Dadagulella rondoensis ( Verdcourt, 1994 ) Rowson & Tattersfield, 2013

Rowson, Ben & Tattersfield, Peter, 2013, Revision of Dadagulella gen. nov., the “ Gulella radius group ” (Gastropoda: Streptaxidae) of the eastern Afrotropics, including six new species and three new subspecies, European Journal of Taxonomy 37, pp. 1-46 : 30-31

Dadagulella rondoensis ( Verdcourt, 1994) comb. nov.

Figs 41 , 84 ; Table 1

Gulella rondoensis Verdcourt, 1994: 137-139 , fig. 1.

Gulella rondoensis – Verdcourt 2006: 48.

Type material examined

TANZANIA: holotype SMF.310150 : 1 ad., Rondo Forest Reserve, Rondo Plateau, Lindi District (10.12°S, 39.22°E), evergreen forest with Milicia Sim , Albizia Durazz. , Dialium L. , etc. in small gully and amphitheatre around a well on escarpment, 650 m alt., leg. Bidgood, Abdallah & Vollesen , 10 Feb. 1991 (examined digital photograph only).

Other material examined

None.

Description

SHELL ( Fig. 41 ). Large (4.10 mm high x 2.20 mm wide), of 6.25 whorls. Subconical (maximum width being in bottom third of the shell, at body whorl). Spire narrowly acuminate, almost cyrtoconoid (convex) rather than coeloconoid (spire angle 52°). Apex sharply pointed. Embryonic whorls punctate or malleate, rather than merely granulate. Later whorls with relatively fine ribs (about 14 per mm on penultimate whorl). Sutures of intermediate depth. Umbilicus narrowly open. Peristome incomplete parietally. Dentition weak, 3-fold (although could be interpreted as 2-fold), consisting of: one lamellalike parietal tooth, with a swelling above it that recalls the one in D. conoidea ; one weak palatal tooth, not forming a parieto-palatal sinus; and one very weak, shallow columellar swelling. Further minute swellings just perceptible in the holotype ( Fig. 41 ) were not noted by Verdcourt (1994) who interpreted the dentition as 2-fold. Shells and anatomy of juveniles unknown.

Range and habitat

Forest at the type locality, southeastern Tanzania.

Remarks

This species differs from D. conoidea comb. nov. in its weaker dentition, smaller size, and in having punctate apical whorls. Along with D. conoidea comb. nov. and D. delta sp. nov. it has weaker dentition than other Dadagulella gen. nov. However, both D. rondoensis comb. nov. and D. conoidea comb. nov. are distinctively more conical, i.e. less ovate than other Dadagulella gen. nov. These two are attributed to the genus somewhat speculatively, on the basis of their acuminate spire and pointed apex. These features mean they do not obviously fit into Gulella or any of its named subgenera, or indeed other plausible streptaxid genera. No anatomical or juvenile shell data are available for either species, both being known from single specimens. The punctuate apex of D. rondoensis comb. nov., unique in Dadagulella gen. nov., may not be significant in this respect (see Rowson 2007b for a discussion on the value of apical sculpture in distinguishing African streptaxid genera). The apex of D. conoidea comb. nov. is less obviously punctuate, although it may have been worn smooth ( Verdcourt 1996). In the description of D. rondoensis comb. nov., Verdcourt (1994) discussed a resemblance only to Gulella galactochila (Crosse, 1885) , a much larger and more broadly acuminate Tanzanian species that we consider to lack the characteristic features of Dadagulella gen. nov. Although G. galactochila has not been dissected, the anatomy of another species very similar to it ( G. udzungwensis van Bruggen, 2003 ) lacks the anatomical features of Dadagulella gen. nov. (Rowson unpublished). In his discussion of D. conoidea comb. nov., Verdcourt (1996) made no reference to either D. rondoensis comb. nov. or G. galactochila , but only to two species that we here treat in Dadagulella gen. nov. ( D. r. radius comb. nov. and D. cuspidata comb. nov.). We contend firstly that D. rondoensis comb. nov. and D. conoidea comb. nov. are more similar to one another than either is to G. galactochila , and secondly that the resemblance between D. conoidea comb. nov., D. r. radius comb. nov. and D. cuspidata comb. nov. extends also to D. rondoensis comb. nov.. Our attribution of them to Dadagulella gen. nov. reflects this point of view.

Figures

Figs 41-42. Adult shells of Dadagulella gen. nov. species. 41. D. rondoensis (Verdcourt, 1994) comb. nov., holotype, Rondo (photo by R. Janssen). 42. D. conoidea comb. nov., holotype, Kwamgumi (after Verdcourt 1996).

Fig. 84. Distribution of Dadagulella gen. nov. species, based on published records and material examined here (for additional records of D. meredithae comb. nov. in northern Malawi see van Bruggen 2000). The inset on the left corresponds to the map on the right.