Diplopoma rigidulum ( Morelet, 1851 )

Watters, G. Thomas, 2014, A revision of the Annulariidae of Central America (Gastropoda: Littorinoidea), Zootaxa 3878 (4), pp. 301-350 : 335-336

Diplopoma rigidulum ( Morelet, 1851)

Figures 8 L–W, 12 C, 13 B, F, H

Type material. NHMUK 1893.2.4.704-5 (2), syntypes (fig. 8 K); ANSP 14098 (1), syntype.

Type locality. “ rupestria prov. Vera-Paz” [but NHMUK 93.2.4.704-5 label reads: “Peten. S. Luis”].

Type figured. Unfigured.

Cresonymy.

Cyclostoma rigidulum Morelet, 1851: 18 ; Pfeiffer, 1852b: 154; Richardson et al., 1991: 52; Watters, 2006: 442.

Cistula ? rigidula ( Morelet, 1851) . Pfeiffer, 1852a: 418; Pfeiffer, 1853a: 191.

Cistula rigidula ( Morelet, 1851) . Adams & Adams, 1856: 294; Pfeiffer, 1858: 134 –135; Pfeiffer, 1865: 144; Bland, 1866: 61; Pfeiffer, 1876: 189.

Adamsiella rigidula ( Morelet, 1851) . Fischer & Crosse, 1888: 175, 176; Morlet, 1888: 358; Fischer & Crosse, 1890: 179, 182, pl. 42, figs. 12, 12a, 12b.

Choanopoma rigidulum ( Morelet, 1851) . Martens, 1890: 14, 16, pl. 1, fig. 3.

Choanopoma rigitulum [sic] ( Morelet, 1851). Martens, 1890: caption to pl. 1.

Ctenopoma rigidulum ( Morelet, 1851) . Fischer & Crosse, 1890: 188.

Cyclostoma rigidula Morelet, 1851 . Baker, 1924b: 42.

Licina (Choanopomops) rigidulum ( Morelet, 1851) . Baker, 1928: 48 –49.

Choanopoma (Choanopoma) rigidulum ( Morelet, 1851) . Haas & Solem, 1960: 130.

Choanopoma (Choanopomops) rigidulum ( Morelet, 1851) . Solem, 1961: 195 –196, pl. 10, fig. 1, pl. 12, fig. 24a, map 1; Thompson, 2011: 47, 278, 280.

Parachondrops rigidulus ( Morelet, 1851) . Watters, 2006: 48, 442.

non Annularia (Annularis [sic]) rigidula “Morelet” Haas, 1949: 137 [= Adamsiella osberti Tristram, 1861 , fide Solem, 1961: 196].

Distribution and habitat. Endemic to limestone outcrops of the Maya Mountains and Vaca Plateau in Petén and Alta Verapaz departments, Guatemala, and Cayo and Toledo districts, Belize. Specimens have been found from 75–600 m altitude. Found under rocks and among scree in karstic rainforests; in and among caves. Often abundant.

Conservation. Large portions of this species’ range in Belize are in forest and nature reserves, as well as national parks. There are no records from the Guatemalan Maya Biosphere Reserve.

Other material (specimens examined: 326 specimens). Belize. Cayo District: GTW 8713a (3), UF 135055 (52), Rio Frío Cave; GTW 8713b (1), Mountain Pine Ridge Forest Reserve; GTW 8713c (1), Grego coll. (7), San Ignacio; UF 146240 (14), UF 146271 (16), Duffy Bank area 4.9 km SE of San Ignacio, 110m; UF 146316 (2), UF 146330 (12), on road to Xunantunich temple 0.5 km N of Benque Viejo Del Carmen, 100 m; UF 207341 (29), limestone hill 14.0 km SSE of Benque Viejo Del Carmen, 300 m; UF 135086 (1), UF 146288 (9), UF 146303 (13), Xunantunich temple, 110 m; UF 207468 (2), hill 1.0 km NE of Arenal, 150 m; UF 207451 (10), limestone hill road cut at Guacamallo bridge over East Branch Macal River, 600 m; UF 207399 (138), Caracol temple, 600 m; UF 207424 (31), limestone hill 12.5 km NE of Caracol, 510 m; UF 207491 (11), limestone cliff on E side of East Branch Macal River 1.0 km NW of Black Rock, 120 m; UF 207368 (7), limestone hill 10.0 km SE of Benque Viejo Del Carmen on road to hydroelectric dam, 350 m. Toledo District: UF 206762 (2), UF 207810 (19), UF 207843 (18), limestone ridge 1.0 km S of Aguacate, 100 m; UF 207751 (4), UF 207772 (1), limestone ridge 2.0 km N of Blue Creek, 75 m; UF 207885 (21), limestone hill 3.2 km E of Blue Creek, 75 m. Guatemala. Petén Department: UF 155813 (1), 2.3 km N of Poptún; UF 155790 (9), on Modesto Mendez Fores Road 7.5 km S of Poptún; GTW 8713f (5), km 369 on road from Rio Dulce to Flores; GTW 8713d (7), km 375 on road from Rio Dulce to Flores; GTW 8713h (1), km 333 on road from Rio Dulce to Flores. Alta Verapaz Department: GTW 8713e (6), road out of Lanquín, GTW 8713g (20), B'onb'il Pek Cave area.

