Parvanachis dichroma, 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 : 211-212

Parvanachis dichroma n. sp.

( Figures 1 C, D, 5B, 5E)

Types. Holotype, Fig. 1 C, (USNM 1231302), Chumical, Panama, 29 Jan. 2006, 4.43 mm long. 59 paratypes, USNM 1231303–1231306, see Table 1.

Etymology. named to note the strong contrast between the white shell and its brown markings.

Diagnosis. Small species with a biconic axially ribbed shell, bright white with two spiral rows of chestnut markings and a reddish-chestnut anterior tip.

Material. This species was found intertidally on and under rocks in a habitat with fine, pale muddy sand. About 60 were collected; they occurred more densely than similar species where they were found and tended not to be mixed with other small columbellid species. Three adults were sectioned (one male, two females with one female cross sectioned, one longitudinally sectioned), three males dissected.

Shell ( Figs. 1 C, D): Shell small, biconic, 4.1 to 5.1 mm long (avg. 4.50 mm) and 2.00 to 2.20 mm wide (avg. 2.05 mm) in 15 specimens measured. Adult shells with 4 to 5 teleoconch whorls (avg. 4.3). Protoconch smooth, white, with 3 to 3.25 whorls and no real sinus. Predominant sculpture consists of rounded, slightly sinuous axial ridges (16 to 19 on the body whorl), with spiral grooves between ridges on the spire whorls and often on the body whorl. A weak subsutural groove cuts across the tops of the axial ridges. Shell translucent, white. Spire whorls have a single band of wavy axial chestnut makings in the middle of the whorl, with an additional row present on the basal half of the body whorl. These form two large blobs on the outer lip. Tip of siphonal canal in adults dark purplish brown. Aperture white. Aperture edge thickened, denticulate, with a shallow posterior notch. Parietal wall with a ridge of denticles.

Body coloration: Anterior part of body cream colored except for white specks overall. Behind the mantle edge, preserved specimens are black, which can easily be seen through the shell; this may be an artifact of preservation.

Operculum ( Fig. 5 B): Operculum ovoid, with bilobed scar, no keel. Nucleus terminal, with a darker spot in the middle.

Radula ( Fig. 5 E): In four adult male specimens dissected, lateral teeth 28 to 34 µm long by 12 to 15 µm wide, with rectangular center plates. Two radulae that were complete had 137 and 155 tooth rows. Lateral teeth have three pointed secondary cusps, the bottom one pointed and curved down, and separated from the distal two by a wide gap.

Reproductive anatomy: Male reproductive anatomy typical for the genus. Primary seminal vesicle coiled, contains both pink staining and typical dark staining sperm, with a low epithelium overall. Spermiduct gives off short mantle cavity duct adjacent to the kidney. Anterior spermiduct embedded in the body wall has a thin coat of circular muscle. Anterior spermiduct enters hemocoel near penis base and forms a long loop adjacent to the proboscis. The loop has a complex pale purple-staining mucoid epithelium that continues into the penis base, after which the duct becomes non-secretory. Penis tip densely supplied with subepithelial mucus cells. Penis long and very narrow, with a short filament tip (as in Fig. 2 B). It rests in the mantle cavity.

Female reproductive anatomy typical for the genus, with a short glandular complex having an eosinophilic anterior portion and a pale purple-staining posterior portion ( Fig. 3 A). Gland mass similar in dimensions from anterior to posterior. To the posterior right of the gland mass is a thick walled, coiled gonopericardial duct, part of which may function in sperm storage or absorption. Reproductive system has no bursa; vestibule short, with a simple, non-muscular wall.

Remarks. This species closely resembles Parvanachis oxillia (Duclos in Chenu, 1846) in terms of the size and color pattern. The identity of the latter has been difficult to determine, because the Chenu publication contains only figures, and localities are not given for most species. The syntype lot of Columbella oxillia , MNHN 6414, is labeled with a locality of Panama, but it does not specify whether the material came from the Pacific or the Caribbean. A photograph of one of the syntypes (http://coldb.mnhn.fr/CatalogNumber/MNHN/IM/6414) suggests that P. oxillia has a narrower form and somewhat more acute spire, with a more varicose lip and a relatively large posterior labial denticle. In this it more closely resembles P. obesa (see Fig. 1 A) than it does the current species, and Rosenberg (2009) lists it as a synonym of the Caribbean P. obesa .

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 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 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.