Thiago Q. Araujo, Simon King-Trudeau, Joanna VanDyke, Rick Hochberg
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引用次数: 0
Abstract
Freshwater gastrotrichs have a biphasic lifecycle that reputedly involves the production of three types of eggs: apomictic and fast hatching (tachyblastic ova), apomictic and delayed hatching (opsiblastic ova), and plaque-bearing eggs (potentially derived from mixis). While some details of oogenesis and eggshell structure are known for tachyblastic ova, there are few details on other egg types. Here, we provide the first ultrastructural description of the oviposited opsiblastic eggs of the freshwater gastrotrich, Lepidodermella squamata. Scanning electron microscopy revealed the eggshell surface to be ornamented with long flattened pillar-like structures centered on polygonal plates that are pitted along their periphery. Transmission electron microscopy showed the pits to lead to a vast labyrinth of tubular spaces and larger cavities throughout the thick apical layer of the shell. The basal layer of the shell is amorphous and connected to a network of fine fibers that traverse an extra-oocyte space and forms a protective sheet around the uncleaved oocyte. The uncleaved oocyte has a dense layer of peripheral ooplasm surrounding a core of organelles including mitochondria, membrane-bound secretion granules, endoplasmic reticulum, and a single nucleus in a granular, ribosome-rich cytoplasm. Secretion granules are the most abundant organelles and presumably contain lipid-rich yolk that will be used as energy for delayed cleavage, thus functioning in temporal dispersal. These data are compared to the fine structure of invertebrate resting eggs across the phylogenetic spectrum to determine the novelty of opsiblastic egg structure in L. squamata.
期刊介绍:
The Journal of Morphology welcomes articles of original research in cytology, protozoology, embryology, and general morphology. Articles generally should not exceed 35 printed pages. Preliminary notices or articles of a purely descriptive morphological or taxonomic nature are not included. No paper which has already been published will be accepted, nor will simultaneous publications elsewhere be allowed.
The Journal of Morphology publishes research in functional, comparative, evolutionary and developmental morphology from vertebrates and invertebrates. Human and veterinary anatomy or paleontology are considered when an explicit connection to neontological animal morphology is presented, and the paper contains relevant information for the community of animal morphologists. Based on our long tradition, we continue to seek publishing the best papers in animal morphology.