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）阀上的捕食痕的形态组与介形类生态的关系，根据其形态，将介形类阀上的捕食痕分为抛物线形、圆柱形和不规则形孔。具捕食痕的介形类主要有桑迪底栖动物、泥质底栖动物和以海生植物为食的底栖动物。植生种在最近的珊瑚礁介形类中占优势，具有捕食疤痕。钻孔被认为是由肉食性原生动物和其他腹足类动物产生的，如抛物线孔、圆柱孔和部分不规则孔。但是，肉食性腹足类仅生活在桑迪或淤泥质底质上，因此，攻击植物介形类的捕食者仍有待研究。不规则形状的孔经常伴随着在孔周围的外阀表面上的划痕、刮擦和溶解的疤痕。这些证据可能表明，不规则形状的孔不仅包括钻孔，而且还包括切割或刺穿的捕食疤痕。在某些介形虫的瓣膜上也发现有溶孔。本文作者将一种介形虫与其预期的选择性捕食者放在同一个容器中饲养，试图识别产生捕食疤痕的捕食者，但没有成功。值得注意的是，在未来的试验中，容器中的水应保持在一个良好的条件下，和“候选人”的捕食者应选择考虑的结构的附属物有关的捕食。

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.