Bullacta exarata ( Philippi, 1849 )

details, Publication, authors, including instructions for, information, subscription, http, www. tandfonline. com, loi & tnah 20, 2010, Systematics, phylogeny, and natural history of Bullacta exarata (Philippi, 1849): an endemic cephalaspidean gastropod from the China Sea, Journal of Natural History 44 (33 - 34), pp. 2015-2029 : 2017-2021

Bullacta exarata ( Philippi, 1849)

Bullaea exarata Philippi, 1849, p 141 ( China Borealis ; types untraceable, probably lost; neotype here designated: MNHN 4494 , Paris, H = 14 mm).

Bullacta exarata Thiele 1926, p 106 ; 1931, p 386; Tchang 1934, p 3, pls 1–7; Habe 1952, p 143; Guangyu 1997, p 109, text figures 8, 18–20, pl 10, Figure 6 ; Burn and Thompson 1998, p 955, Figure 16.34; Higo et al. 1999; Guangyu 2004, p 146, pl 83, Figure P.

Haminea exarata Kobelt 1896, p 107 , pl 15, Figure 18; Menke 1854, p 46; Pilsbry 1895, p 362, pl 40, Figure 97.

Atyscaphander exarata Annandale 1924, p 34 , Figures 4 , 5 .

Bullaea caurina Benson, 1856, p 128 .

Philine caurina Pilsbry 1895, p 9 . Bullacta caurina Bergh 1901, p 293 , pl 22, Figures 31–39, pl 23, Figures 1–8 ; Pruvot-Fol 1953, p 8, 25, 97.

Haminea sinensis A. Adams, 1850, p 582 , pl 104, Figure 98; Sowerby 1868, sp. 21, pl 4.

Sinohaminea tsangkouensis Tchang, 1933, p 371 .

Diagnosis. Shell external: H in adults between 14 and 19 mm; shape ovo-philinoid, with spiral striae throughout, fragile, whitish, translucent. Aperture slightly longer than H. Cephalic shield with quadrangular shape; parapodial lobes short, not covering the shell laterally. Male copulatory system opening laterally on right side of mouth; bipartite; both parts connected at the atrium: one containing accessory glands and other the penis and prostate; penis invaginable, muscular, armed with apical sharp long hook; prostate large, tightly coiled in a complex coiled structure. Jaws narrow, embedded on margin of labial cuticle. Rachidian teeth absent; wide central toothless area; lateral teeth large, thin, pointed with broader base. Three gizzard plates, corneous, with eight V-shape transverse ridges; ridges bordered by short cylindrical sharp elements; gizzard spines absent. Cerebral and pleural ganglia fused; pedal ganglia separated; cerebral–pleural and pedal ganglia of similar size and larger than other ganglia.

Barcode. GenBank accession number GQ332576

Material examined. Mouth of Kinko River , Chongko City, Chungchong-Namdo, South Korea, one specimen dissected, BMNH 20070443 , H = 17 mm, 10 June 2006, mud tidal flat. Tahé-Kiang, China, four specimens dissected, coll. MNHN Paris [David coll. No 15, 1872], H = 14, 17, 18 mm. Swatow, China, four shells, BMNH 1906.5.8.91-94; two shells, RMNH. MOL.122353, H = 10 mm. China, two shells, BMNH ( Mrs De Burgh colln) . China, three shells, BMNH ( V.W. Macandrew colln). China, three shells, BMNH 1852.4.64-66.

Description. Shell ( Figure 1 ): external, formed by last whorl, fragile, ovo-philinoid, with conspicuous spiral striae all over, whitish, translucent. Columellar lip smooth, narrow, and white; columella reduced to internal folded cord of periostracum. Parietal callus absent. Spire absent. Aperture wide, longer than H. Periostracum fine, yellowish.

External body: cephalic shield with quadrangular shape, well-developed posteriorly, covering anterior part of shell, posterior notch absent. Eyes not visible through skin in preserved specimens. Pair of Hancock organs located laterally on anterior sides of head; smooth, quadrangular, slightly elevated from rest of epidermis. Parapodial lobes short, not covering laterally the shell. Foot shorter than shell, complemented by posterior pallial lobe. Operculum absent in adults.

Reproductive system ( Figures 2 , 3 ): separated into two parts: male copulatory system in cephalic region opening laterally at the right side of mouth and hermaphroditic gonoduct in posterior part of body (not studied; glands were burst); both parts interconnected through external seminal groove that lies laterally along right side of body. Male copulatory system: genital opening followed by short atrium bifurcated into two distinct parts (hereafter designated as penial and glandular); penial part with invaginable penis enclosed in thick sheath; penis muscular, armed with apical sharp long hook; penis connected to long wide pair of ducts fused axially to each other, continuous with large prostate; prostate tightly coiled in a complex convoluted duct structure. Glandular part with tubular shape; two wider glandular regions, distal one convoluted, ending as a narrow terminal blind caecum.

