Parvanachis nigricans ( Sowerby, 1844a )

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 : 220-221

Parvanachis nigricans ( Sowerby, 1844a) new comb.

Figures 7 D, 7H, 8E–H

Columbella nigricans Sowerby I, 1844a : p. 143, pl. 40 fig. 172. Duclos in Chenu, 1848: pl. 21 figs. 7-8. Adams, C.B., 1852: pp. 95-96. Reeve, 1858: sp. 137, pl. 23, fig. 137.

Mitrella (Astyris) nigricans Sowerby, 1844 . Mörch, 1860: p. 94 (not figured).

Anachis nigricans (Sowerby, 1844) . Carpenter, 1863: p. 345. Strong & Hertlein, 1939: p. 184, not figured. Keen, 1958: p. 383, sp. 444 (illustration from Reeve, 1858). Abbott, 1974: p. 197, sp. 2067 (not figured).

Columbella (Seminella) nigricans (Sowerby) . Tryon, 1883: p. 168, pl. 57, fig. 2

Columbella (Seminella) nigricans Sowerby. Kobelt, 1897 : p. 137, taf. 20, figs. 5, 6.

Anachis (Costoanachis) nigricans (Sowerby, 1844) . Keen, 1971: p. 581, sp. 1186.

Costoanachis nigricans (Sowerby, 1844) . Skoglund, 1992: p. 88.

Types. Five syntypes, NHMUK 1966396, collected by Cuming in the Galapagos. Sowerby’s figure is not good enough to match to a specimen. Keen (1971) figures the syntypes along with Reeve’s illustration, however the photo quality is not good enough for specimen identification. Photos of the syntypes from K. Monsecour and the British Museum were used to help identify the species.

Taxonomic history. Sowerby described this species from the Galapagos, as blackish with a whitish suture and pale aperture edge; Reeve (1858) echoes this. Adams (1852) recognized the extensive variation in color and pattern found in Panama shells, but insomuch as he reported having 120 mostly dark colored large specimens and 500 small ones with more variable coloration, he undoubtedly had both this and P. adamsi described above. Tryon (1883) described it as dark, but allowed for a lighter band on the body whorl. Keen (1971) also follows Sowerby’s lead in describing the species as dark brown to blackish.

Diagnosis. Medium sized biconic axially ridged species 7 to 9 mm long, with variable coloration consisting of a tan to dark purple-brown base color, with oblique lighter markings and occasionally a white subsutural band. Sculpture denser and more strongly developed than other species.

Material. This species was found intertidally on the sides of rocks, more commonly on offshore islands. USNM has material from Baja California to Panama. About 70 specimens were collected from five localities. Two adults were sectioned and three were dissected.

Shell ( Figs. 8 E–H): Shell medium-sized, biconic, 6.80 to 8.80 mm long (avg. 7.63 mm) and 2.65 to 3.80 mm wide (avg. 3.09 mm) in 19 specimens measured. Some adults from Isla San Pedro Gonzalez were smaller. Adults have 5.5 to 6.5 (avg. 5.8) teleoconch whorls. Protoconch similar in color to teleoconch but generally paler, with 3 to 3.5 (avg. 3.2 in 16 specimens) whorls. Primary sculpture of dense axial ridges (16 to 19 on the penultimate whorl) with spiral grooves between axial ridges and a well-developed subsutural groove. Shell coloration variable, tan or grayish to dark purple-brown, with oblique paler markings. Some with a spiral subsutural white band and/ or a spiral band of whitish blotches below periphery. Aperture reflects outer color, with labial denticles anterior to the posterior notch. Parietal ridge with denticles located over the spirals underneath.

Body coloration: Body and foot cream colored, with black mottling and white dots overall. Head dark, cephalic tentacles pale, with black bands at middle. Siphon with a black ring near tip and black specks closer to body. Body under shell mostly pale, with a dark mantle edge.

Operculum ( Fig. 7 D): Operculum oblong oval, with terminal nucleus, keel and bilobed scar. Pigmentation similar overall.

