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Can you please explain what is Balanus and Chathamalus
Balanus amphitrite is a small, roughly conical barnacle that reaches a maximum diameter of about 20 mm. It has white walls with vertical bands of purple or red-brown stripes. Both the stripes and the white spaces between them are typically wider at the bottom and narrow toward the top. The walls are often smooth, but sometimes have shallow vertical ridges Balanus amphitrite is the type of barnacle called an "acorn" rather than a "gooseneck" barnacle. Acorn barnacles have an outer wall made of rigid plates, and attach directly to rock, wood or other substrates without an intervening, fleshy stalk. The animal lives inside these walls and feeds by extending a set of appendages, which it uses as a kind of net to capture food particles, out through an opening at the top. The opening is closed by a lid that opens by flexing out to the sides. This lid, called the operculum, consists of two symmetrical halves, each made of two roughly triangular, rigid plates that interlock along one edge and are attached to an inner membrane. The larger plate at the barnacle's "head" end is called the scutum  and the smaller plate at the hind end is the tergum .

Balanus amphitrite is a common fouling barnacle in harbors, and there are many records of this species on the hulls of ships around the world. It occurs on rocks, pilings and seawalls; on the shells of living oysters, mussels and crabs; and in warmer waters, on mangrove roots. Although Balanus amphitrite tolerates water temperatures down to 12°C, it requires temperatures of at least 15-18°C and salinities of at least 10-15 ppt to breed.

Chthamalus proteus is a small light brown or gray-white barnacle (to about 1 cm diameter). Its conical shell is variable in external appearance depending on age, crowding, and degree of weathering. Shell plates may be smooth or ribbed. It is a nuisance fouling organism.

Barnacles have specialized paired appendages, called cirri, that they use as a scoop net, reaching out into the water and extracting food particles. When they cirri are drawn back, food is scraped off into the mouth. Dense population of Chthamalus proteus on a pier piling in Hilo Harbor in 1997.

These barnacles are hermaphrodites, but cross-fertilization occurs in dense populations. In such cases, males deposit sperm directly into the mantle cavity of adjacent functional females via a long tube. Fertilized eggs are brooded in the mantle cavity, and it may be several months before the free-swimming plank tonic larvae are released.


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