Diplacanthus tenuistriatus Traquair
This medium to large acanthodian had very bold, striated spines. The spines were very deeply inserted in the body and because they were not easy to bend, this fish was not an easy meal for any predator.
Diplacanthus is extremely rare in the Sandwick Fish Bed and loose spines can be found on other localities on Orkney only very seldom. The specimen shown is from Achanarras.
Between the pectoral spines are two small spines that are positioned flat
along the ventral side of the fish. These spines are called the anterior
intermediate spines. A bit further on the ventral site towards the pelvic spines
another two spines are found called the posterior intermediate spines. The first
are not visible on the drawing because they lay flat against the belly. The
shoulder girdle can be roughly compared with Diplacanthus crassisimus.