Also known as Arthritic Spider Conch, Arthritic Spider Shell, Chiragra Spider, Gouty Spider Shell, Spider Conch, Spider Shell, True Conch.
Found over coarse coral, rubble, sand, in seagrass beds, and in tide-pools, of coral reefs rich in algae growth.
They feed on algae and plants.
Juveniles do not have the appendages of the adult shells.
Length - 17cm
Depth - 0-25m
Stomboids are a small group of sea snails, commonly found in tropical waters. Usually identified by their large stalked eyes. Their shells are often dull on the outside but can be bright inside.
Stromboids are edible and in some areas are regarded as a delicacy. Ref: https://en.wikipedia.org/wiki/Harpago_chiragra
Update to my comment of Jan. 17, 2021: I have seen a specimen of this species (picture of a live one) on a reef of one of the Cook Islands, so this mollusk appears to occupy the entire stretch of the central-south Pacific Ocean from the central Coral Sea eastwards to the easternmost fringes of French Polynesia, including the Line Islands NNW of the Marquesas archipelago.
Update to my comment posted on May 20, 2020: Harpago rugosus is also found in the Samoan Archipelago - in the November 1949 issue of "The Scientific Monthly" (vol. 69, #5), there is an article by the late conchologist Tucker Abbott titled "Samoa -A Shell Collector's Paradise." In it, there is a black and white plate showing seven Lambis species. The shell illustrated in the top row middle is clearly this species.
The Rugose Spider Conch (Harpago rugosus) is not found in the intervening area between New Caledonia and the Society Islands, to my knowledge. It appears there are two separate population pools: the Coral Sea and French Polynesia, including the Line Islands.
No they are not, nudibranch are sea slugs
Are Arthritic Spider Shells Nudibranchs?
Thank you for the information, we try to get it right but don't always succeed!
The Arthritic Spider Conch is not restricted to the Western Indian Ocean - it is found further east as far as the Philippines. The "Rugose" Spider Conch is not another name for this species - the Rugose Spider Conch (as per Sowerby, 1842) is found from the middle of the Coral Sea east to French Polynesia, and may be a hybrid between the Arthritic and Chiragra Spider Conches.