Comprehensive DescriptionRead full entry
[[ Atlantoraja ZBK ]]
Materials & methods
Thirty-seven egg capsules of A. cyclophora and 19 of A. platana were obtained from female specimens captured by bottom trawl during August-September 2001 and March-April 2002 off southern Brazil. The specimens were captured between latitudes 30°40'S and 34°30'S at 100 and 300 m. Egg capsules were fixed in 4% formalin and preserved in 70% ethanol. Terminology of capsule morphology and methods of measurements follow Templeman (1982) and Gomes & Carvalho (1995). The egg capsules were extracted from the uteri and/or cloaca. Texture and color of the capsule and presence and location of adhesion fibrils and lateral keel were recorded for each fresh egg capsule.
Measurements recorded on each egg capsule were: length, width, length of the anterior and posterior horns, greatest dorso-ventral height and the thickness of the lateral keel in the middle of the egg capsule. All measurements were made with Vernier calipers with 0,1 mm precision. Differences were tested using a t-test (Sokal & Rohlf 1987) with a significance level of 0.05.
Measurements are presented in Table 1. The egg capsules of A. platana were significantly wider (t=-9.03, P<0.05, df=54) and had significantly longer posterior and anterior horns than those of A. cyclophora (t=9.34, P<0,05, df =51; t=-6.06, P<0.05, df=51, respectively). No significant difference was detected between species in length and height of the egg capsules (t=1.12, P>0.05, df =55; t=-1.43; P>0.05; df =40 respectively). The outline of the velum in dorsal view was markedly convex in A. cyclophora and slightly convex or even flat in A. platana (Fig. 1).
Freshly collected and fully formed egg capsules were of a medium brown color with a yellow metallic shine that changed to dark brown in formalin. Only one egg capsule was found per oviduct in both species. The base of the horns, the lateral margins and the ventral face of the complete egg capsule were covered by a layer of sticky, shiny yellow fibrils. In both species the entire dorsal face of the egg capsule was longitudinally and uniformly striated with ridges having a width and height of about 0.5 mm. On the ventral face the striations were also present but the ridges were lower and narrower and obscured by the layer of fibrils. In lateral view, the egg capsules of both species were asymmetrical. The ventral face was almost flat and the dorsal face was markedly convex with the highest point situated anteriorly (Fig. 2).
The rajoid genera occurring in the continental shelf of southern Rio Grande do Sul State, are Sympterygia ZBK , Rioraja ZBK , Psammobatis ZBK and Atlantoraja ZBK (Vooren 1997). When the size of the egg capsules overlaps, other features may be used for identification. The egg capsules of Atlantoraja ZBK and Rioraja ZBK have a lateral keel while Sympterygia ZBK has a lateral flange. Moreover, in this area, Sympterygia acuta ZBK uniquely has tendrils up to 44 cm long (Oddone & Vooren 2002). The small size of the capsules of Psammobatis ZBK distinguishes them from those of all other skates of this area. For instance, the egg capsules of P. extenta reach 30 mm in length (Braccini & Chiaramonte 2002). Egg capsules of Rioraja agassizi and Sympterygia ZBK are rather smooth, without marked longitudinal striation as in A. cyclophora and A. platana . In the former genera, both capsule faces are equally convex in lateral view, the opposite of the situation in Atlantoraja cyclophora and A. platana , where the dorsal face of the egg capsule is markedly convex and the ventral face is rather flat.
The egg capsule of Atlantoraja castelnaui , the third member of Atlantoraja ZBK , is much larger than that of A. platana and A. cyclophora . It attains a length of up to 100 mm and a width of about 70 mm (Oddone pers. obs.) being therefore, easily distinguishable from egg capsules of the other co-occurring species. Moreover, the egg capsule faces of A. castelnaui are smooth and the capsule is equally convex, as in other genera.
In conclusion, egg capsules with a length of 60-75 mm, with a convex dorsal face and longitudinal striations belong to A. platana or A. cyclophora . Egg capsules with posterior horns longer than 100 mm are those of A. platana , and egg capsules with posterior horns shorter than 80 mm are those of A. cyclophora . Egg capsules with intermediate values of posterior horn length can be identified to species by observing the shape of the velum. Though mean egg capsule width of A. platana is significantly wider, the use of the egg capsule width for discerning between these two species requires caution due to the high overlap of the widths.
The degree of development and location of masses of silky and sticky fibrils vary between species of Rajidae (Clark 1922). In Raja eglanteria ZBK from the North Atlantic and Sympterygia acuta ZBK , they are situated exclusively along the posterior horns or tendrils (Luer & Gilbert 1985; Oddone & Vooren 2002), which may be an exception within Rajidae . In Raja garmani ZBK from the North Atlantic, the masses of fibrils are situated in the lateral keels and in the faces of the capsule to a lesser degree (McEachran 1970). In A. cyclophora and A. platana such fibrils are exclusively over the ventral side of the egg capsule. The position of the attachment fibrils may be strictly related to the way in which each species attaches the egg capsules to the sea bottom. According to our observations, the egg capsules of A. cyclophora and A. platana probably attach themselves through the ventral face to the bottom or eventually to masses of algae or sea debris immediately after extrusion. According to Iglesias et al. (2002), the presence of just one egg capsule per oviduct suggests single oviparity in both species. Single oviparity has been observed in Psammobatis extenta (Braccini & Chiaramonte 2002) and unlike oviparous sharks, could be a general pattern of Rajidae .