Evaluation of cotyledons in a number of terrestrial isopods (Crustaceae: Isopoda) in Iran

The evolution of terrestrial isopods to on the land required several morphological, anatomical and physiological adaptations. The presence of the brood pouch or marsupium in ovigerous females was among the most important features allowing inhabitation of this group in the terrestrial habitats. Cotyledons are specialized structures occurring inside of the marsupium in the advanced terrestrial isopods. These organs involve in secretion of marsupial fluid and in feeding and supplying oxygen for offspring inside the brood pouch. In the present study, cotyledons in seven species of terrestrial isopods including Protracheoniscus major, Mongoloniscus persicus, Hemilepistus elongates, Porcellionides pruinosu, Agabiformius lentus, Porcellio evansi and Porcellio mehrdadi were evaluated based on their shape, relative size, number and arrangement. The results indicated that the shape of the cotyledons was the same in all species as conical. In all species but P. major, there were four cotyledons arranging as one per second to fifth segments whereas in the latter species, there were 12 cotyledons arranging as three per second to fifth segments.