he DNA sequence of a 612-nucleotide fragment of the mitochondrial cytochrome oxidase subunit III gene (CO III) from three Mediterranean octopodid species namely: Octopus vulgaris, O. macropus and Eledonmoschata, has been determined. The perecentage of nucleotide composition of A/T,C/G was investigated. The CO III gene in these species revealed higher values of A+T against moderately low G+C content. COMPARE computer software program was applied for determining the percentage of pairwise sequence differences (P) between different species. The results of the present work are discussed with those previously obtained for O. bimaculoides, O. bimaculatus, O. dofleini, O. rubescens, O. cyanea and O. californicus. They indicated that O.vulgaris and O. macropus belong to the DNA distance-based tree of O. bimaculatus, while E. moschata is an outgroup in relation to the other species.

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Two species of octopuses were collected from Abu Quir, Alexandria, Egypt, Octpus vulgans and Octopus macropus. The mantle muscles were fixed in absolute ethyl alcohol. DNA was extracted and RAPD-PCR was conducted using 4 primers. The distance morphometric analysis of two species was applied on Arm length, Mantle length, Mantle width and body weight. The estimation of genetic distance was 0.55. In addition, morphometric studies showed no significant difference in mantle length and mantle width in both males and females. On the other hand, Arm length and body weight of 50% of males and females showed significant differences. In conclusion, the result of RAPD-PCR together with the morphometric may suggest that the two species may be two subspecies.

and dissected to obtain their eyes and put in suitable fixative. After that, the routine ultrastructure techniques were applied for examination of the retina and cornea by the transmission electron microscope. The results revealed that the retina is formed of two layers; the visual cells and the connective tissue. The visual cells contain a small amount of a granular endoplasmic reticulum, rounded mitochondria and oval nuclei with distinct nucleoli. From each four different visual cells, four rhabdomeres united to form a prismatic rhabdome. Examination with higher magnification power showed presence of groups of 8 to 9 lamellated structures that form dense membranes with different lengths. These lamellated structures are similar to the myelin membranes and present in all cells but not connected to the plasma membrane. The cornea is made of three layers; the outer epithelial layer of hexagonal cells that have small mitochondria and oval nuclei. The median thick layer of fibrous connective tissue and the inner endothelium layer of cuboidal cells having small mitochondria and large rounded nuclei.

Two types of morphologically confused crabs were collected from Abu Quir, Alexandria, Egypt, Callinectes spidus and Callinectes ornatus. The carapace of these crabs was first removed, and the abdominal muscles were fixed in absolute ethyl alcohol. DNA was extracted and restricted by three enzymes, and RFLP technique was conducted. Molecular weight, optical density, flowing bands and Gel-Pro-Analyzer technique were also applied. Morphometric analysis of the two species was applied on the carapace width, carapace length and body weight. The estimation of similarity index applied on the two species was 0.59. In addition, morphometric studies showed no significant difference in the body weight and carapace length of all samples of both males and females. On the other hand, the mean width of carapace of 16.7% of the male samples showed significant difference, while the rest of male and female samples (83.3%) showed no significant difference. In conclusion, the result of RFLP together with the morphometric data may suggest that the two studied crabs belong to one species.