**FIGURE 1. **Hermaphrodite *Eulimnadia dahli.* 1) Antennae. 2) Brood chamber with egg clutch. 3) Head. 4) Phyllopod appendages. 5) Telson. 6) Trunk.

**FIGURE 2.** *Limnadia badia* female (1) and male (2). Carapace dimorphism prominent on dorsal margin associated with presence/absence of brood chamber. *Limnadopsis occidentalis* female (3) and male (4) displaying similar carapace dimorphism to that seen in *L. badia*, despite gross morphologic difference. Female (5) and male (6) *Cyzicus mexicanus*. The dimorphism in Cyzicus is more subtle than that seen within the Limnadiidae, the female (5) being slightly more elongate with a flattened postero-ventral margin. 'Female' morphotype (7) and 'male' morphotype (8) of *Carapacestheria disgragaris*. All scale bars equal 1 mm.

**FIGURE 3.** Modes of shape change represented by eigenshape (ES) axes 1-4. Eigenshapes produced via standard eigenshape analysis (*sensu* MacLeod 1999) of digitized outlines of 120 total specimens of *E. dahli, E. texana, L. badia and L. stanleyana*. Dark-light shading indicates representative shapes with low to high scores on each of the four axes.

**FIGURE 4.** A plot of 120 extant specimens (*E. dahli, E. texana, L. badia and L. stanleyana*) by sex (red = female/hermaphrodite, blue = male) on the first and second eigenshape axes. Mean shapes for males (blue) and females/hermaphrodites (red) shown both separate and overlapping to highlight dimorphism.

**FIGURE 5. **Hierachical cluster analysis (Ward's method) of* *all 120 extant specimens using eigenshape axes 1-4. Note distinct clustering of two groups with little error. Terminal nodes labeled with species/sex abbreviations.

**FIGURE 6.** Plot of *C. mexicanus* on eigenshape axes 1 and 2 with dendrogram of hierarchical cluster analysis (Ward's method) using the first four eigenshapes. Mean shapes for males (blue) and females (red) shown separate and overlapping to highlight dimorphism.

**FIGURE 7.** Plot of *L. occidentalis* on eigenshape axes 1 and 2 with dendrogram of hierarchical cluster analysis (Ward's method) using the first four eigenshapes. Mean shapes for males (blue) and females (red) shown separate and overlapping to highlight dimorphism.

**FIGURE 8. **Plot of *C. disgragaris* on eigenshape axes 1 and 2. Mean shapes for morphotype 1 'male' (blue) and morphotype 2 'female' (red) highlight possible dimorphism with associated Hierarchical cluster analysis (Ward's method) using eigenshape axes 1-4. The designation of specimens to either two morphotypes is based on the distinct two-group clustering.

**FIGURE 9. **Plot of *E. texana* males and self-fertilizing hermaphrodites on eigenshape axes 1 and 2 with dendrogram of hierarchical cluster analysis (Ward's method) using the first four eigenshapes.

**FIGURE 10.** Plot of *L. badia* males and females on eigenshape axes 1 and 2 with dendrogram of hierarchical cluster analysis (Ward's method) using the first four eigenshapes.