46 



R. BOTTGER-SCHNACK 



rostral area to posterior margin of caudal rami, calculated as sum of 

 individual somites): 1096 jam [traditional method: 800 urn, range: 

 750-880 um, based on 36 specimens (Bottger-Schnack et al. 1 989)] . 



Body proportions different from f. typica, with prosome 2.5 times 

 length of urosome, excluding caudal rami, 2.0 times urosome length 

 including caudal rami. P2-bearing somite with insignificant 

 dorsoposterior swelling in lateral aspect (arrowed in Fig. 11B). 

 Integumental pores on prosome as indicated in Fig. 11 A, B. Gran- 

 ules and raised structures on exoskeleton less pronounced than in f. 

 typica. 



Proportional lengths of urosomites similar to f. typica. Genital 

 double-somite 1.8 times as long as maximum width (measured in 

 dorsal aspect); largest width measured at anterior third, lateral 

 margins of genital double-somite weakly rounded at anterior third, 

 posterior part nearly straight. Double-scalloped sclerotization 

 between genital apertures, pore pattern on dorsal surface as indi- 

 cated in Fig. 11C. 



Anal somite (Fig. 1 1C) as in f. typica. 



Caudal ramus (Fig. 1 IF) about 2.8 times as long as wide, shorter 

 than in f. typica. Proportional length of caudal setae as in f. typica, 

 except for seta VI 1.6 times longer than caudal ramus. 



Antennule (Fig. HE) and antenna (Fig. 12A) as in f. typica, 

 except for slight differences in the ornamentation of setae on second 

 endopod segment in the antenna (seta I; setae C and D). 



Labrum(Fig. 12B,C) similar to f. typica, except for integumental 

 pockets with free margin serrate along half the distance only (Fig. 

 12B). 



Mandible (Fig. 12D),maxillule(Fig. 12E), maxilla (Fig. 12F)and 

 maxilliped (Fig. 12G) as in f. typica. 



Swimming legs 1-4 (Fig. 13A-D) as in f. npica, except for P4 

 enp-3 outer distal spine only 2/3 the length of distal spine. Distal 

 spines on endopods of P1-P4 somewhat longer than in f. typica. 



P5 (Fig. 1 1G) and P6 as in f. typica. 



Egg-sacs paired, containing appr. 30-35 eggs each (diameter 40- 

 50 um). 



Adult male (Fig. 7D-F, 14). 



Body length: 985 um [traditional method: 590 um. range: 550-650 

 um (single extreme value 730 urn), based on 17 specimens (Bottger- 

 Schnack et al. 1989)]. Sexual dimorphism in antennule. antenna, 

 maxilliped, P1-P3 (endopod) and P5-P6, caudal ramus and in 

 genital segmentation. 



Prosome 2.3 times length of urosome, excluding caudal rami, 2.0 

 times urosome length including caudal rami. Proportional lengths 

 (%) of urosomites similar to f. typica. Length to width ratio of 

 genital somite 1.7 : 1, longer than in f. typica. Ornamentation of 

 genital flaps as in Fig. 14E. Caudal rami about 1.9 times longer than 

 wide, shorter than in f. typica. Caudal setae with proportional 

 lengths as in f. typica, except for seta VI less than 2/3 the length of 

 seta IV and 2.4 times longer than caudal ramus. 



Sexual dimorphism in antennule (Fig. 14B), antenna (Fig. 14G), 

 maxilliped (Fig. 14C) and in P5-P6 (Fig. 14D, E), as well as in enp- 

 3 of P1-P3 (Fig. 7C, D) similar to f. typica. Seta on body near P5 

 naked. 



Taxonomy 



The original description of O. vemtsta by Philippi ( 1 843) was rather 

 poor and the single male specimen was lost by accident before the 

 mouthparts could be documented. Dana's subsequent (1849, 1852) 

 records of Antaria obtusa and A. crassimana were included under the 

 synonymies of both O. venusta and O. mediterranea by Giesbrecht 

 ( 1 892 ), reflecting the author's undecisiveness on this matter. Lubbock 

 ( 1 860) described the species (as Oncwa pyriformis) from the equato- 

 rial Atlantic and the southern Indian Ocean, and synonymized it with 



Dana's A. obtusa. He was the first to record male-female pairs 

 ('couples') of the species and erroneously believed that he had also 

 been the first author to report the males; however, as the original 

 account of O. venusta by Philippi was based on a male specimen. 

