NEW SPECIES OF SYRTICOLA FROM JAPAN 



93 



DISCUSSION 



Syrticola intermedius is the second species to be reported 

 from the Indo-Pacific, the other species (under the name (?) 

 Notopontia galapagoensis) being originally described from a 

 sandy beach in the Galapagos (Mielke, 1982). Both species 

 resemble each other morphologically. A comparison of the 

 major diagnostic characters (Table 2) reveals two species 

 groups in the genus Syrticola. The European group includes 

 S. trispinosus, S. flandricus and S. mediterraneus and is 

 characterized by a 6-segmented antennule (segments 6 and 7 

 fused) and the anal operculum possessing small spinous 

 processes (Fig. 5H). The number of these projections ranges 

 from (rarely) to 5, though specimens with a single small 

 process have not been recorded yet (Willems et al., 1987). 

 The second species group encompasses the two Indo-Pacific 

 species which share a 7-segmented antennule and an opercu- 

 lum drawn out into a single median strong spike. Both species 

 also share the plesiomorphic 2-segmented condition of the 

 male P3 endopod, but the significance of this character is 

 limited since not all the males are known in the European 

 species group. The zoogeographical and morphological sepa- 

 ration does not warrant the upgrading of these groupings to 

 generic rank, however, since S. intermedius exhibits certain 

 characters found in the European species. Outgroup compar- 

 ison with Notopontia and Leptopontia suggests that the 

 spiniform nature of the outer exopodal spine and the loss of 

 the inner baseoendopodal seta are apomorphic character 

 states for the fifth legs, linking the Japanese species with its 

 European congeners. The outline of the anal operculum links 

 S. intermedius to (?) N. galapagoensis, justifying the latter's 

 re-allocation to Syrticola by Willems et al. (1987). 



The possession of an aesthetasc-like structure on the syn- 

 coxa of the maxilla in 5. intermedius is unusual. 

 Re-examination of S. flandricus showed an unmodified seta 

 in this position, in addition to the pinnate one also present in 

 5. intermedius. Two setae are also reported on the syncoxal 

 endite of 5. mediterraneus and in the outgroup taxa Notopon- 

 tia and Leptopontia. The report of 3 setae on this endite in 5. 

 galapagoensis (Mielke, 1982) therefore probably results from 

 an misinterpretation of an aesthetasc-like structure. Without 

 differential interference contrast microscopy the flaccid distal 

 part is easily overlooked, thereby accentuating the lateral 

 ichitinized margins as setoid structures. The relative lengths of 

 the enditic 'setae' in Mielke's (1982: Abb. 18E) illustration 

 are suggestive of this interpretation. 



The status of 5. trispinosus remains enigmatic as ever. A. 



Table 2 Comparison of Syrticola species. 



Scott's species is clearly closely related to 5. flandricus. 

 Willems & Claeys (1982) list a number of differences but 

 except for the structure of the fifth leg, all of these can be 

 attributed to deficiencies in the original decription. This, 

 however, does not rule out S. trispinosus as a distinct species 

 since the discovery of an as yet undescribed species of 

 Syrticola in the North Sea has proven species discrimination 

 in this genus to be rather unreliable. Pending re-examination 

 of topotypes from the Isle of Man, S. trispinosus is relegated 

 to species inquirenda. 



KEY TO SPECIES 



1. Antennule 9 7-segmented, anal operculum with one large, 



median spike 2. 



Antennule 9 6-segmented, anal operculum with several small, 

 spinous processes 3 . 



2. P3 endopod without inner seta; outer exopodal element P5 



setiform galapagoensis (Mielke. 1982). 



P3 endopod with inner seta; outer exopodal element P5 spini- 

 form intermedius sp. nov. 



3. P5 exopodal lobe with 2 spiniform elements 



trispinosus (A. Scott, 1896). 



Only one element of P5 exopodal lobe spiniform 4. 



4. P3 endopod without inner seta 



mediterraneus Willems et al. , 1987. 



P3 endopod with inner seta 



flandricus Willems & Claeys, 1982. 



Acknowledgements. Drs Geoffrey Boxshall (The Natural History 

 Museum) and Philippe Bodin (Universite de Bretagne Occidentale) 

 are gratefully acknowledged for commenting on earlier drafts of the 

 manuscript. We also would like to acknowledge the captain and the 

 crew of the TR/V Toyoshio-maru of the Hiroshima University and 

 Mr. M. Okada and Mr. Y. Endo for assistance at sea. Part of this 

 study was supported by research grants of the Research Institute of 

 Marine Invertebrates (1989) and the Narishige Zoological Science 

 Award (1992) awarded to one of us (S.O.). R.H. is a visiting research 

 fellow of the Institute of Zoology, University of Gent, Belgium. This 

 is communication no. 623 of the Centre for Estuarine and Coastal 

 Ecology, Yerseke, The Netherlands. 



trispinosus 



flandricus 



mediterraneus 



galapagoensis 



intermedius 



Antennule 9 



Inner seta P3 endopod 9 



Endopod P3 cf 



Duter element exopodal lobe P59o" 



Inner seta endopodal lobe P5 9 



Anal operculum processes 



;3ody length 9 (um) 

 Body length cf (um) 

 Distribution 



6-segmented 



? 



? 



spiniform 



absent 



6-segmented 



present 



? 



spiniform 

 absent 



6-segmented 

 absent 



1-segmented 



spiniform 



absent 



7-segmented 

 absent 



2-segmented 

 setiform 

 present 



7-segmented 



present 



2-segmented 



spiniform 



absent 



several, 



several, 



several, 



one, 



one, 



small 

 500 



small 

 460-530 



small 

 540-660 



large 

 280-340 



large 

 485 



? 



? 



460-500 



310-350 



460 



Irish Sea 



North Sea 



Mediterranean 



Galapagos 



Japan 



