Semibalanus balanoides

Semibalanus balanoides

''Semibalanus balanoides'' is a common and widespread boreo-arctic species of acorn barnacle. It is common on rocks and other substrates in the intertidal zone of north-western Europe and both coasts of North America.
Northern Rock Barnacle - Semibalanus balanoides Common, intertidal barnacles that resemble volcanoes. They have a membranous base and the outer shell consists of white, overlapping, shell-like plates that grow with the animal.

Habitat: Covering rocks in the intertidal zone. Geotagged,Semibalanus balanoides,Summer,United States,barnacle,barnacles

Appearance

Adult ''S. balanoides'' grow up to 15 millimetres in diameter, and are sessile, living attached to rocks and other solid substrates. They have six greyish wall plates surrounding a diamond-shaped operculum. The base of the shell is membranous in ''Semibalanus,'' unlike other barnacles which have calcified bases. When the tide rises to cover the barnacles, the operculum opens, and feathery ''cirri'' are extended into the water to filter food from the seawater. When the tide falls, the operculum closes again to prevent desiccation; the reduction from the primitive condition of eight wall plates to six is believed to decrease water loss even further by reducing the number of sutures through which water can escape.
Northern Rock Barnacle - Semibalanus balanoides Common, intertidal barnacles that resemble volcanoes  or dragon eyes. This rock had multiple generations as you can see from the variations in size.

They have a membranous base and the outer shell consists of white, overlapping, shell-like plates that grow with the animal.

Habitat: Encrusted on rocks in the low tide zone
 Geotagged,Semibalanus balanoides,Spring,United States,barnacle,northern barnacle

Distribution

''S. balanoides'' is found in the intertidal zone in the world's northern oceans. Its distribution is limited in the north by the extent of the pack-ice and in the south by increasing temperature which prevents maturation of gametes. The mean monthly temperature of the sea must drop below 7.2 °C for it to breed.

In Europe, ''S. balanoides'' is found on Svalbard and from Finnmark to north-west Spain but excluding part of the Bay of Biscay. It is common throughout the British Isles, except in parts of Cornwall, the Scilly Isles and south-western Ireland. On the North American coast of the Atlantic Ocean, it reaches as far south as Cape Hatteras, North Carolina, and on the Pacific coast, it reaches as far south as British Columbia. ''S. balanoides'' is the most common and widespread intertidal barnacle in the British Isles, and the only intertidal barnacle of the north-east coast of North America.
Northern Rock Barnacle - Semibalanus balanoides Common, intertidal barnacles that resemble volcanoes.  They have a membranous base and the outer shell consists of white, overlapping, shell-like plates that grow with the animal.  Geotagged,Northern Rock Barnacle,Semibalanus,Semibalanus balanoides,Spring,United States,acorn barnacle,barnacle

Habitat

''S. balanoides'' can be the dominant species of rocky shores, where it grows in a range of situations, from very sheltered to very exposed. It is typically found lower on the shore than another barnacle, ''Chthamalus montagui,'' although with some overlap. ''S. balanoides'' can tolerate salinities down to 20 psu, allowing it to colonise parts of estuaries. On semi-exposed shores, ''S. balanoides'' may form a patchwork with patches of seaweeds, such as ''Fucus serratus,'' and limpets; the fronds of the seaweeds brush the barnacle larvae from the rocks, allowing limpets to colonise it instead. At the southern limit of its range, including Cornwall, ''S. balanoides'' is replaced by ''Chthamalus montagui.'' Although capable of living in the sublittoral zone, ''S. balanoides'' tends to be restricted to the intertidal by predation and by competition from species such as the blue mussel, ''Mytilus edulis'', and the algae ''Ascophyllum nodosum'' and ''Chondrus crispus.''
Northern Rock Barnacle (Adults, Juveniles, and Cypris) - Semibalanus balanoides The adults are the large barnacles to the right. The juveniles are the smaller ones in the middle. And, the cypris are the brownish, ovalish specks to the left in the photo. 