 Lubbock's opinion was erroneous. Claus' (1866) description of 

 Antaria coerulescens from Nice has been synonymized with O. 

 venusta by Giesbrecht (1892). Claus described several characters, 

 such as the heavily sclerotized exoskeleton and its surface ornamen- 

 tation, which are typical for the species, but at the same time recorded 

 the P4-bearing somite as being heart-shaped and pointed, which is not 

 the case in O. venusta. Brady's (1883) illustrations [Challenger 

 Expedition] of Antaria obtusa (Dana), were also synonymized with 

 O. venusta by Giesbrecht (1892), but he suspected that Brady's 

 specimens might include O. mediterranea as well. According to 

 Brady's illustration (Fig. 11), the P4 endopod exhibits a length ratio 

 ofdistal spine to outer distal spine (1.2 : 1) more similar to O. venusta 

 (1.3: 1 ) than to O. mediterranea ( 1 .55 : 1 ). His illustration of the male 

 urosome (Fig. 3), however, shows laterally produced genital flaps, 

 which is not typical for O. venusta, but can be observed in O. 

 mediterranea (Bottger-Schnack & Huys, 1997, their Fig. 4A, D). 



Giesbrecht ( 1 892) redescribed O. venusta on the basis of material 

 from Naples, reviewed the earlier literature on Antaria and Oncaea 

 and summarized the synonymies of the respective species known at 

 that time (see above). He stated that, judging from its general 

 habitus, Dana's form variety of A. gracilis would also resemble O. 

 venusta. However, as the P4-bearing somite of Dana's specimen is 

 pointed in lateral view (Plate 86, Fig. 12) as in O. mediterranea, and 

 not rounded as in O. venusta, Giesbrecht's opinion is not followed 

 here. [Dana's typical A. gracilis (Plate 86, Fig. 1 lb) is figured with 

 egg-sacs attached, which conceal great parts of the urosome. Thus 

 its unusual, narrow form cannot be used as a specific character for 

 identification as was proposed by Giesbrecht.] 



Recently, an excellent redescription of O. venusta was provided 

 by Heron & Bradford-Grieve (1995), based on material from the 

 Gulf of Naples and from various locations in the Atlantic and 

 Pacific. The authors did not figure the minute element on the 6th 

 segment of the antennule. and did not report on the sexual dimor- 

 phism in the coxobasal seta on the antenna and in the endopodal 

 spines of P1-P3. Re-examination of their material (1 9and 1 dfrom 

 Naples, kindly put at my disposal by G. Heron) showed, however, 

 that these characters are also present in O. venusta from Naples and 

 that the specimens from the Red Sea are conspecific. A further 

 discussion of their material will be given below under Form variants. 



Form variants 



Farran (1929) distinguished two form variants of O. venusta, f. 

 typica and f. venella, which differed mainly in size: the typical form 

 measured 1.08-1.16 mm (9) and 0.78-0.81 mm (3) in total body 

 length, while females of the venella form measured 0.91-1.07 mm. 

 No males of the venella form were recorded by Farran (1929). 

 Females of the two forms differed furthermore in general habitus, f. 

 typica being more 'pear-shaped' than f. venella, and in the length 

 ratio of prosome : urosome, which was smaller in f. typica (1.3:1) 

 than in f. venella (1.5:1). 



Sewell ( 1 947) recorded two size variants among female O. venusta 

 in the northern Arabian Sea and found no overlap in size between the 

 two groups (1.18-1.25 mm and 0.85-0.91 mm, respectively). He 

 described some morphological differences other than size, which 

 included ( 1 ) length to width ratio of prosome, which was larger in f . 

 venella than in f. typica, (2) length to width ratio of caudal ramus, 

 which was larger in f. typica than in f. venella and (3) slight 

 differences in the proportions of urosomites and caudal ramus 

 between the two forms. 



