The phylum Annelida exhibits high morphological diversity coupled with its extensive ecological diversity, and the process of its evolution has been an attractive research subject for many researchers. Its representatives are also extensively studied in fields of ecology and developmental biology and important in many other biology related disciplines. The study of biomineralisation is one of them. Some annelid groups are well known to form calcified tubes but other forms of biomineralisation are also known. Herein, we report a new interstitial annelid species with black spicules, Thoracophelia minuta sp. nov., from Yoichi, Hokkaido, Japan. Spicules are minute calcium carbonate inclusions found across the body and in this new species, numerous black rod-like inclusions of calcium-rich composition are distributed in the coelomic cavity. The new species can be distinguished from other known species of the genus by these conspicuous spicules, shape of branchiae and body formula. Further, the new species’ body size is apparently smaller than its congeners. Based on our molecular phylogenetic analysis using 18S and 28S sequences, we discuss the evolutionary significance of the new species’ spicules and also the species' progenetic origin.

环节动物门表现出高度的形态多样性和广泛的生态多样性，其进化过程一直是许多研究人员的一个有吸引力的研究课题。它的代表还在生态学和发育生物学领域进行了广泛的研究，并且在许多其他生物学相关学科中也很重要。生物矿化研究就是其中之一。众所周知，一些环节动物群会形成钙化管，但也知道其他形式的生物矿化。在此，我们报告了一种新的具有黑色针状体的间质环节动物，Thoracophelia minutasp. 11 月，来自日本北海道余市。骨针是遍布全身的微小碳酸钙内含物，在这个新物种中，大量富含钙成分的黑色棒状内含物分布在体腔中。新种可以通过这些显眼的针状体、鳃的形状和体型与该属的其他已知种区分开来。此外，新物种的体型明显小于其同类。基于我们使用 18S 和 28S 序列进行的分子系统发育分析，我们讨论了新物种针状体的进化意义以及该物种的后代起源。