46 



R. HUYS AND S. CONROY-DALTON 



have been significantly higher had the geographic coverage been 

 wider. Indicative of this is the discovery of three species of 

 Clytemnestra in a small sample from the Great Barrier Reef. Pre- 

 liminary examination of material from Brazilian waters (Rio Grande 

 do Sul) revealed a similar sympatry for both Clytemnestra and 

 Goniopsyllus. Although the discovery of several closely related 

 species in both genera is noteworthy, it is not unexpected nor 

 exceptional for a marine planktonic taxon. For example, recent 

 taxonomic studies have uncovered several important species com- 

 plexes in the Oncaeidae (Heron, 1977; Heron & Bradford-Grieve, 

 1995; Bottger-Schnack, 1999). Although this family is morphologi- 

 cally distinctive and arguably the most speciose in the marine 

 plankton, the continuing discovery of pseudo-sibling species and 

 frequent confusion about the validity of rank of its species and 

 morphs tarnish its literature, both taxonomic and ecological. Current 

 research on another planktonic poecilostomatoid genus, Pachos 

 Stebbing, resulted in the recognition of several new but previously 

 misidentified species (Huys & Krsinic, in prep.). 



The taxonomy of pelagic harpacticoids is plagued by consider- 

 able conservatism and inadequate study of morphological features. 

 With the exception of the mesopelagic tisbid genera (Boxshall, 

 1979) all planktonic harpacticoids were known well before the turn 

 of the century (Kr0yer, 1846; Dana, 1847, 1849; Boeck, 1865; 

 Brady, 1883; Giesbrecht, 1891; T. Scott, 1894), yet, their morpho- 

 logical definition and supposedly cosmopolitan breadth of their 

 distribution have hitherto remained unchallenged. The genus 

 Microsetella Brady & Robertson currently encompasses only two 

 species, however, one can expect its number of species to increase 

 by an order of magnitude if the many undescribed sibling species are 

 considered (unpubl. data). Similarly, Euterpina acutifrons (Dana, 

 1 847) is commonly regarded as a cosmopolitan species but compari- 

 son of distant 'populations' suggests that there is no factual 

 justification for this universally accepted view. 



In Fleminger & Hulsemann's (1977) scholarly study demonstrat- 

 ing the taxonomic divergence in three sympatrically occurring 

 sibling species of Calanus in the North Atlantic, one sentence 

 deserves wide currency: '. . ., the quality of knowledge about 

 circulating oceanic habitats and their entrained ecosystems rests 

 upon the reliability of three interrelated sets of information: system- 

 atics of the biota, routine identifications of species, and assessments 

 of their ranges, horizontally and vertically'. Unfortunately, routine 

 identifications in ecological investigations are generally not condu- 

 cive to the recognition of sibling species and all too often wide 

 geographical distributions have been uncritically accepted as the 

 natural consequence of potentially broad oceanic dispersal. The 

 latter perception is often coloured by underlying assumptions of the 

 lack of isolating physical barriers and global uniformity in the open 

 pelagic environment. Pseudo-sibling species can only be readily 

 distinguished once the appropriate characters are considered. Our 

 study demonstrated that for the last 1 10 years species discrimination 

 in the Clytemnestridae was based exclusively on generic characters, 

 the current recognition of cryptic species being only an artifact of 

 previous ignorance. Hence, there is considerable doubt involved in 

 collating records of the occurrence of these species from the litera- 

 ture to produce distribution maps. Though C. scutellata and G. 

 rostratus have universally been regarded as cosmopolitan, this 

 distributional concept is now no longer tenable and the compilation 

 of distribution records must start from scratch. It would be best to 

 consider earlier records primarily as evidence of the occurrence of 

 the respective genera, a useful attribute considering their virtual 

 absence at latitudes above 60° N and 45° S. 



