Abstract. A low diversity fossil assemblage dominated by Mongolitubulus spines, from the Early Cambrian Geres Member of the
Shabakhty Formation at Koksu, Malyi Karatau, Kazakstan, enables identification
of its sclerite variability within the scleritome. No other sclerotised
structures could be matched with the spines, indicating that these were the
only sclerotised part of the body and periodically were shed out. The
prominent spines of Mongolitubulus
have a scale-like external ornamentation and fibrous internal structure.
Possibly they armed the body of a lobopodian, similar to Xenusion.
The Mongolitubulus spines belong to
a series of Cambrian phosphatic fossils, the other end members of which are
sclerites of Microdictyon, the
second most abundant component of the Koksu assemblage. The latter
superficially resemble schizochroal trilobite eyes, but in life covered the
dorso-lateral sides of the body segments, as is evident from complete
specimens from the Chinese Chengjiang locality. A pair of sclerites of Microdictyon,
representing uncompleted exuviation, from Koksu show that each hole
originally contained a non-phosphatised lenticular body. This makes a compound
eye nature of the Microdictyon sclerites likely, and even their homology with
arthropod eyes cannot be excluded.