Studies of sea turtle epibiosis have focused on the diversity and ecology of facultative commensalisms and less attention has been given to parasitic associations, in which the epibiont species derives nutrients from the tissue of the host turtle. We present the first description and quantitative survey of the parasitic isopods Excorallana costata, Excorallana bicornis and Excorallana oculata on loggerhead (N = 79) and hawksbill turtles (N = 23), and E. costata on olive ridley turtles (N = 9), nesting on Praia do Forte, Bahia, Brazil during the 2009–2010 season. Excorallana costata was the most common isopod species (N = 651), followed by E. bicornis (N = 77) and E. oculata (N = 20). Patterns include: (1) E. costata exhibited a higher frequency and intensity of parasitism than E. bicornis and E. oculata and (2) loggerheads hosted parasitic isopods at a higher frequency and intensity than hawksbills and olive ridleys. We also detected temporal shifts in the occurrence and intensity of parasitism across the nesting season, which strongly suggests that turtles were parasitized by all three isopod species during their internesting periods. Because parasitic isopods were observed only rarely prior to the 2009–2010 turtle-nesting season and have continued to be common in subsequent seasons, it is important to gain a better understanding of the basic biology of these interactions, the reasons for their recent emergence, and the potential biological impacts on turtle, as well as isopod, populations.

Population energy budgets of four sympatric isopods, Burmoniscus ocellatus, Burmoniscus sp. (Philosciidae), Formosillo raffaelei and Orodillo maculatus (Armadillidac), were calculated at two sites in a Hong Kong mixed forest. Mean population standing stock of the four species ranged from 1.25 to 13.61 kj m-2. Mean total isopod biomass at the two sites was 0.85 and 1.85g m-2. Annual production of the four species varied from 4.24 to 30.43 kj m-2 with 5.2–26.4% (energy content) allocated to reproduction. Annual production of the four species combined at the two sites was 23.22 and 50.15kJ m-2. ratios varied from 2.24 to 4.27. Annual population consumption on mixed litter by the four isopod species ranged from 28.4 to 183.0 kj m-2. Total annual consumption by all species at the two sites was 233.7 and 360.2 kj m-2 (1.96 and 2.53% of annual litter fall). Isopod respiratory rales were proportional to body weight, with an exponent ranging from 0.68–0.78 at 23°C. The annual population metabolism of the four species varied from 14.62 to 86.11 kj m-2. Total annual isopod metabolism at the two sites was 116.33 and 185.95 kj m-2. These results are discussed with reference to the role of isopods in litter breakdown and energy flow in the Hong Kong forest.

Although many physiological characteristics are very labile, it is proposed that some are stable enough to provide evidence concerning the routes by which terrestrial animals moved on to land. Osmotic tolerance and osmoregulatory ability are investigated first. Marine littoral invertebrates tolerate wide osmotic changes but osmoregulate little. Freshwater invertebrates osmoregulate well, but over a narrow range. Terrestrial prosobranchs of the family Pomatiasidae, which have wide tolerance, may have originated directly from the sea. The Cyclophoridae, which are intolerant, may have moved to land from fresh water. Isopods and talitrid amphipods may all have had direct marine origins with no freshwater phase. Secondly, terrestrial animals of marine origin may have blood with higher osmotic pressures than those passing through fresh water. In prosobranchs, isopods and amphipods, the evidence agrees with the conclusions suggested from character one. Thirdly, the production of hypo-osmotic urine in terrestrial animals may be evidence of freshwater origin. The evidence again supports the initial suggestions about prosobranchs and amphipods. It is concluded that because there is little selection pressure acting on these characters on land, they can be used as evidence of ancestry. Possible use of further characters is discussed.