allied to the genus ''Atlanta'' of Lesueur, with a note on some other pelagian shells lately taken on board the ship Malcolm". ''Journal of the Asiatic Society of Bengal'' '''4''': 173-176. ''Oxygyrus'' is on the page 174.</ref> | taxon = Oxygyrus keraudrenii | authority = (Lesueur, 1817)<ref>Lesueur C. A. (1817). "Mémoire sur deux nouveaux genres de mollusques, Atlante et Atlas". ''Journal de Physique'' '''85''': 390-393.</ref> | synonyms_ref = | synonyms = }}

'''''Oxygyrus keraudrenii''''' is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae.<ref name="WoRMS">{{WRMS species|138839|''Oxygyrus keraudrenii'' (Lesueur, 1817)|||Gofas, S. (2009). Oxygyrus keraudrenii (Lesueur, 1817). In: Bouchet, P.; Gofas, S.; Rosenberg, G. (2009) World Marine Mollusca database. Accessed through: World Register of Marine Species at <nowiki>http://www.marinespecies.org/aphia.php?p=taxdetails&id=138839</nowiki> on 14 August 2010}}</ref>

''Oxygyrus keraudrenii'' is the only species in the genus '''''Oxygyrus'''''.<ref name="Seapy 2010"/>

==Description== ''Oxygyrus keraudreni'' (along with ''Atlanta peronii'') attains the largest size (shell diameter to 10 mm) among the Atlantidae.<ref name="Seapy 2010"/><ref name="Welch 2010">Welch J. J. (2010). "The "Island Rule" and Deep-Sea Gastropods: Re-Examining the Evidence". ''PLoS ONE'' '''5'''(1): e8776. {{doi|10.1371/journal.pone.0008776|doi-access=free}}.</ref> Body coloration is light bluish-purple, with the color darkening with age.<ref name="Seapy 2010"/> The larval shell is calcareous and displays a distinctive pattern of zigzag-shaped spiral ridges that are evenly spaced and cover the shell surface.<ref name="Seapy 2010"/> The teleoconch is composed of conchiolin, a transparent cartilaginous material, and its surface lacks sculpture.<ref name="Seapy 2010"/> With growth the teleoconch overgrows the protoconch and eventually surrounds it.<ref name="Seapy 2010"/> A shell spire, as seen in all other atlantids, is lacking and the spire region is termed involute.<ref name="Seapy 2010"/> The conchiolin keel is glass-like and has a truncate anterior edge that ends at the shell aperture.<ref name="Seapy 2010"/>

The shell of this easily recognisable species is completely involute, with a similar 'umbilicus' at both the top and the base of the shell.<ref name="Janssen 2007"/> This feature makes it impossible to count the number of protoconch whorls, as only one is visible in each of them.<ref name="Janssen 2007"/> The juvenile shell initially is slightly wider than high, but gets relatively wider during growth.<ref name="Janssen 2007"/> Its surface is slightly irregularly covered with approximately 20-24 spiral lirae in a zigzag-shape that usually leave a narrow zone free just below the periphery.<ref name="Janssen 2007"/> In between these lirae the shell's surface is granulated.<ref name="Janssen 2007"/> The apertural margin of the shell is deeply sinuated, as can be seen from the shape of the growth lines and also at the place where the ornamented protoconch changes quite suddenly to the much less clearly ornamented teleoconch (this transition is well-illustrated by Thiriot-Quiévreux, 1973, fig. 1A, and Batten & Dumont, 1976, fig. 24).<ref name="Janssen 2007"/>

{| ||left|thumb|apical view of very small juvenile shell shows typical zigzag-shaped spiral ridges ||left|thumb|apical view of a juvenile shell |}

In the largest available specimen from Pliocene of Philippines, the teleoconch has one complete whorl, widening rapidly, which makes the shell about twice as wide as high.<ref name="Janssen 2007"/> In this specimen the apertural margin is irregularly broken, indicating that the teleoconch might even have more than one calcified teleoconch whorl in complete specimens.<ref name="Janssen 2007"/> In another specimen from Philippines (H = 1.60, W = 2.52 mm), the teleoconch has three quarters of a whorl.<ref name="Janssen 2007"/> On the post-larval shell a vague spiral ornament is present and the peripheral belt remains visible as a slightly produced zone reaching the apertural margin.<ref name="Janssen 2007"/>

