Fig. 2: Gas exchange in whole and halved acorn worms (S. kowalevskii).
From: Ion regulation at gills precedes gas exchange and the origin of vertebrates
a,b, Oxygen uptake (a) and ammonia excretion (b) in whole worms (black), posterior halves (white) and anterior halves (grey) in normoxia at 10 °C and 20 °C and in hypoxia at 20 °C. Posterior halves lack the pharynx and gills. Data are presented as mean ± s.d. with individuals superimposed (n = 8 for all groups, except n = 6 for ammonia excretion at 10 °C). Letters indicate significant differences within treatments (one-way ANOVA with Tukey’s post-hoc test; P < 0.05). Ammonia excretion not measured in hypoxia (see Methods). Exact P-values: P = 0.8256 (a, 10 °C), P = 0.8732 (a, 20 °C), P = 0.0253 (a, hypoxia), P = 0.6115 (b, 10 °C) and P = 0.0826 (b, 20 °C).
