SYSTEMATIC 



225 



Palaemonidae 



pontoniinae 

 Periclimenes, sub-gen. Periclimenes sp. 



Occurrence. St. WS 996, 100-50 m., 1 late larval stage, Fig. 1. 



This late larval stage of a pontoniid is very interesting and apparently belongs to a species of 

 Periclimenes, sub-gen. Periclimenes. It bears a close resemblance to Gurney's ' larva of an unknown 

 genus' (Gurney & Lebour, 1941, p. 117, fig. 9m, n) from 'Discovery' Station 278 off North Africa, 

 and probably belongs to the same genus. These peculiar larvae have the very unusual feature of a long 

 antennular flagellum which surpasses the length of the body. These two specimens, belonging to 



Fig. 1. Periclimenes sp., late larval stage, c. 10 mm. long, a, showing complete antennule; b, the 

 same, enlarged, antennular flagellum cut off; r, telson. 



separate species and possibly to separate genera, are apparently the only known instance of such 

 a phenomenon. Gurney included his figure in order to compare it with Rhinchocinetes rigens, which 

 in the late larval stages possesses an extremely long antennal flagellum comparable with the present 

 antennular flagellum. In Gurney's figure the flagella are figured in each case (fig. 9//, m) as loosely 

 held at the side and behind, but in the live Rhinchocinetes larva observed by myself (Gurney & Lebour, 

 1941, p. 119) the antennal flagella, nearly four times the length of the body, were carried straight out 

 in front, the two together closely approximated, and having a ram-like appearance. In the present 

 larva here described, the antennular flagellum is carried straight in front in an exactly similar way 

 (Fig. 1 a). The purpose of these analogous organs is probably to help suspend the animal in the 

 water-layer in which it habitually swims. Gurney's figure m and the present larva agree in many 

 features besides the long antennular flagellum, and almost certainly belong to the same genus although 

 they differ enough to be placed in separate species. The present larva is bent at the third abdominal 



