ABSTRACT
Development of Pomacea canaliculata from the gastrula stage until the first day after hatching is described. Trochophore embryos are developed after gastrulation, showing the prototroch as a crown of ciliated orange-brownish cells. However, no true veliger embryos are formed, since the prototroch does not fully develop into a velum. Afterward, the connection between the fore- and midgut is permeated and the midgut becomes full of the pink-reddish albumen, which is stored into a central archenteron's lake, from where it is accumulated into the large cells forming the midgut wall ("giant cells"). Electron microscopy of giant cells in late embryos showed that albumen is engulfed by large endocytic vesicles formed between the irregular microvilli at the top of these cells. By the end of intracapsular development, giant cells become gradually replaced by two new epithelial cell types which are similar to those found in the adult midgut gland: the pre-columnar and the pre-pyramidal cells. Pre-columnar cells have inconspicuous basal nuclei and are crowned by stereocilia, between which small endocytic vesicles are formed. Pre-pyramidal cells have large nuclei with 2-3 nucleoli and show a striking development of the rough endoplasmic reticulum. The genesis of the three cell lineages (giant, pre-columnar and pre-pyramidal cells) is hypothetically attributed to epithelial streaks that occur at both sides of the midgut since early stages of development.
Subject(s)
Animals , Snails/cytology , Snails/embryology , Snails/ultrastructure , Gastrula/cytology , Organogenesis/physiology , Digestive System/embryologyABSTRACT
The survival, reproduction and embryonic development of Strombus pugilis, were determined during a period of ten months under laboratory conditions. Seven progenitors were collected in Contoy Island, Quintana Roo, Mexico and later transferred to the laboratory, where they were placed in aquarium with 80 1 of sea water and fed with "pellets". A total of 30 egg masses were collected, one on September and the other on April. The estimated total length of one egg mass was 11.24 m; the mean number of embryos obtained per 2 cm was 264, obtaining an estimated total of 157 500 embryos in the egg mass. The means of the physical-chemical parameters during the study were: salinity 37.6 +/- 0.5% per hundred, pH 7.5 +/- 0.5 and temperature 28 +/- 0.2 degrees C. The maintenance and water recirculation system used to sustain the breading stock is excellent both for reproduction of the organism and for obtaining egg masses under controlled conditions.
Subject(s)
Animals , Male , Female , Snails/physiology , Snails/growth & development , Snails/embryology , Time Factors , Laboratories , Larva/growth & development , Oviposition/physiology , Reproduction/physiology , Ovum/growth & developmentABSTRACT
Stages from oviposition to veliger hatching are described for Strombus pugilis under laboratory conditions. Two egg masses from Playa Seyba, México, (20 degrees 45' N, 91 degrees 45' W) were used (three sub-samples per mass). Each sub-sample was immersed in a 11 container at 29 +/- 1 degrees C. This description is based on stages known from Strombus gigas, which include number of: fertilized eggs, morulae, gastrulae, trochophore larvae with slow movements, larvae with primordium foot, larvae with eyes, larvae with statocyst and veliger larvae. Eggs with first division appeared five hours after oviposition in the three replicates of each mass, although in greatest number in one of the egg masses. Trochophore larvae with slow movements appear after 50-54 hours and veligers hatch after 90 hours.