Electron microscopic study on oocytes, nurse cells and yolk formation inLeptestheria dahalacensis(Crustacea, Conchostraca)

Abstract

Electron microscopic study of Leptestheria dahulacensis reveals that the oocyte and its three nurse cells are interconnected by intercellular bridges. Along the contact zone between the plasma membranes of two adjacent cells desmosomes and a few gap junctions are visible.In the early stages of vitellogenesis the four cells (enclosed in a follicle) reveal similar nuclear and cytoplasmic ultrastructural features and similar synthetic activity, all four producing two types of yolk globules. The oocyte alone then develops numerous microvilli reaching towards the follicle cells and complctes the vitellogenesis. Some pinocytotic vesicles are formed in the oocyte plasma membrane at this time. The protein yolk appears to be of mixed origin, with a much smaller exogenous component. The nurse cells are unable to develop microvilli towards the follicle cells (but not towards the oocyte), and therefore seem to be unable to incorporate protein yolk from the hemolymph.The results of the present ultrastructural study are discussed in the light of data available on the oogenesis and vitellogenesis in crustaceans, particularly of other non-malacostracans.

Structure of the Hermaphroditic Gonads in a Japanese Cephalocarid Crustacean, Sandersiella sp. with Special Reference to the Oogenetic Mode

“…dichotomus (Munuswamy and Subramoniam, 1985) and in the cladoceran branchiopods, Sida crystal/ina, Daphnia magna, Eurycercus lame/latus, Bythotrephes longimanus and Leptodora kindtii (Rossi, 1980). On the other hand, some unique ovarian features superficially resembling those in the chelicerate-type ovaries have been described in the notostracan branchiopods, Triops cancriformis (Longhurst, 1955;Trentini, 1978;Trentini and Scanabissi-Sabelli, 1978;Tommasini and Scanabissi-Sabelli, 1992), T. longicaudatus (Ando and Makioka, 1992) and Lepidulus apus (Longhurst, 1955), and the conchostracan branchiopods, Limnadia lenticularis (Zaffagnini and Minelli, 1970) and Leptestheria dahalacensis (Zeni and Zaffagnini;. Tommasini and Scanabissi-Sabelli (1992) distinguished these two different ovarian structural features among the branchiopods, but they did not tell which is more primitive because they could not compare these features with any archetype.…”

“…In the most primitive chelicerates, such as horseshoe crabs and scorpions, the ovaries are typical specimens of the chelicerate-type. In the primitive mandibulates, such as branchiopod crustaceans, however, the ovaries are of the mandibulate-type in anostracans (Criel, 1980;Munuswamy and Subramoniam, 1985;Tommasini and Scanabissi-Sabelli, 1992) and cladocerans (Rossi, 1980;Tommasini and Scanabissi-Sabelli, 1992), but of the remarkably transformed mandibulate-type superficially looking like the chelicerate-type in notostracans (Trentini, 1978;Trentini and Scanabissi-Sabelli, 1978;Ando and Makioka, 1992;Tommasini and Scanabissi-Sabelli, 1992) and conchostracans (Zeni and Zaffagnini, 1989;Tommasini and Scanabissi-Sabelli, 1992). In one of the most primitive crustaceans, the cephalocarid Hutchinsoniella macracantha, an outline of the female reproductive system has been described (Sanders and Hessler, 1970;, leaving structural and functional details of the ovary behind.…”