Morphometric data for colonies of Tabulipora sp.

One of the challenges for bryozoans is avoiding refiltering of water that has already had its plankton removed. Larger colonies develop colony-wide maculae-centered feeding currents to avoid refiltering water, and generally have elevated maculae (monticules). We hypothesize that height and spacing of monticules is inversely proportional to curvature of the colony surface. Larger flatter colonies should have higher and more closely spaced monticules. We compare two Permian palaeostomate bryozoans whose colonies form branches with elliptical cross-sections: the smaller and more elliptical cystoporate Evactinostella crucialis from Western Australia (n = 17) and the larger and flatter trepostome Tabulipora sp. from eastern North Greenland (n = 15). Using calipers and digital elevation models we measured curvature, monticule height, and number of monticules per area. Results indicate that Evactinostella branches are at least twice as curved as those of Tabulipora, their monticules are 1/2 the height of Tabulipora, and their monticules are 22% less densely spaced than those of Tabulipora. In Evactinostella colonies, surface curvature is inversely proportional to monticule height and spatial density which is not true for Tabulipora. Therefore, we conclude that the smaller and more curved the colony surface, the less the colony needs robust colony-wide feeding currents created by tall closely spaced monticules.

苔藓虫（Bryozoa）面临的关键挑战之一，是避免对已滤除浮游生物的水体进行重复过滤。体型更大的苔藓虫群体，会形成以群体整体的maculae（即monticules，虫室丘）为核心的摄食水流以规避重复过滤，且通常具有隆起的maculae（即monticules，虫室丘）。我们提出假说：虫室丘的高度与间距，与群体表面的曲率呈负相关关系；体型更大、表面更平坦的群体，其虫室丘应更高且间距更为紧密。我们选取两种二叠纪古口类苔藓虫（Palaeostomate bryozoans）开展对比研究，二者的群体均形成具有椭圆形横截面的分枝：来自西澳大利亚的体型更小、形态更偏椭圆的泡孔目（Cystoporata）苔藓虫*Evactinostella crucialis*（样本量n=17），以及来自北格陵兰东部的体型更大、表面更平坦的隐口目（Trepostomida）*Tabulipora* sp.（样本量n=15）。我们借助游标卡尺与数字高程模型，测量了群体表面曲率、虫室丘高度以及单位面积内的虫室丘数量。实验结果表明：*Evactinostella*的分枝曲率至少为*Tabulipora* sp.的两倍，其虫室丘高度仅为后者的1/2，且虫室丘的空间密度比后者低22%。在*Evactinostella*的群体中，表面曲率与虫室丘高度及空间密度呈负相关关系，但这一规律并不适用于*Tabulipora* sp.。因此我们得出结论：群体表面曲率越大、体型越小，则该群体对由高且间距紧密的虫室丘所形成的强群体整体摄食水流的需求越低。