Austrocypraea jimgracei, Southgate & Roberts, 2022

Southgate, Paul C. & Roberts, Mike, 2022, A new species of Austrocypraea (Mollusca, Gastropoda, Cypraeidae) from the Pliocene of Flinders Island, Tasmania, ZooKeys 1123, pp. 173-185 : 173

Austrocypraea jimgracei sp. nov.

Figs 1 , 2 , 3

Material examined.

Holotype. Australia, Lackrana, Flinders Island , Tasmania; 40°06'37"S, 148°10'18"E; May, 2012; P.C. Southgate and M. Roberts leg.; dry specimen (fossil); among spoil material excavated for farm dam; TMAGZ10628.

Paratypes. Australia; same location as holotype; May, 2012- Feb, 2021; P.C. Southgate and M. Roberts leg.; dry specimens (fossils); among spoil material excavated for farm dam; TMAGZ10629 (1 specimen) ; AM F.156043 (1 specimen); AM F.156044 (1 specimen); MR 635 (1 specimen); PS CF.174/175 (2 specimens).

Other material.

Australia; same location as holotype; May, 2012-Feb, 2021; P.C. Southgate and M. Roberts leg.; dry specimens (fossils); among spoil material excavated for farm dam; PS CF.305/306 (2 specimens); MR 657/658 (2 specimens); TMAGZ10630 (five partial specimens) .

Diagnosis.

Austrocypraea jimgracei sp. nov. can be separated from all other members of the genus, fossil and extant, by a combination of the following characteristics: shell ovate to sub-pyriform, humped, highest point towards posterior, shell height around 71% length, shell width around 59% length; anterior extremity subtruncate, not extended in lateral profile, supported by well-defined anterior lateral flanges; protoconch paucispiral, spire projecting, overlain by callus. Aperture gently curved to the left posteriorly, widening slightly towards anterior; evenly spaced, relatively strong dentition; 13-17 columellar teeth, restricted to aperture, larger towards anterior; 17-21 labral teeth are longer, incised, and restricted to aperture margin. Fossula is broad, concave and smooth centrally, with shallow, barely discernible longitudinal depression or slightly raised ridge sometimes present; fossular margin with 4-6 denticles, visible in ventral view; anterior denticles not linked to adjacent columellar teeth by transverse ridges, but fine ridges may link posterior fossular denticles to adjacent columellar teeth. Columella smooth posterior to the fossula, lacking a defined columella ridge. Labral margin heavily callused, forming a distinct marginal edge, bent up towards the dorsum centrally; shallow anterior and posterior labral grooves may accommodate small, irregular, often elongate, pustules dorsal to the labral marginal edge; marginal edge may be weakly crenulate where marginal pustules intersect.

Description.

Average size for the genus (Table 1 ); shell length 23.1-25.5 mm (mean 24.5), W/L = 69-73% (mean 71%), H/L = 58-61% (mean 59%), H/W = 82-85% (mean 84%); ovoid to sub-pyriform, maximum shell height towards posterior; protoconch paucispiral, rounded; spire projecting, overlain by callus (Fig. 1 ). Shell formula: [24 (71-59-84) 19:15]. Dorsal surface smooth except for weak longitudinal growth lines. Basal callus strongly developed; base rounded. Shell margins callused; left margin rounded, smooth; labral marginal callus well developed, with distinct marginal edge, bent up towards the dorsum centrally (Fig. 2A ); more sharply margined anteriorly and posteriorly, forming shallow labral grooves that may accommodate pustules or small tubercules, often elongate, dorsal to the marginal edge (Fig. 2B, C ). The right marginal edge may be slightly crenulate where pustules intersect. Anterior and posterior canals are deep and bordered by strong projecting callus; anterior canal with dorsoventral orientation, not angled; anterior terminal subtruncate, hardly extended, supported by anterior lateral flanges; anterior tips moderately pointed. Posterior canal short, bent to the left; bordered on the left by well-developed columellar callus, not extending as far as the posterior end of the labrum. Aperture gently curved to the left posteriorly, widening anteriorly. Fossula broad (Fig. 3 ), concave and constricted posteriorly; bordered anteriorly by a well-defined terminal pleat, thickening where it joins the terminal ridge. Fossula margin with 4-6 denticles becoming weaker posteriorly; anterior denticles not linked to adjacent columellar teeth by transverse ridges; poorly developed ribs may link the smaller denticles at the posterior end of the fossula with collumellar teeth, where the fossula merges with the columella (Fig. 3B ). Very weak ridges may extend onto the fossula from the marginal denticles and from the anterior-most columellar teeth, but they do not join; central fossula smooth, with shallow, longitudinal depression (Fig. 3E ) or slightly raised ridge on the central fossula sometimes evident (Fig. 3A ). A well-defined fossular gap is present at the anterior end of the fossula margin, between the anterior-most marginal denticle and the dorsal extremity of the terminal pleat. Columella lacks a defined columellar ridge and is smooth posterior to the fossula. Columellar teeth (13-17, Table 1 ) spaced about one tooth width apart; present along the length of the columella, terminating at the anterior edge of columella callus bordering the posterior canal; anterior columella teeth stronger, first tooth generally stronger than those posterior to it, and separated from the terminal ridge by a prominent anterior gap. Labral teeth (17-21, Table 1 ) restricted to aperture, longer anteriorly, more elongate and more numerous than columella teeth.

