SYSTEMATIC AND BIOLOGICAL ACCOUNT 47 



Stephanomia rubra (Vogt), 1852. (Text-figs. 12-18.) 

 Agalmoptis punctata Kolliker, 18536. 



This well known, but not well described or figured Mediterranean species, which I have examined 

 alive at Villefranche, and of which there is a good deal of material preserved in the British Museum 

 (Nat. Hist.) collections, was taken by 'Manihine' in the Gulf of Aqaba; and in the Red Sea and 

 west Indian Ocean by 'Discovery II'. 



Although specimens living at Villefranche are easy to identify from the sum of the characters, and 

 because of the restricted fauna, it is not easy to establish the presence of this species in another fauna 

 by deduction from the identification of loose nectophores taken in the tow-net. But this, as a rule, 

 is the only sort of evidence that is available, and for many years past I have been working to achieve 

 such an aim. 



There is a species of Physonect whose nectophores can easily be confused with those of Stephanomia 

 rubra by the less expert, and that is Agalma elegans. Of course the living or complete animal cannot be 

 confused, on account of their very different tentacles. If we compare the nectophores of the two 

 species, and bear in mind that fully grown nectophores look very different from young ones, we find 

 the following distinctions: 



1. General shape of nectophores. If nectophores of A. elegans and Stephanomia rubra are examined 

 together as they lie, abaxial sides uppermost on the bottom of a watch-glass of formalin, it will be seen 

 that the paired lateral wings or wedges of Agalma elegans are proportionately longer than those of 

 Stephanomia rubra. It will also be noticed that on each side, on a level with the ventral (adaxial) wall 

 of the nectosac of Agalma elegans, there is a vertical ridge that runs from the upper (apical abaxial) 

 to the lower (oral adaxial) lateral ridge. In other words, the lateral facets, in A. elegans, have the 

 ' latero-ventral (adaxial) triangle ' cut off by a complete vertical ridge to form a separate facet. It will 

 be seen, too, that in A. elegans the upper (apical, abaxial) lateral ridge forms a prominent tooth half- 

 way between the ostium and the ventral (adaxial) wall of the nectosac. In Stephanomia rubra there 

 is sometimes a slight prominence at this point, but usually not a well-marked tooth. 



In a strictly lateral view of Agalma elegans (Text-fig. 24 A) the vertical ridge, described above, can 

 be seen, with appropriate staining, running down in line with the adaxial (ventral) wall of the nectosac : 

 and it will be noticed that the upper part of the adaxial, median ' thrust-block ' (in which runs the 

 pedicular canal), does not project so far in A. elegans (Text-fig. 24 B) as it does in Stephanomia rubra 

 (Text-fig. 12 C,B,D). The much greater length of the long (abaxial-adaxial) axis of the nectophore 

 when compared with that of the vertical (oro-aboral) axis is another distinguishing feature of the 

 nectophore of. Agalma elegans. 



2. Lateral radial canals. Another useful distinguishing feature of Stephanomia rubra is the way in 

 which the lateral radial canal dips down as it runs on to the lateral face of the nectosac, before making 

 its ascending, abaxial run to the semicircular dorso-lateral curve, and descent to the circular velar 

 canal. In a strictly lateral view this dipping down of the lateral radial canal as it runs on to the lateral 

 face of the nectosac takes it well below the level of the inner end of the pedicular canal, and below the 

 horizontal part of the lateral canal that runs on the adaxial wall of the nectosac (Text-fig. 12D). 

 In Agalma elegans the lateral canal does not dip down noticeably as it runs on to the lateral wall of the 

 nectosac, but runs horizontally (Text-fig. 24 A). 



It should be pointed out that in both A. elegans and Stephanomia rubra and many other Physonects, 

 immature nectophores, when viewed from above (apically), have the upper lateral ridges somewhat 

 folded in towards the sagittal plane, so that care must be taken, when comparing nectophores, to 

 allow for immaturity. 



