Iophon unicorne Topsent 1907

Iophon unicorne Topsent, 1907

(Fig. 3 F)

Iophon unicorne Topsent, 1907: 72. Boury-Esnault & van Beveren 1982: 87–89, fig. 25. Desqueyroux & Moyano 1987: 49. Desqueyroux-Faúndez 1989, 120, pl. 3, figs 17a–d, pl. 12, figs. 68–70. Pansini et al. 1994: 75. Gutt & Koltun 1995: 231. Cattaneo-Vietti et al. 1999: 540. Campos et al. 2007b: 745, figs. 10–17, tab. 2.

Synonymy:

Iophon spatulatum Kirkpatrick, 1907: 276, 1908: 29 –30, pl. 21, figs. 5, 5a–c, pl. 25, figs. 5a–d. Koltun 1964: 58, pl. 10, figs. 1– 9, 1976: 182. Desqueyroux 1975: 64, pl. 3, figs. 36–40. Sarà et al. 1990: 254. Barthel et al. 1997: 48.

Material. Several fragments of probably about 3 specimens from station 048-1 (SMF 11807, 11812, 11845), 602.1 m, 70° 23.94' S, 8° 19.14' W, 12.01.2008. Material examined for comparison: Iophon flabellodigitatum Kirkpatrick, 1907: BMNH 1908.2.5.153, holotype, wet specimen, BMNH 1908.2.5.153.C, holotype, slide, BMNH 1908.2.5.153.K, holotype, slide, Colln of the National Antarctic Expedition HMS “Discovery”, described in Kirkpatrick 1908.

Description. Our fragmentary specimens are massive sponges, overgrowing bryozoans. Skeleton consisting of an anisotropic reticulation of anisoxeas, not very well preserved in specimens, with a tangential ectosomal crust of tylotes. Spicules anisoxeas with the point on one end usually characteristically bent, 410–510 x 15 µm, slightly curved acanthotylotes with slender tyles at each end, usually bearing small terminal spines, 280–340 x 10 µm, palmate anisochelae with distally oriented spines on the top of the side with short alae, 15–17.5 µm, and bipocilla 10–12.5 µm.

Remarks. This species has been recorded and documented several times (Topsent 1907; Burton 1929; Koltun 1964; as I. spatulatus, Boury-Esnault & van Beveren 1982, Campos et al. 2007b) and can therefore be considered well-known. However, the taxonomy of the species is still problematic: Burton (1929) united all Antarctic Iophon spp. under the name of Iophonopsis radiatus (Topsent, 1901). This decision was not generally accepted, although the synonymy of I. unicorne and Iophon spatulatum Kirkpatrick, 1907 seems doubtless (Ríos et al. 2004). There are also several similarities between I. unicorne and Iophon flabellodigitatum Kirkpatrick, 1907 which raise the question, whether these two species are reliably distinguishable. According to Ríos et al. (2004), who plead for the maintenance of the two species, the main difference is the shape of the acanthotylotes, which in I. unicorne are slightly curved, while those in I. flabellodigitatum are straight. Also, the tyle on one end of the acanthotylotes bears one strong distal spine in I. flabellodigitatum, while in I. unicorne both ends of the acanthotylotes are equally covered by small distally oriented spines. The curvature of the acanthotylotes seems to be a weak characteristic, which we can also observe in our sponge, in which acanthotylotes are only slightly, but distinctly, curved. Thus, the significance of such a character appears questionable. Acanthotylotes with one distal spine significantly longer than the other have been recorded previously from I. unicorne (Campos et al. 2007b; Ríos 2006). Considering, that these spines are of length between 1 and 10 µm, one can also be doubtful about this point. Thus, we come to the conclusion, in accordance with Ríos (2006), that the differences between I. unicorne and I. flabellodigitatum are very weak and that a synonymization of these species appears to be necessary, although this is not done by us, because we lack the material needed for such a taxonomic decision.