Hammer Coral

Overview

Fimbriaphyllia ancora, commonly known as the hammer coral, is a large-polyp stony coral recognized for its distinctive, fleshy tentacles that feature T-shaped, anchor, or hammer-like tips. This colonial species is a significant component of Indo-Pacific reef ecosystems, where it contributes to the structural complexity of the marine environment.

Distribution & habitat

This species is widely distributed across the tropical Indo-West Pacific, ranging from the Maldives in the west to Australia and Japan in the east. It typically inhabits shallow reef environments, including reef lagoons and the tops of reef flats. While it can be found in various conditions, it is often most abundant in protected, calm waters where it may form extensive colonies covering large areas of the substrate.

Appearance

The hammer coral is characterized by its large, tubular tentacles that remain extended during both the day and night. These tentacles exhibit a range of colors, including blue-grey, green, or orange, often accented with pale cream or white borders. Beneath the fleshy polyps lies a flabello-meandroid calcium carbonate skeleton, which is usually hidden from view when the coral is fully expanded.

Biology & behavior

Fimbriaphyllia ancora is known for its competitive nature; it can be aggressive toward neighboring corals, using long sweeper tentacles or mesenteric filaments to sting and digest the tissues of competing species. A unique reproductive trait recently identified in this species is the ability of many colonies to change sex annually, alternating between male and female roles over consecutive years. The species also reproduces asexually through budding.