The type c eye morphology is only seen in one other species of atlantid (''Atlanta helicinoides'') and one carinariid (''Cardiapoda richardi'').<ref name="Seapy 2010"/> The shape of the operculum is unique among atlantids, broadly triangular, approaching trapezoidal in shape, and lacking the apical spiral part present in all other atlantids.<ref name="Seapy 2010"/> Also unique to the operculum is that when the animal retracts into its shell, only about one-half of the operculum covers the shell aperture.<ref name="Seapy 2010"/> The radula is very large and is triangular in shape.<ref name="Seapy 2010"/>

Recent specimens of ''Oxygyrus keraudreni'' have an uncalcified shell of conchiolin in the adult stage.<ref name="Janssen 2007"/> Janssen (2007) have found an indication that, during the Pliocene, individuals of this species were yet further calcified than are extant specimens.<ref name="Janssen 2007"/> This could point to a developmental trend involving a reduction of calcareous matter in the course of time, as a gradual weight reduction beneficial for holoplanktonic life.<ref name="Janssen 2007"/> The distinct peripheral belt demonstrates that a conchiolin keel was present.<ref name="Janssen 2007"/>

==Distribution== The geographical distribution is cosmopolitan in tropical to subtropical waters.<ref name="Seapy 2010"/>

=== Fossil distribution === From the fossil record ''Oxygyrus keraudrenii'' has been found from Pliocene in Tiep, Roxas ([https://web.archive.org/web/20111009181040/http://www.scriptageologica.nl/s/scripta/images/vol07/nr135/07135a02fig1.jpg map]) and Anda, Pangasinan, Luzon, Philippines in 2001 (published in 2007).<ref name="Janssen 2007"/> ''Oxygyrus keraudrenii'' is known, in very few specimens only, from Jamaica (Janssen, 1998) and the Mediterranean Pliocene (Italy, Spain, France; Janssen, 2004).<ref name="Janssen 2007"/> The French occurrence was dated as Zanclean and thus it may be assumed that ''Oxygyrus'' occurred approximately since the Miocene-Pliocene transition.<ref name="Janssen 2007"/> Miocene representatives or related forms are unknown.<ref name="Janssen 2007"/>

== Habitat == ''Oxygyrus keraudreni'' is a shallow-dwelling species that normally occurs in low abundances.<ref name="Seapy 2010"/> In the Indian Ocean was ''Oxygyrus keraudreni'' found essentially limited to the upper 100 m of the water column, with 90% between 50 m and the surface.<ref name="Seapy 2010"/> Similarly, off Hawaii was it recorded low in numbers of individuals whose vertical range was limited to the upper 90 m of the water column, with most individuals occurring at night in the upper 45 m.<ref name="Seapy 2010"/> In another study from the same area off Hawaii it was found that ''Oxygyrus keraudreni'' was captured in nighttime tows but was either absent or nearly so from comparable daytime ones.<ref name="Seapy 2010"/> The results from the latter two studies suggest the possibility of daytime net avoidance.<ref name="Seapy 2010"/>

==References== This article incorporates CC-BY-3.0 text from references.<ref name="Janssen 2007">{{cite journal| author=Janssen A. W.| title=Holoplanktonic Mollusca (Gastropoda: Pterotracheoidea, Janthinoidea, Thecosomata and Gymnosomata) from the Pliocene of Pangasinan (Luzon, Philippines)| journal=Scripta Geologica| year=2007| volume=135| url=http://www.scriptageologica.nl/07/nr135/a02| access-date=20 August 2010| archive-url=https://web.archive.org/web/20110724165136/http://www.scriptageologica.nl/07/nr135/a02| archive-date=24 July 2011| url-status=dead}}</ref><ref name="Seapy 2010">Seapy R. R. (2010). ''Oxygyrus keraudreni'' Benson 1835. Version 1 April 2010. http://tolweb.org/Oxygyrus_keraudreni/28753/2010.04.01 in The Tree of Life Web Project, accessed 20 August 2010.</ref> {{Reflist}}

Category:Atlantidae Category:Extant Pliocene first appearances Category:Gastropods described in 1835 Category:Taxa named by William Henry Benson