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Studies of the osmotic and ionic responses of the supralittoral rock pool inhabitant Tigriopus brevicornis (Crustacea: Copepoda) showed that this species of orange harpacticoid copepod is an unusually euryhaline osmoconformer. Body fluid osmolalities were 297–3691 mOsm kg−1 over a medium range of 151–3440 mOsm kg−1. Whole body sodium increased from 3·65 to 15·0 μmol Na+ mg DW−1 (dry weight) over the medium range 80–1900 mM Na+. Comparative studies on Artemia nauplii and the prawn Palaemon elegans revealed the characteristic hyper-hyporegulation of both organisms. Body density of T. brevicornis remains greater than that of the external medium over the salinity range 5–100 psu because of changes in body fluid osmolality and body volume. Median body density values for T. brevicornis ranged from 1·0359 g ml−1 in 5 psu (median density of 5psu seawater–1·0017 g ml−1) to 1·0848 g ml−1 in 100 psu (median density of 100 psu seawater=1·0751 g ml−1). Tigriopus brevicornis is principally a benthic forager and needs to remain negatively buoyant over a wide salinity range. Environmental monitoring of five supralittoral rockpools was conducted over a year. Live or dormant T. brevicornis were found in salinities of 4–150 psu; temperatures of −1 to +32°C and oxygen concentrations of 0 to >20 mg l−1. It is probably of advantage to T. brevicornis to be an osmoconformer; it is perhaps energetically efficient for such a small organism (~1 mm) and avoids buoyancy problems at high salinity. [ABSTRACT FROM PUBLISHER]

This study sheds light on the evolution of aquatic and terrestrial feeding modes in vertebrates, using two aquatic turtles as models. The estuarine aquatic diamondback turtle Malademys terrapin has a feeding mechanism that is similar to the basic feeding mechanism of terrestrial tetrapods (jaw gape cycles incorporate slow opening, fast opening, fast closing and slow closing phases). Strikes upon prey also involve neck extension and cycles of the forelimbs. Malademys terrapin modulate their feeding behaviour and jaw action in relation to the nature of the prey item. Mussels are approached by walking on the substratum, and limb cycles are of small amplitude during the strike. Crabs, whether encountered in mid-water or on the substratum, are approached by swimming, and the strikes partly produced by vigorous upstrokes of the forelimbs, that occur simultaneously with neck extension. Crabs are dangerous prey, and the turtles often strike with the gape already at maximum, minimizing the time needed to bite a limb or other part of the crab. The tongue is not involved in food capture, but has a major role in food manipulation and transport prior to swallowing. Although transport cycles are similar to ingestion cycles, ingestion and transport are easily separable in the species. Malademys terrapin exhibit great distension of the throat during the strike, but this does not appear to generate adequate suction to aid capture of hard-shelled prey; it is suggested that throat distension reduces pressures in front of the advancing snout, thus preventing pressure waves displacing or alerting prey. The pelagic marine turtle Dermodielys coriacea, which specializes in gelatinous prey, relies heavily on suction for ingestion, which overlaps considerably with transport. [ABSTRACT FROM PUBLISHER]