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Most animals rely upon rigid skeletal structures to withstand the negative pressures required for inhalation. Some soft-bodied invertebrates (innkeeper worms, sea cucumbers) have pumping cloacae that are able to "inhale" without any hard supporting structures. Geometric analyses suggest that inhalation cannot be produced by relaxation of coelomic pressure and contraction of radial muscles connecting the body wall. Coelomic pressure must be maintained for body wall support and radial muscle antagonism. Mathematical models predict that maximum attainble suction in a hydrostatically supported sac-within-a-sac like the cloaca-body wall system will be proportional to coelomic pressure and exponentially related to the ratio of body wall diameter to cloacal diameter. A mechanical model gives results consistent with these predictions. "Cloacal" suctions are proportional to "coelomic" pressure, and maximum suction (20 x coelomic pressure) is produced when the cloaca is small relative to the body wall. In vivo reco...

The design and utilization ofa small (16 g in air, 6 g in water) ultrasonic transmitter for animal track ing and bio-telemetry of muscle activity are described. To our knowledge this is the first use of such devices to telemetera specific behavior(ingestion) from a free-rang ing marine predator. The transmitter produces regularly recurring short tracking pulses, and bongpulses triggered by the action potentials ofa muscle. Pulses are transmit ted through conductive estuarine water by a piezoelectric ring transducer at a frequency of about 75 KHz. The preparation of a subject animal, insertion of electrodes, and attachment of the transmitter are described for the telemetry of mandibular muscle contraction in the blue crab. The transmitter provides a signal that corresponds unequivocally with feeding activity and allows enumera tion of bites required to consume a food item. Number of bites, and feeding time, are both positively correlated with the size of the prey specimen. As a test of the tech nique's feasibility, a blue crab was equipped with one of the transmitters and released in a subestuary of Chesa peake Bay. The crab was tracked continuously for 96 hours while every contraction ofthe mandibular muscle was recorded. The crab traveled 4000 m along the subes tuary at an average speed of 12 rn/h, but showed periods of rapid movement of up to 325 m/h. The crab fed 2â€"7 times per day, with a feeding bout comprising 15â€"2750 bites. The limited data did not indicate that either move ment or feeding exhibit a die! or tidal cycle.

1. This study tests the hypothesis that physical factors limit the ranges of five species of limpets (Acmaea) inhabiting the splash zone (Zone I) and upper midtidal (Zone II) of the Central California rocky shore. Two criteria are considered necessary to establish the hypothesis. First, interspecific differences in adaptation to physical factors must permit exploitation of different portions of the intertidal gradient. Secondly, physical conditions, by occasionally causing mortality, must set the limits of ranges at different levels depending upon the interspecific differences in physiological tolerances.2. Dilution by winter rainwater runoff probably presents no osmotic threat to Acmaea. No pronounced differences are evident in either resistance to or tolerance of dilution. All five species tolerate immersion in fresh water for periods in excess of the maximum exposure expected in nature. Under exceptional circumstances some Zone I limpets may experience entrapment and lethal dilution in fresh water seep...