Description. Shell conical, high-spired, thin, last 1/3 – 1/2 of whorl solute. Smallest adult specimen seen 6.4 mm in length, largest 9.6 mm, average 8.6 mm (decollate). Protoconch usually lost in adult, 1.5 large, rounded, smooth, tan whorls, not clearly demarcated from teleoconch. Teleoconch of 3 – 4 rounded whorls. Umbilicus narrow, open. Spiral sculpture absent except for 2 – 3 cords in the umbilicus. Axial sculpture of numerous coarse, erect, regularly and distantly spaced lamellae, ca. 40 – 50 on the final whorl. These lamellae are often broken rendering the edges ragged or serrate. Suture strongly indented. Tufts absent but the axial lamellae are thicker and taller at the suture. On solute portion of final whorl they form a serrated ridge and the sculpture on the axial side of this ridge is nearly absent. Aperture nearly circular. Inner lip smooth, narrowly exserted. Outer lip lamellate, widely reflected perpendicular to whorl, more or less evenly expanded, somewhat narrower facing umbilicus, strongly auriculate posteriorly, solute from previous whorl. Base color dingy white. Patterned with ca. 4 – 5 diffuse brown bands, sometimes broken into spots, bands do not continue over adapertural face of peristome, bands visible inside aperture. Peristome white, occasionally orangish. Operculum multispiral with a calcareous, slightly oblique lamella. Radula and anatomy unknown.

Sides of animal brown, head pale tan (fig. 13 B); antennae pale yellow, tips abruptly pale tan; area between bases of antennae pale purplish brown, diffuse. Eyes black.

Variation in specimens. Specimens are remarkably uniform in most characteristics, varying primarily in the number of axial lamellae and adult size.

Comparison with other species. Diplopoma osberti is similar but lacks the coarse, axial sculpture. This species differs from other Central American species in the greater degree to which the final whorl is solute.

Remarks. Solem (1961) speculated that D. osberti was the upland form of D. rigidulum . While it is correct that D. rigidulum generally occurs at lower elevations than does D. osberti , the latter is a distinct species narrowly endemic to the karst region around Lanquín, Alta Verapaz, Guatemala.

Original description (translated here from Latin). “Shell turreted, a good part truncate, lamellate-costae, scaly, waxy horn-colored, decorated around with 4–5 interrupted reddish bands; spire conic-turret, apex smooth. 7.5 convex whorls, suture deeply marked, last solute, deflected down, more or less extended. Aperture oblong, colored the same inside; peristome double, outer lip lamellate, extensive, top right produced into a concave angle.” 12 mm.

Etymology. L. diminutive of rigidus, a little rigid.

Figures

FIGURE 8 A – E. Paradoxipoma enigmaticum new species. A – B. UF 479320, holotype, 9.4 mm. C. UF 479320, paratype, 8.3 mm. D. UF 479320, paratype, 7.7 mm. E. UF 479322, paratype, 8.4 mm, detail of operculum. FIGURE 8 F – K. Diplopoma osberti (Tristram, 1861). F. Fischer & Crosse, 1890: pl. 42, figs. 13, 13 a, 13 b. G. UF 190089, 11.4 mm. H. UF 190089, 9.8 mm. I. UF 190089, 9.5 mm. J. UF 190061, 10.9 mm. K. GTW 16017 a, 10.1 mm. FIGURE 8 L – W. Diplopoma rigidulum (Morelet, 1851). L. NHMUK 1893.2. 4.705, syntype, ca. 12 mm, photo courtesy J. Ablett (NHMUK). M – N. UF 155790, 8.8 mm. O. GTW 8731 a, 9.7 mm. P. Grego coll., 9.5 mm. Q. GTW 8713 c, 9.5 mm. R. GTW 8731 e, 9.1 mm. S. UF 15813, 6.4 mm. T. GTW 8713 g, 9.4 mm. U. UF 146240, 9.3 mm. V. UF 135055, 8.6 mm. W. UF 207341, 9.6 mm.