ABSTRACT
A taxonomic survey on the modes of reproduction in aquatic invertebrates shows that the hemocoelomates namely Arthropoda and Mollusca do not reproduce asexually (Table 1.1). Hence, they may not retain Embryonic Stem Cells (ESCs) to clone the whole animal and reproduce asexually. With ongoing differentiation during early development, the stemness of stem cells progressively decreases from totipotency to pluripotency, multipotency, oligopotency and nally to unipotency. As they have the capacity to regenerate one or more of their appendages, crustaceans seem to have retained adequate mass of Oligopotent Stem Cells (OlSCs) only. To achieve cloning by asexual reproduction in cnidarians, turbellarians and colonial ascidians, the minimum mass of Pluripotent Stem Cells (PSCs) required is estimated to range between 100 and 300 (Y. Rinkevich et al., 2009). It has, however, been claimed that it can be achieved with as small as 10-15 PSCs in parasitic colonial rhizocephalans (Isaeva, 2010). In fact, Shukalyuk et al. (2005, 2007) have brought some evidence in support of their claim that these rhizocephalans possess adequate mass of stem cells to reproduce asexually.
