Ascarosepion latimanus

Lore & Background

The type specimen of Ascarosepion latimanus was collected in New Guinea and is deposited at the Muséum National d'Histoire Naturelle in Paris. The species has a wide geographic range, and it is probable that it represents a species complex rather than a single species, though more taxonomic work is needed. In 2023, the species was moved into genus Ascarosepion, where it is grouped with 13 other species including the Metasepia cuttlefish, the reaper cuttlefish, and the giant cuttlefish.

The broadclub cuttlefish grows to 50 cm in mantle length and 10 kg in weight. It displays a range of colors and textures, commonly light brown or yellowish with white mottled markings; males are sometimes dark brown during courtship and mating. The arms have longitudinal white bands that appear as broad white blotches when extended, and some arms have longitudinal brown bands extending to the head. The dorsal mantle may show a saddle mark with small white and brown spots, narrow brown transverse bands, and bold white transverse stripes and spots. The eyes are yellow around the ventral margins, and the fins are pale with white transverse stripes and narrow white bands along outer margins.

A. latimanus is a coastal species occurring in coral reefs in shallow water to 30 m. In the western Pacific, off Guam and off Okinawa, it is found in shallows from January to May, with eggs hatching in 38 to 40 days. It is diurnal and appears to mesmerize prey using a display of rhythmic color bands along its body. It preys on fishes and crustaceans, including shrimp and prawns of the genus Palaemon. Breeding males are territorial, defending a coral head (typically Porites); females lay eggs after mating in the male's territory. Courtship is highly ritualized and includes striking visual displays. Males frequently guard females, and mating occurs head-to-head, with the male placing spermatophores in the buccal membrane below the female's mouth. After laying, the eggs harden and are very hard to remove from the coral. Hatchlings hide among coral and rubble, often mimicking mangrove leaves in coloration and posture.

Reader's Guide

The broadclub cuttlefish is significant as the most common cuttlefish on coral reefs and the second largest cuttlefish species. Its wide distribution from eastern Africa to southern Japan and northern Australia, with records from southern Australia and Madagascar likely misidentifications, underscores its ecological importance in reef systems. The species exhibits complex hunting behavior using motion camouflage: it hunts prey such as shore crabs by swimming directly toward them while making a 'passing-stripe' display on its front. The cuttlefish colors its head white and forms six arms into a forward-pointing cone, with two arms stretched sideways. Dark stripes move downward over the forward-facing parts, and the posture masks mantle movements. This combination reduces the crab's reaction to looming, effectively deceiving the prey. The species' ritualized courtship and territorial defense of Porites coral heads highlight its role in reef dynamics. The uncertainty that it may represent a species complex indicates that further taxonomic work is needed to clarify its species limits, making it a subject of ongoing scientific interest.

Did You Know?

• The broadclub cuttlefish is the second largest cuttlefish species, reaching 50 cm mantle length and 10 kg weight.
• It is probable that Ascarosepion latimanus represents a species complex rather than a single species.
• The species was moved into genus Ascarosepion in 2023, grouped with 13 other species including the giant cuttlefish.
• Hatchlings often mimic mangrove leaves in coloration and posture to hide among coral rubble.