''Chthamalus stellatus'',

common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often contrast ...

Poli's stellate barnacle, 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 ...

acorn barnacle Acorn barnacle and acorn shell are Common name, vernacular names for certain types of stalkless barnacles, generally excluding goose barnacles, stalked or gooseneck barnacles. As adults they are typically cone-shaped, symmetrical, and attached to r ...

common on rocky shores in

South West England South West England, or the South West of England, is one of nine official regions of England. It consists of the counties of Bristol, Cornwall (including the Isles of Scilly), Dorset, Devon, Gloucestershire, Somerset and Wiltshire. Cities and ...

Ireland Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic Ocean, in Northwestern Europe, north-western Europe. It is separated from Great Britain to its east by the North Channel (Grea ...

, and

Southern Europe Southern Europe is the southern regions of Europe, region of Europe. It is also known as Mediterranean Europe, as its geography is essentially marked by the Mediterranean Sea. Definitions of Southern Europe include some or all of these countrie ...

. It is named after

Giuseppe Saverio Poli Giuseppe Saverio Poli (26 October 17467 April 1825) was an Italian physicist, biologist and natural historian. His collections, together with those stored in the Royal Bourbon Museum, were the foundation of the Zoological Museum of Naples. Th ...

Description

''C. stellatus'' is a

sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...

barnacle A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in eros ...

that attaches to rocks and other firm materials in the

intertidal zone The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...

using its

membranous A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. ...

base. It is basically cone-shaped but can assume a more tubular shape in a crowded colony. Like other sessile barnacles, as an adult ''C. stellatus'' is a

suspension feeder Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feedin ...

that stays in its fixed shell and uses its feathery, rhythmically beating appendages – actually modified legs – to draw

plankton Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...

and

detritus In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...

into its shell for consumption. The chalky white shell of ''C. stellatus'' has a kite-shaped opercular opening when it is a juvenile and an oval operculum opening when it is an adult. The shell is made up of six solid wall plates of approximately equal size. Its relatively narrow rostral plates remain separate from its rostrolateral plates and do not fuse. ''C. stellatus'' has bright blue tissue with black and orange markings which can be seen when its opercular aperture is not tightly closed. Depending upon environmental conditions and the amount of food available, it can reach up to in diameter.

Reproduction

Like most barnacles, ''C. stellatus'' is

hermaphroditic In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many taxonomic groups of animals (mostly invertebrates) do not have separ ...

and capable of self-fertilisation when isolated, but individuals typically take on either a male or female role in order to mate. Their

penis A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males do n ...

es are significantly longer than their bodies and are used by the stationary "functional males" to search the area for an equally stationary "functional female" neighbour to fertilise. Barnacles of this species produce about 1,000 to 4,000 eggs per brood when functioning as female. The fertilised eggs remain inside the shell of the adult until they are released as

nauplii Nauplius, Nauplia or Nauplios , may refer to : Greece-related * Nauplius (mythology), in Greek mythology, the son of Poseidon and Amymone, the father of Palamedes, and also the name of an Argonaut * Nauplia Nafplio ( ell, Ναύπλιο) is a ...

, free swimming

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

e which float on currents along with other

. After several moults they

metamorphose Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some insec ...

into a

cyprid A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive ...

, a stage at which they cannot feed. The cyprid swims in search of a suitable surface on which to attach itself, head first, in order to metamorphose into the familiar, hard-shelled, immobile form. The duration of its breeding season can be temperature dependent, and it produces fewer

brood Brood may refer to: Nature * Brood, a collective term for offspring * Brooding, the incubation of bird eggs by their parents * Bee brood, the young of a beehive * Individual broods of North American Periodical Cicadas: ** Brood X, the largest b ...

s near the northern limit of its range.

Habitat and range

''C. stellatus'' attaches to exposed rocky shores in the mid to low eulittoral zone in the northeastern

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

. It especially favours islands and headlands as opposed to bays and more protected areas. It is a southern, warm-water species but has been discovered as far north as

Shetland Shetland, also called the Shetland Islands and formerly Zetland, is a subarctic archipelago in Scotland lying between Orkney, the Faroe Islands and Norway. It is the northernmost region of the United Kingdom. The islands lie about to the no ...

and as far east as the

Isle of Wight The Isle of Wight ( ) is a county in the English Channel, off the coast of Hampshire, from which it is separated by the Solent. It is the largest and second-most populous island of England. Referred to as 'The Island' by residents, the Isle of ...

. A 2021 examination of specimens from the

Cape Verde , national_anthem = () , official_languages = Portuguese , national_languages = Cape Verdean Creole , capital = Praia , coordinates = , largest_city = capital , demonym ...

Islands revealed that while they were morphologically similar to ''C. stellatus'', genetic differences between them are larger than those found between different species of ''

Chthamalus ''Chthamalus'' (χθαμαλός, "flat" or "on the ground") is a genus of barnacles that is found along almost all non-boreal coasts of the northern hemisphere, as well as many regions in the southern hemisphere. These small barnacles have been ...

'', potentially justifying assignment of these populations as an evolutionarily significant unit and

sister clade In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...

to ''C. stellatus''. The vertical distribution of ''C. stellatus'' overlaps with '' Chthamalus montagui'' (considered the same species as ''C. stellatus'' until 1976) and '' Semibalanus balanoides'' with the specific prevalence of one species over another in a given locale possibly related to differences in the distribution of the species' larval stages.

References

{{DEFAULTSORT:Chthamalus Stellatus Barnacles Crustaceans of the Atlantic Ocean Crustaceans described in 1791 Taxa named by Giuseppe Saverio Poli