Tibia fusus: an elegant seashell

Tibia fusus (Linnaeus, 1758) is large seashell with an extremely long and narrow siphonal canal. Its shell has been called the "spindle tibia shell" or the “shinbone tibia shell.” This latter name is because of the resemblance of the long siphonal canal of the shell to the shinbone of a human leg. The tibia is the anterior (frontal) leg bone of the two bones in the leg below the knee.

The specimen illustrated here is 220 mm long (8 ¾ in.) and 34 mm wide (1 ¼ in.). Its precise locality is not known.

The largest reported specimen of T. fusus is 310 cm long (12.2 inches), including the long siphonal canal.

This first image is the front side (aperture) view.  The long siphonal canal is an open slit for the first 3/4 of its length; the rest of it is sealed on the outside.

Why the siphonal canal is so long is not known, but perhaps it allows the snail (gastropod) to be more stealthy when it is hunting prey. The siphonal canal is a sensory organ, and because its end is far away from the bulk of its animal/shell, then the prey might not be aware of the presence of the gastropod.

Notice the six "finger-like" projections on the outer lip of the aperture.

Tibia fusus is the type species ("the definer") of the genus Tibia. 

This second image is the back side (abapertural or dorsal) view.

Although most the shell of this species is smooth, its first 10 or so whorls are reticulated (cross-hatched by spiral and longitudinal ribs). This reticulation is a main characteristic of this species.



















This third image is a side view of the shell showing the outer lip.


Tibia fusus lives in offshore, tropical marine waters where there is an abundance of sand, at depths of 5 to 50 m. The species is known from the Eastern Indian Ocean and Western Pacific, especially from Indochina, China Sea, Taiwan, southern Japan, the Philippines to Indonesia, Australia, and Oceania. It is widespread because its embryos develop into free-floating planktonic larvae, which eventually develop into free-swimming juvenile veligers.

The image on the left is an enlargement of the aperture, showing the six "fingers" on the outer lip.
These fingers give the shell stability when the snail
is crawling around.

The image on the right is an enlargement of the outer lip of the aperture. Note how curved the "top" finger is. Its central part is grooved, so as to create a furrow.










The fossil record of T. fusus is Miocene (in France, Japan and Taiwan) to Recent. Most malacologists (scientists who study modern mollusks) assign genus Tibia to family Strombidae, wherea many molluscan paleontologists (scientists who study fossil mollusks) assign Tibia to family Rostellariiidae.

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>