COLONY GROWTH AND PATTERN IN THE TWO-TENTACLED HYDROID, PROBOSCIDACTYLA FLAVICIRRATA

¹ Friday Harbor Laboratories, University of Washington, and Department of Organismic Biology, University of California, Irvine

1. The colony of the hydroid Proboscidactyla covers the terminal portions of a sabellid worm tube. The colony is axially patterned. In distal regions stolons run parallel to the form tube axis while in proximal regions they form an anastomosing network. Gastrozooids are situated at the tube rim, gonozooids in a whorl behind gastrozooids, and dactylozooids in the proximal colony regions.

2. Gastrozooids will migrate actively forward when they are not at the edge of a substratum. The gonozooid associated with each gastrozooid generally moves with it.

3. The colony appears to be in a steady-state condition. The whorl of gastrozooids, and associated gonozooids, migrates forward as the tube rim advances due to secretion by the worm. The stolon system is generated behind the advancing gastrozooids. The proximal end of the colony progressively loses its regularity and definition. The axiate patterns of the colony at any moment thus trace out the history of the colony.