Two spiny seashells

I have always been impressed with the elegant beauty of very spiny seashells, and this post focuses on two of them. Both are trochid gastropods (snails) with a turban-shaped shell having a nacreous or mother-of-pearl interior. Trochids, which are herbivores [algae eaters], are now classified as vetigastropods, whereas in earlier (outdated) literature, they were classified as archaeogastropods. 

Angaria sphaerula (L. C. Kiener, 1839) is from coral-reef environments in the Philippine Islands area. Angaria belongs to family Angariidae, the so-called "Dolphin shells," and Angaria is the sole genus of this family. Angaria is characterized by having a reddish turbinate shell, with a depressed spire, and spiral ornamentation consisting of tubercles or nodules, which can be spiny. The stout and flattened spines along the top of the shell are used probably for mimicry to resemble coral growth, as opposed to the much smaller and sharper spines (most likely used for protection from predatory animals) found elsewhere on the shell. There is also a stout operculum inside the aperture (if you look closely in the first image below, you can see the dark-brown operculum. Other species of Angaria are known also from Indo-Pacific tropical waters.

Two views of Angaria sphaerula. The shell is 42 mm diameter and 31 mm high (including the spines) from the Philippines.


Guildfordia triumphans (Philippi, 1841), the so-called "triumphant star shell," is from relatively deep-waters (about 300 m depth) tropical waters off the coast of Japan. This torched gastropod has approximately 10 long and narrow spines radiating from the outside edge of its shell. These spines most likely provide support to keep the shell from sinking into the muddy substrate on which the shell lives.

Two views of Guildfordia triumphans, 65 mm diameter, from Japan.

For taxonomic details about the modern classification of these two vetigastropods, see WoRMS, World Register of Marine Species
<www.marinespecies.org>