Mexistrophia inexpectata Thompson, 2011

Original Description

"Mexistrophia inexpectata new species

Diagnosis: Relatively slender, pupiform shell with nine or more whorls. Sculpture nearly uniform over shell surface, consisting of fine oblique thread-riblets . Peristome narrowly reflected and reinforced internally by thick callus. Spermathecal duct lacking an appendix.

Description: Shell (Figures 11-1.9) pupiform. Cylindrical spire bearing low domed-shaped apex. Shell wall opaque or weakly translucent. Ground color light brown with sparse lighter irregular spots and streaks. White streaks most conspicuous on upper ends of ribs . Peristome and adjacent interior or aperture white . Deeper within inner wall and axis rust-colored . Shell 9.8-12.4 mm long, 3.3-3.5 mm wide, and 0.38- 0.35 times as wide as long, with 9.1-11.0 whorls. Suture weakly impressed. Protoconch with two smooth whorls slightly elevated above following whorls. Following whorls sculptured with numerous oblique thread-riblets nearly equally developed over shell surface. Riblets do not crenulate suture. Umbilicus imperforate or narrowly

rimate. Thick peristome weakly reflected and discontinuous across parietal wall, where it is replaced by thin glaze. Peristome reinforced internally by thick callus. Aperture ovate, slightly higher than wide, 0.24-0.37 times shell length, and 0.69-0.76 times shell width, slightly prosocline , nearly vertical in lateral profile (Figure 18). Axis conspicuously enlarged in apical

whorls, straight in cylindric part of shell, very narrow, becoming narrowly perforate or solid by last two whorls (Figure 19 ). (Measurements based on the holotype and ten paratypes are given in Table 3.)

Anatomy: Reproductive anatomy (Figures 23-35) (Five specimens examined (UF 226408): Genital atrium (atr) moderately long and stocky.  Penis (pen) moderately long and slender, ending in slender, short, blind diverticulum (div).  Penis lined internally with six longitudinal columns, lacks verge or stimulator. Penis retractor muscle (prm) long and slender, originating on inner lung wall and inserting on diverticulum end.  Right ocular retractor muscle (rom) passing mesad to genital system and inserting into right pedal retractor muscle, attached to vagina (vag) by short slips of muscle (Figure 25). Epiphallus (epi) entering the penis (pen) shortly below diverticulum, long, stout, and poorly differentiated from vas deferens (vas). Elliptical spermatheca (sper) resting against side of oviduct-prostate at base of albumen gland. Spermathecal duct (spd) relatively stout and lacking appendix. Duct uniting with free oviduct (fovi) to form short but well developed vagina (vag). Free oviduct short but stocky, about as long as combined length of vagina + genital atrium.

Radula ( figures 29-30 ) (Two specimens examined, UF 226408): Radular ribbon 0.55 mm wide by 1.34 mm long. Radular formula 18-1-18 . Transverse tooth rows horizontal, nearly straight, not curving upward at margins. Eighteen lateral + marginal teeth present. Lateral teeth transition without morphological distinction into marginal teeth. Central tooth as wide as adjacent lateral

teeth, 16 mm wide, trapezoidal, tricuspid. Mesocone acuminate, extending beyond tooth base, bordered on each side by short acuminate ectocone, All seven lateral teeth bicuspid with large acuminate mesocone and smaller acuminate ectocone. Marginal teeth with large lanceolate mesocone and single acuminate ectocone.

Type Locality: A west-facing hillside on a limestone exposure, 0.5 km north of El Refugio, Nuevo Léon, Mexico (23.921°N, 99.719°W), 2360 m alt. The type locality is in a grassy open "piñon" (pine) forest with scattered agave and small oaks. Snails were collected from among and under flags of limestone.

Type Material: Holotype UF 226407; collected 24 July, 1994 by Fred G. Thompson, Elizabeth Mihalcik, Crady Taylor, and Val J. Roessling; Paratypes UF 435014 (85) , CN MO 3371 (10); same data as the holotype;  UF 267253 (33); collected [January, 1996 by Val J. Roessling; all from type locality.

Distribution: Nuevo León State, known only from the type locality.

Etymology: The species name iuexpectatus is from the Latin and alludes to the fact that the reproductive system differs from what I anticipated before dissecting the species.

Remarks: Shell measurements of the three species of Mexistrophia may be compared as in Table 4.  Mexistrophia inexpectata is separated from M. reticulate and M . obsoleta by its slender size and by its larger number of whorls.

Table 3.  Mexistrophia inexpectata new species. Measurements in mm of the holotype  (UF 226407) and 10 paratypes (UF 485014) selected to show variation.  SL = standard length, SW = standard width, ApH = aperture height; ApW = aperture width, Wh = Whorls.

                          SL       SW      ApH    ApW        Wh      SW/SL   ApH/SL   ApW/SW

Holotype         11.4      3.5       3.0       2.4       9.2       0.31        0.26        0.69

Para types

min                  9.8       3.3       2.7       2.3       9.1       0.28        0.24        0.69

max                 12.3     3.6       3.0       2.6      11.0      0.35        0.27        0.76

avg                  11.38   3.42     2.84     2.46     9.71     0.32        0.26        0.72

STD                 0.56     0.10     0.17     0.09     0.51     0.02        0.01         0.02"

(Thompson, 2011:186-188)

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