Reproductive System Structure, Development and Function in Cephalopods with a New General Scale for Maturity Stages

The main types of reproductive system structure, development and functions in cephalopods are described from personal observations and use of the literature. There is one type in males and three in females which are order specific. These have provided a basis for examining possible evolutionary trends in reproductive system development and in reproductive strategies within coleoid cephalopods and for developing a general scale for maturity staging for males and females. Development of the cephalopod reproductive system consists of two main phases. The first includes sexual cell differentiation, growth and maturation (i.e. juvenile phase and physiological maturation). The second begins after maturation of sexual cells. It includestheirtransportand accumulation in different parts of the reproductive system and their conversion into spermatophores in males and eggs with protective coverings in females (i.e. physiological maturity, functional maturation and maturity). It was found that species with different life styles within each order have similar reproductive systems. This may be attributable to the relative youth in an evolutionary sense of the main groups of living cephalopods. A general scale of seven maturity stages for cephalopods was developed. Distinct characteristics of each stage are described and supplemented with a generalized drawing of gonad structure. In the first phase of reproductive system development, maturity stages are distinguished by the degree of development of the gonad and accessory glands. In the second phase maturity stages are distinguished by the fate of the mature sexual cells, particularly by their transport and location in different parts of the reproductive system up to the time of spawning.