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  • Malcolm was our cook during the kayak expedition. Here he is holding a large male land crab (Discoplax hirtipes) at our second campsite, which was at Ngeremdiu Beach. Malcolm told me that female crabs migrate from land to the water to release their brood at the turning of the high tide during full moon. We saw a few females releasing eggs here at Ngeremdiu Beach, and also at the next campsite on Ngchuus Beach. See separate photos of female crab releasing eggs, and of the resulting zoea.
    terrestrial-crab-discoplax-hirtipes-...tif
  • This is a cloud of crab larvae, just after release in shallow water by a female land crab (Discoplax hirtipes). At 100% magnification, the individual larva are easily distinguishable. See separate image of female crab in the act of releasing these eggs/ larvae into the water. Photographed at Ngeremdiu Beach, Ngeruktabel Island in Palau.
    crab-larvae-zoea-Discoplax-hirtipes-...tif
  • This is a cloud of crab larvae, just after release in shallow water by a female land crab (Discoplax hirtipes). At 100% magnification, the individual larva are easily distinguishable. See separate image of female crab in the act of releasing these eggs/ larvae into the water. Photographed at Ngeremdiu Beach, Ngeruktabel Island in Palau.
    crab-larvae-zoea-Discoplax-hirtipes-...tif
  • This is a female Discoplax hirtipes terrestrial crab disseminating her brood of fertilized eggs into shallow water during full moon. The crab waited on land at Ngeremdiu Beach for the evening high tide. She entered the water as the tide turned to go out and released her eggs. Once she committed to releasing eggs, it was only a matter of seconds before she completed her task and headed back to the safety of her underground burrow. See separate photograph of the crab eggs in the water.
    female-land-crab-releasing-eggs-pala...tif
  • This is a top-down view of a pair of endangered tri-spine horseshoe crabs (Tachypleus tridentatus) engaged in spawning. The male is clasped onto the rear of the female, preparing to fertilize eggs that she will deposit. Seen here, the female is still burrowing into the substrate. She will dig deeper, until her primary compound eyes and most of her prosoma is buried. The bubbles are the result of pockets of air trapped in the mud and gravel being released due to the female’s excavation.<br />
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Spawning takes place in the intertidal zone, which is the reason that substantial quantities of air are present in the sediment. It is also the reason that the water is murky and somewhat hazy, as there is mixing of fresh water flowing in from land.<br />
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Although these animals are called crabs, they are not members of the Subphylum Crustacea. They belong to a separate Subphylum—Chelicerata—which also comprises sea spiders, arachnids, and several extinct lineages such as sea scorpions. The earliest known fossils of horseshoe crabs date back 450 million years ago, qualifying these animals as living fossils, as they have remained largely unchanged.<br />
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Tachypleus tridentatus is the largest of the four living species of these marine arthropods, all of which are endangered.<br />
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Though habitat loss and overharvesting of these animals for food are primary contributors to the population decline of horseshoe crabs, the biomedical industry is also a major factor. Horseshoe crabs are bled for their amoebocytes (akin to white blood cells), which are used to derive an extract that reacts in the presence endotoxin lipopolysaccharide, which is found in the membranes of gram-negative bacteria. Estimates suggest that between three and 30% of the animals die as a result. There have also been suggestions that taking up to a third of each animal's blood adversely affects their ability to undertake vital functions, such as procreation, even if the animals survive.
    tachypleus-tridentatus-horseshoe-cra...tif
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Tony Wu Underwater Photography

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