Histomorphological investigation of the mature externa of Heterosaccus dollfusi (Crustacea, Rhizocephala)

The present investigation is the first in Egypt to give histomorphological data about Heterosaccus dollfusi , a rhizocephalan parasitic barnacle of the brachyuran crab Charybdis longicollis , collected from the eastern Mediterranean coast of Egypt at shallow depths (10–20 m). The structure of the mature externa and its male organs are essential for perception of both the taxonomy and reproductive biology of these specialized parasites. We use scanning electron microscopy and histological methods coupled with morphological description to investigate the anatomy of mature externa. The mature externa is distinguished by a visceral mass which comprises the ovary, paired colleteric glands, paired male receptacles and paired receptacle ducts. Attention is focused on the developmental stages of male organs and/or tracing of spermatozoa after settlement of male cypris implantation of the trichogon during fertilization process. For the first time, the lateral tube that connects the left male receptacle with the right, smaller receptacle was observed in sagittal section and illustrated in the diagrammatic figure of male organs. This tube is probably the generator of sperm ribbons. As well, the existence of the spermatozoa inside the lumen of this connecting tube may indicate their free movement between the two receptacles. Moreover, strips of sperm that drag from the sperm ribbon ball, and surround the developing ovules can also be seen in the mantle cavity.