Beak morphometrics of short arm octopus (Amphioctopus fangsiao) in different sea areas of China in autumn

Short arm octopus, Amphioctopus fangsiao, is widely distributed along the coast of China, and also is one of the important commercially explored cephalopod species in China. Based on 393 samples of A. fangsiao collected along the coast of China, including the Yellow Sea, East China Sea and South China Sea during October to November in 2015, the variation of ten standardized beak morphometrics was studied among the different areas and the discriminant analysis was also established based on the beak morphology. The results showed that the body size of A. fangsiao located in Yellow Sea and East China Sea was similar, and the individuals in South China Sea were smaller than other areas; the standardized beak in South China Sea was also smaller than other two areas. ANOVA test showed that the beak morphometrics in East China Sea and Yellow Sea had no significant difference except for lower beak wing (P>0.01), and beak morphometrics in South China Sea had significant difference compared to other two areas (P<0.01). Principal component analysis suggested that the lower beak mophometrics represented first component factor, and upper beak morphometrics represented the second and third component factors for all the individuals from three different areas. Six beak morphometrics were selected for the stepwise discriminant analysis, and the correct classification rate was over 80% for three different areas. The result of classification tree analysis showed that lower beak morphometrics (lower hood length and lower wing length) can be a good criterion for quick identification of the octopus from different areas. In conclusion, this study has confirmed that the beak morphology has different patterns in different areas due to the varied environments, and also showed that beak is a suitable criterion for identifying the population variation for cephalopods.