Zoological Studies

Vol. 39 No. 1, 2000

Burrow Architecture of the Spionid Polychaete Polydora villosa in the Corals Montipora and Porites

Pi-Jen Liu1,2 and Hwey-Lian Hsieh1,*

1Institute of Zoology, Academia Sinica, Taipei, Taiwan 115
2Institute of Marine Biology, National Taiwan Ocean University, Keelung, Taiwan 202

Pi-Jen Liu and Hwey-Lian Hsieh (2000) The spionid polychaete, Polydora villosa, is found only in living corals in the Penghu Archipelago, Taiwan. Polydora villosa builds burrows inside the coral skeleton and secretes mucus to form fragile mud-tubes in the burrows with openings projecting approximately 2 mm above the coral surface. X-ray radiographs of sections of the branching-shaped corals, Montipora angulata, M. hispita, and M. informis, and of the massive-shaped corals, Porites lichen, P. lobata, and P. lutea, have revealed that the burrows consist of 2 parts: a narrow, U-shaped passage and several straight, elongated tunnels. The U-shaped passages are located at the dead ends of the burrows, and the straight elongated tunnels are at the free, open end. Longitudinal and transverse sections of the burrows reveal that the straight elongated tunnels are encircled by a thick layer of calcium carbonate, but the U-shaped passages are not. The U-shaped passages directly intersect the growth direction of the corals, and the surfaces of the passages show traces of etching as examined under a scanning electron microscope. This suggests that the U-shaped passages are formed initially by Polydora villosa through active boring into the coral. At a later stage, the elongated tunnels are formed when the corals grow concurrently with the tube construction of Polydora villosa, indicating that the formation of burrows is passive at this time. The straight elongated tunnels are simple in Porites, but are branched in Montipora, whereas tunnel lengths are shorter in Porites than in Montipora. The branched morph of Montipora is often inhabited by Polydora villosa. We speculate that interactions between the coral Montipora and the worms may result in modification of the growth form of Montipora from an encrusting or columnar morph to a branched one. In contrast, the shape of Porites is not affected by the worm and retains its original massive form.

Key words: Polydorid polychaete, Burrow morphology, Coral.

*Correspondence: Tel: 886-2-27899546. Fax: 886-2-27858059. E-mail: zohl@ccvax.sinica.edu.tw