Onithochiton maillardi ( Deshayes, 1863 )

Schwabe, Enrico, 2004, The Polyplacophora (Mollusca) collected during the First International Marine Biodiversity Workshop for Rodrigues (western Indian Ocean), with the description of a new species, Journal of Natural History 38 (23), pp. 3143-3173 : 3157-3160

Onithochiton maillardi ( Deshayes, 1863)

( figures 9 , 10 , 17F )

Chiton maillardi Deshayes, 1863: 38 , pl. 5 figure 14 ; von Martens, 1880: 300 (as ‘ C. ( Tonicia ?) maillardi ’); Nierstrasz, 1905: 107; 1906: 513.

Toniciopsis maillardi: Thiele, 1893: 371 .

Tonicia (Onithoplax) maillardi: Thiele, 1929: 22 .

Onithochiton mailardi [sic!]: Bergenhayn, 1933: 34.

Onithoplax maillardi: Cotton, 1964: 88 .

Onithochiton maillardi: Pilsbry, 1893: 250 , pl. 55, figure 20; Leloup, 1941: 9, text figures 5–8 ; 1960: 42, figure 11A ; 1974: 5; 1981a: 35; Kaas and Van Belle, 1980: 80; 1998: 117; Ferreira, 1983: 277 [as synonym of Onithochiton literatus (Krauss, 1848) ]; Kaas, 1986: 18; Drivas and Jay, 1998: 33, figure 9 ; Slieker, 2000: 50,

pl. 13, figure 29.

Tonicia maillardi: Kaas, 1996: 374 .

Type. Syntypes ( MNHN) .

Type locality. Réunion (Bourbon). Material examined. 1 spm, 15.7 6 7.2 mm: Pointe Coton, 19 ‡ 40.833 ’ S ,

63 ‡ 29.548 ’ E, reef crest, 18 September 2001; 5 spms, 6.8 6 4.4 mm, ca 10.9 6 5.8 mm (curled), ca 9.5 6 6.7 mm (pd), 14.7 6 8.3 mm, 17.3 6 11 mm: RDS 15, Rivière Banane, 19 ‡ 40.261 ’ S, 63 ‡ 28.582 ’ E, reef crest.

Description

Animal elongate-oval with a broad ‘naked’ girdle ( figure 17F ). Tegmentum surface consists of concentric grooves in head valve, lateral areas and postmucronal area. Pleural areas and antemucronal area with longitudinal grooves. Large lenses arranged radially in lateral areas and within the grooves of the head valve.

Tegmentum. Valve surface smooth, except for openings of aesthetes. Head valve semicircular with distinct concentrically arranged, irregular grooves and a

shallow notched posterior margin ( figure 9A ). Intermediate valves with smooth jugum, and a beaked apex. Lateral areas concentrically grooved, not elevated, pleural areas longitudinally grooved ( figure 9C ). Mucro of triangular tail valve slightly elevated and situated terminally ( figure 9D, E ). Postmucronal area very small, concentrically grooved and with a steep slope. It is separated from antemucronal area by a slightly elevated, rather coarse diagonal ridge. Antemucronal

area sculptured as pleural areas of intermediate valves.

Ocelli arranged radially in diagonal ridge of tail valve, in lateral areas and within the grooves of head and tail valve, measuring about 30 M m in diameter ( figure 9B ).

Articulamentum. Thick and white, with large and triangular apophyses in second valve. They are connected by a shallow, pectinated jugal lamina. Apophyses of tail valve are trapezoid and connected by a shallow, deeply notched jugal lamina ( figure 9D ). Slit formula: 8/1/0 (callus), slits deep, resulting in rather long teeth, which are broad and pectinated on outside. Slit rays present in head and intermediate valves.

Perinotum. Rather wide and appears naked. Dorsally covered with short, straight, blunt spicules, 62.5 6 20.2 M m, with strong ribs in their upper half ( figures 9F , 10A–D ). Interspersed are short, broad, slightly curved spicules (64.5 6 12.2 M m) and slender, smooth needles, 97 6 10.4 M m ( figure 10A, D ). Margin bears long (117–146 6 21–25 M m), paddle-like spicules, and a fringe of scales, which measure approximately 35 6 21 M m ( figure 10A ). Ventrally, the girdle paved with radial rows of rectangular scales, grooved in their distal part, measuring 18.8–25 6 28–34.4 M m ( figure 10E ).

Radula. The partly disarticulated specimen has 52 tooth rows of which 46 are mineralized. The slender, nearly rectangular, central tooth has anteriorly a sharp keel and a single, rounded blade. First lateral tooth very large, wingshaped and the lower half is considerably extended. Major lateral tooth has a long keeled shaft and a four-cuspidated head. Innermost denticle smallest, the remaining denticles are larger and of equal size. The very large, spoon-like blade of the spatulate uncinal tooth supports the head of the major lateral tooth ( figure 10F ).

Ctenidia . There are 27 abanal and holobranchial ctenidia on both sides of the foot in a 15.7 mm long specimen.

