The Thyasiridae is the most species-rich family of bivalves in the abyssal and hadal zones of the northwestern Pacific Ocean. In recent years, with at least 14 thyasirid species found in that region at depths exceeding 3,000 m. Some of them are the numerically dominant species in bottom communities. However, all members in that family have not yet been identified to the species level. Based on the material collected from 1953 to 2016 by five deep-sea expeditions, three new species of Thyasiridae (Mollusca: Bivalvia) are described from the abyssal and hadal zones of the northwestern Pacific. “Axinulus” roseus sp. nov. was found in the Kuril-Kamchatka Trench at 9,000–9,583 m depth. This species has a large rhomboidal shell with strong commarginal sculpture, a well defined, long and deep lunule and escutcheon without an auricle, a ctenidium consisting of a single demibranch, extensively lobed lateral pouches, and a large prodissoconch with specific sculpture. It is one of the dominant species in terms of abundance in macrobenthic communities in the deepest basin of the Kuril-Kamchatka Trench with a population density of up to 396 ind. m−2. The species has a shell length of up to 9.0 mm and it is the largest thyasirid with a single demibranch. “Axinulus” oliveri sp. nov. was found in a vast region of the northwestern Pacific on the abyssal plain adjacent to the Kuril-Kamchatka Trench, on the abyssal slope of the Kuril Islands, and in the Kuril-Kamchatka Trench at 4,648–6,168 m depth. This species is characterized by its ovate-rhomboidal shell, a well defined, deep and long escutcheon with a distinct auricle, a ctenidium with a single demibranch, and extensively lobed lateral pouches. It is widespread in the northwestern Pacific and forms populations with a density of up to 36 ind. m−2. Scanning electron microscopic observation of the gills of “A.” roseus sp. nov. and “A.” oliveri sp. nov. revealed that these species are not chemosymbiotic. “Axinulus” roseus sp. nov. and “A.” oliveri sp. nov. are provisionally assigned to the genus Axinulus, because they differ from the type species of the genus in a number of morphological and anatomical features. Parathyasira fragilis sp. nov. was found on the abyssal plain adjacent to the Kuril-Kamchatka Trench at 5,249–5,399 m depth. This species is distinguished by its very thin, fragile, dorsoventrally elongated, rhomboidal shell with very long anterodorsal margin and a long, wide, flat lunule. The taxonomic position of the new species is discussed.

中文翻译：

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来自西北太平洋深海平原和千岛-堪察加海沟深海深处的三种新的深海鱼科（软体动物：双壳类动物）

Thyasiridae 是太平洋西北部深海和浅海带中物种最丰富的双壳类家族。近年来，在该地区超过 3,000 m 的深度发现了至少 14 种 thyasirid 物种。其中一些是底层群落中数量上占优势的物种。然而，该科的所有成员还没有被鉴定到物种水平。根据 1953 年至 2016 年五次深海探险收集的材料，描述了来自西北太平洋深海和深海带的三个新物种 Thyasiridae（软体动物：双壳纲）。“Axinulus”roseus sp。十一月 在 9,000-9,583 m 深的千岛-堪察加海沟中发现。该物种有一个大菱形外壳，带有强烈的边缘雕刻，一个轮廓分明、长而深的月牙和无耳廓的盾徽，一种由单个半分支、广泛裂开的侧袋和一个带有特定雕塑的大型 prodissoconch 组成的 ctenidium。它是千岛-堪察加海沟最深盆地大型底栖动物群落丰度的优势物种之一，种群密度高达 396 ind。米-2。该物种的壳长可达 9.0 毫米，它是最大的 thyasirid，具有单个半分支。“Axinulus” Oliveri sp。十一月 发现于太平洋西北部的广阔区域，靠近千岛-堪察加海沟的深海平原、千岛群岛的深海斜坡和千岛-堪察加海沟，深度为 4,648-6,168 m。这个物种的特点是它的卵形菱形外壳，一个轮廓分明、深而长的盾形罩，有一个明显的耳廓，一个带有单个半枝的栉盖，和大裂的侧袋。它广泛分布于西北太平洋并形成密度高达 36 ind 的种群。米-2。“A”鱼鳃的扫描电镜观察。蔷薇属 十一月 和“A” 奥利弗里公司 十一月 揭示这些物种不是化学共生的。“Axinulus”roseus sp。十一月 和“A” 奥利弗里公司 十一月 暂时归入 Axinulus 属，因为它们在许多形态学和解剖学特征上与该属的模式种不同。Parathyasira fragilis sp. 十一月 在与千岛-堪察加海沟相邻的深海平原上发现，深度为 5,249-5,399 m。该物种的特征在于其非常薄、易碎、背腹拉长的菱形外壳，具有非常长的前背缘和一个长而宽的扁平月牙。讨论了新种的分类地位。