Monostiolum is a genus of sea snails, marine gastropod mollusks in the family Pisaniidae.
General characteristics (Original description) The shell is small, with an elevated spire and a single terminal varix. The nucleus bears a protoconch that is immersed in the first nepionic whorl, leaving a distinct apical pit. The subsequent whorls are axially ribbed, although the ribs become obsolete on the later whorls of the adult shell. The coloration is similar to that of Colubraria s. s., and the sutures are appressed. The operculum is elongate-ovate and has an apical nucleus.
The animal has slender tentacles, with the eyes prominently situated on their outer bases. The verge is sickle-shaped and recurved over the back of the neck. The radula is long and bears teeth closely resembling those of Pisania maculosa (Lamarck, 1822) (synonym of Pisania striata (Gmelin, 1791))> and Pisania fusiformis (Blainville, 1932) (synonym of Solenosteira fusiformis (Blainville, 1832)). The dental formula is 1/3 1/3 1/3, and the base of the rachidian tooth is not excavated anteriorly.
Species Species within the genus Monostiolum include: Monostiolum atlanticum (Coelho, Matthews & Cardoso, 1970) Monostiolum auratum Watters & Finlay, 1989 Monostiolum crebristriatus (Carpenter, 1856) Monostiolum fumosum Watters, 2009 Monostiolum harryleei Garcia, 2006 † Monostiolum heatherae Petuch, 1994 † Monostiolum hungaricum (Csepreghy-Meznerics, 1954) Monostiolum nocturnum Watters, 2009 Monostiolum pictum (Reeve, 1844) Monostiolum rosewateri Watters & Finlay, 1989 Monostiolum simonei Watters, 2016 Monostiolum tessellatum (Reeve, 1844) † Monostiolum varians (Michelotti, 1847)
Species brought into synonymy Monostiolum nigricostatum (Reeve, 1846): synonym of Sinetectula nigricostata (Reeve, 1846) (superseded combination Monostiolum weberi (Watters, 1983): synonym of Bailya weberi (Watters, 1983)
References
Watters G.T. & Finlay C.J. (1989) A revision of the western Atlantic Recent species of the genus Monostiolum Dall, 1904, and Bailya (Parabailya) new subgenus (Gastropoda: Buccinidae). The Veliger 32(1): 47-59. [3 January 1989] page(s): 55