INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

KINGDOM MULTICELLULAR ANIMALS (METAZOA)

SUBKINGDOM TRUE MULTICELLULAR ANIMALS (EUMETAZOA)

SECTION TRIPLOBLASTIC (TRIPLOBLASTICA), OR BILATERAL (BILATERIA) ANIMALS

SUBSECTION MOLTING ANIMALS (ECDYSOZOA)

PHYLUM ARTHROPODS (ARTHROPODA)

SUBPHYLUM GILL-BREATHING (BRANCHIATA), OR CRUSTACEANS (CRUSTACEA)

CLASS MAXILLOPODA (MAXILLOPODA)

SUBCLASS BARNACLES (CIRRIPEDIA)

Includes exclusively marine, highly specialized sessile filter-feeding or parasitic forms. More than a thousand modern species are known. The fauna of the Black Sea contains no more than 10 species, and the Sea of Azov has only one. The length of barnacles ranges from a few millimeters to 2-5 cm.

Externally, barnacles do not resemble crustaceans: their body is covered by two Skin folds—the mantle, resembling that of Mollusks. The mantle of non-parasitic forms secretes calcareous plates outwardly, forming a protective carapace. The antennules and the entire anterior part of the HEAD transform into an attachment organ; in some species, this is a long muscular stalk, while in others, it is a flat, broad sole. The antennae and compound eyes atrophy, and other head appendages simplify, surrounding the oral opening located at the posterior part of the head. In some species, the head region disappears entirely. Individual plates of the carapace can part, and thoracic legs in the form of thin, segmented cirri extend from the resulting slit; hence the name - barnacles (cirripeds). The abdomen and its appendages are reduced (Fig. 334).

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Fig. 334. Barnacles (from Birshtein and Pasternak): a, c - external appearance of an acorn barnacle and a goose barnacle, respectively;

b, d - their internal Structure, respectively

1 - adductor Muscle; 2 - oral cone; 3 - thoracic legs; 4 - copulatory organ; 5 - abdomen

Barnacles, with few exceptions (genus Alcippe), are hermaphrodites. In some species, alongside hermaphroditic individuals, there are dwarfed "complementary" males. Finally, there are species whose normal individuals can be either females or hermaphrodites, and both the former and the latter harbor dwarf males. Development occurs with metamorphosis. The larvae are the nauplius, metanauplius, and an additional stage—the cypris larva, which possesses a bivalve cuticular shell, making the larva resemble ostracod crustaceans of the genus Cypris.

Among the barnacles of the order Thoracica, the so-called acorn barnacles (genus Balanus) and goose barnacles (genus Lepas) are widely known. In acorn barnacles, the head forms a broad sole, and the entire body is covered with calcareous plates (Fig. 334, a, b). The crustacean's body is positioned inside the shell with its abdomen facing upward. Locomotion and Water filtration are carried out using movable shell plates and biramous thoracic legs bearing numerous setae ("cirri"). In goose barnacles (Fig. 334, c, d), the anterior part of the head is elongated into a stalk, and the body is covered by a laterally flattened shell composed of five to six plates. Some acorn barnacles attach to the skin of whales; species of the genus Coronula feed by filtering water, whereas Tubicinella and others become parasites, feeding on the Tissues and Blood of whales.

Among parasitic species, Representatives of the order Rhizocephala (Rhizocephala)—parasites of decapod crustaceans—have the most peculiar structure. There are about 250 species. Very widespread, including in the Black Sea, the crab parasite Sacculina carcini externally looks like a sac located under the host's abdomen (Fig. 335). In reality, this is only part of the parasite's body containing the reproductive Organs. The other part consists of ROOT-like outgrowths extending from the sac and entangling all the host's Internal Organs. Nutrition is osmotic: through the thin integuments of the outgrowths, the crab's Body Fluids enter the parasite's Organism.

Fig. 335. Sacculina carcini on the abdomen of a crab (from Birshtein and Pasternak):

1 - branching within the crab's body; 2 - external body part of sacculina