2010-2013 Ryland et al. UK first Schizoporella japonica records

Schizoporella japonica Ortmann was described from Japan but was subsequently introduced on Pacific oysters to the Pacific coast of North America, where it is now well established. In this paper we record it for the first time in European waters. The initial discovery was in a marina at Holyhead, North Wales, in July 2010 but S. japonica has since been observed abundantly in the Orkney Islands (from May 2011) and, subsequently, at other localities in northern Scotland. Introduction seems most likely to have been on an ocean-going vessel. The British material is here fully described and illustrated with SEMs and colour photographs; some unusual characters are discussed. Unlike other recently introduced bryozoans, S. japonica is a cold-water species and its breeding season in Britain extends through the winter. Extensive confusion between this and other species of Schizoporella on the west coast of Canada and the USA led us to make thorough morphometric comparisons between the species concerned (Schizoporella unicornis (Johnston in Wood), Schizoporella errata (Waters) and Schizoporella pseudoerrata Soule, Soule and Chaney). Zooid size in cheilostomate bryozoans is variable and often an unreliable character for species separation but shape (and therefore ratios between variables,which are independent of size) are often valuable: S. japonica zooids have a much greater length:width ratio than the other species. Density of frontal pseudopores provides a useful discriminatory character. Schizoporella unicornis, repeatedly reported in error from the Pacific coast of North America, does not occur there; it is a European species. Full comparisons are made between S. japonica and S. unicornis for European identification and between S. japonica, S. errata and S. pseudoerrata (which are also illustrated) for North American localities.日本裂孔苔虫（Schizoporella japonica Ortmann）的模式产地为日本，后随太平洋牡蛎传入北美太平洋沿岸并成功定殖。本文首次记录该物种在欧洲水域的分布：2010年7月于北威尔士霍利黑德的一处游艇港（marina）首次发现其踪迹，自2011年5月起，奥克尼群岛已大量观测到该物种，随后苏格兰北部其他多地亦有发现。其传入途径极有可能为远洋船舶携带。本文对英国采集的该物种标本进行了全面描述，并辅以扫描电子显微镜（Scanning Electron Microscope, SEM）成像与彩色照片；同时讨论了部分异常形态特征。与其他近期引入的苔藓虫不同，日本裂孔苔虫为冷水性物种，其在英国的繁殖季贯穿冬季。此前加拿大与美国西海岸的研究曾将该种与其他裂孔苔虫物种混淆，为此我们对相关类群开展了详尽的形态计量学对比，涉及物种包括单角裂孔苔虫（Schizoporella unicornis (Johnston in Wood)）、红斑裂孔苔虫（Schizoporella errata (Waters)）以及假红斑裂孔苔虫（Schizoporella pseudoerrata Soule, Soule and Chaney）。唇口目（Cheilostomata）苔藓虫的个虫（zooid）大小存在变异，通常难以作为物种区分的可靠依据，但形态特征（即与个体大小无关的变量比值）往往具备分类价值：日本裂孔苔虫的个虫长宽比显著高于其余三种。额部伪孔密度可作为有效的物种区分特征。此前北美太平洋沿岸多次误报存在单角裂孔苔虫，实则该种为欧洲特有物种。本文针对欧洲物种鉴定需求，全面对比了日本裂孔苔虫与单角裂孔苔虫；同时针对北美沿岸分布类群，全面对比了日本裂孔苔虫、红斑裂孔苔虫与假红斑裂孔苔虫（亦附插图）。