Omalogyra liliputia ( Laseron, 1954 )

Sartori, André F. & Bieler, Rüdiger, 2014, Three new species of Ammonicera from the Eastern Pacific coast of North America, with redescriptions and comments on other species of Omalogyridae (Gastropoda, Heterobranchia), Zootaxa 3872 (1), pp. 1-21 : 13

Omalogyra liliputia ( Laseron, 1954)

Figures 1 , 7

Helisalia liliputia Laseron, 1954, pp. 16–17 , figs 45,45a.

Omalogyra liliputia ( Laseron, 1954) — Ponder & de Keyzer, 1998, p. 864, fig. 15.185 B, D.

Examined material (10 specimens). LACM 79-58 , 9 specimens (5 SEM, 1 previously light-photographed), rocky substrate, Long Reef , Sydney, New South Wales, Australia, 33°44.5’S, 151°19.2’E, intertidal; leg. James H. McLean, 13 May 1979 ; FMNH 339463 , 1 specimen, same collection data as LACM 79-58 .

Type locality. Castle Rock, Middle Harbour, Port Jackson , New South Wales

Diagnosis. Omalogyra of uniform coloration, sculptured by faint axial ribs and fine growth lines; inner lip concave, aperture sub-crescent; shell diameter c. 0.6 mm at 2 1/2 whorls.

Description. Shell planispiral, tightly coiled. Shell wall very thin, pellucid, glossy, amber in coloration. Protoconch of c. 1.2 whorls, much lighter than the teleoconch in coloration, sculptured only by microscopic, irregular nodules on the nuclear shell, gradually fading out toward the boundary with the teleoconch. Protoconch 2 poorly marked or absent; boundary between protoconch and teleoconch very well marked. Teleoconch of c. 1.2 whorls, sculptured by faint, irregularly spaced axial ribs, and by fine growth lines; shell devoid of spiral ornamentation. Apical and umbilical sutures deeply impressed; outer lip uniformly rounded; inner lip concave, flaring slightly. Aperture sub-crescent.

Shell dimensions (in mm) and whorl counts:

Remarks. This is the type species of the genus Helisalia Laseron, 1954 , by original designation. The original description and illustrations by Laseron (1954), who tentatively assigned Helisalia to the family Liotiidae , were based on light microscopy alone and are insufficiently detailed. Marshall (1988) regarded Helisalia liliputia as possibly belonging to Orbitestellidae Iredale, 1917 , whereas Healy (1993) and Ponder & de Keyzer (1998) relocated this species to Omalogyra . Healy (1993) described the sperm ultrastructure of O. liliputia , noting that it shares with O. atomus Philippi, 1841 a glycogen helix and paracrystalline material in the midpiece. Ponder & de Keyzer (1998) published the first SEM image of the shell of O. liliputia in apical view, as well as a diagram of the live animal. Here, we provide a re-description based on SEM micrographs of shells collected c. 10 km north of the type locality.

O. liliputia shares a morphologically simple shell, devoid of pronounced sculpture, with several other Omalogyra species , namely O. antarctica Egorova, 1991 , O. atomus , O. disculus Palazzi, 1988 , O. fuscopardalis Rolán, 1992b , O. simplex (O. G. Costa, 1861) and O. zebrina Rolán, 1992b .

The uniform coloration of the teleoconch of O. liliputia immediately separates this species from the Atlantic O. zebrina , O. fuscopardalis and Atlantic/Mediterranean O. simplex , all of which display coloration patterns on their teleoconch. O. liliputia differs from Atlantic O. disculus in having a higher, less discoidal shell (compare Figure 7G herein with fig. 3 in Rolán, 1992a [reproduced by Rolán, 2005, fig. 842]) and from the northern hemisphere O. atomus in displaying a larger degree of overlap of the body whorl over the previous whorl, which results in a more curved inner lip and less rounded aperture (compare Figure 7G herein with illustrations of O. atomus in apertural view by Palazzi, 1988, fig. 26, Gaglini, 1993, p. 928-04 and Gofas, 2011, p. 357).

The circum-antarctic O. antarctica is the only southern hemisphere species of Omalogyra that resembles O. liliputia . However, they differ in a number of aspects ( Egorova, 1991; Engl, 2012): (1) O. antarctica reaches 1.4 mm in diameter and is much larger than O. liliputia at the same whorl count; (2) O. antarctica has a proportionally lower aperture, with an outer lip that is flattened apically and basally, whereas in O. liliputia the outer lip is uniformly rounded; and (3) O. antarctica is ornamented only by growth lines, whereas O. liliputia has weak axial ribs.

Figures

FIGURE 1. Apical views of the shell (A) and protoconch (B) of Omalogyra liliputia (Laseron, 1954) (specimen 1), showing the placement of measurements used in this study. Abbreviations: pd, maximum diameter of the protoconch; sd1, maximum diameter of the shell; sd2, maximum diameter of the shell perpendicular to sd1. Scale bars: A = 0.2 mm; B = 0.1 mm.

FIGURE 7. Omalogyra liliputia (Laseron, 1954) A–C. Specimen 1, apical views; A. General view; B. Detail of the protoconch; C. Coloration; D–E. Specimen 2, umbilical views; D. General view; E. Detail of the protoconch (interpreted boundaries P1/P2 and P2/teleoconch at white and black arrowheads, respectively); F. Specimen 3, dorsal view; G. Specimen 4, apertural view. Scale bars: A, C, D, F, G = 0.2 mm; B, E = 0.1 mm.