Parvanachis mullineri ( Poorman, 1983 )

Maintenon, Marta J., 2014, Taxonomic revision of the species of Parvanachis Radwin, 1968 (Gastropoda: Columbellidae) from the Gulf of Panama, Zootaxa 3753 (3), pp. 201-225 : 217

Parvanachis mullineri ( Poorman, 1983)

Figures 6 E–H, 7B, 7F

Anachis (Parvanachis) mullineri Poorman, 1983 : pp. 8–9, figs. 4, 7.

Types. Holotype, SDMNH 81612, from Bahia de Santiago, Colima, Mexico.

Taxonomic history. This species has been mostly unrecognized since its relatively recent description. The specimens from Panama do not match it perfectly, but given the phenotypic variation in columbellids and the different localities, it seems likely that they are the same thing. The illustrated holotype appears very similar to the Panama specimen in Fig. 6 E. Poorman emphasizes the distinction of this species based on the varicose outer lip, pronounced anal sulcus and lamellose edge of the columellar callus. The latter two features are not particularly unusual in columbellids, but the varicose outer aperture edge is unusual, though it appears not to be present in all specimens.

Diagnosis. Small (4 to 6 mm long) species with a biconic, axially ribbed shell, often with an unusually thick outer lip. Shell straw colored with a band of alternating white and dark blotches immediately below the suture and a wide unmarked band at the periphery. A second band of dark axial markings is present below the periphery.

Material. A total of nine specimens were collected at Isla Venado and Punta Calafate, including five adults. In the Smithsonian’s dry collection, a few lots of these were found from locations ranging from southern Baja California to Ecuador. Because there were relatively few specimens and variation in the shell is important, these were not sectioned and the two specimens dissected were broken rather than dissolving the shell.

Shell ( Figs. 6 E–H): Shell biconic, 4.1 to 5.3 mm long (avg. 4.90 mm) and 1.8 to 2.5 mm wide (avg. 2.27 mm) in five adult specimens measured. Adult shells have 3.75 to 4.25 teleoconch whorls (avg. 4.15). Protoconch smooth, off white, with 3.5 to 3.75 (avg. 3.55 in six specimens) whorls and a narrow sinus. Shell sculptured primarily with axial ridges (15 to 19 on the body whorl), and spiral grooves between axial ridges on the spire whorls. Shells similar to P. pygmaea but differing slightly in pattern. Shell base color straw, with a wide band below the suture consisting of occasional white spots overlain on a dark band or blotches. The body whorl has a band of axially elongated dark blotches below the periphery and usually a separate row of spots on the base. The anterior tip of the shell is white, often with a spiral band of small dark markings. Aperture edge thickened, varicose in some specimens, with a few denticles internally and a couple large dark blobs on the dorsal aperture edge. Aperture edge with a shallow posterior sinus. Parietal callus with a weakly denticulate ridge. Aperture color reflects that of the shell exterior.

Body coloration: Same as P. pygmaea .

Operculum ( Fig. 7 B): Operculum oblong, with a keel and a bilobed muscle scar and a terminal nucleus.

Radula ( Fig. 7 F): Radula similar to that of P. pygmaea . Lateral teeth about 38 µm long in two subadults dissected, with three pointed secondary cusps; the basal cusp is pointed down and embedded in radular membranes. Center plates are rectangular, 30 –35 µm wide by 7.5 µm deep. The subadults dissected had 131 and 139 tooth rows.

Remarks. This species is very similar to Parvanachis pygmaea and was found in the same locations, though it was much less common. The shell is slightly smaller and stouter, with about one fewer teleoconch whorl and onehalf more protoconch whorls. Though there is overlap, these differences are both statistically significant; T = 3.70, P = 0.001, DF = 23 for the mean number of teleoconch whorls and T = 4.00, P = 0.002, DF = 12 for the mean number of protoconch whorls. P. mullineri also has less erosion at the apices, whereas the apex of P. pygmaea from the same locality typically is eroded; this may indicate a slight difference in habitat or shell chemistry. The color pattern in the Panama specimens of P. mullineri has the subsutural bands of white and dark markings mixed, with a wide unmarked spiral band below that, and typically two rows of markings below the periphery. P. pygmaea tends to have the two bands of markings mostly if not completely separated (dark anterior and white posterior), with a narrower unmarked band below. The labial edge in this species also tends to be thicker than in P. pygmaea , to the point of being varicose in some specimens, with large dark blotches on the dorsal aperture edge.

Figures

FIGURE 6. Parvanachis shells. All are preserved specimens, so some dark areas on the body whorls of the shells are the coloring of the preserved animal visible through the shell. Scale bar = 1 mm. A – D. Parvanachis pygmaea, USNM 1231314, Playa Rio Mar. E – H. Parvanachis mullineri. E – G. USNM 1231315, Isla Venado. H. USNM 1231316, Punta Calafate.

FIGURE 7. Parvanachis operculae and radulae. Scale bars: A – D, 200 µm; E – H, 20 µm. A – D. Operculae. A. P. pygmaea. B. P. mullineri. C. P. adamsi. D. P. nigricans. E – H. Radulae. E. P. pygmaea, 40 X. F. P. mullineri, 40 X. G. P. adamsi, 20 X. H. P. nigricans, 20 X.