The evolutionary paleobiological study on the predation scars on the valves of reef ostracodes

本研究的主要目的是明确琉球群岛浅水介形类（包括活介形类和化石介形类）瓣上捕食痕的形态类群与介形类生态学之间的关系。捕食痕，即穿透介形虫瓣的孔洞，根据其形态分为抛物线形、圆柱形和不规则形三种。有捕食伤痕的介形类包括沙底栖动物、泥底栖动物和海生植物栖动物。植物种类在最近的礁介形类中占主导地位，这些介形类带有捕食伤痕。研究认为，肉食性鲷和其他腹足类动物产生的钻孔有抛物线形孔、圆柱形孔和部分不规则形孔。但是，食肉腹足类动物只生活在沙质或泥泞的底部，因此，攻击植物介形类动物的捕食者仍有待研究。通过在孔周围的阀外表面刮、刮、解，常伴有不规则形状的孔。这些证据可能表明，这些不规则形状的孔不仅包括钻孔，还包括切割或刺穿的捕食痕迹。在一些介形虫阀中也发现溶液孔。溶洞可由消化液或无机溶液引起。作者将特定种类的介形虫与预期的捕食者饲养在同一个容器的水箱中，并试图识别捕食者以产生捕食伤痕，但失败了。值得注意的是，在未来的试验中，应保持容器中的水的良好状态，并考虑与捕食相关的附属物结构来选择捕食者的“候选”。

The main purpose of this study is to clear the relationships between the morphological groups of predation scars on the valves of the shallow-water ostracodes from the Ryukyu Islands, including both living and fossil, and the ecology of the ostracodes.The predation scars, which are the holes penetrating through ostracode valves, are grouped into the parabolic, cylindrical and irregular-shaped holes based on their morphology. The ostracodes bearing predation scars concist of the sandy bottom inhabitants, muddy bottom inhabitants and dwellers living on sea plants. The phytal species prevail in the recent reef ostracodes bearing predation scars. The carnivorous naticids and other gastropods have been considered to produce the drillholes such as the parabolic, cylindrical holes and part of the irregular-shaped holes. But, the carnivorous gastropods live only on sandy or muddy bottoms, and therefore, the predators attacking the phytal ostracodes remain to be inquired. The irregular-shaped holes frequently accompany the scars by scratching, scraping and solution on the outer valve surfaces around the holes. These evidences might suggest that the irregular-shaped holes include not only drillholes, but also the predation scars by cutting or piercing. Solution holes are also found in some ostracode valves. The solution holes can be due to digestive-solution or inorgamic solution.The author reared some ostracodes of a particular species with its expected selective predators in the same container in a water tank, and tried to identify the predator to produce the predation scars, but failed. It is notable for the future trials that the water in the container should be kept in a good condition, and the 'candidates' of predators should be selected in consideration of the structures of appendages relevant to predation.