Variation. Available specimens show variation in the angle of slope of the fossula, the number and form of fossular marginal denticles, and the presence, or otherwise, of a shallow depression or a slightly raised ridge on the central part of the fossula (Fig. 3 ). Pustules dorsal to the anterior and posterior labral margins may or may not be present or visible, and this probably relates to specimen maturity and the degree of preservation. Pustules may produce a weakly crenulate marginal edge in some specimens where (and if) they intersect. This feature is present in the holotype and its development is likely related to specimen maturity and the degree of callus development.

Differential diagnosis.

Shell shape in cowries is commonly expressed using a 'shell formula’ which reports linear shell measurements, and their ratios, as well as normalised tooth counts ( Bridges and Lorenz 2013). The shell formula of Austrocypraea jimgracei sp. nov. is compared with those of all other Austrocypraea fossil species, for which morphometric data are available, in Table 2 . In terms of shell shape (i.e., W/L, H/L and H/W), A. jimgracei sp. nov. is closest to A. amae and A. rumballi (Table 2 ) and a broader range of shell characteristics is compared for these three species in Table 3 . The new species is similar in size and dimensions to A. amae , where shell width relative to length (71%), height relative to length (60%), and height relative to width (84%) are very similar to values of 71%, 59% and 84%, respectively, for the same parameters in A. jimgracei sp. nov. (Table 2 ). The anterior extremity of A. amae is shorter and less produced, and the anterior canal is wider, deeper and more angled than in A. jimgracei sp. nov. The anterior lateral flanges supporting the anterior extremity of A. jimgracei sp. nov. are more developed than in A. amae . The posterior extremity is more produced in A. jimgracei sp. nov. than in A. amae , particularly on the right side. The new species can be easily separated from A. rumballi by its much larger size.

Clear differences in fossula structure also separate A. jimgracei sp. nov. from A. amae and A. rumballi . The fossula of A. amae is crossed by ribs which are continuous with the anterior columellar teeth and extend to the inner margin of the fossula (Table 3 ). Denticles on the inner fossular margin of A. jimgracei sp. nov. are separated from adjacent anterior columellar teeth by a smooth central area of the fossula. The fossula of A. rumballi is similar to that of A. jimgracei sp. nov. but differs by protruding further into the aperture, having a greater number of denticles on the inner margin (generally 6-7), and transverse ridges that link the denticles to columellar teeth, at least posteriorly ( Yates 2008). An interesting feature of the fossula of A. rumballi is an indistinct tubercle or longitudinal ridge in the middle of the fossula between the terminal ridge and the first or second transverse ridge of the fossula ( Yates 2008). A shallow longitudinal depression or slightly raised ridge is sometimes present in the middle of the fossula of A. jimgracei sp. nov. (Fig. 3 ); however, the form of this feature varies and it is absent in some specimens.

The Miocene species A. contusa and A. goudeyana have similar size and proportions to A. jimgracei sp. nov., and the form of the anterior extremity, supported by distinct anterior lateral flanges, may also be similar for these species. However, A. contusa and A. goudeyana are readily separated from A. jimgracei sp. nov. because of their more produced anterior extremity, narrower aperture, which has consistent width throughout, and stronger dentition that may extend onto the columella. The form of the heavily callused labral margin of A. jimgracei sp. nov., that is bent up towards the dorsum centrally, is unique within the genus. Other species within the genus, such as A. contusa , A. goudeyana and A. subcontusa , may also develop a well-defined thickened labral margin, but unlike that of A. jimgracei sp. nov., when present, it generally forms a thin step-like rim to the shell margin that does not bend up towards the dorsum. The shells of a number of Austrocypraea species, including the extant A. reevei , have shallow contusions or ‘malleation’ on the dorsal surface of the shell, but this is not a ubiquitous feature of the genus. For example, malleation is prominent on the shells of A. contusa and A. goudeyana , less prominent and generally restricted to the posterior half of the body whorl in A. rumballi and A. amae , obscure or absent in A. scalena , but totally lacking in A. onkastoma , A. archeri , A. subsidua and A. parallela , and in all examined specimens of A. jimgracei sp. nov.

Etymology.

Named in honour and in memory of the late Jim Grace of Lackrana, Flinders Island, on whose property all specimens of the new species were recovered.

Distribution.

Known only from the Cameron Inlet Formation, Lackrana area, Flinders Island, Tasmania.

Figures

Figure 1. Austrocypraea jimgracei sp. nov.; dorsal, ventral and marginal (labral) aspects A holotype, TMAGZ 10628 B paratype 1, TMAG Z 10629 C paratype 5, senior author collection (PS CF. 174)

Figure 2. Detail of labral margin of the holotype of Austrocypraea jimgracei sp. nov. (TMAGZ 10628) showing labral margin (A), posterior labral groove (B) and anterior labral groove (C).

Figure 3. Detail of the fossula of sectioned shells of Austrocypraea jimgracei sp. nov., showing variation amongst specimens (TMAGZ 10630). Arrows indicate a slightly raised ridge (A) and shallow longitudinal depression (E) sometimes present on the fossula.