Contributions to Zoology, 85 (4) – 2016Jonas Keiler; Stefan Richter; Christian S Wirkner: Revealing their innermost secrets: an evolutionary perspective on the disparity of the organ systems in anomuran crabs (Crustacea: Decapoda: Anomura)

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External morphology

Kiwa puravida (Fig. 2H I) and Aegla cholchol (Fig. 2H II) possess a carapace slightly longer than it is broad, while Lomis hirta (Fig. 2H III) possesses a more rounded carapace which is slightly broader than it is long (proportions illustrated in Fig. 2H). Overall, the dorsal aspect of the body in all three taxa is fairly oval since the pleon is bent under the cephalothorax (Fig. 2D-F), though not to the same degree: in A. cholchol (Fig. 2H II), the first to fourth pleonal segments are visible, while in K. puravida (Fig. 2H I) and L. hirta (Fig. 2H III), only the first and second pleonal segments are visible. The pleurotergites in L. hirta (Fig. 3F) are less convexly bent than in K. puravida (Fig. 3E) and A. cholchol (Fig. 3D) and the second pleonal segment in L. hirta is markedly longer than the subsequent ones (Fig. 4G). In K. puravida and A. cholchol, the third to seventh thoracic sternites are confluent to form a sternal plate, or plastron (Fig. 2D-G). In L. hirta, the plastron is formed by the fourth to seventh thoracic sternites, while the third thoracic sternites (arrow, Fig. 2G) are set off from the plastron and dorsally bent. The eighth thoracic sternites in all three species are distinctly separate from the plastron (Fig. 5E). In A. cholchol (Fig. 2D), the plastron has an almost straight posterior margin, while that in K. puravida (Fig. 2E) and L. hirta (Fig. 2G) displays a markedly triangular emargination. In L. hirta, the plastron is partly (male; Fig. 2F) or completely (female; Suppl.-Fig. S2) covered by the bent pleon, while it remains uncovered in K. puravida (Fig. 2E) and A. cholchol (Fig. 2D).


Fig. 2. External integumental structures (volume renderings). A-C. Lateral view of Kiwa puravida (A), Aegla cholchol (B) and Lomis hirta (C). Dashed and dotted lines indicate the different height ratios of the branchiostegites present in K. puravida (A) and L. hirta (B). Arrow indicates linea anomurica; arrowhead indicates posterior extension of the lower branchiostegite (lbs). D-G. Ventral view of A. cholchol (D), K. puravida (D), L. hirta (F-G; males); pleon virtually cut in G to show plastron (plas). Arrow in G points at the vertically oriented 3rd thoracic sternites. Asterisk indicates 6th pleonal segment. H. Schematic drawings of the various different shaped integumental structures in the studied species: I. K. puravida, II. A. cholchol. III. L. hirta. Pleon in in vivo condition. Red values show the relative ratios of carapace length to width without rostrum (width set to 1.0). Blue values show the relative length of the body (with pleon bent in vivo). Scale varies between drawings. I-K. Posterior view of bent pleon in K. puravida (I), A. cholchol (J), and L. hirta (K). Dotted yellow lines indicate divide between tergites and pleurites. Abbreviations: bst, branchiostegite; p1-p5, pereiopods; pl, pleon; pl1-6, pleonal segments; plas, plastron; st3, 3rd thoracic sternite; st8, 8th thoracic sternite.