Purple Acorn Barnacle (Balanus amphitrite)


Photo courtesy of Andrew Gryrus


Binomial: Balanus amphitrite Darwin 1854 (= Amphibalanus amphitrite Pitombo 2004)
Vernacular: striped barnacle, the purple acorn barnacle and Amphitrite's rock barnacle


Balanus amphitrite Darwin 1854
Balanus, being the name of the genus refers to chestnut or acorn in Latin. Da Costa (1778) named the unknown-then-shelled animals as Acorn shells since they have comparable morphology to an acorn or a chestnut: they have hardened exterior shell (shell or wall plates for barnacles.
Amphitrite is known to the goddess of the oceans and the wife of King Poseidon in Greek Mythology. There is no written explanation to the naming of ‘amphitrite’ to the barnacle, probably named it as such of its physical abilities to withstand desiccation when not submerged under seawater and permanently attach to a hard substratum on the coastline. Balanus amphitrite are hermaphrodites as opposed to its feminine background name.

Amphibalanus amphitrite Pitombo 2004
‘Amphibalanus’ is a combination of the words amphitrite and balanus. Genus Amphibalanus derived from phylogenetic revision of which a new subfamily Amphibalaninae was proposed and derived from original subfamily Balaninae (Pitombo, 2004). Pitombo (2004) evaluated evolutionary relationships amongst the subfamilies within family Balanoidea hence proposed a fourth subfamily the Amphibalaninae as being a monophylectic group, Amphibalanus gen. nov. and its allies based on new diagnostic morphological characters. Therefore, Balanus amphithrite automatically reverted into Amphibalanus amphithrite from this revision.

Curent Status of Scientific Name
Currently, the debacle of nomenclature i.e. usage of Barnacle amphitrite or Amphibalanus amphithrite still exist (Clare & Hoeg, 2008; Carlton & Newman, 2010). Clare and Hoeg (2008) supported retention of B. amphitrite due to “scarce” referencing of A. amphitrite, and outright critism of Pitombo (2004)’s methology of phylogenetic revision. They have suggested adaptation of a compromise nomenclature i.e. Balanus amphitrite (=Amphibalanus amphitrite) or vice-versa for the species. Carlton & Newman (2010), on the other hand refuted such claims stating that names changes, especially to non-systematists is often slow and does not reflect rejection from the scientific community and supports Pitombo’s revision.

Vernacular Etymology
In terms of vernacular names, it was named ‘striped barnacle’ because its wall plates have longitidunal coloured striations, however this term also encompasses other barnacle species e.g. Balanus cirratus. Also termed “Purple acorn barnacle” due to colour of the striations i.e. purple on its plates.

Balanus amphitrite and varieties (Figs 2a to 2o). Picture courtesy of Darwin-Online


Kingdom Animalia -- Animal, animals, animaux
Phylum Arthropoda -- arthropodes, arthropods, Artrópode
Subphylum Crustacea Brünnich, 1772 – crustace, crustáceo, crustacés
Class Maxillopoda Dahl, 1956
Subclass Thecostraca Gruvel, 1905
Infraclass Cirripedia Burmeister, 1834 -- barnacles, bernacles
Superorder Thoracica Darwin, 1854 -- barnacles
OrderSessilia Lamarck, 1818 -- sessile barnacles
Suborder Balanomorpha Pilsbry, 1916 -- acorn barnacles
Superfamily Balanoidea Leach, 1817
Family Balanidae Leach, 1817/ Amphibalanidae Pitombo, 2004)
Genus Balanus Da Costa, 1778 /Amphibalanus Pitombo, 2004)
Species Amphitrite Darwin, 1854

Classification adapted from ITIS and Pitombo (2004).


Darwin (1854) initially described Balanus amphitrite as multivariate species of which he had named B. amphitrite and identified other eight varieties namely Balanus amphitrite var. communis, venustus, pallidus, niveus, modestus, stutsburi, obscurus, variegatus, and cirratus. All of them shared the following morphological and anatomical characteristics of the following:
Shell longitudinally striped with purple or pink; sometimes with the stripes confluent; sometimes wholly white. Scutum internally with a prominent broad adductor ridge (Refer to figure below)

Figure 1 a. top view and b. internal view of tergum (top-right) and scutum (bottom-left) and c. external view of scutum and d. internal view of scutum.



