''Gemmula samueli'' is an extinct

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 ...

Turridae Turridae is a taxonomic family name for a number of predatory sea snails, marine gastropod mollusks in the superfamily Conoidea. MolluscaBase (2018). Turridae H. Adams & A. Adams, 1853 (1838). Accessed through: World Register of Marine Specie ...

, the turrids.

Description

Dimensions: length 12 mm; breadth 4 mm; length of the aperture 7 mm. The fusiform shell is elongate. The turbinate

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 ...

is composed of three smooth

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, the suture of which is marginate. In the brephic stage the margination is much accentuated, and at a later period of growth gives way to a row of small, distant granules. In the same manner, the median, tuberculated carina of the adult commences in the brephic stage by large obtuse uodulations. The shell is thus described by Mr. Tenison-Woods: "It is a polished shell, with whorls angular in the middle, supporting a single, somewhat distant series of coarse, blunt, somewhat square tubercles. These are exactly on the line of the sinus, and at each side the lines of growth curve away from it. The sinus itself is deep, broad, and somewhat quadrate. The aperture is long and round, rather square posteriorly, and the canal is long and only slightly curved." The marginate character of the protoconch is noteworthy ; from its metamorphosis in later stages of growth, it would appear that the species has descended from a stock in which the suture was accompanied by a large flat keel, though no shell of that character has been recorded as occurring in the Australian Tertiaries. Another point of interest in this species is its compound character: it possesses the tubercular sutural coronation and produced spire characteristic of ''

Clavatula ''Clavatula'' is a genus of sea snails, marine gastropod mollusks in the family Clavatulidae. Description In this genus, the shell is fusiform, with a well-produced spire. The whorls are coronated with tubercles or short spines at the suture;. T ...

'', and shows what value is to be placed on that feature. The special nature of the peripheral keel and the arcuate, long

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 ...

somewhat resemble '' Surcula''. Whilst the position of the suture and other general features of the shell recall ''Pleurotoma''. Clearly it was pregnant with evolutionary possibilities.Harris G.F.. (1897) Catalogue of Tertiary Molluscs in the British Museum of Natural History
/ref>

Distribution

Fossils of this marine species have been found in

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

strata in Victoria, Australia.

References

{{DEFAULTSORT:Gemmula Samueli samueli Gastropods described in 1879