西沙赵述岛潮滩星虫形态特征及其环境适应性

Morphological Characteristics and Environmental Adaptability of Sipuncula in Tidal Flat of Tree Island in Xisha

基于2018年夏季赵述岛潮滩现场调查数据,研究西沙赵述岛潮滩内星虫物种组成,并结合沉积物和组织切片分析星虫对环境的适应性特征。在潮滩上设置3个取样站进行定性和定量研究,并对星虫肠道内沙粒组成和摄食消化结构进行测定与观察。结果显示,西沙赵述岛潮滩现存罗岛管体星虫(Siphonosoma rotumanum)、库岛管体星虫(S.cumanense)和富岛管体星虫(S.funafuti),组成比例为4︰2︰1,三种管体星虫生长环境相同,栖息层次均为10~15 cm。管体星虫肠道内均充满沙粒,去除沙粒后可观察到小型颗粒碎屑(<10μm,占90%)、硅藻类、桡足类(300μm)和植物纤维碎片等。下行肠(前肠)内大颗粒(粒径>0.25mm)沙粒比例(77.65%)高于上行肠(后肠)(62.67%),下行肠内小颗粒(粒径≤0.25mm)沙粒(22.34%)低于上行肠(37.33%),表明管体星虫对珊瑚礁砂砾具有细化作用。管体星虫(体重为8.5 g)吻部和躯干部角质层厚度分别为59.08μm和231.92μm,收吻肌由9000~9500个肌纤维组成,表明发达的角质层是对珊瑚礁粗糙底质的适应,收吻肌可以保证完成摄食过程。下行肠内的褶皱、肌纤维明显少于上行肠和直肠,表明管体星虫的消化过程主要发生在后段,这可能与珊瑚礁底质中的有机质含量低有一定关系。

To study the species composition and morphological characteristics of Siphonosoma in Zhaoshu Island,an onsite investigation was conducted in the tidal flat in Zhaoshu Island in Summer 2018.The environmental adaptability of Siphonosoma in tidal flat were analyzed based on the sediment characteristic and light microscopic observation of tissue biopsies.Three sampling section were selected in the tidal flat to collect and identify the macrobenthos qualitatively and quantitatively,and the sand grain size composition in gut and slices of gut were determined.The results indicated that,There are three species of Siphonosoma,and they are S.rotumanum,S.cumanense and S.funafuti,the species composition was about 4︰2︰1.The three species lived in the same environment and disturbed the same level of 10-15 cm.The gut of Siphonosoma was filled with sand,and the small organic particles,diatoms,copepods and plant fibers were found in gut.The large particles in down-gut were more than that in the upward-gut,and the small paticles in down-gut was less than that in the upward-gut.The result indicated that the gut of Siphonosoma has grain refinement effects to sediment particles.The cuticle of introvert retractor muscle and body wall were 59.08μm and 231.92μm,respectively.The introvert retractor muscle consisted of 9000-9500 muscle fibers,and there were some mastoid in the skin.The thicker cuticle and strong introvert retractor muscle were two adaptions of Siphonosoma to the coral reef sediment environment.The numbers of folds and muscle fibers in down-gut were less than that in the upward-gut.This may be correlated to the low content of organic matter in the coral reef sand.