Parvanachis adamsi, Maintenon, Marta J., 2014

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 : 218-220

Parvanachis adamsi n. sp.

Figures 7 C, 7G, 8A–D

Types. Holotype, Fig. 8 A, (USNM 1231317), Chumical, Panama, 29 Jan. 2006, 5.93 mm long. 227 paratypes, USNM 1231318–1231323; see Table 1.

Etymology. This species is named for Charles Baker Adams, who did extensive work on the Panamic fauna.

Taxonomic history. C.B. Adams (1852) discusses under Columbella nigricans large typical specimens, and a number of smaller atypical specimens with a wide variation in color, that are almost certainly this species. Similarly, as mentioned above, Carpenter (1857) describes P. pygmaea as being quite variable in shell coloration with many essentially dark overall, which likely indicates that he had this new species mixed in with it. In 1864, he reported his previous findings of Anachis pygmaea in the Mazatlan collection, and Adams’ specimens of Columbella pygmaea , as being Anachis pygmaea var. auriflua , which he apparently intended to describe in the Annals and Magazine of Natural History; but this never occurred and no types were designated, thus that name is a nomen nudum and there is no way to be certain what he intended to use the name for. P. adamsi and P. nigricans especially are difficult to initially sort out without access to a large number of specimens.

Diagnosis. Biconic axially ridged species 4 to 7 mm long, with variable coloration consisting of a straw to dark brown base color, usually with oblique dark markings and a white subsutural band. Axial ridges large, less dense than other species, with 14 to 16 on the penultimate whorl.

Material. About 200 specimens were collected, in the middle to high intertidal zone, on the sides of rocks. The large numbers were collected due mostly to the species' high degree of variability. Two adult specimens were sectioned, and three dissected.

Shell ( Figs. 8 A–D): Shell biconic, 4.15 to 6.85 mm long (avg. 5.78 mm) and 1.93 to 2.95 mm wide (avg. 2.59 mm) in 24 adult specimens measured. Adults have 4 to 6 teleoconch whorls (avg. 4.9). Primary sculpture of heavy, well separated axial ridges with underlying spiral grooves best developed on the first spire whorl, mostly lacking on the anterior whorls. Protoconch off white, with 3 to 3.5 (avg. 3.25 in 11 specimens) whorls. Shell color and pattern varies; pale beige or yellowish to tan, usually with oblique brown or black lines, spots or blotches, and often a white spiral band below the suture (but note the specimen in Fig. 8 D is almost entirely without markings). Anterior tip of siphonal canal pale. Aperture similar in color to exterior, with labial denticles anterior to the posterior canal, weakly denticulate parietal ridge.

Body coloration: Body cream colored with diffuse black mottling and white dots, and black spots on sole of foot. Siphon cream colored with black bands at the middle and tip, cephalic tentacles have medial and basal black bands

Operculum ( Fig. 7 C): Operculum ovoid, nucleus terminal. Keeled, bilobed muscle scar. Pigmentation slightly darker near keel.

Radula ( Fig. 7 G): Radula narrow, with 124 to 130 tooth rows in three adults dissected. Lateral teeth 38 µm long in both by 18 µm across the basal cusp on all three. Center plates rectangular, 33 µm wide and 13 µm deep in one specimen. Lateral teeth with three secondary cusps, gap between basal cusps slightly wider than that between distal cusps. Basal cusp broadly triangular, comes to a strong hooked point.

Reproductive anatomy: Male reproductive system similar to that of P. nigricans . The coiled seminal vesicle ( Fig. 4 A) contains pink-staining atypical sperm cells that are mixed with dark purple staining sperm cells, and the epithelium is flat overall. A wide, densely ciliated duct to the mantle cavity is present at the back of the anterior body cavity. The spermiduct anterior to the pallial duct enters the body wall and narrows, and the portion that runs along the body wall has a thick muscle coat and a low, nonsecretory epithelium. The anterior spermiduct makes a long loop in the body cavity adjacent to the proboscis. The spermiduct in the loop has a tall, pale purple-staining mucoidal epithelium with terminal nuclei. The spermiduct at the penis base is non-secretory, but toward the tip the duct becomes wide with subepithelial mucoid cells. The penis is wide at the base, the duct sinuous (as in Fig. 2 D). A flap of tissue projects from the side of the penis near the middle; internally this has no obvious differentiation from the rest of the penis wall, but the duct straightens after that point. The penis tip is filament-like. The distal portion of the penis at rest is stored in a penial pouch.

Female system typical for Parvanachis , with a gonopericardial duct, and no bursa copulatrix. Gland mass stains red overall, with a purple staining band through the middle closer to the posterior end. The gland lumen is pouched. Anterior end of gland mass with a short (almost nonexistent) flat-walled vestibule. Gonopericardial duct coiled, with ciliated cuboidal epithelium near gland mass. Closer to the pericardium duct becomes thicker walled and slightly folded. Reproductive system in female sectioned contained no sperm, however pericardium was full of cellular material and secretions.

Remarks. This species is very similar to both P. nigricans and to P. pygmaea and P. mullineri . Color and pattern can be similar in all four, but this species has the oblique shell color elements seen in P. nigricans . P. nigricans is larger and has coarser sculpture; it has denser axial ridges (16 to 19 on the penultimate whorl), better developed spiral grooves over most of the shell, and a more strongly developed subsutural groove, but weaker parietal denticles. Parvanachis pygmaea is also similar and roughly the same size, but with a more stereotypic color pattern lacking oblique elements, and having more axial ridges on the penultimate whorl (15 to 18 rather than the 14 to 16 in this species), and a better developed subsutural spiral groove. P. pygmaea , P mullineri and P. adamsi tend to have lighter shells with dark markings, while P. nigricans tends to have a colored shell with pale markings. This species also has the long filament tip on the penis tip seen in P. nigricans , but lacking in P. pygmaea .

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.