Although the geographic location of the collection and/or body 

 size can occasionally be used as indicators of species identity, these 



approaches are limited in areas of sympatry where often more 

 sophisticated techniques are required. Like Clytemnestra in the 

 harpacticoids, Calanus is an unusual calanoid genus in that the 

 morphology of the female P5 does not discriminate all of the species 

 (Frost, 1971, 1974). Bucklin et al. (1995) showed however, that 

 despite their exceptional morphological similarity, species of Calanus 

 are quite distinct genetically. They obtained similar results for the 

 genus Metridia, confirming the distinctiveness of M. lucens (Boeck, 

 1865) and M. pacifica (Brodsky, 1948). Frost (1989) concluded, 

 based on morphological characters other than size, that there are 

 seven species within Pseudocalanus. For some, no absolute mor- 

 phological criterion could be found to distinguish females, however, 

 their validity was inferred from trends in several morphological 

 characters. Sevigny etal. (1989) used patterns of allozyme variation 

 at the GPI (glucose phosphate isomerase) locus to show that Frost's 

 (1989) sibling species were genetically isolated from each other. 

 Their results agreed with McLaren et al. 's ( 1989a-c) studies demon- 

 strating differences in genome size and life cycle characteristics 

 among Pseudocalanus species. Bucklin et al. (1998) showed by 

 DNA sequencing of two mitochondrial genes that the sibling species 

 P. moultoni and P. newmani can be reliably discriminated. Bucklin et 

 a/.'s (1996) genetic analysis of DNA sequence variation separated 

 the widespread Nannocalanus minor into two genetically distinct 

 types that may represent the previously described N. m. forma major 

 and N. m. forma minor which differ primarily in size range and 

 geographic distribution. Finally, McKinnon et al. (1992) demon- 

 strated the presence of three sympatric sibling species of Acartia 

 using allozyme electrophoresis. 



Molecular analysis of marine planktonic copepods is likely to 

 continue to reveal taxonomically-significant genetic partitioning of 

 species populations, including cryptic species. The application of 

 molecular techniques should not however, be an end in itself. 

 Methods used to discriminate sibling species such as protein electro- 

 phoresis or discriminant function analysis profit significantly from 

 or even require a priori morphological recognition of groups or 

 morphotypes whose distinctiveness can be subsequently tested. In 

 fact, how can one demonstrate the accuracy and resolving power of 

 morphological analysis better than to refer to the thorough revisions 

 by Fleminger (1973) and Fleminger & Hulsemann (1974) who 

 presented most compelling evidence for sibling speciation in marine 

 calanoid copepods long before the deluge of molecular data. Failure 

 to recognize the numerous sibling species inevitably results in bad 

 science and has obvious implications for a large field like marine 

 plankton ecology, crippling our understanding of speciation and 

 resource partitioning in the ocean. 



Acknowledgements. We thank A. Lindley and J.M. Gee (Plymouth 

 Marine Laboratory) for providing us with Goniopsyllus material from the 

 Gulf of Cadiz, and, M. Montii and W.J. A. Amaral (Fundacao Universidade 

 do Rio Grande) and Geoff Boxshall for putting Brazilian clytemnestrid 

 collections at our disposal . Prof. F. Krsinic is gratefully acknowledged for his 

 help in collecting material in the Adriatic. This research was partly supported 

 by the ALIS Programme (Project 041 ) which is jointly funded by the Croatian 

 Ministry of Science and Technology (MOST) and the British Council Croatia. 



REFERENCES 



Bjornberg, T.K.S. 1963. On the marine free-living copepods off Brazil. Boletim do 

 Instituto Oceanogrdfico, Sao Paulo 13(1): 3-142. 



, Campaner, F. & Jankilevich, S.S. 1981. Clasificacion de las especies presentes 



en el Atlantico Sudoccidental. pp. 603-679. In: Boltovskoy, D. (ed.), Atlas del 

 zooplankton del Atlantico Sudoccidental y Metodos de Trabajo con el Zooplancton 