Northern rock barnacles are hermaphrodites, but cannot fertilize themselves. Copulation is followed by internal fertilization. The eggs (up to 10,000!) remain inside the shell.  The eggs hatch into free-swimming larvae, which is followed by a unique cypris larval stage. The cypris larvae spend their time seeking a habitable substrate. Once it settles on a spot, it metamorphoses into its adult form, but is called a "juvenile" as it is much smaller than its ultimate size will be.

Habitat: Low tide zone
https://www.jungledragon.com/image/89871/northern_rock_barnacle_cypris_larvae_-_semibalanus_balanoides.html Cyprid,Geotagged,Semibalanus balanoides,Spring,United States,cypris

Reproduction

Breeding takes place in winter at an optimal temperature of 14 °C . ''S. balanoides'' is hermaphroditic, but cannot fertilise itself. Gametes are transferred with a penis which may be up to 7.5 centimetres long; barnacles that are further apart than about 5 cm are therefore unable to reproduce together. One barnacle may inseminate another up to eight times, and up to six concurrent penetrations may occur. The penis degenerates after copulation, and a new one is regrown the following year. Up to 10,000 eggs may be produced, and they are stored in sacs within the shell cavity. While the eggs are developing, the adult barnacle does not moult. The eggs hatch into nauplius larvae, which have three pairs of legs, one pair of antennae and a single eye and are released to coincide with the spring algal bloom. These spend several weeks in the water column, feeding on plankton. Over a series of moults, the larva passes through six naupliar instars before changing into a cypris larva, with a two-valved carapace. These larvae can survive weeks embedded in sea ice. The cypris larva does not feed but seeks out a suitable substrate for its adult life. Having settled on a substrate, the larva examines the area until it finds another barnacle of the same species and then attaches itself to the substrate with its antennae, whereupon it metamorphoses into the adult. Sexual maturity is usually only reached after two years, and adults of ''S. balanoides'' may live for up to seven years, depending on their position on the shore.
Northern Rock Barnacle - Semibalanus balanoides Common, intertidal barnacles that resemble volcanoes or dragon's eyes :P. They have a membranous base and the outer shell consists of white, overlapping, shell-like plates that grow with the animal.

Habitat: Adhered to a snail in the intertidal zone
https://www.jungledragon.com/image/81089/northern_rock_barnacle_-_semibalanus_balanoides.html Geotagged,Semibalanus balanoides,Spring,United States,barnacle,northern rock barnacle

Food

''Semibalanus balanoides'' is a filter feeder, using its thoracic appendages, or ''cirri,'' to capture zooplankton and detritus from the water. If there is a current, then the barnacle holds its cirri stiffly into the flow, but when there is no current, the barnacle beats its cirri rhythmically. Plankton levels are highest in Spring and Autumn, and drop significantly during Winter, when the barnacles are dependent on reserves of food which they have stored.
Waiting for the water Semibalanus balanoides (in Dutch: zeepokken) on groynes at the Dutch beach coast Geotagged,Semibalanus balanoides,The Netherlands

Predators

Predators of ''Semibalanus balanoides'' include the whelk ''Nucella lapillus,'' the shanny ''Lipophrys pholis,'' the sea star ''Asterias vulgaris,'' and nudibranchs. Although they have no eyes, barnacles are aware of changes in light, and withdraw into their shells when threatened. Parasites of ''S. balanus'' include ''Pyxinoides balani,'' a protozoan which lives in the barnacle's midgut, and ''Epistylis horizontalis,'' a ciliate which lives on the gills. The isopod ''Hemioniscus balani'' occurs from France to the Faroe Islands and the Oslofjord, and from Labrador to Massachusetts, and is a parasite of ''S. balanoides,'' effectively castrating the barnacle if it is heavily infested. The lichens ''Arthropyrenia sublittoralis'' and ''Pyrenocollema halodytes'' may colonise the shells of barnacles.

References:

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Taxonomy
KingdomAnimalia
DivisionArthropoda
ClassMaxillopoda
OrderSessilia
FamilyArchaeobalanidae
GenusSemibalanus
SpeciesS. balanoides