COI sequence variation High A+T content and positional biases, for example, slight bias against cytosine (17.3%) in first position, in favor of thymine (45, 7%) in the second position and a substantial bias against guanine (2.9%) in the third position of the mitochondrial COI gene fragment was found in all individuals of Acetes indicus, A. serrulatus, A. japonicus, A. sibogae analyzed in this study (Table 3 This basic compositional pattern is similar to COI gene region sequences in other crustacean groups, including Raymunidae (Macpherson and Machordom, 2001), Portunidae (Chu et al., 1999; Pfeiler et al., 2005), Bresiliidae (Shank et al., 1999), Gammaridae (Meyran et al., 1997), as well as some Penaeidae shrimp species (Baldwin et al., 1998; Maggioni et al., 2001; Quan et al., 2004; Tong et al., 2000; Zitari-Chatti et al., 2009). Regarding amino acid substitutions, COI is considered one of the most conservative genes in the mitochondrial genome (Black et al., 1997). ) and therefore only the substitution of three amino acids was detected in this study. Translation of the 552 bp COI gene fragment resulted in a 184 amino acid sequence with no stop codons or in-frame indels. Together with the base composition patterns and base substitutions discussed above, these observations showed that the COI gene fragment amplified in this study was not a nuclear mitochondrial pseudogene (Numts) (Bensasson et al., 2001; Song et al. , 2008; Zhang and Hewitt, 1996) that have been reported in crustaceans, including the snapping shrimp, Alpheus (Williams et al., 2002; Williams and Knowlton, 2001).4.2 Interspecific variation in Acetes sp. and cryptic diversity From the phylogenetic trees inferred from the COI sequence (Figure 2 – 3...... in the center of the document...... genes. Integrative and comparative biology. 42(5), 941 – 952.Williams, S.T. , Knowlton, N., 2001. Mitochondrial pseudogenes are pervasive and often insidious in the snapping shrimp genus Alpheus Molecular Biology and Evolution 18(8), 1484 – 1493.Xiao, Y., Greenwood, JG, 1993. The biology of. Vinegars (Crustacea: Sergestidae). A. D. Ansell, R. N. Gibson and M. Barnes (eds.), Oceanography and Marine Biology: An Annual Review, 31, pp. 259 - 444. , Hewitt, G.M., 1996. Nuclear integrations: challenges for mitochondrial DNA markers Trends in Ecology & Evolution 11(6), 247 – 251. Zitari-Chatti, R., Chatti, N., Fulgione, D., Caiazza. , I., Aprea, G., Elouaer, A., et al., 2009. Mitochondrial DNA variation in the caramote shrimp Penaeus (Melicertus) kerathurus across a transition zone in the Mediterranean Sea Genetics. 136(3), 439 – 447.