Reproduction and development ofAnemonia sulcata (Anthozoa, Actiniaria). II. Early development, blastula and gastrula

Abstract

Reproduction and development of Anemonia sulcata (Anthozoa, Actiniaria). II. Early development, blastula and gastrula. Early developmental stages of the Anemonia germ are characterized by asynchronously dividing nuclei and an extreme delay of blastomere differentiation. The nuclei migrate to the periphery, whereas nutritive substances remain in the interior. Following this stage, the appearance of cell boundaries results in the formation of the blastoderm and the simultaneous division of the yolk into many fragments. Most of them are exclusively filled with reserve material; only very few contain zooxanthellae or nuclei. On the embryo's surface, conically shaped bundles of long microvilli are obvious. They appear to be less regularly arranged than the spines of oocytes before insemination. Pigment granules that have originated from fusing Golgi vesicles are crowded peripherally in the blastoderm cells. In the nucleoplasm single annulate lamellae that seem to be cut off from the nuclear envelope can frequently be found. There is no further cellular differentiation until gastrulation is completed. Though yolk-containing cellular fragments occupy nearly the whole blastocoel, entoderm formation occurs by invagination. Ultrastructural observations provide evidence of the existence of interstices between entoderm ceils that allow all nutritive substances to pass gradually into the gastric cavity. In the region of the blastoporus there are cellular processes enveloping reserve material. Presumably, these observations indicate a so-called "filtration of nutritive yolk" (Korschelt & Heider, 1909) that might represent an additional mode for the transfer of yolk-containing cellular fragments from blastocoel into gastrocoel. EINLEITUNG

Ultrastructural observations of the early and late stages of gorgonian coral (Junceella juncea) oocytes

“…A dense 1-2-m microvilli layer was present on the oocyte surface for protection. Longer microvilli (10-20 m) have been found in some sea anemone oocytes (Larkman and Carter, 1984;Schäifer, 1984). In the present study, reticulated vitelline coats were observed to enclose the oocytes.…”

Ultrastructural features of the trophonema and oogenesis in the starlet sea anemone, Nematostella vectensis (Edwardsiidae)

“…Vitellogenesis has been detailed on the ultrastructural level in the sea pen Pennatula aculeata (Eckelbarger et al 1998), a pennatulid anthozoan (octocoral), but its ovarian structure and vitellogenic processes differ significantly from what little we know of sea anemones. Vitellogenesis in sea anemones is initiated either before or after the entry of germ cells into the mesoglea from the gastrodermis (Schäfer & Schmidt 1980; Schäfer 1984). Larkman (1983) determined that, in A. fragacea , vitellogenesis is usually initiated after (occasionally before) oocytes enter the mesoglea, and it was suggested that a significant amount of yolk synthesis was autosynthetic due to the presence of abundant biosynthetic organelles (Larkman 1984a).…”

“…While the process of spermatogenesis and mature sperm morphology have proven to be taxonomically useful (e.g., Daly et al 2003), far less is known about anthozoan oogenesis, particularly on the ultrastructural level. Morphological studies of oocytes have been limited to descriptions of the unusual microvilli (termed “spines,”“cytospines,” or “spires”) (Clark & Dewel 1974; Dewel & Clark 1974; Spaulding 1974; Schmidt & Schäfer 1980; Schroeder 1982), the fine structure of specific ooplasmic organelles (Larkman 1980, 1984a; Schäfer & Schmidt 1980; Van‐Praët 1990; Van‐Praët et al 1990), the “cortical reaction” (Dewel & Clark 1974; Schroeder 1982; Schäfer 1984), and the migration of early oocytes from the endoderm into the mesoglea during early oogenesis (Larkman 1983). There have been no comprehensive ultrastructural studies of oogenesis in any sea anemone, especially the process of vitellogenesis.…”

The many faced symbiotic snakelocks anemone (Anemonia viridis, Anthozoa): host and symbiont genetic differentiation among colour morphs

“…Moreover, previous studies investigating the nature of A. viridis morphs did not systematically consider A. viridis as a holobiont. A. viridis' gastrodermal tissue harbours millions of dinoଏagellate cells (Muscatine et al 1998;Suggett et al 2012;Zamoum and Furla 2012;Ventura et al 2016) belonging to the family Symbiodiniaceae (LaJeunesse et al 2018) that live in a close trophic relationship (Davy et al 1996) and that are vertically transmitted (Schäfer 1984). The Symbiodiniaceae associated to A. viridis belong to the temperate clade A (LaJeunesse et al 2018; or A' sensu Savage et al 2002;Visram et al 2006) presenting not only an intra-clade genetic diversity partially structured by host species but also an intra-host genetic diversity (Visram et al 2006;Forcioli et al 2011;Casado-Amezúa et al 2014).…”