page_title: Megatrema anglicum
section_title: Ecology
hierarchical_section_title: Megatrema anglicum / Ecology
caption_attribution_description: Français&#160;: Caryophyllia smithii - Banyuls-sur-Mer, Sec de Rédéris&#160;: 08/85
context_page_description: Megatrema anglicum is a species of acorn barnacle that grows in association with or semi-parasitically on corals and octocorals. It is found in the intertidal zone on the coasts of northwestern Europe and in the Mediterranean Sea.
context_section_description: In British waters, where it is at the northern limit of its range, Megatrema anglicum is found in association with the solitary cup coral Caryophyllia smithii, and in the Mediterranean it is often associated with the sunset cup coral (Leptopsammia pruvoti). However, it has been found growing on corals of at least eight different genera.
  The cyprid larvae of the barnacle settle around the rims of the stony cups of the coral where they seem unaffected by the nematocysts (stinging cells). They become firmly attached and, except for their operculum, are overgrown by the epithelium of the coral. The barnacles benefit from this arrangement by being in an elevated position for better harvesting of food particles and by being free of competition from other organisms that are unable to withstand the coral's stinging cells. The coral probably derives no benefit from the arrangement so the barnacle can be considered an obligate  semi-parasite. It is also likely to benefit from some diffusion of nutrients from the coenosarc (living tissue) of the coral which overgrows it, another reason for considering it parasitic.
caption: Caryophyllia smithi, the cup coral on which Megatrema anglicum is frequently found
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