Radula: Radula ( Fig. 7 H) narrow, with lateral teeth about 50 µm long. Center plates only slightly wider than deep. Each lateral tooth with three evenly spaced secondary cusps. Basal cusp pointed but embedded in membranes. Radulae in two male specimens had 148 and 153 tooth rows.

Reproductive anatomy: Male anatomy similar to that of P. adamsi . Seminal vesicle with a low epithelium, contains both pink and purple staining sperm ( Fig. 4 B). Wide, densely ciliated mantle cavity duct present at back of body cavity. Spermiduct narrows on entering the body wall; body wall spermiduct with a thick muscle coat and low, non-secretory epithelium. Anterior spermiduct with a single long loop in the body cavity adjacent to the proboscis. Anterior spermiduct loop with secretory reddish and pale purple-staining complex columnar epithelium ( Fig. 4 D). Penis long and narrow ( Fig. 2 D), with a tissue flap at the base ( Fig. 4 G) consisting of connective tissue and mucus cells, similar to the rest of the penis wall. Spermiduct in penis base sinuous, with a low, nonsecretory epithelium ( Fig. 4 F). Spermiduct in middle region of penis wide and thickly muscular, with mixed complex columnar and mucoidal secretory cells ( Fig. 4 F). Distal third of penis narrows ( Fig. 4 F) to very long filament tip, duct with non-secretory epithelium. Penis at rest curled into back of mantle cavity, lacking a penial pouch.

Females with a gonopericardial duct but no bursa copulatrix. Gland mass stains red overall, with a purple staining band through middle toward the posterior end. Anterior end around lumen stains more purplish-red. Gland lumen pouched. Vestibule short, not muscular, with a smooth wall. Gonopericardial duct long and coiled, with a low epithelium close to the gland mass. Pericardial end of duct increases in diameter and becomes thicker walled and slightly folded; this portion may act in sperm digestion, however no sperm was present in the system of the female sectioned.

Remarks. This species is similar to both P. adamsi and P. pygmaea ¸ but is larger and more strongly sculptured than both. It has traditionally been counted as a species of Costoanachis perhaps because it is slightly larger than other species of Parvanachis included here, but its shell characteristics, anatomy and radular morphology are more similar to the Parvanachis species herein than to any Anachis or Costoanachis species investigated.

The following species has traditionally been considered a Parvanachis , but its anatomy is quite different, and more consistent with species of Anachis , as described above.

Figures

FIGURE 2. Gonoducts of Panamic Parvanachis species. A. Generalized oviduct of Parvanachis. B. Generalized spermiduct of Parvanachis. C. Pallial spermiduct of Parvanachis pygmaea. D. Pallial spermiduct of P. nigricans.

FIGURE 4. Histological sections from the male reproductive tract of Parvanachis. Scale bar = 200 µm. A. Cross section of upper body of P. adamsi showing gonad and seminal vesicle. B. Cross section of upper body of P. nigricans showing the seminal vesicle. C. Cross section through pallial spermiduct loop of P. pygmaea. D. Cross section of mid body of P. nigricans showing the spermiduct loop. E. Semi-longitudinal section of mid-penis of P. pygmaea. F. Semi-longitudinal section through penis of P. pygmaea showing transition from the wide central portion with glandular duct to the filament tip. G. Cross section of body of P. nigricans with a portion of the body wall spermiduct and a partial longitudinal section through the penis showing the basal flap at the upper middle. H. Cross section through the body of P. nigricans with a partial longitudinal section of the penis, showing the transition from the wider glandular portion to the non-secretory filament tip.

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.

FIGURE 8. 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 adamsi, n. sp. A. Holotype, USNM 1231317, Chumical. B – C. Paratypes, USNM 1231319, Chumical. D. Paratype, USNM 1231318, Punta Calafate. E – H. Parvanachis nigricans. E – F. USNM 1231328, Isla Taboga. G – H. USNM 1231329, Isla San Pedro Gonzales, Islas Perlas.