400 DISCOVERY REPORTS 



PART III. PHYLLOSOMA 



For the purposes of this report I have examined and measured about 400 Phyllosomas 

 from the Discovery collections, but it must be confessed that the results are disappoint- 

 ing. About a dozen different forms, generic or specific, have been recognized and are 

 mentioned or described below, but it cannot be claimed that any real progress is made 

 in identifying these forms, and even the question of the recognition of generic or 

 specific characters is left uncertain. This uncertainty is mainly due to the incompleteness 

 of the series of stages available. In no case are the earliest stages present, so that it is 

 impossible to determine the number of stages passed through. This is a point of some 

 importance, since the distribution of the adult must depend largely upon the duration 

 of larval life and the direction and speed of the currents to which the larvae are exposed. 

 The absence of these early stages may in part be explained by the season at which the 

 samples were taken. According to Stephensen (1923) breeding of Scyllarus arctiis, for 

 example, is mainly confined to June and July, and this is probably true for other Loricata 

 of the Mediterranean and Atlantic, but at Plymouth the Phyllosoma of PaUmirus vulgaris 

 may be taken from February to August (Lebour). Although a number of the Discovery 

 samples in which Phyllosomas occur were taken at dates at which early stages could not 

 be expected (e.g. St. 100, October 1926) there were occasions when they might well have 

 been taken. For example, great numbers of Phyllosomas were caught near St Paul's 

 Rocks in May 1931, when breeding must have been active, but the earliest stages of 

 Paniilinis present were 7-9 mm. in length which I have supposed to be in stage V. 

 Stephensen's material of Scyllarus arctus from the Mediterranean is instructive in this 

 connection, since he also seems to have had relatively few of the earliest stages, as shown 

 in his table (p. 75) which may be summarized thus: 



Stages 12345 678 



Specimens 2 8 23 59 87 112 88 24 



On the other hand, at Plymouth, whereas stage I is quite commonly taken in the 

 Eddystone area, later stages are relatively rare. It may well be that the earliest stages 

 are passed through fairly rapidly in inshore waters, and that the ' Discovery ', and also 

 the 'Thor', were usually towing outside their range. 



While the lack of these early stages deprives one of the means for estimating the 

 duration of larval life, the absence of the last stage also in some cases makes identifica- 

 tion impossible. This is peculiarly disappointing when the Phyllosoma presents features 

 of special interest, as in the case of the form described as " Themis}'' This form, and 

 also the one here called " Parribaais} " , are here referred to the Scyllaridae for reasons 

 which are given below, but such an identification I am most reluctant to accept, for the 

 reason that both these forms seem much more closely to resemble the Palinuridae, and, 

 if they are really Scyllaridae, there are two quite distinct types of scyllarid Phyllosoma. 

 This would imply a separation of the Scyllaridae into two groups, a separation which 

 ca.nnot, so far as I know, be justified on adult structure. 



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