Argyrotheca sp.

Bitner, Maria Aleksandra, 2008, New data on the recent brachiopods from the Fiji and Wallis and Futuna islands, South-West Pacific, Zoosystema 30 (2), pp. 419-461 : 439-440

Argyrotheca sp.

( Fig. 10A, B )

MATERIAL EXAMINED. — Fiji. MUSORSTOM 10, Bligh Water, stn DW 1334, 1 complete specimen, 1 ventral valve, 1 dorsal valve.

DEPTH RANGE. — 251- 257 m.

MEASUREMENTS. — Length 1.7 mm, width 1.9 mm, thickness 0.9 mm.

DESCRIPTION

Shell minute, subquadrate, wider than long, biconvex with the ventral valve more convex. Surface smooth to covered with very weakly marked ribs. Anterior commissure with a shallow sulcus on the dorsal valve. Foramen large, triangular, hypothyrid, bordered by two narrow deltidial plates. Pedicle collar wide, supported by a septum. Dorsal valve interior with deep sockets and a high triangular median septum that begins at the mid-length and slopes anteriorly with four serrations ( Fig. 10B ). Anterior ends of descending branches join the median septum. The internal margin of the valve is covered with tubercles.

REMARKS

The limited material, found only in one station, prevents more detailed taxonomic determination. The genus Argyrotheca is uncommon in the Pacific. In Australia it is represented by two species ( Blochmann 1910, 1914). The South Australian species Argyrotheca australis ( Blochmann, 1910) differs from the Fiji specimens in being much larger and having ribbed ornamentation. The studied specimens are also easily distinguishable from the species from off Tasmania, A. mayi Blochmann, 1914 which is triangular in outline and lacks tubercles on the inner margin.

In size, outline, ornamentation and the presence of tubercles on the inner margin the specimens from Fiji are similar to those from Bikini Atoll described as Argyrotheca sp. by Cooper (1954), and later, after obtaining a larger sample, as Argyrotheca arguta by Grant (1983).

The specimens described herein display also, both externally and internally, similarities to the common Mediterranean and Atlantic species, A. cordata (Risso, 1826) . The latter species has been recently discovered in the Red Sea ( Logan et al. 2005).

Figures

FIG. 10.A, B, Argyrotheca sp., inner and lateral views of dorsal valve (MNHN BRA-3091),SEM,Fiji,Bligh Water,MUSORSTOM 10,stn DW 1334, 251-257 m; C-G, Frenulina sanguinolenta (Gmelin, 1791), SEM;C, D, inner and tilted views of dorsal valve (MNHN BRA-3089),Fiji, Beqa Lagoon,SUVA 4,stn DW 09,37-41 m;E-G, dorsal,lateral andanterior views of complete specimen (MNHN BRA-3090),Fiji,Lau Ridge, BORDAU1, stn DW1451,400-460m; H-J,Fallax neocaledonensis Laurin,1997,dorsal,lateral and anteriorviewsof completespecimen(MNHN BRA-3087),Fiji,Lau Ridge,BORDAU 1, stn CP 1458,1216-1226 m. Scale bars:A, B, 500 μm;C, D, 1 mm;E-G,2 mm; H-J,0.5 cm.