Barnacle clusters  2/18/14


Barnacles are a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and are hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive settings. Around 1,000 barnacle species are currently known.

Our barnacle clusters are from the tropical waters ranging from the Indian Ocean thru Indonesian to the northern shores of Australia

They are sessile (nonmobile) and most are suspension feeders, but those in infraclass Rhizocephala are highly specialized parasites on other crustaceans. They have four nektonic (active swimming) larval stages.

suspension feeders or 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.

(REF: Walters, Martin; Johnson, Jinny (2007). The World of Animals) (REF: "Cirripedia". World Register of Marine Species. Flanders Marine Institute. )

Barnacles are encrusters, attaching themselves temporarily to a hard substrate or a symbiont such as a whale (whale barnacles), a sea snake (Platylepas ophiophila), or another crustacean, like a crab or a lobster (Rhizocephala). The most common among them, "acorn barnacles" (Sessilia), are sessile where they grow their shells directly onto the substrate. Pedunculate barnacles (goose barnacles and others) attach themselves by means of a stalk.

(REF:P. Doyle; A. E. Mather; M. R. Bennett; A. Bussell (1997). "Miocene barnacle assemblages from southern Spain and their palaeoenvironmental significance". Lethaia. 29 )

Free-living barnacles are attached to the substratum by cement glands that form the base of the first pair of antennae; in effect, the animal is fixed upside down by means of its forehead. In some barnacles, the cement glands are fixed to a long, muscular stalk, but in most they are part of a flat membrane or calcified plate. These glands secrete a type of natural quick cement made of complex protein bonds (polyproteins) and other trace components like calcium. This natural cement is able to withstand a pulling strength of 5,000 pounds-force per square inch and a sticking strength of 22–60 pounds-force per square inch.

A ring of plates surrounds the body, homologous with the carapace of other crustaceans. These consist of the rostrum, two lateral plates, two carinolaterals, and a carina. In sessile barnacles, the apex of the ring of plates is covered by an operculum, which may be recessed into the carapace. The plates are held together by various means, depending on species, in some cases being solidly fused.

A carapace is a dorsal (upper) section of the exoskeleton or shell

(REF: "What are barnacles?". Ocean Facts. National Ocean Service, National Oceanic and Atmospheric Administration)

Inside the carapace, the animal lies on its stomach, projecting its limbs downwards. Segmentation is usually indistinct, and the body is more or less evenly divided between the head and thorax, with little, if any, abdomen. Adult barnacles have few appendages on their heads, with only a single, vestigial pair of antennae, attached to the cement gland. The eight pairs of thoracic limbs are referred to as "cirri" which are feathery and very long. The cirri extend to filter food, such as plankton, from the water and move it towards the mouth.

The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the creature's body, each of which is in turn composed of multiple segments.

(REF: "thorax" at Dorland's Medical Dictionary) (REF:"Definition: Thorax". Oxford Learner's Dictionaries. )(REF: "Encyclopedia of Life".) (REF: Lacalli, Thurston C. (September 2009). "Serial EM analysis of a copepod larval nervous system: Naupliar eye, optic circuitry, and prospects for full CNS reconstruction". Arthropod Structure & Development. 38)

Barnacles have no true heart, although a sinus close to the esophagus performs a similar function, with blood being pumped through it by a series of muscles. The blood vascular system is minimal. Similarly, they have no gills, absorbing oxygen from the water through their limbs and the inner membrane of their carapaces. The excretory organs of barnacles are maxillary glands.

The main sense of barnacles appears to be touch, with the hairs on the limbs being especially sensitive. The adult also has three photoreceptors (ocelli), one median and two lateral. These photoreceptors record the stimulus for the barnacle shadow reflex, where a sudden decrease in light causes cessation of the fishing rhythm and closing of the opercular plates. The photoreceptors are likely only capable of sensing the difference between light and dark. This eye is derived from the primary naupliar eye.

(REF: Lacalli, Thurston C. (September 2009). "Serial EM analysis of a copepod larval nervous system: Naupliar eye, optic circuitry, and prospects for full CNS reconstruction". Arthropod Structure & Development. 38)

The word "barnacle" is attested in the early 13th century as "bernekke" and originally referred to a species of goose. Because the full life cycles of both barnacles and geese was unknown at the time, (geese spend their breeding seasons in the Arctic) a folktale emerged that geese hatched from barnacles. It was not applied strictly to the invertebrate until the 1580s. The ultimate meaning of the word "barnacle" is unknown

(REF: "barnacle (n.)". Online Etymology Dictionary.) (REF: "all the evidence shows that the name was originally applied to the bird which had the marvellous origin, not to the shell..." Oxford English Dictionary, 2nd Edition )

Barnacles have two distinct larval stages, the nauplius and the cyprid, before developing into a mature adult.

