26 



R. BOTTGER-SCHNACK 



distinguished only by a few characters, including microstructure of 

 the mouthparts and on the exoskeleton, which require a level of 

 detail not generally adopted in most taxonomic descriptions. Such 

 integumental microstructures have been used to differentiate bet- 

 ween closely related species of cyclopoid (Ueda etal, 1996; Rocha, 

 1998) and oncaeid (Bottger-Schnack, 1999; Bottger-Schnack & 

 Huys, in press) copepods. 



The phylogenetic relationships of the Oncaeidae are not well 

 understood. The diphyletic status of the family has recently been 

 recognized by Huys & Bottger-Schnack (1996/97), who proposed 

 the new family Lubbockiidae to accommodate Lubbockia Claus, 

 1862 and related genera, retaining only Oncaea Philippi, 1843, 

 Conaea Giesbrecht, 1891 and Epicalymma Heron, 1977 in the 

 Oncaeidae. The large type genus Oncaea sensu lato, which cur- 

 rently contains over 70 validly described species (Heron & 

 Bradford-Grieve, 1995), has been recognized as a paraphyletic 

 assemblage (Huys & Bottger-Schnack, 1 996/97). A detailed phyloge- 

 netic analysis of the three oncaeid genera at the species level is 

 currently in progress and will result in the recognition of numerous 

 new genera. Some preliminary results of the phylogenetic study 

 were briefly presented by Bottger-Schnack & Huys (1998). 



The Red Sea is an extreme environment, with constant and 

 unusually high deep-sea temperatures (21.7°C) and salinities (40.5 

 PSU) (Edwards, 1987). Due to these unique environmental conditi- 

 ons an impoverished zooplankton fauna is found in the Red Sea, 

 which is characterized by the absence of true deep sea species 

 (Weikert, 1982, 1987). This phenomenon was also reported for 

 oncaeid copepods (Bottger-Schnack, 1994, 1999) and their esti- 

 mated species number in the Red Sea (about 26) appears to be low in 

 comparison to the adjacent Arabian Sea, where the vast majority of 

 the about 70 recorded oncaeid species and forms is made up by deep- 

 living representatives (Bottger-Schnack, 1994). The surface waters 

 in the Red Sea show a considerable increase in salinity from the 

 southern entrance to the central-northern areas (Morcos, 1970). Due 

 to the less favourable environmental conditions in the north, species 

 numbers of planktonic taxa generally decrease from south to north 

 (e.g.Halim, 1969;Kimor, 1973; Almeida Prado-Por, 1983; Bottger- 

 Schnack, 1995). For oncaeid copepods, however, a corresponding 

 regional decrease in species number from south to north is less 

 pronounced (Bottger-Schnack, 1995). This unexpected result was 

 assumed to be at least partly attributable to the taxonomic difficul- 

 ties encountered in the identification of oncaeids, since the proportion 

 of unidentified form variants recorded in the south was much higher 

 than in the north. In a subsequent taxonomic study five new species 

 of oncaeids were described, four of which occurred mainly or 

 exclusively in the southern area (Bottger-Schnack, 1999), thereby 

 indicating some latitudinal difference in species numbers for this 

 copepod group. 



The ecology of oncaeid copepods in the Red Sea has been 

 investigated intensively during the past years within the framework 

 of multidisciplinary environmental research programmes (Thiel et 

 ah, 1986; Weikert, 1988). The species diversity, vertical distribution 

 and diurnal vertical migration, as well as some biological parame- 

 ters, such as variation in body length and breeding activity or 

 feeding of oncaeid copepods were studied on the basis of routine 

 sampling with fine nets of 0. 1 mm or 0.05 mm mesh size in the upper 

 500 m or 1000 m of the water column during different seasons and 

 in various regions [see Bottger-Schnack (1999) for a review of the 

 literature]. The taxonomy of Red Sea Oncaeidae is less well known, 

 however. Boxshall & Bottger (1987) and Bottger-Schnack & 

 Boxshall (1990) described four new oncaeid species from the central 

 Red Sea, and provided a redescription of Oncaea atlantica Shmeleva. 

