Horseshoe Crab Essay

Horseshoe crabs are marine living fossils, probably traced back to 485 million years ago. There are two horseshoe crab species found in Hong Kong.
Horseshoe crabs are an ancient marine chelicerates, identified as the Class Merostomata and Order Xiphosura. The animals are identified by the having appendages around their middle of the mouth and their swimming legs at their end of their body. They are in close linkage with trilobites and arachnids which are spiders and scorpions. Amazingly, they are not closely related to the "real" crabs which are crustaceans. Four extant species of horseshoe crabs are found and have survived over the geological period. They are classified to three genera in two families under the Superfamily Limulacea. They have nearly not been changed or evolved in millions years. The oldest horseshoe crab fossils are probably traced back to the Cambrian period, which is nearly 485 million years ago. Therefore, they are treated as living fossils.

Xylocopa iridipennis
They are large bees habited worldwide. 500 species of carpenter bees are in the 31 subgenera. Their common name is due to the fact that nearly all species build their nests in burrows in dead wood or structural timbers, which except those in the subgenus Proxylocopa, which nest in the ground. Members of the related tribe Ceratinini are sometimes referred to as "small carpenter bees".
Xylocopa iridipennis are large, hardy, shiny and in black color. Some of them having yellow pattern on their heads. They may be mistaken for bum or blebees.
The marginal cell in the front wing is thin and stretched. Their apex bends are away from the costa. The front wing has small stigmata. Their labrum is hidden by the short mandibles when closed. Their clypeus is smooth. The thoracic mesonotum is upright . It is part of the incommon surface. It is almost perpendicular to the dorsal surface. The basitarsi are of the same length as the associated tibiae, and the hind pair of basitarsus is