Internal Mold of a Gastropod (Sea Snail)
cf. Neptunea antiqua (Red Whelk) • Internal Mold (Steinkern) - Invertebrate Body Fossil
Geological Period
Neogene to Quaternary (likely Pliocene or Pleistocene)
Estimated Age
2.5 to 5.0 million years
Preservation Type
Internal mold or 'steinkern' formation where sediment filled the shell and lithified before the original aragonite/calcite shell dissolved or was abraded away.
Condition Assessment
Fair to Good. The specimen is heavily water-worn and weathered, which is expected for beach-found material. It is a partial mold, missing the extreme apex and the siphonal canal tip.
Taxonomic Classification
Phylum: Mollusca, Class: Gastropoda, Order: Neogastropoda, Family: Neptuneidae (likely)
Morphological Description
The specimen exhibits a dextral (right-handed) spiral coiling pattern. It is an internal mold, showing the negative space of the whorls. Visible features include a robust spire, deep suture impressions where the original shell once sat, and a rounded body whorl. The surface is relatively smooth, lacking external shell ornamentation like ribs or nodes which have been lost to erosion.
Rock Matrix
Sandy calcarenite or indurated siltstone typical of the 'Crag' deposits, likely stained with iron oxide (limonite) giving it a buff or cream color.
Formation & Location
Derived from the Red Crag Formation or Norwich Crag Formation, commonly found as beach-rolled pebbles along the coast of Southwold, Suffolk, UK.
Size & Dimensions
Approximately 6-8 cm in length; typical for mature Neptunea specimens from the British Pliocene/Pleistocene deposits.
Value & Rarity
Estimated Market Value
$10 - $25 USD
Auction Estimate
$15 - $30 USD
Rarity Assessment
Common. Gastropod molds are very frequent finds on the Suffolk coast between Aldeburgh and Southwold.
Scientific Significance
Provides evidence of cool-temperate marine paleoenvironments in the North Sea basin during the late Cenozoic. These fossils help track the 'Crag' sea migrations and climate cooling leading into the Ice Age.
Preparation Recommendations
No invasive preparation is required. Rinse with distilled water to remove salt from beach exposure. Dry thoroughly and store in a stable, low-humidity environment to prevent salt crystallization within the porous matrix.
Notable Features
The distinctive spiral grooves represent the 'steinkern' effect, clearly showing the internal volume of the snail. Its beach-rolled texture gives it a smooth, tactile quality unique to Southwold coastal finds.
Notes
Southwold