''Exomilus pentagonalis'', common name the orange rib drillia, is a species of

sea snail Sea snail is a common name for slow-moving marine gastropod molluscs, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with slugs, which are distinguished from snails primarily by the ...

, a marine

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

mollusk in the family

Raphitomidae Raphitomidae is a family of small to medium-sized sea snails, marine gastropod mollusks in the superfamily Conoidea.Bouchet P. & Rocroi J.-P. (Ed.) (2005). "Classification and nomenclator of gastropod families". ''Malacologia'' 47(1-2). . 39 ...

Description

The length of the shell attains 3.5 mm, its diameter 1.25 mm. (Original description) The minute shell is telescope-shaped and rather thick. It contains

whorl A whorl ( or ) is an individual circle, oval, volution or equivalent in a whorled pattern, which consists of a spiral or multiple concentric objects (including circles, ovals and arcs). Whorls in nature File:Photograph and axial plane floral ...

s without the

protoconch A protoconch (meaning first or earliest or original shell) is an embryonic or larval shell which occurs in some classes of molluscs, e.g., the initial chamber of an ammonite or the larval shell of a gastropod. In older texts it is also called ...

. The protoconch is absent. The spire is gradated, the whorls straight-sided in the anterior three-fourths, and bevelled at an angle of 45° to the posterior suture, which is distinct and simple. The sculpture consists of five longitudinal ribs, continuous, narrow, erect and prominent. The interspaces are nearly flat, giving a pentagonal section. The spiral sculpture consists of Sublenticular inconspicuous longitudinal and spiral striae, which cross the ribs. The

body whorl The body whorl is part of the morphology of the shell in those gastropod mollusks that possess a coiled shell. The term is also sometimes used in a similar way to describe the shell of a cephalopod mollusk. In gastropods In gastropods, the b ...

shows five longitudinal ribs, squarely rhomboidal, angulated near the suture, and carinated at the periphery, the ribs having projecting points here, and the carina being curved between them. The body whorl is excavately contracted below. Scarcely visible sublenticular longitudinal striae in upper part; rather less obsolete spiral striae. These are more valid below the carina, where seven can be counted on the ventral aspect. The aperture is narrow, elongately oblong. The outer lip is varicosely thickened by a rib. The margin is thin, simple, and sharp, straight for four-sevenths of its length, between the angle and the carina, curved towards the notch in the lower two-sevenths, and containing a well marked sinus in the upper seventh, rather more than a semi-circle, not quite reaching to the suture. The columella is straight, slightly concave below. The inner lip is inconspicuous. Ornament unicoloured dull stony-white.Verco, J.C. 1896. ''Descriptions of new species of marine Mollusca of South Australia. Part I.; Transactions of the Royal Society of South Australia v. 20 (1895–1896)
public domain.

Distribution

This marine species is endemic to Australia and occurs off New South Wales, South Australia and Tasmania.

References

* Hedley, C. 1907. ''The results of deep sea investigation in the Tasman Sea. Mollusca from eighty fathoms off Narrabeen.'' Records of the Australian Museum 6: 283–304 * Hedley, C. 1922. ''A revision of the Australian Turridae''. Records of the Australian Museum 13(6): 213–359, pls 42–56 * May, W.L. 1923. ''An Illustrated Index of Tasmanian Shells: with 47 plates and 1052 species''. Hobart : Government Printer 100 pp.
Tucker, J.K. 2004 ''Catalog of recent and fossil turrids (Mollusca: Gastropoda)''. Zootaxa 682:1–1295

External links

* {{DEFAULTSORT:Exomilus Pentagonalis Raphitomidae Gastropods of Australia Gastropods described in 1896