Barnacle

Barnacles are dominant species on the littoral zone (middle shore).

They are encrusted, or firmly attached to the hard rocky substratum,

hence prevented from being washed away by the wave action of exposed shores.

The body possesses a cement gland which secretes an extremely adhesive substance

that stick the barnacle on rock. The barnacle lives a sessile way of life, i.e. it does not move.

This common barnacle species in Hong Kong is Tetraclita squamosa.

Each individual looks like a mini-volcano.

Barnacle 藤壺 belongs to a taxonomic group of the

Phylum Arthropoda, Class Crustacea, sub-class Cirripedia.

(What a surprise ! It is NOT a mollusc. Reference : A colour guide to HK animals p.154)

When it is immersed in sea water, it extends modified limbs (cirri)

which look like "combs" to filter planktons as food.

There are stalked barnacle and acorn barnacle.

The hard calcareous shell is not solid, instead it has many air spaces

which help insulate against heat gain, especially at its exposure stage during low tide.

The structure of interlocking cavities divided by hard plates conserves building materials,

yet it is of adequate mechanical strength.

Diag. below : a ventral view of the XS of a barnacle shell.

Being sessile, it depends on getting planktons from sea water.

Its feeding tentacles (= cirri) are feathery, they " comb " planktons.

Diagram below : part of a dissected barnacle

Here are a drawing and a photograph taken from books published 1921 (Thomson) and 1962 (Stanek) respectively.

Acorn barnacle (藤壺) Balanus

Goose barnacle (中譯 "龜足") Lepas anatifera