''Knefastia nigricans'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

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 Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...

in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Pseudomelatomidae Pseudomelatomidae is a family of predatory sea snails, marine gastropods included in the superfamily Conoidea (previously Conacea) and part of the Neogastropoda ( Bouchet & Rocroi, 2005). In 1995 Kantor elevated the subfamily Pseudomelatomina ...

, the turrids and allies.MolluscaBase eds. (2023). MolluscaBase. Knefastia nigricans (Dall, 1919). Accessed through: World Register of Marine Species at: https://www.marinespecies.org/aphia.php?p=taxdetails&id=593930 on 2023-08-16

Description

(Original description) The slender, acute shell is blackish brown with the anterior part of 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 ...

pale reddish brown. It has a conspicuous

periostracum The periostracum ( ) is a thin, organic coating (or "skin") that is the outermost layer of the shell of many shelled animals, including molluscs and brachiopods. Among molluscs, it is primarily seen in snails and clams, i.e. in gastropods and ...

and a closely appressed suture separated by a single cord from the constricted anal fascicle. It contains nine

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 (lost) protoconch. The axial

sculpture Sculpture is the branch of the visual arts that operates in three dimensions. Sculpture is the three-dimensional art work which is physically presented in the dimensions of height, width and depth. It is one of the plastic arts. Durable sc ...

consists of (on the body whorl eight) prominent angular ribs with wider interspaces, beginning abruptly at the shoulder rapidly dwindling anteriorly and obsolete on the base. These ribs are crossed by (on the body whorl about 14) widely spaced slender cords, slightly nodulous at the intersections. The

aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. An opt ...

is narrow. The

anal sulcus The anal sulcus, also called the anal sinus or anal canal, in Gastropods is a notch, a shelly tube at the top of the aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and fo ...

is shallow. The outer lip is sharp, simple and with a slight subsutural callus. The inner lip is erased. The columella is straight. The

siphonal canal The siphonal canal is an anatomical feature of the shells of certain groups of sea snails within the clade Neogastropoda. Some sea marine gastropods have a soft tubular anterior extension of the mantle called a siphon through which water is ...

is wide and very slightly recurved.Dall (1919) Descriptions of new species of Mollusca from the North Pacific Ocean; Proceedings of the U.S. National Museum, vol. 56 (1920)
(described as ''Turricula (Knefastia) nigricans'')

Distribution

This marine species occurs in the Pacific Ocean off Lower California.

References

* Abbott, R. T. (1974). American seashells. The marine Mollusca of the Atlantic and Pacific coast of North America. ed. 2. Van Nostrand, New York. 663 pp., 24 pls. {{DEFAULTSORT:Knefastia Nigricans nigricans Gastropods described in 1919