A SEM STUDY OF PRIMARY SCALES IN THE EMBRYO OF THE LESSER SPOTTED DOGFISH, SCYLIORHINUS-CANICULA (CHONDRICHTHYES, SCYLIORHINIDAE)

The caudal and dorsolateral << primary scales >> of Scyliorhinus canicula (L.), an oviparous catshark, were studied in embryos and newborns by scanning electron microscopy (SEM) and compared to ordinary placoid scales, which erupt shortly before birth. Four rows of germs corresponding to the caudal scales developed as soon as the lateral line reached its subcaudal terminus nearby. These scales erupted in a sequence, beginning at the tip of the tail at mid development. Their shapes were mushroom-like. Two rows of germs corresponding to the dorsolateral scales developed at the same time, but eruption only occurred towards the end of development. Their shapes were nail-like. Both types of primary scales are specialized placoid scales, of still controversial functions. Similar scales are present in various Scyliorhinidae, and they can serve as useful meristic characters in the diagnosis of species.