''Janua pagenstecheri'' 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 ...

of marine

polychaete Polychaeta () is a paraphyletic class (biology), class of generally marine invertebrate, marine annelid worms, common name, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that ...

. It is widely distributed around the

British Isles The British Isles are a group of islands in the North Atlantic Ocean off the north-western coast of continental Europe, consisting of the islands of Great Britain, Ireland, the Isle of Man, the Inner and Outer Hebrides, the Northern Isles, ...

and across north-western Europe, and has been described as "probably the commonest spirorbid in the world". ''Janua pagenstecheri'' lives attached to substrates such as

seaweed Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...

s including ''

Corallina officinalis ''Corallina officinalis'' is a calcareous red seaweed which grows in the lower and mid-littoral zones on rocky shores. It is primarily found growing around the rims of tide pools, but can be found in shallow crevices anywhere on the rocky shor ...

'', rocks, stones, shells, and the

carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...

s of

crab Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...

s. ''J. pagenstecheri'' inhabits a shell made of calcium carbonate in the form of a dextral spiral, with the tube up to 2 mm in diameter. The animal exists in two

colour morph In biology, polymorphism is the occurrence of two or more clearly different morphs or forms, also referred to as alternative ''phenotypes'', in the population of a species. To be classified as such, morphs must occupy the same habitat at the s ...

s: one bright yellow, which occurs in shallow water, and one much paler, which occurs in deeper water. It differs from ''

Spirorbis spirorbis ''Spirorbis spirorbis'' is a small (3–4 mm) coiled polychaete that lives attached to seaweeds and eel grass in shallow saltwater. They have a smooth, white, sinistral (left-handed) coiled shell encasing an orange body about 3 mm in l ...

'' in that ''S. spirorbis'' retains its eggs in the tube, while ''J. pagenstecheri'' incubates them a few at a time in its operculum, and grows a new cap for the operculum after releasing the embryos. The species was described by

Armand de Quatrefages Armand refer to: People * Armand (name), list of people with this name *Armand (photographer) (1901–1963), Armenian photographer *Armand (singer) (1946–2015), Dutch protest singer *Sean Armand (born 1991), American basketball player *Armand, ...

in 1865, and named after

Heinrich Alexander Pagenstecher Heinrich may refer to: People * Heinrich (given name), a given name (including a list of people with the name) * Heinrich (surname), a surname (including a list of people with the name) *Hetty (given name), a given name (including a list of peo ...

, professor of

zoology Zoology ()The pronunciation of zoology as is usually regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the Animal, animal kingdom, including the anatomy, structure, embryology, evolution, Biological clas ...

at the

University of Heidelberg } Heidelberg University, officially the Ruprecht Karl University of Heidelberg, (german: Ruprecht-Karls-Universität Heidelberg; la, Universitas Ruperto Carola Heidelbergensis) is a public research university in Heidelberg, Baden-Württemberg, ...

and the first director of the Hamburg natural history museum.

References

{{Taxonbar, from=Q1822449 Serpulidae Animals described in 1865 Taxa named by Jean Louis Armand de Quatrefages de Bréau