Umbilia tomdarraghi, Southgate & Militz, 2023

Southgate, Paul C. & Militz, Thane A., 2023, A new species of Umbilia Jousseaume, 1884 (Mollusca, Cypraeidae) from the Pliocene fauna of the Roe Plains, Western Australia, ZooKeys 1169, pp. 1-13 : 1

Umbilia tomdarraghi sp. nov.

Figs 1 , 2

Umbilia hesitata - Darragh 2002: 380, fig. 9 a-f.

Umbilia hesitata - Wilson and Clarkson 2004: 342, pl. 352, fig. b.

Umbilia hesitata - Goudey 2015: 41, figs b, c.

Umbilia hesitata - Lorenz 2018: 106, fig. 19.

Material examined.

Holotype. Australia • Madura district, Roe Plains, Western Australia; October 1988; G.W. Kendrick leg.; dry specimen (fossil); among spoil material excavated from quarry, 2.5 km north of Hampton microwave repeater tower (31°56'34"S, 127°34'47"E); WAM 89.636b.

Paratypes. Australia • 1; same location as holotype; October 1988; G.W. Kendrick leg.; dry specimen (fossil); WAM 89.636a (paratype 1) • 1; same location as holotype; October 1988; G.W. Kendrick leg.; dry specimen (fossil); WAM 89.636c (paratype 2) • 1; same location as holotype; October 1988; G.W. Kendrick leg.; dry specimen (fossil); MV P121294 (paratype 5) • 1; among spoil material in Main Roads quarry 16 km south of Madura Roadhouse, Madura (32°02'22"S, 127°02'50"E), Roe Plains , Western Australia; August 1985; G.W. Kendrick leg.; dry specimen (fossil); WAM 85.1462 (paratype 3) • 1; among spoil material in pit, 1.5 km north of Hampton microwave repeater tower (31°56'34"S, 127°34'47"E); October 1984; A. Rowe leg.; WAM 84.2136 (paratype 4) • 1; among spoil from foundation holes for Hampton microwave repeater tower (31°56'34"S, 127°34'47"E); April 1969; T.A. Darragh leg.; MV P302721 (paratype 6) • 1; same locality as preceding; June, 2004; P. Hunt leg. ; PH collection (paratype 7) • 1; among spoil material alongside Eyre Highway, east of Madura, Western Australia, March 1995 (material probably sourced from Main Roads quarry 16 km south of Madura Roadhouse , Madura (32°02'22"S, 127°02'50"E); A. Bishop leg.; AB collection (paratype 8) • 1; among spoil material north of Hampton microwave repeater tower (31°56'26"S, 127°35'26"E); July 2007; C. Goudey leg.; CG collection (paratype 9) • 1; among spoil material at Hampton microwave repeater tower (31°57'52"S, 127°34'50"E); J. Fell leg.; JF collection (paratype 10) .

Other material.

Australia; Roe Plains , same location as holotype; dry specimen (fossil); among spoil material; CG (1 repaired specimen) .

Diagnosis.

Shell pyriform to ovately pyriform, humped; dorsal summit towards posterior, W/L = 59%, H/L = 48%; spire impressed; protoconch projecting and prominent, positioned to the left side and visible when the shell is viewed from a dorsal aspect. Coarse columellar teeth extending onto base. Anterior and posterior terminals extended; anterior lateral flanges well-developed, thickened; anterior extremity broad, flattened, rounded; anterior tips blunt. Anterior dorsal tubercules absent; a small, raised callus on left side only; anterior groove absent.

Description.

Of average shell length for the genus (76-87 mm; Table 1 ); shell pyriform to ovately pyriform, humped, with highest point towards posterior; W/L = 59.4%, H/L = 48.3%, and H/W = 81.3%. Shell formula [82(59-48-81) 20:17]. Anterior and posterior extremities extended; anterior extremity rounded, supported by broad, thickened, lateral flanges; anterior tips rounded, not pointed; posterior terminal curved to left with right posterior tip extending further; dorsum smooth. Single anterior tubercule evident as small, raised callus on left side only; anterior groove absent; base convex, broad, flattened anteriorly. Aperture widening anteriorly, narrowest at anterior end of posterior canal; apertural teeth coarse, evenly spaced, and well developed along whole length and on both sides of the aperture; columellar teeth extending onto base. Labral teeth (28-35) more numerous than columellar teeth (22-30). Shell margins rounded, smooth; spire umbilicate; protoconch large (4.8 ± 0.4 mm diameter; n = 6), projecting and prominent, positioned to the left so that the penultimate body whorl has greater exposure on the right side of the spire (Fig. 2A, B ). Fossula narrow, smooth, and slightly concave.

Differential diagnosis.

