Chiton magnificus Deshayes, 1827

Schwabe, Enrico, Försterra, Günter, Häussermann, Verena, Melzer, Roland R. & Schrödl, Michael, 2006, Chitons (Mollusca: Polyplacophora) from the southern Chilean Comau Fjord, with reinstatement of Tonicia calbucensis Plate, 1897, Zootaxa 1341, pp. 1-27 : 9-10

Chiton magnificus Deshayes, 1827

(Figures 7, 8, 15)

Chiton magnificus Deshayes, 1827: 454 .

Detailed bibliography and synonymy in Bullock (1988: 163).

Size: Maximum length 90 mm ( Bullock 1988). Body outline: Broad­oval, slightly carinated, rather flat. Color: In general dark bluish grey (orange red specimens also occur) with brighter dots and various black marks. Valves: Head valve semicircular, with wide Vshaped to straight posterior margin unnotched in middle, with numerous radially arranged, shallow ribs; intermediate valves rectangular with slightly concave posterior margin at both sides of faintly protruding apex, lateral areas slightly elevated, sculptured with up to 5 radial ribs between a wider diagonal ridge and a very wide posterior rib; tail valve semicircular with an anterior mucro, postmucronal area with same sculpture as head valve and lateral areas. Aesthetes appear porous, occurring in interspaces of faintly elevated radial ribs, generally brighter in coloration than underlying areas. Growth marks visible on all valves. Articulamentum: Strongly developed, bluish­white, apophyses short, trapezoid, jugal sinus serrated, slit formula: 14 / 1 / 14, slit rays present in all valves, teeth strongly grooved outside, teeth short, sharp. Perinotum: Dorsally covered with solid, smooth, roundish­triangular, obtusely pointed scales of two different sizes. Scales situated closest to valves smaller than scales towards the outer margin, clear boundary visible. Perinotum fringe consisting of smooth, sharply pointed, straight, brownish, calcareous spicules. Elongate, ventral scales opaque and arranged in radial rows. Ctenidia (Moll 20034098, 28 mm body length): 48 ctenidia on each side of foot arranged holobranchially; ctenidia close to anus smaller than those under 7th valve. Radula (specimen of 28 mm body length): Radula 13.5 mm long, 78 teeth rows, 64 of them mineralized. Radula cartilage 4.9 mm in length. Central tooth very slender, with simple backward directed blade. First lateral tooth of double size, distally extended to simple spoon­like inwarddirected blade. Head of second lateral tooth shows simple discoidal blade, slightly pointed in middle of cutting edge.

Material: Of the 14 specimens collected in the investigated area, five are from station 5 (6–30 m) and nine from station 7 (2.3–30.5 m) (see Table 1 ). One specimen ( ZSM Moll 20050026) from station 3 was found in the immediate vicinity of an underwater thermal spring at a depth of 28 m. The surrounding area was densely covered by a mat of filiform sulphur­oxidising bacteria ( Figure 8 ).

Distribution: Chiton magnificus occurs from Perú southwards to the Chonos Archipelago. It inhabits rock pools and boulder fields with strong water exchange ( Bullock 1988). It was reported from depths between 0–13 m (Zagal & Hermosilla 2001). The new material in this study extends its depth distribution down to 30.5 m.

Remarks: Bullock (1988) interpreted this species as Chiton magnificus magnificus . Based on similarities in shell characters and perinotum and on the basis of nearly complete geographical isolation he also considered Chiton bowenii King & Broderip, 1831 to be a subspecies of Chiton magnificus , being aware that there are intermediate forms in the transition zone around Chiloé Island. Reid & Osorio (2000) already discussed the problems with Bullock’s conclusions, pointing out that he mentioned both subspecies from Chiloé Island. Unfortunately, we do not have enough material to revise the Chiton magnificus complex. While Reid & Osorio’s specimens from the Chonos Archipelago look more like the southern Chiton bowenii , the specimens reported herein correspond well with the specimens illustrated by Bullock (1988: figures 57, 58), which could be syntypes of Chiton subfuscus Sowerby in Broderip & Sowerby, 1832. Except for some minor shell differences, the latter species does not differ significantly from C. magnificus , and thus Bullock (1988) regarded them as synonymous.

One of the examined specimens (ZSM Moll 20050027) was infested by endoparasitic nematodes. According to Dr. Nicola Reiff (Munich), two larger females (2.1–2.5 mm) were found which most probably belong to the family Chromadoridae . A more detailed examination of the parasites is in progress.

Figures

FIGURE 8. Underwater photograph of a bacteria mat at an underwater spring with sulphurous water at station 3, the upper chiton is Tonicia chilensis (Frembly, 1827) (ZSM Moll 20050025) illustrated specimen measures 17.3 mm in length, the lower Chiton magnificus Deshayes, 1827 (ZSM Moll 20050026) illustrated specimen measures 15.6 mm in length. 9. Underwater photograph of Tonicia atrata (Sowerby, 1840) in situ (ZSM Moll 20050020) at station 3, illustrated specimen measures c. 30 mm in length. 10. Underwater photograph of Tonicia calbucensis Plate, 1897 in situ (NRS). 11. Underwater photograph of Tonicia chilensis (Frembly, 1827) in situ (NRS) at station 7. 12. Underwater photograph of Tonicia smithi Leloup, 1980 in situ (ZSM Moll 20050012) at station 12, illustrated specimen measures c. 50 mm in length. 13. Underwater photograph of Plaxiphora aurata (Spalowsky, 1795) in situ (ZSM Moll 20034100) at station 7, illustrated specimen measures c. 28 mm in length.