During the nauplius stage a fertilised egg hatches into a nauplius: a one-eyed larva comprising a head and a telson, without a thorax or abdomen. This undergoes six moults, passing through five instars, before transforming into the cyprid stage. Nauplii are typically initially brooded by the parent, and released after the first moult as larvae that swim freely using setae.

In biology, setae are any of a number of different bristle- or hair-like structures on living organisms.

The cyprid larva is the last larval stage before adulthood. In Rhizocephala and Thoracica an abdomen is absent in this stage, but the y-cyprids (post‐naupliar instar) has three distinct abdominal segments. It is not a feeding stage; its role is to find a suitable place to settle, since the adults are sessile. The cyprid stage lasts from days to weeks. It explores potential surfaces with modified antennules; once it has found a potentially suitable spot, it attaches head-first using its antennules and a secreted glycoproteinous substance. Larvae assess surfaces based upon their surface texture, chemistry, relative wettability, color, and the presence or absence and composition of a surface biofilm; swarming species are also more likely to attach near other barnacles. As the larva exhausts its finite energy reserves, it becomes less selective in the sites it selects. It cements itself permanently to the substrate with another proteinaceous compound, and then undergoes metamorphosis into a juvenile barnacle.

(REF: William A. Newman (2007). "Cirripedia". In Sol Felty Light; James T. Carlton (eds.). The Light and Smith Manual: Intertidal Invertebrates from Central California to Oregon (4th ed.)) (REF: Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004). Invertebrate Zoology (7th ed.) (REF: Donald Thomas Anderson (1994). "Larval development and metamorphosis". Barnacles: Structure, Function, Development and Evolution. Springer )

Typical acorn barnacles develop six hard calcareous plates to surround and protect their bodies. For the rest of their lives, they are cemented to the substrate, using their feathery legs (cirri) to capture plankton.

Once metamorphosis is over and they have reached their adult form, barnacles continue to grow by adding new material to their heavily calcified plates. These plates are not moulted; however, like all ecdysozoans, the barnacle itself will still moult its cuticle.

(REF: E. Bourget (1987). Barnacle shells: composition, structure, and growth.)

Most barnacles are hermaphroditic, although a few species are gonochoric or androdioecious. The ovaries are located in the base or stalk, and may extend into the mantle, while the testes are towards the back of the head, often extending into the thorax. Typically, recently moulted hermaphroditic individuals are receptive as females. Self-fertilization, although theoretically possible, has been experimentally shown to be rare in barnacles.

A hermaphrodite is a sexually reproducing organism that produces both male and female gametes. Animal species in which individuals are of different sexes, either male or female but not both, are gonochoric, which is the opposite of hermaphroditic.

(REF: Holub AM, Shackelford TK (2020). "Gonochorism". In Vonk J, Shackelford TK (eds.). Encyclopedia of Animal Cognition and Behavior)

The sessile lifestyle of barnacles makes sexual reproduction difficult, as the organisms cannot leave their shells to mate. To facilitate genetic transfer between isolated individuals, barnacles have extraordinarily long penises⁠. Barnacles probably have the largest penis to body size ratio of the animal kingdom, up to eight times their body length.

Barnacles can also reproduce through a method called spermcasting, in which the male barnacle releases his sperm into the water and females pick it up and fertilise their eggs.

The Rhizocephala superorder used to be considered hermaphroditic, but it turned out that its males inject themselves into the female's body, degrading to the condition of nothing more than sperm-producing cells.

(REF: "Biology of Barnacles". Museum Victoria. 1996) (REF: Ewen Callaway (2009-04-07). "Penis length isn't everything … for barnacle males") (REF: Mechanism of Fertilization: Plants to Humans)

Scientific classification

Domain: Eukaryota

Kingdom: Animalia

Phylum: Arthropoda

Subphylum: Crustacea

Class: Thecostraca

Subclass: Cirripedia

Burmeister, 1834


One Barnacle cluster 3 to 5 inches...... $3.50


One Barnacle Cluster 5 to 7 inches ......$7.75


One Barnacle Cluster 7 to 10 inches ......$11.25


One Barnacle cluster 10 to 12 inches.... $17.75


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