Chthamalus antennatus Click to enlarge image
Acorn Barnacle, Chthamalus antennatus Image: Dr Isobel Bennett
© Australian Museum

Fast Facts

  • Classification
    Species
    antennatus
    Genus
    Chthamalus
    Family
    Chthamalidae
    Suborder
    Balanomorpha
    Order
    Thoracica
    Subclass
    Cirripedia
    Class
    Maxillopoda
    Subphylum
    Crustacea
    Phylum
    Arthropoda
    Kingdom
    Animalia
  • Size Range
    1.2 cm

Introduction

On any visit to the rocky shore in Sydney, you are almost guaranteed to see barnacles. You may even see several species on the one occasion.

Identification

Acorn barnacles like Chthamalus antennatus look like miniature volcanoes.

Habitat

Acorn barnacles live on intertidal rocky shores.

Distribution

Acorn barnacles are found in New South Wales, Victoria and Tasmania.

Other behaviours and adaptations

Acorn barnacles are extremely abundant and gather in large groups towards the high-tide mark on rock platforms.

Breeding behaviours

Barnacles have an infamous reputation for their large penis size. Their reproductive organ may be up to 10 times their body size, a useful adaptation for fertilising adjacent females. Most barnacles are hermaphrodites, having both male and female reproductive organs. Barnacles clustered together may exchange sperm. Barnacles separated by long distances are either not fertilised or fertilise themselves to produce clones.