Alvinia gallinacea 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 minute 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...

 with an operculum

Operculum (gastropod)

The operculum, meaning little lid, is a corneous or calcareous anatomical structure which exists in many groups of sea snails and freshwater snails, and also in a few groups of land snails...

, 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 or micromollusk

Micromollusk

A micromollusk is a descriptive term for a shelled mollusk which is extremely small, even at full adult size. The word is usually, but not exclusively, applied to marine mollusks, although in addition, numerous species of land snails and freshwater mollusks also reach adult size at very small...

 in the family Rissoidae

Rissoidae

Rissoidae is a large family of very small and minute sea snails with an operculum, marine gastropod mollusks in the clade Littorinimorpha.-Distribution and habitat:...

.

Original description

Crisilla picta was originally collected by Reverend Robert Boog Watson

Robert Boog Watson

Robert Boog Watson was a Scottish malacologist and minister of the Free Church of Scotland best known as the author of the report on the Scaphopoda and Gastropoda collected by on the H.M.S. Challenger expedition to survey the world's oceans during the years 1873-1876. Watson also described...

 in Madeira and it was sent to British malacologist John Gwyn Jeffreys

John Gwyn Jeffreys

John Gwyn Jeffreys was a British conchologist and malacologist.He was born in Swansea into a propertied Welsh family and educated at Swansea Grammar School. He went to London to qualify as a barrister, which he did. His greater passion however was for conchology...

, who described it as a new species under name Rissoa picta in 1867. Jeffreys's original text (the type description) reads as follows:
The height of the shell is 0.075 inch (0.1905 cm). The width of the shell is 0.05 inch (0.127 cm).