When compared to extant Umbilia armeniaca and U. hesitata , shell form of U. tomdarraghi sp. nov. is morphometrically more similar to U. hesitata (F = 7.9, R 2 = 0.09, P <0.001) than to U. armeniaca (F = 23.2, R 2 = 0.14, P <0.001, Fig. 3A ). The explicit distinction between U. tomdarraghi sp. nov. and U. hesitata , when independently assessed using morphometric data for all three U. hesitata subspecies ( U. hesitata hesitata , U. h. beddomei and U. h. suprastrata ), showed clear separation (F = 6.9, R 2 = 0.08, P <0.001), with U. hesitata being significantly more variable in shell form (F = 10.1, P <0.01) than U. tomdarraghi sp. nov. (Fig. 3B ). When compared to individual subspecies of U. hesitata , shell form of U. tomdarraghi sp. nov. is most similar to U. h. suprastrata , but U. h. suprastrata is more similar to both U. h. hesitata and U. h. beddomei than it is to U. tomdarraghi sp. nov. (Fig. 3B ; Table 2 ). It is notable that variability in shell form among the type series specimens of U. tomdarraghi sp. nov. is similar to that of U. h. hesitata , U. h. beddomei , and U. h. suprastrata (Table 3 ). Univariate comparisons of L, W/L, H/L, H/W, nLT, and nCT showed U. tomdarraghi sp. nov. to differ from U. h. hesitata by significantly greater W/L, lower H/W and lower nCT, from U. h. beddomei by significantly greater L and lower H/L, and from U. h. suprastrata by significantly lower H/L and lower nCT (Fig. 4 ). Key conchological features differentiating U. tomdarraghi sp. nov. from U. h. hesitata , U. h. beddomei , and U. h. suprastrata include coarser, extended columellar teeth; the broader, flatter, blunter anterior extremity; lack of both distinct anterior dorsal tubercules and an anterior groove; a flatter base; and a much larger, protruding protoconch (Table 4 ).

A second species of Umbilia , U. fodinata (Darragh, 2011), occurs with U. tomdarraghi sp. nov. within the Roe Calcarenite. While Darragh (2011) originally assigned this species to the genus Zoila Jousseaume, 1884, in the most recent review of the family, Lorenz (2017, 2018) placed the species within Umbilia and this position is adopted here. Like U. tomdarraghi sp. nov., the spire of U. fodinata protrudes beyond the last shell whorl, but it is readily distinguished from U. tomdarraghi sp. nov. by its smaller size (72 mm), shell form (W/L 65%; H/L 54%), well-developed fossula, less extended posterior extremity, more tapered and shorter anterior extremity, and in the structure of the anterior-most columellar teeth, which are longer and coarser than those elsewhere on the columella and extend further onto the base ( Darragh 2011).

Pliocene strata of the Cameron Inlet Formation at Flinders Island, off the north-east coast of Tasmania, around 2,000 km from the Roe Plains, contain at least three species of cowries, including two species of Umbilia : U. furneauxensis Southgate et al., 2021 and U. hesitata ( Sutherland and Kershaw 1970; Darragh 1985; Southgate et al. 2021; Southgate and Roberts 2022). Umbilia furneauxensis differs from U. tomdarraghi sp. nov. by its much smaller size (<60 mm), extension of apertural dentition to at least midway on the base and labrum, and heavily callused margins that may form a dimpled surface extending to the base. Flinders Island fossils assigned to U. hesitata can be distinguished from U. tomdarraghi sp. nov. by their much greater extension of both anterior and posterior extremities, restriction of their finer columellar teeth to the aperture, lengthening of the anterior-most labral teeth, a more convex base, and a more umbilicate spire with less prominent protoconch. However, comparison of U. tomdarraghi sp. nov. with U. hesitata from the Cameron Inlet Formation is done with caution at this stage because available specimens (n = 16, MV collection) vary considerably in shell form and conchological features to such an extent that they may not represent a single taxon.

Umbilia tomdarraghi sp. nov. superficially resembles the Miocene species U. eximia (G.B. Sowerby I, 1845) and U. hallani Hawke, 2020. It differs from the former by its much less prominent extremities, lack of prominent anterior dorsal tubercules, and by differences in the structure of the columellar teeth which, in U. eximia , are generally broad, deeply incised, and rectangular in cross section. Umbilia hallani is readily distinguished from U. tomdarraghi sp. nov. by its much smaller size with a more inflated body whorl and rostrate anterior extremity, and by the moderately formed anterior dorsal tubercules, separated by a diagonal groove.

Etymology.

Named to honour Dr T.A. Darragh, invertebrate paleontologist at Museums Victoria, Melbourne, Australia, in recognition of his significant contribution to our understanding of Australian marine molluscs, both fossil and living.

Distribution.

Known only from the Roe Calcarenite of the Roe Plains, Western Australia.

Figures

Figure 1. Umbilia tomdarraghi sp. nov.; dorsal, ventral and marginal aspects A holotype WAM 89.636 b B paratype 4, WAM 84.2136 C paratype 1, WAM 89.636 a.

Figure 2. A, B detail of the spire and protoconch of Umbilia tomdarraghi sp. nov. A holotype WAM 89.636 b B paratype 1, WAM 89.636 a C U. hesitata hesitata D U. hesitata suprastrata.

Figure 3. A nMDS ordination (stress = 0.14) of the resemblance matrix for Umbilia armeniaca, U. hesitata and U. tomdarraghi sp. nov. B nMDS ordination (stress = 0.19) of the resemblance matrix for the three U. hesitata subspecies and U. tomdarraghi sp. nov. Shaded ellipses indicate the 95 % confidence interval of taxa (species or subspecies) centroids. The coefficient of determination (R 2) and probability that distances between centroids arose by random chance (P) are presented.

Figure 4. Box plots showing univariate comparisons of A length (L) B width to length ratio (W / L) C height to length ratio (H / L) D height to width ratio (H / W) E normalised labral tooth count (nLT) and F normalised columellar tooth count (nCT) among the accepted subspecies of Umbilia hesitata (U. h. hesitata, U. h. beddomei, U. h. suprastrata) and U. tomdarraghi sp. nov. Diamonds represent group means, boxes illustrate first and third quartile as box edges and median as central line. Shared superscripts identify means that are not statistically different (Holm-adjusted P ≥ 0.01) among taxa.