Morphologically, the gladius consists of a feather-shaped plate, the proostracum that tapers toward the posterior end of the gladius, becoming a funnel-shaped conus with a smallish rostrum (Arkhipkin et al, 2012).
Eight morphometric characteristics of the gladius (gladius length [GL], conus length [CL], maximum width of conus [CW], proostracum length [PL], maximum width of prostracum [PW], length from anterior tip of conus to the widest point of proostracum [PWL], length from anterior tip of conus to proximal end of lateral plates [LPL], the width between two anterior apices of lateral plates [LPW]) were measured from each sample to the nearest 1 mm (Fig.
The proostracum contributes to a large proportion of GL (>80 %) and has a higher longitudinal growth rate than conus (Table 6).
The measurements are mantle length (ML), conus length (CL), maximum width of conus (CW), proostracum length (PL), maximum width of prostracum (PW), length from anterior tip of conus to the widest point of proostracum (PWL), length from anterior tip of conus to proximal end of lateral plates (LPL), width between two anterior apices of lateral plates (LPW), fin length (FL), and fin width (FW).