Page 396 - Introduction to Paleobiology and The Fossil Record

ECDYSOZOA: ARTHROPODS 383

(b)

(a) (c)

Figure 14.21 Carboniferous shrimps: (a) Tealliocaris woodwardi from the Gullane Shrimp Bed, near
Edinburgh (×4); (b) Waterstonella grantonensis from the Granton Shrimp Bed, near Edinburgh (×2);
(c) Crangopsis socialis and Waterstonella grantonensis from the Granton Shrimp Bed (×2). (Courtesy of
Euan Clarkson.)

described from the Granton Shrimp Bed by structions and, at some levels in the strati-
Euan Clarkson (University of Edinburgh) and graphic record, have been used for correlation.
his colleagues (Fig. 14.21). Ostracodes have weak segmentation with a
poorly defined head, thorax and abdomen;

the animal is contained within the two shells,
Ostracodes
with the carapace united dorsally by an elastic
Ostracodes are crustacean arthropods, abun- ligament and a variably developed hinge.
dant and widespread in aquatic environments. Growth is by periodic ecdysis or molting. Fol-
They have small bivalved carapaces, hinged lowing each molt phase the carapace initially
along the dorsal margin (Fig. 14.22a). The develops as a pair of chitinous valves enclos-
carapace is perforate and completely covers ing the animal; most of the carapace is

the entire animal when closed. Most ostra- then calcified, except the dorsal margin that
codes are benthic, swimming, crawling or remains as a chitinous ligament forcing the
burrowing at the sediment–water interface in valves apart when the internal adductor
muds or silts with abundant organic material. muscles relax. The central muscle scars vary
A few, such as the myodocopids, are plank- across the class (Fig. 14.22b), from complex
tonic and some are commensal or parasitic. patterns in the Leperditicopida to a single scar
They are very useful for environmental recon- in some members of the Palaeocopida.