SEVEN SPECIES OF RED SEA ONCAEA 



65 



recorded under the name O. clevei in previous records. 



Sewell (1947, p. 258) recorded the species from the northern 

 Arabian Sea, but it is not clear whether his material included O. 

 paraclevei as well, because he stated that 'the dorsal projection on 

 the 2nd thoracic segment varies considerably in its development', 

 which is typical for the latter species. 



Tanaka (1960) recorded both sexes of O. clevei from the South 

 China Sea and off Cape Good Hope. His drawing of the female 

 urosome (Plate XXVIII, Fig. 7) resembles that of O. clevei rather 

 than O. paraclevei, but his description of the male is meagre and 

 could also be assigned to any other oncaeid. 



Chen et al. (1974) described the species from the Yellow Sea and 

 the East China Sea. Their figure of female urosome lacks genital 

 apertures and/or the sclerotization between them, which is necessary 

 to separate O. clevei from the closely related O. paraclevei. Thus, a 

 positive identification cannot be given without examination of their 

 specimens. 



More recently, Itoh [in: Chihara & Murano (1997)] recorded the 

 species from Japanese waters; his dorsal view of the female shows 

 the two characters typical for O. clevei. 



Several other records of O. clevei from different localities in the 

 Indo-Pacific are known [see Malt ( 1983a) for a review], but are not 

 considered here because they did not include figures or a description 

 that positively identified the species. In the Eastern Mediterranean 

 Sea, neither O. clevei nor related species were found (Bottger- 

 Schnack, 1 997 ), thus corroborating the limitation of this subgroup to 

 the Indo-Pacific area. The fact that O. clevei was not recorded in the 

 detailed account of the oncaeid fauna from the New Zealand area by 

 Heron & Bradford-Grieve (1995), confirms its restriction to low 

 latitudes (Malt, 1983a). 



Geographical distribution 



Oncaea clevei is distributed throughout the Red Sea, with lowest 

 abundances in the northern area (Bottger-Schnack. 1990a, b, 

 1995). It was not found in small mesh net samples from the 

 northernmost part of the Red Sea, in the Gulf of Aqaba (unpubl. 

 data). In the southernmost Red Sea and at Bab al Mandab. abun- 

 dances of the species were up to two orders of magnitude higher 

 than in the central part (Bottger-Schnack, 1995). The data from 

 both areas include an unknown number of O. paraclevei sp.nov., 

 however, which was not separated from O. clevei during the quan- 

 titative counts. Thus, the actual regional difference in abundance 

 remains uncertain. 



In the northern Arabian Sea. O. clevei was recorded from the 

 epipelagic zone by Bottger-Schnack (1996), however, the potential 

 co-occurrence of O. paraclevei was not investigated. 



Vertical distribution and vertical migration 

 The depth distribution of O. clevei remains uncertain, as the species 

 was counted together with O. paraclevei during the earlier quantita- 

 tive investigations in the Red Sea (Bottger-Schnack, 1988, 1990a. b, 

 1995). Generally, the two species were confined to the epipelagic 

 zone (0-100 m) with occasional occurrences below that depth. 

 Individual specimens found down to 950 m depth during summer 

 (unpubl. data) might be regarded as contaminants from shallower 

 depths or as moribund specimens. Within the epipelagic zone, O. 

 clevei and O. paraclevei exhibited a unimodal distribution in the 

 upper epipelagic zone (0-20 or 0-40 m), staying above the strong 

 seasonal thermocline, which usually develops during autumn 

 (Bottger-Schnack, 1990a). No indication of a significant diurnal 

 vertical movement became apparent and also no seasonal variation 

 in the depth distribution of the two species was noted in the central 

 Red Sea (Bottger-Schnack, 1990b). 



In the deep southern Red Sea and in the Strait of Bab al 



Mandab/Gulf of Aden area, the depth distribution of the two 

 species was similar to that observed in the central area, with 

 maximum abundances in the upper 20 to 40 m layer (unpubl. 

 data). In the shallow southern Red Sea, however, two population 

 centres were found, situated at depths of 0-20 m and 100-125 m. 

