Rectacirsa fregata Iredale, 1936
Description: Shell minute, moderately slender, of 6 teleoconch whorls, with a microscopically pitted intritacalx. Protoconch of 3½ smooth, elongate whorls, ending with a varix, a little tilted. Teleoconch whorls well rounded, sutures deep, with separated, elevated axial ribs. Ribs 11 on the last whorl. Interspaces with fine striae, about 10 on last whorl (holotype) or with pitted intritacalx. Last whorl with strong basal rib at which axial ribs terminate; base smooth. Aperture roundly oval, with strong flattened varix externally. Umbilicus closed. Colour dirty white.
Size: Holotype 4 mm in length.
Distribution: Known from holotype from 250 fathoms (457 m) off Sydney, and one other specimen collected 40 years later from the same locality.
Comparison: This species is shown in Fig. 2a, compared with Cylindriscala distincta in Fig. 2b. Compared with C. distincta it has a smaller and inclined protoconch, and a microscopically pitted intritacalx. There are 11 axial ribs on the last whorl while C. distincta has 16.
Remarks: Only one specimen of this species has been identified since it was described in 1936. This is shown in Fig. 1.
The holotype is quite unlike the specimen described and figured by Iredale in his description, although it is probably a specimen of this species. The holotype lacks a protoconch, and is so badly worn that only faint patches of the intritacalx can be seen. In his discussion following his species description, Iredale refered to another shell which was "too imperfect to describe", and it is likely that this is the specimen that has mistakenly survived as holotype. Kaicher (1980, card 3096) has illustrated this incorrect specimen.
Fig. 1: Off Sydney, 457 m (C.461150)
Fig. 2: a. R. fregata Same specimen as Fig. 1. b. C. distincta Off Nowra, NSW, in 550 m (C.310500)
Copyright Des Beechey 2008