Tuesday, November 1, 2016

The large shallow-marine gastropod Forreria belcheri, past and present history

Forreria belcheri (Hinds, 1843) is a rather large gastropod found today along the west coast of Southern California and Baja California, Mexico. Forreria belongs to the family Muricidae, commonly referred to as the "rock shells." Forreria belcheri is the type species of genus Forreria.

This gastropod has a fossil record that extends back about 8 million years to the late Miocene. In the past, it ranged farther north (to central California) than it does today. It lives today mainly offshore on sandy bottoms in relatively shallow water of 60 to 100 feet deep, but it can also be found in bays, lagoons, and mudflats. This gastropod is carnivorous and uses its file-like radular teeth to drill holes through shells of oysters and mussels, as well as other mollusks. 

Forreria belcheri is characterized by a large, heavy shell that can be as much as 6 inches (15 cm) long. The shell is heavy and adult specimens have about 12 spiny nodes on its whorls. Its opening (aperture) is large and the anterior end of its shell is twisted and upturned. 

The first two views in the below series of photographs show the front (apertural) side of a modern specimen from Baja California, Mexico versus a Pleistocene specimen from Newport Beach Mesa, Southern California. The last two views of this series show the back side (abapertural) of the same modern and Pleistocene specimens, respectively.

Forreria belcheri: A modern specimen (13 cm height) vs. a Pleistocene specimen (11.6 cm height).

The next two views show the spatial arrangement of the spiny nodes on the spire whorls of the same two specimens: Modern specimen (on left) vs. Pleistocene specimen (on right). The Pleistocene specimen is somewhat worn and has its lower right-hand spire coated by bryozoans.

This last view, which is of the side of the modern specimen, shows how the twisted anterior end also turns upward (a characteristic feature).

1 comment:

  1. Specimens from the late Miocene of the Salinas Valley are a new species distinct from F. belcheri even thought they were referred to F. belcheri by Addicott.