Comments

Although slightly inconsistent in sculpture, the examined material agrees well with two studied syntypes (dry, soft parts removed; 20.1 6 11 mm and 11.2 6 6.3 mm). At present the genus Onithochiton Gray, 1847 is in a state of taxonomic chaos. The validity of such species as O. erythraeus Thiele, 1910 , O. literatus (Krauss, 1848) and O. lyellii (Sowerby in Broderip and Sowerby, 1832) was debated in the past by several authors ( Kaas, 1979; Leloup, 1980; Ferreira, 1983; Strack, 1993). They are currently accepted as valid, but more material and a thorough revision of the genus is needed to get a better understanding of these taxa.

Figures

FIG. 9. Onithochiton maillardi (Deshayes, 1863). (A) Dorsal view of head valve; (B) detail of head valve, to show the lense of macroaesthetes; (C) dorsal view of the second valve; (D) dorsal view of tail valve; (E) lateral view of the tail valve; (F) dorsal girdle elements in situ. Scale bars: 1 mm (A, C, D); 30 Mm (B); 500 Mm (E); 200Mm (F).

FIG. 10. Onithochiton maillardi (Deshayes, 1863). (A) Dorsal girdle, close-up of the ringshaft needles in situ; (B) isolated dorsal girdle spicule; (C) lateral view of a dorsal girdle spicule from mid-girdle; (D) isolated ringshaft needle from dorsal-marginal girdle; (E) ventral girdle scales in situ; (F) radula. Scale bars: 50 Mm (A, E); 20 Mm (B, C); 30 Mm (D); 100 Mm (F).

FIG. 17. (A) Parachiton hylkiae mauricejayi Schwabe, 2002, complete animal, posteriorlateral view (length: 7 mm); (B) Callochiton deshayesi Thiele, 1909, complete animal, dorso-lateral view (length: 2.5 mm); (C) Callistochiton barnardi Leloup, 1981, complete animal (now partly disarticulated), dorsal view (length: 4.2 mm); (D) Choneplax indica Odhner, 1919, complete animal, dorso-lateral view (length: 5.7 mm); (E) Cryptoconchus oliveri n. sp., paratype, complete specimen, dorsal view (length: 15.6 mm); (F) Onithochiton maillardi (Deshayes, 1863), complete specimen, dorsal view (length: 15.7 mm); (G, H) Lucilina indica (Leloup, 1981): (G) complete specimen, dorsal view (length: 5.8 mm); (H) holotype, partly dissected specimen, dorsal view (length: 8 mm).

FIG. 14. Cryptoconchus oliveri n. sp. (A) Dorsal view of head valve; (B) close-up of the tegmentum region of the head valve; (C) dorsal view of the second valve; (D) close-up of the posterior tegmentum region of the second valve; (E) dorsal view of the tail valve; (F) close-up of the tegmentum of the tail valve. Scale bars: 1 mm (A, C); 200 Mm (B, D, F); 500 Mm (E).

FIG. 5. Callistochiton barnardi Leloup, 1981. (A) Dorsal view of head valve; (B) dorsal view of second valve; (C) dorsal view of tail valve; (D) lateral view of tail valve; (E) radula; (F) radula, close-up of central tooth. Scale bars: 1 mm (A–C); 500Mm (D); 100 Mm (E); 50 Mm (F).

FIG. 6. Callistochiton barnardi Leloup, 1981. (A) Dorsal girdle scales in situ; (B) dorsal girdle scales, margin; (C, E) dorsal-marginal view of girdle, close-up of the tips of clapper; (D) dorsal-marginal view of girdle to show needle in situ; (F) ventral girdle scales in situ. Scale bars: 100 Mm (A, B); 25 Mm (C); 50 Mm (D–F).

FIG. 7. Lucilina indica (Leloup, 1981). (A) Dorsal view of head valve; (B) dorsal view of second valve; (C) dorsal view of tail valve; (D) lateral view of tail valve; (E) close-up of postmucronal area to show the lenses of macroaesthetes; (F) radula. Scale bars: 1 mm (A–C); 500Mm (D); 20Mm (E); 100 Mm (F).

FIG. 8. Lucilina indica (Leloup, 1981). (A) Close-up of central tooth of radula; (B) dorsal girdle spicules, in situ; (C) dorsal-marginal girdle, flattened marginal spicules in situ; (D) dorsal girdle scales in situ, close-up; (E) ventral girdle scales in situ; (F) ventral girdle scales, close-up to show the scale sculpture. Scale bars: 50Mm (A, C, E, F); 10 Mm (B); 20 Mm (D).

FIG. 11. Choneplax indica Odhner, 1919. (A) Dorsal view of head valve; (B) dorsal view of second valve; (C) close-up of the second valve, left pleural area, right jugal area; (D) dorsal view of the tail valve; (E) radula; (F) close-up of the central tooth. Scale bars: 500 Mm (A, D); 1 mm (B); 50Mm (C); 100 Mm (E); 20 Mm (F).