Nierstraszella Sirenko, 1992

Sigwart, Julia D., 2009, The deep-sea chiton Nierstraszella (Mollusca: Polyplacophora: Lepidopleurida) in the Indo-West Pacific: taxonomy, morphology and a bizarre ectosymbiont, Journal of Natural History 43 (7 - 8), pp. 447-468 : 449-451

Genus Nierstraszella Sirenko, 1992

Type species

Lepidopleurus lineatus Nierstrasz, 1905 by original designation ( Sirenko 1992, p. 84).

Diagnosis

Animal of medium size, up to 27 mm long, elongate oval, rather elevated (dorsal elevation 0.40 on valve II), subcarinate, side slopes convex. Head valve semicircular, posterior margin widely V-shaped. Valves smooth, not sculptured, valve surface rough, but covered with thick periostracum which may form raised pustules. Tail valve with central mucro, not prominent. Outer appearance of valves (periostracum) golden yellow to orange, sometimes covered in black mineral deposit. Girdle variable, covered in small, blunt to club-shaped spicules. Gills variable in size, up to 20 per side. Radula major lateral teeth tricuspid in juvenile specimens and bicuspid in adults.

Remarks

The genus Nierstraszella (the sole genus in the family Nierstraszellidae ) has a distinctive thick periostracum layer, which in N. lineata grows into complex patterns of raised pustules ( Figure 1 ). The radula of Nierstraszella varies ontogenetically, the major lateral tooth is tricuspid in juvenile specimens and bicuspid in older (larger) individuals ( Sirenko 1992). The girdle is dorsally and ventrally covered in short, blunt spicules and dorsally with scattered longer spines.

There are seven taxon names proposed for species in Nierstraszella , placed either in Leptochiton Gray, 1847 or historically as Lepidopleurus Risso, 1826 . Sirenko (1992) considered all of these to be junior synonyms of N. lineata . He proposed that all conchological variation reported in these taxa was the result of plasticity in the overlying thick periostracum, which grows into quite complex zigzag patterns of raised pustules on N. lineata . Removing the periostracum layer with bleach or KOH, reveals the aesthete openings, which Sirenko (1992) argued were identical in all involved taxa. The radular morphology also presents little difference between proposed taxa.

Sirenko (1992) further proposed that Nierstraszellidae represented a phylogenetically intermediate group between Lepidopleurida and Chitonida . This was before his work on Ferreiraellidae (another group restricted to sunken wood; Sirenko 1997).

Figures

Figure 1. Two species of Nierstraszella; N. andamanica comb. nov., nom. rev. (top) and N. lineata (bottom). Note the raised texture created by periostracum pustules on N. lineata, and the abraded patches (white) where periostracum as rubbed away on N. andamanica. Scale bar applies to both images. Specimens are from the Solomon Islands, ‘‘Salomon 2’’ sta. CP2264 (N. andamanica) and sta. CP2226 (N. lineata).