 More recently, O. mediterranea (Claus) was redescribed from this 



area, including a thorough review of the taxonomic history of this 

 allegedly cosmopolitan species (Bottger-Schnack & Huys. 1 997). In 

 a recent taxonomic study, 11 species of Oncaeidae were described or 

 redescribed from the Red Sea, which belong to the conifera/similis- 

 group as defined in the phylogenetic study of Bottger-Schnack & 

 Huys (1998). A new genus, Triconia, was proposed to accommodate 

 all oncaeid species belonging to this group (Bottger-Schnack, 1 999). 



As part of an ongoing taxonomic study of Red Sea Oncaeidae, the 

 present paper describes seven species, which belong to the venusta- 

 group as defined by Bottger-Schnack & Huys (1998). In their 

 cladogram of oncaeid species it is equivalent to species group 2. 

 This core-group includes Oncaea venusta Philippi, the type species 

 of the genus, and is considered here as Oncaea sensu stricto. Oncaea 

 s.str. is defined by a combination of characters including the absence 

 of a conical projection on the distal margin of P4 endopod, ornamen- 

 tation of the labrum and of the dorsal blade of the mandible, sexual 

 dimorphism in the antenna and in the endopods of the swimming 

 legs. Oncaea s. str. is considered as the sister-group of Triconia 

 Bottger-Schnack, 1999, and the establishment of the revised genus 

 is briefly substantiated in the present paper. A detailed discussion of 

 phylogenetic relationships of Oncaea s.str. within the Oncaeidae 

 will be published separately (Huys & Bottger-Schnack, in prep.). 



Oncaea s.str. currently includes 8 species, 6 of which had previ- 

 ously been reported from the Red Sea (Bottger-Schnack, 1994) and 

 are redescribed in the present account. For O. mediterranea, 

 redescribed recently by Bottger-Schnack & Huys (1997b), some 

 short corrective notes will be given. A new species similar to O. 

 clevei Friichtl will be described. The taxonomic status of O. curta 

 Sars, for which no material was available, will be discussed on the 

 basis of literature data. 



The type species of Oncaea s.str.. O. venusta, was recently 

 redescribed in detail by Heron & Bradford-Grieve (1995), based on 

 specimens collected in the Gulf of Naples, near the type locality in 

 the Mediterranean Sea. Their account does not contain information 

 about the two size variants of the species, forma typica and forma 

 venella (Farran, 1929), which are generally known to occur in 

 tropical and temperate areas (Malt, 1983b), but are poorly docu- 

 mented morphologically. Apart from a distinct size difference, only 

 few minor differences in body morphology have been reported for 

 the two forms so far (Farran, 1929; Sewell, 1947; Ferrari, 1975; 

 Boxshall, 1977a). In the Red Sea, both size variants of O. venusta 

 occur. They differ considerably in spatio-temporal distribution 

 (Bottger-Schnack, 1990b, 1995), which may indicate reproductive 

 isolation. Both forms of O. venusta will be redescribed in detail in 

 the present account, including observations with scanning electron 

 microscope (SEM). Particular attention is paid to microstructures in 

 the mouthparts and on the exoskeleton. which might provide new 

 and helpful information for the separation of the two forms. The 

 relationship of the two Red Sea forms with the species occurring in 

 the Mediterranean Sea is defined upon re-examination of specimens 

 from Heron & Bradford-Grieve's material. The present knowledge 

 on the world-wide distribution of the two venusta forms is reviewed. 



The two size variants of O. media as defined by Sewell (1947) 

 have recently been recognized as distinct species by Heron & 

 Bradford-Grieve (1995). They assigned forma major to O. media 

 Giesbrecht (except for his Plate 47, Fig. 11), and described forma 

 minor as a new species, O. scottodicarloi. Both species occur in the 

 Red Sea and are briefly redescribed in the present paper, including 

 some important morphological details not noted by these authors. O. 

 waldemari, which is very similar to O. media and O. scottodicarloi, 

 had recently been described from Brazilian waters by Bersano & 

 Boxshall (1994). Due to some descriptive errors, however, the 

 authors did not notice the close relationship of O. waldemari with 



