Trimeric Coelom Organization in the Larvae of Phoronopsis harmeri Pixell, 1912 (Phoronida, Lophophorata)

摘要

Phoronida is a relict group of marine invertebrates traditionally considered to be the most primitive bilaterally symmetric animals (Bilateria). Phoronida larvae were fist described under the original generic name Actinotrocha. Masterman [8], who studied actinotrochs, put forward the archicoelomate concept, which was later developed by Remane [10], Ulrich [13], Siewing [12], and others. In the early 20th century, Masterman [8] and other authors [3, 5, 9] reported that the coelom of Phoronida larvae contained three compartments, which were considered to be homologous to three coeloms of the dipleurula. The idea of a trimeric coelom in actinotrochs was later supported by other authors [7, 11-14]. Recent electron microscopic study performed by a Germanresearch team headed by Bartolomaeus [2, 6] did not confirm the presence of three coelom compartments in Phoronida. However, the organization of the body cavity in Phoronida larvae is still discussed. We report here some evidence suggesting that the larvae of some Phoronida species actually have a trimeric coelom.