CLASSIFICATION OF BALANUS OR ACORN BARNACLE
PHYLUM :- ARTHROPODA (Jointed appendages.)
CLASS :- CRUSTACEA (Thick exoskeleton, antennae 2 pairs)
SUB-CLASS :- CIRRIPEDIA (Sessile adults without compound eyes and antennae, with carapace and mandibular palps and with 6 pairs of biramous thoracic limbs)
ORDER :- THORACICA (Non-parasitic, carapace of calcareous plates and 6 pairs of thoracic appendages.)
GENUS :- Balanus
It has cosmopolitan distribution but especially found along Pacific coast, North Atlantic coast, West Indies and Washington to Alaska.
HABIT AND HABITAT
Balanus is attached to rocks and molluscan shells in great numbers between tide-marks in shallow water. It may attach to any floating object also.
GENERAL CHARACTERSTICS OF BALANUS OR ACORN BARNACLE
- Commonly called as Rock barnacle or Acorn barnacle.
- Stalk is absent to the shell covering the animal is directly attached to the substratum or rocks.
- Head is short and broad.
- Mantle surrounding the body is covered by six calcareous plates, consisting of unpaired carina, rostrum and 2 pairs of carino-lateral plates. Edges of the plates overlap and fit together forming cylinder. Outer surface of each plate shows 3 divisions, a central portion and two wings.
- Opening of the shell is provided with a movable fourfold lid or operculum, composed of 2 scuta and 2 terga.
- In water the barnacle protrudes through the opening six pairs delicate, curled, fringed and jointed thoracic legs to collect food.
- Life cycle includes nauplius larva.
Balanus titinnabulum has food value in some countries. Barnacles are highly modified crustaceans in which hermaphroditism is common. Male and female live in permanent association.
The animal contains carina, scuta, terga and protruding thoracic appendages and all above features, hence it is Balanus.