(Kindly refer to Fox's Guide to Invertebrate Anatomy Online for reference of morphological terms of a Balanomorph barnacle.)

Shell: Wall of six plates, smooth; parietes with a single row of tubes with or without transverse septa; radii solid, transverse teeth on sutural edge with denticles on lower side only (Pitombo, 2004)

Basal surface: Basis tubiferous, tubes in a single layer (Pitombo, 2004).

Operculum: Scutum with a conspicuous adductor ridge. Tergum with spur having abrupt change in the direction of growth lines, with spur and furrow margins coincident, basal margin with well-developed depressor muscle crests projecting beyond border.

Oral cone: Second maxilla withanterior margin of distal lobe having smooth, acuminate setae with enlarged and modified tips.

Cirri (feet-like appendages): Cirrus III with inner face of endopod with pinnate setae rarely with bifurcate (complex) setae. Cirri IV-VI with erect hooks below posterior angles of distal articles of rami.

Cirri I, II, III, IV, V and VI (Figures b- g) of Balanus amphitrite, Figure courtesy of Harding (1962) (awaiting confirmation)



When submerged in water, B. amphitrite, like other balanomorph barnacles, cast out cirri for feeding. There are two forms of feeding, macro-feeding and micro-feeding

Macro-feeding/ Captorial feeding

During macro-feeding, and B. amphitrite, withdraw out its cirri and grabs food particles rhymtically at high beat (Crisp & Southward, 1961). Usually larger cirri are usually employed for this method of feeding and range of food size captured from this method are usually in millimeters, for example proteinaceous materials and planktons.

Watch a short of clip of macro-feeding by an adult Balanus amphitrite (courtesy of Youtube User, platypus1979 )

Micro-feeding/ Filter-feeding

Cirri acts as an filter that filters smaller food particles, usually several microns in size, for example diatoms (Crisp & Southward, 1961). Smaller cirri is used as opposed to large cirri. Cirri outside the oral cavity are relatively perpendicular to flow of water (La Barbera, 1984). This form of feeding is less efficient due to slow filtration rates.


Barnacle fouling on an aluminium tin can. Photo by Leong Chin RIck


There is no specific mention on the life history of Balanus amphitrite. It is assumed that its life history are similar to most balanamorph barnacles (Charnov, 1987). Their life cycle consists of four main stages, (1) egg (released from adult), (2) planktonic nauplius (six-stages, more detailed description of each stage here) , (3) cypris larva and (4) attached and sessile adult (Refer to figure below).

Balanus amphitrite is hermaprodhite (Darwin, 1854) however one individual usually cross-fertilises with another individual (Charnov, 1987) The penis in a barnacle is extensible, highly maneuvreable, and can extend several body diameters.

VIdeo on sessile barnacle mating, click here

Stages in a life cycle of a typical Balanomorph barnacle (Family Balanidae). Figure adapted from National Institute of Oceanography (pending approval)


Balanus amphitrite was found to be originated from the Southwestern Pacific and Indian Oceans (Zullo 1963). It is distinctly euryhaline and eurythermal in its tolerance (

Warmer temperate and tropical seas and intertidal beaches ; extremely common; Mediterranean, Smyrna, Sicily, Coast of Portugal, West Coast of Africa, River Gambia, West Indies, Demerara, Natal, Madagascar, Red Sea, Mouth of the Indus, Ceylon, Philippine Archipelago, East Indian Archipelago, Pacific Ocean, east coast of Australia, New Zealand; extremely common on ships' bottoms; often attached to floating timber, canes, &c.; often associated with B. tintinnabulum;attached to pebbles and various shells Darwin (1854).


