Santander, February 19th-22nd 2008 - Aranzadi

Shells in the Middle Ages: archaeomalacological remains from the city walls at Pontevedra (Galicia, Spain)
203
GASTROPODS
NR
MNI
Littorina littorea 68 68
Neptunea contraria 1 1
Charonia lampas 1 1
Patella vulgata 2 2
Patella intermedia 1 1
Patella sp. 1 1
Gibbula sp. 1 1
Nassarius reticulatus 1 1
BIVALVES
NR
MNI
Ostrea edulis 755 364
Ruditapes decussatus 310 178
Cerastoderma glaucum 325 166
Mytilus galloprovincialis 62 21
Glycymeris glycymeris 1 1
Pecten maximus 15 3
Venus verrucosa 1 1
Total 1469 734
TOTALS 1545 810
Table 1. Abundance of taxa from Pontevedra city walls (Spain).
substrates, usually in estuaries or in sandy beaches.
Pecten maximus and Venus verrucosa live in sandy
substrates, usually in sandy beaches.
There is a preference for mollucs from estuarines
or sandy beaches (Ostrea edulis, Ruditapes
decussatus and Cerastoderma glaucum) (ca 88 %).
The good conservation of the specimens clearly
indicates that molluscs were gathered alive, most
probably for food, and were not collected dead in
the shores. Specimens collected dead in the beaches
are usually eroded and not intact.
For example, five Cerastoderma glaucum specimens
preserve the ligaments joining the right and
left valves. Fragmentation only affects the bivalves,
mainly Pecten maximus and Mytilus galloprovincialis,
and to a lesser degree, Ostrea edulis, Ruditapes
decussatus and Cerastoderma glaucum.
Only one specimen, a Glycymeris glycymeris
valve, displayed alterations to its surface, and had
been gathered after prolonged exposure to coastal
hydrodynamics. No other specimens were found
with other organisms incrusted on their surfaces
(barnacles, etc.).
A number of the flat oyster valves showed evidence
of human alterations, as a result of extracting
the animal by leverage (Fig. 3 left). These alterations
are found on the opposite side of the shell to the
hinge.
The absence of alterations by fire suggests that
molluscs were probably eaten fresh or were boiled.
4. MALACOLOGICAL REMAINS FROM THE CITY
WALLS AT PONTEVEDRA (SPAIN): BIOMETRY
Biometric analysis has been carried out for the
shells of the most common species in the deposit:
Ostrea edulis, Cerastoderma glaucum and
Ruditapes decussatus (Table 2).
To determine if the bivalves of a certain size
were gathered selectively, the right valves of the
species were chosen as these totalled a higher
MNI. The variable “length” was used for all the
shells. In view of the data, a preference can be
seen for medium and large-sized specimens of all
the species.
The modern-day commercial size of oysters
(left valves) in the Galician Rias Bajas is 60-70mm,
a length they reach at an age of 18-24 months.
Bearing in mind this information, the percentage of
oysters with lengths ≥ 60mm is 65.1%. However,
the range with the largest number of specimens is
between 60-70 mm (33.1%). Few archaeological
specimens are longer than 90mm (4 shells), whereas
modern oysters can reach 150mm in length.
Figure 3. Specimens of Ostrea edulis (left), Cerastoderma glaucum (middle) and Ruditapes decussatus (right), from Pontevedra city walls (Spain).
MUNIBE Suplemento - Gehigarria 31, 2010
S.C. Aranzadi. Z.E. Donostia/San Sebastián