Marginella orstomi is a species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of colorful small sea snail

Snail

Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...

, a marine

Marine (ocean)

Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

 gastropod mollusk in the family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Marginellidae

Marginellidae

Marginellidae, or the margin shells, are a taxonomic family of small, often colorful, sea snails, marine gastropod molluscs in the clade Neogastropoda.- Taxonomy :...

.

The marine malacofauna of West Africa is rich in Marginellidae. The holotype

Holotype

A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...

 of Marginella orstomi was collected at a depth of between 200 and 250 m, off Pointe Noire, Republic of Congo. (A related species was dredged from a more northern locality off the coast of Congo.) The species is also related to Marginella huberti Clover, 1972, from Lobito

Lobito

Lobito is a town and municipality in Benguela Province in Angola.It dates from 1905 and owes its existence to the bay of the same name having been chosen as the sea terminus of the Benguela railway to the far interior, passing through Luau to Katanga in the Democratic Republic of the Congo. The...

, Angola

Angola

Angola, officially the Republic of Angola , is a country in south-central Africa bordered by Namibia on the south, the Democratic Republic of the Congo on the north, and Zambia on the east; its west coast is on the Atlantic Ocean with Luanda as its capital city...

.

Description

The shell is of medium size, elongate pear-shaped, with 4½ whorl

Whorl (mollusc)

A whorl is a single, complete 360° revolution or turn in the spiral growth of a mollusc shell. A spiral configuration of the shell is found in of numerous gastropods, but it is also found in shelled cephalopods including Nautilus, Spirula and the large extinct subclass of cephalopods known as the...

s. The shell has a ground coloration of dirty yellow with dark areas, and a pattern consisting of many dark grey transverse irregular zigzag lines sometimes crossed by spiral rows of small dots.

The apex

Apex (mollusc)

Apex is an anatomical term for the tip of the mollusc shell of a gastropod, scaphopod, or cephalopod mollusc.-Gastropods:The word "apex" is most often used to mean the tip of the spire of the shell of a gastropod...

 of the shell is sharp, the angle of the spire

Spire (mollusc)

A spire is a descriptive term for part of the coiled shell of mollusks. The word is a convenient aid in describing shells, but it does not refer to a very precise part of shell anatomy: the spire consists of all of the whorls except for the body whorl...

 is about 70°. The aperture

Aperture (mollusc)

The aperture is an opening in certain kinds of mollusc shells: it is the main opening of the shell, where part of the body of the animal emerges for locomotion, feeding, etc....

 is straight and rather narrow, about ¾ of the length of the shell. The color pattern on the outside of the body whorl

Body whorl

Body whorl is part of the morphology of a coiled gastropod mollusk.- In gastropods :In gastropods, the body whorl, or last whorl, is the most recently-formed and largest whorl of a spiral or helical shell, terminating in the aperture...

 is visible on the inside of the aperture, and the outer lip is thickened and deflected outward. On the outside about 30 to 35 grey transverse stripes are present. The inner surface of the lip is almost smooth, with one tooth near the posterior end. There are four white oblique plait

Plait (gastropod)

A plait is an anatomical feature which is present the shells of some snails, or gastropods. This sculpture occurs often in the shells of marine gastropod mollusks in the clade Neogastropoda, but it is also found in some pulmonate land snails....

s on the anterior half of the columella.

Type material

• Holotype (adult) 28.0 x 15.1 mm Zoölogisch Museum, University of Amsterdam
• Paratype (adult) 23.4 x 12.5 mm Zoölogisch Museum, University of Amsterdam
• Paratype (juvenile) 25.4 x 12.3 mm Zoölogisch Museum, University of Amsterdam

Remarks

Marginella orstomi is closely related to Marginella huberti Clover, 1972, which was collected further south, on the Angolan coast. Both species are characterized by the presence of a white tooth on the inside of the outer lip near the posterior end. Some differences in the shell of both species are mentioned here:

	M. huberti	M. orstomi
Length	17 – 19 mm	23 – 28 mm
Apical angle	80° - 87°	66° - 72°
Outer lip	dentate	smooth
Stripes on outer lip	about 20	about 30