Ultrastructure of Meelsvirus: A nuclear virus of arrow worms (phylum Chaetognatha) producing giant "tailed" virions.

Most known giant viruses, i.e., viruses producing giant virions, parasitize amoebae and other unicellular eukaryotes.

TEM analyses of chaetognath reproductive organs.

Transmission electron microscopy (TEM) enables analysis of subcellular organization. It is especially useful for describing the diverse array of cell types in the gonads and embryos of marine invertebrates. Here, I describe methods for preserving and embedding the reproductive organs of marine arrow worms for TEM, including procedures for staining thick sections for light microscopy and thin sections for TEM.

Morphology of the male system and spermatophores of the arrowworm Ferosagitta hispida (Chaetognatha).

Transmission electron microscopy reveals that the somatic testicular tissues and sperm ducts are elaborations of the epithelial lining of the tail coelom. The testes consist of closely packed spermatogonia embedded between specialized lateral field cells. These cells contain few organelles and appear to function mainly as a compartment boundary.

Ultrastructure of hatchling chaetognaths (Ferosagitta hispida): Epithelial arrangement of the mesoderm and its phylogenetic implications.

The trunk and tail mesoderm of hatchling chaetognaths consists of a simple myoepithelium containing four stereotypically arranged cell types, each matching in position a specific adult tissue. The trunk mesoderm includes lateral cells, longitudinal muscle cells, dorsal and ventral medial cells, and peri-intestinal cells. These correspond, respectively, to the lateral fields, longitudinal body wall muscles, dorsal and ventral perimysial cells, and periintestinal muscles of adults.

Ultrastructure of somatic tissues in the ovaries of a chaetognath (Ferosagitta hispida).

Transmission electron microscopy reveals that the ovaries of Ferosagitta hispida contain four somatic tissues. A myoepithelial ovary wall, continuous with a thin layer of peritoneocytes lining the coelomic cavity, encloses a fluid-filled ovarian space in which oocytes develop. Lamellar extensions of a "follicular reticulum" branch throughout the ovarian space and ensheath developing oocytes.