Morphological analysis of beaks of Uroteuthis chinensis in the northern South China Sea

Beaks are important hard tissues for cephalopods and have become one of the important research materials of cephalopods in fields of fishery biology and marine ecology. Based on the beaks of Uroteuthis chinensis collected during September 2015, we measured their external morphological parameters. According to the principal component analysis, the primary morphology parameters of beaks are upper hood length (UHL), upper crest length (UCL), upper lateral wall length (ULWL), lower lateral wall length (LLWL), upper rostrum width (URW) and lower rostrum length (LRL), which are regarded as typical morphological characteristics of beaks of U.chinensis.Besides, we analyzed the relationship between primary morphology parameters of beaks and their size and sexual maturity, and then established the models between the primary morphological parameters and length and weight. The relationship between UHL, UCL, ULWL, LLWL and mantle length (ML) can be described with exponential models, while the relationship between URW, LRL and ML can be described with linear models. The optimal relationship is between UHL, UCL, ULWL, LLWL and body weight (BW). The relationship between URW, LRL and BW is the best for power function model and logarithm model, respectively. It is also found that the effect of sexual maturity and size on morphological parameters UHL/UCL of beaks is not significant (P>0.05).