Jaws ( Figure 4 ): paired, located on each side of mouth; narrow plate, embedded on margin of labial cuticle; composed of developed denticulate, multifid elements.

Radula ( Figure 4 ): radular formula 25-13.0.13-25. Rachidian tooth absent; wide central toothless area. Lateral tooth large and thin, with smooth edges and broader base.

Gizzard ( Figure 5 ): located between oesophagus and stomach; three corneous plates, with identical shape and size; plates with eight transverse V-shape ridges, with margin slightly hanging over the following ridge; rim of ridges bordered by row of short cylindrical sharp elements. Gizzard spines absent.

Central nervous system ( Figure 6 ): euthyneuran. Circumoesophageal nerve ring post-pharyngeal. Cerebral and pleural ganglia fused; pedal ganglia separated. Cerebral– pleural and pedal ganglia of similar size and larger than others; left and right cerebral– pleural and pedal ganglia connected to each other by commissures. Right parietal ganglion smaller, connected to cerebral–pleural ganglion. Left parietal ganglia imperceptible (maybe absent). Larger supraoesophageal ganglion arising from nerve cord on posterior right side. Smaller suboesophageal ganglion in left nerve cord, contiguous with larger visceral ganglion. Genital ganglion on posterior left side, located behind visceral ganglion where both nerve cords merge.

Phylogenetic analysis. The phylogenetic analysis yielded a clade containing all genera of Haminoeidae including Bullacta with a PP of 0.9 ( Figure 7).

Trophic ecology. Observation of the food items contained in the gut of two specimens of Bullacta exarata revealed exclusively the presence of diatoms embedded in a matrix of mucous with few sand grains; there was a clear dominance of an unidentified species of the order Pennales with sporadic occurrence of Centrales diatoms ( Figure 8 ).

Figures

Figure 1. Shell of Bullacta exarata. (A–B) Neotype (MNHN 4494, Paris; shell height (H) = 17 mm); (C) scanning electron microscope detail of dorsal part of shell showing spiral grooves (MNHN, Paris; H = 17 mm); (D) internal whorl showing the absence of columella; white arrowheads pointing to the folded cord of periostracum that results from the dissolution of the columella (MNHN, Paris; H = 17 mm). Note: Scale bar, (C) 200 µm.

Figure 2. Male genital system of Bullacta exarata (MNHN, Paris, shell height = 17 mm). Notes: at, atrium; bc, blind caecum; ga, genital aperture; gr1, glandular region one; gr2, glandular region two; id, inwards duct; od, outwards duct; pr, prostate; ps, penial sheath; scale bar, 1 mm.

Figure 3. Male genital system of Bullacta exarata. (A) the muscular penis; white arrowhead pointing to apical hook (MNHN, Paris; height = 17 mm); (B) detail of apical hook (MNHN, Paris; height = 18 mm). Note: scale bars, 100 µm.

Figure 4. Jaws and radula of Bullacta exarata. (A) Jaw (MNHN, Paris; height = 17 mm); (B) radula showing the long and sharp teeth (BMNH 20070443; shell height (H) = 17 mm); (C–D) radula with white arrowheads pointing to the toothless central area (C) and base of lateral teeth (D) (MNHN, Paris; H = 14 mm). Notes: Scale bars (A, C) 10 µm; (B) 100 µm; (D) 20 µm.

Figure 5. Gizzard plates of Bullacta exarata. (A) View of whole gizzard with plates (MNHN, Paris; shell height (H) = 18 mm); (B) top view of the central plate (MNHN, Paris; H = 18 mm); (C) lateral view of plate (MNHN, Paris; H = 17 mm); (D) detail of elements around the edge of plate ridges (MNHN, Paris; H = 17 mm). Notes: Scale bars, (A) 1 mm; (B, C) 200 µm; (D) 100 µm.

Figure 6. Central nervous system of Bullacta exarata (BMNH 20070443; shell height = 17 mm). Notes: cpg, cerebral-pleural ganglion; gg, genital ganglion; pag, parietal ganglion; peg, pedal ganglion; sbog, suboesophageal ganglion; spog, supraoesophageal ganglion; vg, visceral ganglion; scale bar, 1 mm.

Figure 8. Scanning electron microscopy images of the gut content of specimens of Bullacta exarata collected from Tahé-Kiang, China. Diatoms are the only food items present. Notes: Scale bars, (A) 10 µm; (B) 20 µm.