Parvanachis minibrunnea, 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 : 212-213

Parvanachis minibrunnea n. sp.

( Figures 1 F, 1G, 5C, 5F)

Types. Holotype, Fig. 1 F, (USNM 1231307), Isla Venado, Panama, 30 Jan. 2006, 3.23 mm long. 32 paratypes, USNM 1231308–1231313, see Table 1.

Etymology. Named for being very small and brown.

Taxonomic history. This species has been identified in collections as Parvanachis albonodosa ( Carpenter, 1857) . Carpenter originally described Anachis albonodosa as greenish white, marked with spots and zigzag lines of brown. The species is based on two specimens (syntypes) in the Reigen collection from Mazatlan, where they were found on sessile bivalves: an adult or subadult in the British Museum, and a broken juvenile at the US National Museum (USNM 716233, Fig. 1 E). Both are greenish white with brown lines and lack spiral grooves. Tryon (1883) discusses these briefly. Brann (1966) has a drawing of the British Museum syntype showing the shell pattern (pl. 56, fig. 654). Keen (1958, 1968) noted the shell characteristics, and stated that A. albonodosa has never been figured or recognized since its original description. She figures the British Museum syntype (1968, 1971; Keen’s two photos (1971) are of the same specimen).

In 1971 however, (perhaps after discussions with Radwin, who she credits for help with the columbellid section of the book), Keen amends her original description of A. albonodosa to describe the shell as light brown with a greenish tint, with white tips to the ribs, which brings the description more in line with P. minibrunnea . She kept her original illustration of the British Museum syntype, which is indeed greenish white with dark markings rather than brown with white markings; but detail in the small greyscale photo is difficult to see. Closer examination of the types of Anachis albonodosa Carpenter indicates that Keen was initially correct. Anachis albonodosa is a very different species, and no other name has been found for the small brown shells with a band of white spots. The two syntypes of A. albonodosa bear no resemblance to any species I have seen from the eastern Pacific. They are however very similar to species of Zafra from the Indo-west Pacific, none of which have otherwise been reported to occur in the Eastern Pacific. A. albonodosa appears to be an adventitious species of Zafra . In light of this, I herein provide a new name for the previously misidentified small brown Panamic species.

Diagnosis. Smallest of the Panamic Parvanachis . Shell narrow, red-brown with a narrow, spiral white band slightly below the suture. Animal cream colored with white specks.

Material. Over 40 specimens were collected under near shore rocks in muddy sand at Isla Venado, Bique and Chumical. Four were sectioned and four dissected.

Shell ( Figs. 1 F, G): Smallest species of Parvanachis ; shells of 12 individuals measured 3.05 to 4.05 mm long (avg. 3.30 mm), 1.35 to 1.55 mm wide (avg. 1.43 mm). Adults with 3.25 to 4 teleoconch whorls (avg. 3.58). Protoconch smooth, cream colored at the apex but darker brown toward the teleoconch, 3.25 to 4 whorls (avg. 3.6, n = 10). Axial sculpture dominant overall, with spiral grooves visible between rounded axial ridges. First teleoconch whorl with similarly strong axial and spiral sculpture so is effectively cancellate. Weak subsutural groove cuts across the axial ridges. Shell red-brown, with a narrow, spiral white band just below the subsutural groove. First teleoconch whorl with three darker spiral bands. Aperture edge thickened, with three vague pale bands on the outer edge, and a few denticles internally. Shallow posterior sinus present in the aperture edge. Parietal callus with axial ridge and sometimes weak denticles, anterior edge of the callus detached. Aperture shows color and markings seen on outside of shell.

Body coloration: Body cream colored, with white speckles.

Operculum ( Fig. 5 C): Operculum oval with a terminal nucleus, pale yellow overall. Muscle scar bilobed, keel weak.

Radula ( Fig. 5 F): Lateral teeth of four adult (two male, two female) specimens dissected 18–20 µm long by 7.5 µm wide, with rectangular center plates. Adult female dissected had a radular ribbon with at least 125 tooth rows. Lateral teeth delicate, with three pointed secondary cusps, the bottom one pointed and curved down, and separated from the distal two by a wide gap.

Reproductive anatomy: Female reproductive anatomy similar to that of other Parvanachis species, with a gonopericardial duct but no bursa copulatrix. Gland mass comprises a single unit that stains red anteriorly, pale purple posteriorly. Capsule gland lumen flat but thick, ciliated. Gonopericardial duct coiled, relatively short and of small diameter close to gland mass, widens closer to pericardium, no obvious glandular portion to the duct. Pericardium in the specimens examined full of sperm, reddish droplets and other pale staining material, wall thick. Anterior end of the gland mass and vestibule with an egg capsule in the vestibule in both females sectioned so details of the form and epithelium could not be ascertained; vestibule short and not muscular.

Male reproductive system similar to that of P. dichroma , having a long spermiduct loop adjacent to the proboscis and a simple penis with a short filament tip (as in Fig. 2 B). Coiled seminal vesicle with primarily dark purple staining sperm, no secondary vesicle. Part of the body wall spermiduct adjacent to the pallial duct very thick, coiled, muscular. Spermiduct loop in body cavity with a tall, pale purple staining mucoidal epithelium and lots of mucoid secretions in the duct. Penial spermiduct straight, wide, nonsecretory, no obvious subepithelial secretory tissues. Penis in sectioned specimens curled back in the mantle cavity, without a pouch.

The following four species ( P. pygmaea , P. mullineri , P. adamsi n. sp. and P. nigricans n. comb.) are discussed together because they are difficult to tell apart, and all have a unique penis morphology not present in the previous species. They are also generally larger. These four species may comprise a monophyletic group, but not all regional species of Parvanachis have been investigated, so I am reluctant to suggest a new genus level group until a more global and more inclusive analysis can be undertaken.

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 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.