Parvanachis diminuta (C.B Adams, 1852 )

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 : 209-211

Parvanachis diminuta (C.B Adams, 1852)

Figures 1 B, 5A, 5D

Columbella diminuta C.B. Adams, 1852 : p. 85, not figured. Reeve, 1858: sp. 115, pl. 20 fig. 115. Turner, 1956: p. 45, pl. 7 fig. 2.

Mitrella (Astyris) diminuta Adams. Mörch, 1860 : p. 94.

Anachis rufotincta Carpenter, 1857 : pp. 511–512, not figured.

Anachis diminuta . Carpenter (1863): p. 344, not figured. Strong & Hertlein, 1939: p. 184, not figured. Keen, 1958: p. 381, sp. 429 (illustration from Turner, 1956).

Columbella (Seminella) diminuta (C.B. Adams) . Tryon (1883): p. 177, pl. 58 fig. 44.

Columbella (Anachis) diminuta C.B. Adams. Kobelt, 1897 : p. 163, taf. 22, figs. 13, 14.

Anachis (Parvanachis) diminuta ( C.B. Adams, 1852) . Keen, 1971: p. 584, sp. 1204 (illustration from Turner, 1956). Abbott, 1974: p. 197, sp. 2064 (not figured).

Parvanachis diminuta ( C.B. Adams, 1852) . Skoglund, 1992: p. 89.

Types. Lectotype, MCZ 186401, from Panama. A photo of the type was available from W. Thorsson to confirm ID.

Taxonomic history. Charles Baker Adams did not illustrate this species when he described it; Reeve illustrated it in 1858. In both cases its shell was described as pale, with a dark base, which is characteristic of this species, and its identity has not been in question. Carpenter (1863) considered it a species of Anachis (which he allied with Pisania based on the operculum) while Tryon (1883) placed it in Columbella (Seminella) and based his illustration on that of Reeve. Anachis rufotincta (with a more reddish anterior end) was named by Carpenter (1857) from Mazatlan, and as reported by Tryon (1883) and later authors, is a synonym.

Diagnosis. Small species with a biconic axially ribbed shell, mottled pale tan with a narrow white spiral below the suture and a dark reddish or purple-brown anterior tip.

Material. Over 100 specimens of this species were collected on the bottoms of rocks in muddy sand. Two were sectioned, two dissected. USNM has dry specimens from Baja California Sur to Panama.

Shell ( Fig. 1 B): Shell small, biconic, 3.5 to 4.3 mm long (avg. 3.84 mm) and 1.55 to 1.95 mm wide (avg. 1.70 mm) in 12 specimens measured. Adult shells with 4 to 4.25 teleoconch whorls (avg. 4.00). Protoconch smooth, off white, 3.25 to 3.5 whorls (avg. 3.14). Dominant sculpture of axial ridges, except on first two teleoconch whorls where strong spiral ridges make the sculpture cancellate. One weak subsutural groove cuts across tops of axial ridges. Shell off-white with vague chestnut blotches that give an overall mottled tan affect, a dark purplish brown base and usually a narrow white band slightly below the suture. Aperture edge thickened, with a few denticles internally. Shallow posterior sinus present in aperture edge. Parietal wall denticulate, anterior edge of callus detached. Aperture white, with purple flush on anterior columellar wall.

Body coloration. Body cream colored with white specks overall.

Operculum ( Fig. 5 A, tip broken): Operculum ovoid with a terminal nucleus, darker centrally, muscle scar bilobed, no keel.

Radula ( Fig. 5 D): One radula obtained whole had 123 tooth rows. Lateral teeth in adult specimens dissected 18 to 20 µm long, 7 µm wide. Lateral teeth with three pointed secondary cusps, the basal cusp pointed and curved toward the membrane, and separated from the distal two by a wide gap.

Reproductive anatomy: Male system typical for Parvanachis . Ciliated duct to mantle cavity present anterior to coiled seminal vesicle. Anterior spermiduct ciliated, moderately muscular, passes forward embedded in body wall from mantle cavity duct to penis base. Long spermiduct loop in hemocoel leaves body wall near penis base and runs back alongside proboscis, then doubles back and enters penis. Spermiduct of internal loop wide, with clustery mucoidal epithelium that continues along most of the length of the penis except for a non-secretory region at the base. Penis tip with subepithelial mucus glands in addition to secretory epithelium. Penis long, relatively thick, simple with a short filament tip. Penis curled back in the posterior mantle cavity at rest.

Female system typical for Parvanachis , including a single gland mass, with muscular gonopericardial duct and no bursa copulatrix. Gland mass stains red (eosinophilic) in the middle, and pale purple (with haematoxylin) on both ends. The female sectioned had an egg capsule in the vestibule, which was otherwise short and thin-walled. Gonopericardial duct wide and coiled, epithelium cuboidal with large basal nuclei; duct has a wide, very thickwalled medial region ( Figs. 3 F, G) with a large mass of red-stained material on one side ( Fig. 3 G), which might be partially dissolved sperm. The epithelium in that region is different than the rest, and the epithelial characteristics are not readily discernible, but the tissue appears to be secretory. Gonopericardial-pallial duct (gpp) splits off in this same region ( Fig. 3 F). Pericardium in the specimen sectioned with a large amount of unoriented sperm.

Figures

FIGURE 1. Parvanachis shells. B – D and F – G are preserved specimens, so 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. Parvanachis obesa, SBMNH 56943. B. Parvanachis diminuta, USNM 1231301, Isla Venado. C. Parvanachis dichroma, holotype, USNM 1231302, Chumical. D. Parvanachis dichroma, paratype, USNM 1231303, Chumical. E. Anachis albonodosa, paratype, USNM 716233, Mazatlan. F. Parvanachis minibrunnea, holotype, USNM 1231307, Isla Venado. G. Parvanachis minibrunnea, paratype, USNM 1231308, Isla Venado.

FIGURE 3. Histological sections from the female reproductive tract of Parvanachis. Scale bars: A – E, 200 µm; F – G, 100 µm. A. Longitudinal section of female gland mass of P. di c hrom a. B. Pericardium of P. pygmaea. C, D, E. Serial cross sections of P. pygmaea showing oviducal glands and gonopericardial duct. F, G. Serial sections of gonopericardial duct of P. diminuta.

FIGURE 5. Parvanachis operculae and radulae. Scale bars: A – C, 200 µm; D – F, 10 µm. A – C. Operculae. A. P. diminuta, 60 X. B. P. dichroma, 60 X. C. P. minibrunnea, 60 X. D – F. radulae. D. P. diminuta, 400 X. E. P. dichroma, 400 X. F. P. minibrunnea.