Great Screw Shell (Tower Shell, Auger-like Turritella)
Phylum: Mollusca, Class: Gastropoda, Order: Littorinimorpha, Family: Turritellidae, Genus: Turritella, Species: T. terebra · Turritellidae (Screw shells or Tower shells) · Gastropod (univalve); high-spired turriform/conical shape; whole shell specimen
Species
Turritella terebra (Confidence: 90%)
Shell Type
Gastropod (univalve); high-spired turriform/conical shape; whole shell specimen
Family
Turritellidae (Screw shells or Tower shells)
Size
Estimated 3-4 inches (75-100mm) in length. This is a mid-sized adult, as the species can reach up to 6 inches (150mm).
Color & Pattern
Uniform creamy white to light beige. The shell appears significantly sun-bleached or weathered, as live specimens typically exhibit warmer brown, tan, or purplish hues with subtle spiral banding.
Rarity
Common. These shells are found in high concentrations in certain areas and are frequently commercially harvested for the shell trade.
Habitat
Marine; common in shallow subtidal zones and continental shelf waters. They prefer muddy or sandy substrates where they live partially buried.
Geographic Range
Indo-West Pacific region, ranging from the coasts of East Africa and the Red Sea to Australia and the Philippines.
Description
An elegant, elongated, many-whorled turreted shell. Each whorl is slightly convex with distinct spiral ridges or 'cords'. The shell tapers to a very fine, sharp point (apex) and features a small, simple circular aperture at the base without a siphonal canal.
Key Features
Extremely high spire with numerous whorls (often 20+ in adults); spiral cord sculpture; lacks an umbilicus; circular aperture with a thin outer lip; lack of siphonal notch found in Augers.
Collector Value
Low to Moderate. While beautiful in form, this specific bleached specimen is common. Unique, high-contrast brown specimens with perfect tips are more desirable for formal collections. Value typically ranges from $1 to $10.
Condition Notes
Fair to Good. The shell is intact with a sharp apex, which is often broken in beach finds. However, the surface is heavily eroded and bleached white, losing its original glossy brown periostracum and pigment.
Interesting Facts
Unlike many gastropods, screw shells are sedentary filter feeders. They lie buried in the sand and use their gills to strain plankton and organic detritus from the water. In the fossil record, they are so abundant they create 'Turritella Agate'.
Ecological Role
Primary consumers; they play a vital role in cleaning the water column via filter feeding. They serve as a food source for bottom-dwelling fish and specialized predatory mollusks like Cones.
Similar Species
Often confused with Terebridae (Auger shells), but classified differently; Augers have a distinct groove or notch at the base for a siphon, which Turritella lacks.
Beach Finding Tips
Look in the drift line after storms in Indo-Pacific tropical regions. Because they are light, they often wash up in the 'high tide' debris. Check muddy bays or near estuary mouths.