. The Biological bulletin. Biology; Zoology; Marine biology. ated for 12 h prior to use. In subsequent trials, the res- ervoirs contained 21 and 24 1 each and were aerated for 14 and 16 h, respectively. After the initial acclimation period, the pump was turned on (90 min before the first introduction of test crabs) to allow water containing potential host-factor to move through the experimental apparatus. A single Pin- nixa was then placed in the middle of the central chamber and its position was monitored every 30 min under red light. The crab was allowed to explore the chamber until it enter
. The Biological bulletin. Biology; Zoology; Marine biology. ated for 12 h prior to use. In subsequent trials, the res- ervoirs contained 21 and 24 1 each and were aerated for 14 and 16 h, respectively. After the initial acclimation period, the pump was turned on (90 min before the first introduction of test crabs) to allow water containing potential host-factor to move through the experimental apparatus. A single Pin- nixa was then placed in the middle of the central chamber and its position was monitored every 30 min under red light. The crab was allowed to explore the chamber until it entered one of the radial chambers (from which it could not exit), at which time its position was recorded, the crab was removed, and the next crab was placed in the central chamber. Crabs generally entered a radial chamber within 90 min of being placed in the central 15 cm Figure 1. Six-chambered choice apparatus used in all experiments. Arrows indicate direction of water flow. appropriate for the experiment being run were replaced, and the tube slit was sewed shut using cotton thread. Worms were allowed to acclimate in running seawater for 72 h after handling before further use. The mean weight of Chaetoptenis used was ± g. Host by conspecific experiment In this experiment, conditioned seawater was pumped into the outside chambers from three treatment reservoirs, with water from a given reservoir pumped into two cham- bers located 180° apart. The reservoirs contained: (1) fil- tered seawater alone (control treatment), (2) filtered sea- water plus two Chaetoptenis in their tubes from which all crabs had been removed (hosts without conspecifics), and (3) filtered seawater plus two Chaetoptenis in their tubes with a heterosexual pair of Pinnixa in each tube (hosts plus conspecifics). Three trials were run with 15, 15, and 14 different test crabs, respectively, and new hosts were used in each trial. All three reservoirs contained 18 1 of seawater at the initiati
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