Figs. 5a-b

Homology of the bursal rays of the Rhabditida and the Strongylida. Scale-bars: 50 μm.

a. Bursal rays of the Rhabditida sensu Osche (1958). Papillae 7 are fused with papillae 8. After Osche (1958), modified.

b. Bursal rays of the Strongylida sensu Chabaud et al. (1970). Papillae 7 are situated on the genital cone. After Chabaud et al. (1970), modified.

Fig. 5c

Schematic representation of the bursal patterns of rays 2 to 6 showing the hypothetical evolutionary steps.

From the basal pattern of type 2-3, the evolutionary steps follow the direction: 2-3 tending to 2-2-1 to 1-3-1 to 1-4 with the intermediary patterns: 2-3 tending to 2-2-1, 2-2-1 tending to 1-3-1, 1-3-1 tending to 1-4. Some lobes have a pattern of type 2-2-1 t 1-4. A. Type 2-3. B. Type 2-3 t 2-2-1. C. Type 2-2-1. D. Type 2-2-1 t 1-3-1. E. Type 1-3-1. F. Type 1-3-1 t 1-4. G. Type 1-4. The small arrows indicate the transition from a type to another. The dotted arrow indicates the hypothetic evolutionary progress of the pattern of the caudal bursae.