SEXUAL DIMORPHISM IN MARMORATUS (OLIVIER) (, HIPPOLYTIDAE)

BY

NASIMA M. TIRMIZI and M. AFZAL KAZMI Invertebrate Reference Museum, Department of Zoology, University of Karachi, Karachi, Pakistan

The Saron contains two closely allied species, S. marmoratu.r (Olivier, 1811) and S. neglectus De Man, 1881. S. marmoratus "is known from the entire indowestpacific region" (Holthuis, 1947: 29), S. neglecttls is believed to be having "the same range of distribution" (: 31). Miyake & Hayashi (1966) while working on the Hippolytid shrimps also state that the two species have the same range of distribution. During the last two years regular collection trips were made to various localities along the West Pakistan coast of the northern Arabian Sea, material was also obtained from the fish market in Karachi. All Saron specimens obtained, 10 a d and 6 YY (all ovigerous) belong to S. marmorattls. It may be pointed out here that Barnard (1950: 688) has recorded S. marmorattls only from South and South East Africa. A close examination of the available material shows that the specimens exhibit a considerable degree of individual variation as well as marked sexual dimorphism. The present paper gives the result of the study of sexual dimorphism. Most of the earlier work on dimorphism is confined to the size of the third maxilliped and the first pair of peraeopods in males, which in some specimens attain a monstrous size. This has been fully dealt with by Kemp (1914). In our collection out of the ten males three have their third maxilliped and first peraeopod enormously developed. In one a the first pair of peraeopods is exceedingly long, attaining approximately the same length as the total length of the body (from the tip of the rostrum to the tip of the telson). This incidentally is the largest male measuring 83 mm, in two others the ratio of the body length to that of the first peraeopod is 81 : 75, 79 : 70 (i.e. 92.6 and 88.6%) respectively. The third maxilliped is complete only in one of these males (c.l. 15.5 mm), where it is 74glo of the total body length, in the other two it is incomplete. Features exhibiting sexual differences are given in the following table which also gives an idea of the extent of individual variation. 284

TABLE I Rostral formula, measurements of body and appendages in mm. Carapace length is taken from the orbital angles to the posterior margin of the carapace. The total body length is from the tip of the rostrum to the tip of the telson; maxilliped and peraeopod are measured from the proximal margin of the coxa to the distal end of = = the dactylus. In the rostral formula ep epigastric tooth, uc upper rostral teeth = on the carapace, ur = upper rostral teeth, lr lower rostral teeth

From table I it can be concluded that in the smaller males (t.l. 38-74 mm) the third maxilliped is either more or just a little less than one third of the total body length, whereas in the only complete large male (79 mm) it measures 74% of the total length. In the females it is a trifle longer than one third of the total body length. The first pair of peraeopods shows also a great sexual difference: in males its length varies from less than a fourth of the body (one male) to about 98% of the body length. In females, it is generally a little more than one third of the body length; there are, however, two exceptions: in one