Although expected to be confined to warm and tropical waters, B. amphitrite was found to be invasive in several colder and temperate countries including Northern America (United States of America), Southern America (Argentina)(Oresanz et al., 2002), Europe (Germany) (Wiegemann, 2008) , Northeast Asia (Japan and Hong Kong) (Qiu, 1999) and Oceania (Australia ands New Zealand) (Foster, 1978).


Darwin (1854) did not designate type specimens and type localities for B. amphitrite and its varieties (Yamaguchi, 1980). However, the original specimen that was studied by Darwin was kept in the British Museum (Harding, 1961). Such a specimen without designation of type specimen is termed a lectotype. The lectotype was originally found on a piece of bamboo (Registration No. :B. M., locality Natal, Dr. Krauss) however its dissected parts keep seperately. Now, its remaining shell on the bamboo has been registered as B.M. 1961. 12. 6. 1c, seperated and mounted opercular valve as B.M. 1961.12.6. 1a and animal parts as B.M. 1961.12.6. 1b (Harding, 1961).

Literature and References

Click here page 240) for the original description of Balanus amphitrite by Charles Darwin.

Anderson, D. T. 1980. Barnacles - structure, function, development and evolution. Chapman and Hall London.

Darwin, C. R. 1854. Living Cirripedia, The Balanidæ, (or sessile cirripedes); the Verrucidæ. London: The Ray Society. Volume 2 Text Image Text & image F339.2

Charnov, E.L. 1987. Sexuality and hermaphroditism in barnacles: a natural selection approach. In Southward A.J. (ed.) Crustacean issues 5, Barnacle biology. Rotterdam: A.A. Balkema, pp. 89–104.

Clare, A.S., and Høeg. J.T.. 2008. “Balanus amphitrite or Amphibalanus amphitrite? A note on barnacle nomenclature.” Biofouling 24(1): 55-7.

Foster, B.A. 1978. The marine fauna of New Zealand: Barnacles (Cirripedia, Thotacica). Memoirs of the New Zealand Oceanographic Institute 69: 1-160.

Henry, D. P. & Mclaughlin, P. A. (1975). The barnacles of the. Balanus amphitrite complex (Cirripedia, Thoracica). Zoologische. Verhandelingen, 141, 1–254

LaBarbera, M. 1984. "Feeding currents and particle capture mechanisms in suspension feeding animals". American Zoologist 24 (1): 71–84.
Lulito, C. 2007.Distribution, abundance and reproduction of the Indo-Pacifric acorn barnacle Balanus amphitrite (Crustacea: Cirripedia). J. Mar. Biol. Ass. U.K., 87: 723-727

Orensanz, J.M., Schwindt, E., Pastorino, G., Bortulas, A., Casas, G., Darrigan, G., Elías, R., Gappa, J.J.L., Obenat, S., Pascual, M., Penchaszadeh, P., Piriz, M.L., Scabarino, F., Spivak, E.D. and E.A. Vallarino. 2002. No longer the pristine confines of the world ocean: a survey of exotic marine species in the southwestern Atlantic. Biological Invasions, 4: 115-143.

Pitombo, F. B. 2004. Phylogenetic analysis of the Balanidae (Cirripedia, Balanomorpha). Zoologica Scripta, 33: 261–276.

Qiu, J.W. 1999. Tolerance of the barnacle Balanus Amphitrite amphitrite to salinity and temperature stress:effects of previous experience. Marine Ecology Progress Series. 188. 123-132

Wiegemann, M. 2008. Wild cyprids metamorphosing in vitro reveal the presence of Balanusamphitrite Darwin, 1854 in the German Bight basin, Aquatic Invasions, 3(2): 235-238.

Yamaguchi, T. 1980. A New Species Belonging to the Balanus amphitrite Darwin Group (Cirripedia, Balanomorpha).Journal of Paleontology, 54(5): 1084-1101

Zullo, V. A. 1963. A Preliminary Report On Systematics And Distribution Of Barnacles (Cirripedia) Of Cape Cod Region. Systematics-Ecology Program, Marine Biology Laboratory, Woods Hole, Massachusetts, 33 p

Links to other types of species pages



Table of Contents

| Invasion