Fine structure and functional role of the coverings of the eggs inMesostoma ehrenbergii (Focke) (Turbellaria, Neorhabdocoela)

112

The paper reviews the following systems: body wall, nervous system, protonephridia, parenchyma, digestive system, reproductive system, and includes a summary of the literature. New information is presented for the catenulid and neoophoran body wall-construction, the kalyptorhynch proboscis, the catenulid and haplopharyngid protonephridial construction, and the prolecithophoran spermatozoon and female germ cell. Examples of new features, as well as examples of how electron microscopy has clarified the relative position of structures and their substructures are given from the subcellular level to the organization of whole organs. Fine structural features linking different turbellarian orders are summarized. They apparently support Karling's (1974) latest assessment of the affinities between the turbellarian orders which is based primarily on light histological data, they add the recognition of a special link between the Macrostomida and Haplopharyngida and they suggest the existence of three main evolutionary lines within the Turbellaria.

Section: Reproductive Systemmentioning

confidence: 99%

Morphology of the Turbellaria at the ultrastructural level

Rieger

1981

112

“…Since all turbellarians possess egg coverings that, with a few exceptions such as the summer egg of Mesostoma ehrenbergii (see Domenici & Gremigni, 1977), are compositionally quite similar (see Smyth & Clegg, 1959), it appears likely that shell granules would be found in entolecithal oocytes of other archoophorans, and in either the oocytes or yolk cells of the ectolecithal eggs of the neoophorans . Among the archoophoran orders, eggshell granules have been observed by light microscopy in various macrostomids (v. Hofsten, 1912;Seilern-Aspang, 1957 ;Reiger, 1981), but their ultrastructure and cytochemistry are not known.…”

Section: Introductionmentioning

confidence: 99%

Embryology of the Turbellaria and its phylogenetic significance

Thomas

1986

Developmental characters -including oocyte and yolk cell structure, patterns of cleavage, and modes of gastrulation -are presented and examined in relation to the phylogeny of the Turbellaria . Eggshell granules, which have been demonstrated to occur in the oocytes of entolecithal eggs and the yolk cells of ectolecithal eggs, are compared among species, and their potential value as a taxonomic character is discussed . The quartet 4d spiral cleavage of the entolecithal egg of polyclads is described as reminiscent of the primitive pattern of early development for the Tlrbellaria . This is compared to duet spiral cleavage of acoels, and possible phylogenetic schemes involving the two types of spiral cleavage are reviewed . The link between the precise spiral cleavage, which characterizes development of most archoophorans, and blastomere separation (Blastomeren Anarchie), which occurs in several neoophoran orders, is established by the occurrence of quartet 4d spiral cleavage in one neoophoran order, and of both quartet spiral cleavage and Blastomeren Anarchie in different species of a second neoophoran order . The epibolic gastrulation of polyclads is described as primitive for the Turbellaria because of its similarity to that of other members of the Spiralia . Although no identical process occurs in neoophoran development, the earlier event of formation of the hull membrane in some neoophorans, and the later event of formation of the definitive epidermis in all neoophorans studied are presented as processes of possible homology to the epibolic gastrulation of polyclads . The lack of correspondence between polyclads and neoophorans in the relationship of the definitive body axes to the egg axis is discussed, and an hypothesis is advanced to account for the differences . The phylogenetic relationships indicated by known developmental phenomena differ only slightly from the scheme presented by Karling in 1974. Hydrobiologia 132, 105-115 (1986).

“…Some sporadic observations have also been published on other neoophorans: the typhloplanoid Mesostoma (see Domenici & Gremigni, 1977); the proseriate Notocaryoplunellu (see Sopott-Ehlers, 1986); the prolecithophorans Vorticeros (see Nigro & Gremigni, 1987), Pseudostomum (see Ehlers, 1985), and Archimonotresis (see Ehlers, 1988); the lecithoepitheliate Gnosonesimu; the prolecithophoran Plugiostomum; the proseriate Monocelis; the triclads Dugesiu, Procerodes, and Cercyru; the dalyellioid Dulyellia; and the kalyptorynchs Phonorhyncus and Gyratrix (see Gremigni, 1988).…”

mentioning

confidence: 98%

Ultrastructural features of cocoon-shell globules in the vitelline cells of neoophoran platyhelminths

Gremigni

Falleni

1991

Self Cite

The Neoophora is characterized by the presence of complex female gonads composed of both germaria and vitellaria. The vitellaria are made up of vitelline cells that differentiate to produce and accumulate reserve substances (proteins, lipid, glycogen) and precursors of the egg capsule or cocoon shell (phenolic proteins). A comparative ultrastructural and cytochemical investigation of shell-forming globules from the vitelline cells of some neoophoran platyhelminths shows that the internal structures of the shellforming globules can be grouped into two (or three) main types. In the first, globule content is characterized by a more or less homogeneous electron-dense substructure evidently arising from repeated coalescence of small vesicles produced by the rough endoplasmic reticulum and Golgi complex. A variant of this type of globule shows intermingling (or concentric) electron-dense and translucent areas producing a pattern resembling brain convolutions ('convoluted pattern'). The second type of shell-globule structure shows a 'multigranular pattern', presumably resulting from repeated fusions of Golgian vesicles followed by incomplete coalescence of the electron-dense content. Comparison of shell-globule structure in different taxa could be useful in elucidating some complex and still-unclear phylogenetic relationships among Platyhelminthes.