Strathmann R R, Bone Q
Biol Bull. 1997 Oct;193(2):153-162. doi: 10.2307/1542761.
Phoronid larvae have an oral hood upstream from a postoral encircling array of ciliated tentacles. Cilia move water over the hood and between the tentacles, from anterior to posterior. When an algal cell or other particle in this current contacts a tentacle, the neighboring part of the hood lifts, and the particle is drawn toward the mouth. The correlation between movements of hood and particles indicates that the particle moves with water entering the enlarged space beneath the hood. Each lift of the hood is preceded by contact between a particle and a tentacle. A hood lift follows contact with a particle anywhere along the length of a tentacle, and clearance rates are thus proportional to the total length of tentacles deployed and the velocity of the current past the tentacles. After being detained at the ciliary bands of tentacles, particles are transported by the hood lift at speeds exceeding measured transport along the frontal ciliated surfaces of other larval forms. Faster transport may aid capture of faster prey. The larva's feeding mechanism is unique to the phylum Phoronida. Larvae of brachiopods, bryozoans, hemichordates, and echinoderms have similar ciliary bands producing feeding currents, but none are known to transport food toward the mouth by suction produced by muscle contractions.
帚虫幼虫在口后环绕排列的纤毛触手的上游有一个口罩。纤毛使水流过口罩并在触手之间从前向后流动。当水流中的一个藻类细胞或其他颗粒接触到一条触手时，口罩相邻部分会抬起，颗粒被吸向口部。口罩和颗粒运动之间的关联表明，颗粒随着水进入口罩下方的扩大空间而移动。口罩每次抬起之前，颗粒与一条触手都会先接触。沿着触手长度的任何位置，颗粒与触手接触后口罩都会抬起，因此清除率与展开的触手总长度以及水流经过触手的速度成正比。颗粒在触手的纤毛带处被滞留后，通过口罩抬起进行运输的速度超过了在其他幼虫形态的前端纤毛表面测量到的运输速度。更快的运输速度可能有助于捕获更快的猎物。幼虫的摄食机制是帚虫动物门所特有的。腕足动物、苔藓虫、半索动物和棘皮动物的幼虫有类似的纤毛带产生摄食水流，但已知没有一种是通过肌肉收缩产生的吸力将食物吸向口部的。