 Re-investigations of the southern plankton samples are required to 

 find out whether O. clevei might be vertically separated from O. 

 paraclevei in that area. For other oncaeid species or forms, which 

 are closely related to each other, such as O. media and O. scotto- 

 dicarloi and the two forms of O. venusta, a corresponding vertical 

 separation had been observed in the shallow parts of the southern 

 Red Sea. 



Seasonal variation in abundance (central red sea) 

 O. clevei I O. paraclevei exhibited a strong seasonal variation in 

 abundance in the central Red Sea, with highest abundances during 

 winter, but low numbers during summer and autumn (Bottger- 

 Schnack. 1995). This indicates a substantial recruitment for 

 populations of the c/em'-subgroup in the central area due to the 

 inflow of southern Red Sea waters during the NE monsoon, which 

 is similar to that observed for O. venusta f. typica. It remains 

 uncertain, however, whether this effect applies likewise for both 

 species of the cleve /-subgroup, as the two species were not sepa- 

 rated earlier. 



Oncaea scottodicarloi Heron & Bradford-Grieve, 1995 



Oncaea scottodicarloi Heron & Bradford-Grieve (1995): 39^1, 

 Figs. I7j-r, 18a-k, 27a. 



Oncda media Giesbrecht, 1892 (partim); Giesbrecht 1892, PI. 47. 

 Fig. 11 only; H.Itoh [in: Chihara & Murano (1997)]: 981, Fig. 

 369a-f. 



TYPE LOCALITY. Gulf of Naples, western Mediterranean Sea. 



Material examined 



( 1 ) Southern Red Sea, 1 3° 40.0'N, 42° 37.4'E: Stn. 708; R/V Meteor 

 leg 5/5: collected 05 August 1987 with MSN 0.05 mm net (Haul 

 47/3); depth 20^40 m; total water depth ca 190 m. 



(a) 2 99, 1 d in alcohol (BMNH 1998.2811-2813). 



(b) 2 99, 2 66 in alcohol (ZMH K-39581). 



(c) 2 99 dissected on slides, 1 9 in alcohol, 1 6 dissected on 

 slides, 1 6 in alcohol (RBS). 



(2) Southern Red Sea. 1 3° 40.0'N, 42° 37.4'E: Stn. 708; R/V Meteor 

 leg 5/5: collected 05 August 1987 with MSN 0.05 mm net (Haul 

 47/2); depth 40-60 m; total water depth ca 190 m. 



(a) 2 66 in alcohol (BMNH 1998.2814-2815). 



(b) 1 9, 1 6 (mating position) in alcohol (ZMH K-39582). 



(c) 2 66 in alcohol (RBS). 



(3) Central-northern Red Sea, 22° 58.4'N. 37° 19.4'E: Stn. 663; R/V 

 Meteor leg 5/5: collected 20 July 1987 with MSN 0.05 mm net 

 (Haul 17/2); depth 150-200 m; total water depth 1200 m: 1 9on 

 slide in lactophenol, numerous 99 and 66 for length measure- 

 ments (RBS). 



(4) North-East Atlantic, upwelling area off Northwest- Africa, 17° 

 36'N, 16° 26'W: Stn. 262 (DIV); R/V Meteor leg 64: collected 

 March 1983 with Messhai [= multiple opening-closing modified 

 Gulf III type sampler, Pommeranz et al. (1979), Pommeranz & 

 Moser (1987)] mesh size 0.05 mm: depth 80 m; total water depth 

 100 m: 1 9dissectedon 1 slide in polyvinyl-lactophenol (RBS). 



(5) North-East Atlantic, upwelling area off Northwest-Africa, 16° 

 09, N, 1 6° 48'W: Stn. 284 (DV); R/V Meteor leg 64: collected 27 

 March 1983 with Messhai [cf. (4)], mesh size 0.05 mm; depth 



