Argyrotheca barrettiana ( Davidson, 1866 )

Rojas, Alexis, Gracia, Adriana & Patarroyo, Pedro, 2015, Brachiopods from off the San Bernardo Archipelago (Colombian Caribbean), with comments on specific synonymies in Tichosina Cooper, 1977, Zootaxa 3914 (1), pp. 55-63 : 59-60

Argyrotheca barrettiana ( Davidson, 1866)

( Fig. 2 L–Q)

1866 Argiope barrettiana Davidson , p. 103, pl. 32, figs. 22–32.

1977 Argyrotheca barrettiana Davidson—Cooper , p. 107, pl. 22, figs. 9–21; pl. 23, figs. 6–7; pl. 32, figs. 22–32. v2009 Argyrotheca cf. jacksoni .—Rojas et al., figs. 2d–e.

v2009 Argyrotheca cuneata .—Rojas et al., p. 124.

Occurrence. Off the San Bernardo Archipelago, Colombian Caribbean: MARCORAL Stations D3 (9° 48.88' N; 76° 12.47' N), D13 (9° 48.082' N; 76° 12.620' W), D15(9° 49.546' N; 76° 11.178' W), D16 (9° 50.322' N; 76° 10.320' W), D21(9° 46.594' N; 76° 12.811' W), D28 (9° 46.64' N; 76° 13.86' W), D30, D31(9° 52.926' N; 76° 11.308' W), D32 (9° 51.855' N; 76° 11.276' W), D34 (9° 52.903' N; 76° 10.119' W) and Pillsbury Station 389 ( Cooper 1977). Gulf of Darien: Cape Tiburon, Pillsbury Station 409 ( Cooper 1977).

Material. One conjoined shell, one dorsal valve, and one ventral valve INV BRA 7. A total of 173 conjoined shells available.

Description. External characters: shell small (maximum observed length 6.3 mm, maximum observed width 9.5 mm), outline variable, usually transversely rectangular, wider than long, maximum width typically at hinge line, rarely anterior to hinge line; foramen large, hypothyrid; anterior commissure broadly and gently unisulcate; surface covered with coarse rounded costae on each valve numbering 12 to 14; costae originating in the beak region and dorsal umbo, radiating anteriorly; interspaces slightly narrower than costae. Internal characters: ventral valve with pedicle collar present, supported by a median septum; ventral median septum relatively low, extending 50% to 60% of the valve length, with three small oval depressions near to the anterior end, rarely fused forming a single groove; dorsal valve with elongate sockets, parallel to hinge line; dorsal septum high, serrated, triangular in lateral profile, with a crest at the anterior end, located slightly anterior to midvalve, decreasing anteriorly.

Remarks. The available shells are similar in both internal and external characteristics with those for the species as originally given in Davidson (1866) based on Jamaican specimens. The Colombian assemblages exhibit more variability in outline, ranging from transversely rectangular, semicircular to subpentagonal. The subpentagonal outline which characterizes Davidson’s material is relatively frequent in our assemblage. The studied shells are similar in their external characteristics, i.e. general outline, convexity, ornamentation and color pattern, with those illustrated by Cooper (1977, pl. 22, figs. 9–19) from the Coralline Archipelago of San Bernardo, Colombia. The studied area is located about 25 km west of this Archipelago. The geographic range of this species in the Colombian Caribbean extends southward, from San Bernardo to the Gulf of Darien ( Cooper 1977). Referring to internal characters, the main difference between our material and that illustrated by Cooper (1977, pl. 32, fig, 29) is the presence of a non-serrated dorsal medium septum in one specimen of the Cooper’s Florida Bay material. This structure in the material studied shows similarities with large Argyrotheca species, namely A. johnsoni Cooper, 1934 , A. crassa Cooper, 1977 , A. rubrocostata Cooper, 1977 and A. barrettiana ( Davidson, 1866) . It differs externally from A. johnsoni and A. crassa in having more and finer ribs. The ribbing of A. rubrocostata is stronger than A. barrettiana . The great inter- and intra-specific variability of both external and internal structures in megathiridoid brachiopods has been recognized by several authors ( Atkins 1960; Cooper 1977; Álvarez et al. 2008a, b). An integrated study of large collections is needed to establish the range of variation of these forms ( Cooper 1977).

Rojas et al. (2009, figs. 2d–e.) illustrated two valves of A. barrettiana collected during the MARCORAL Cruise, both misidentified as A. cf. jacksoni Cooper, 1973 . The ventral valve illustrated in Rojas et al. (2009) is subpentagonal in outline and slightly wider than longer. This shell shape is non-representative of the entire population of A. barrettiana off the San Bernardo Archipelago. As we highlight above, the studied material is highly variable in shape, but it is dominated by shells transversely rectangular in outline, as illustrated in the present paper (fig. 2L–P). In their preliminary report on the brachiopods of the MARCORAL cruise, Rojas et al. (2009) also misidentified some shells of A. barrettiana as A. cuneata (Risso, 1926) . However, that material was not illustrated or described. Recently, Logan & Bitner (2013) discussed the similarities in outline and ornamentation between A. cuneata and A. jacksoni . The first occurs in the Mediterranean and the Red Sea, and the latter is common in the Red Sea and the Persian Gulf ( Bitner et al. 2008; Logan & Bitner 2013). Argyrotheca cf. cuneata has also been reported from the Southern Brazilian shelf by Simoes et al. (2004). The morphological similarity between A. barrettiana and A. cuneata was noted previously by Davidson (1866). Our material has a characteristic scarlet color on the inter-rib spaces absent in A. jacksoni but similar to the color pattern present in A.cuneata . However, the Colombian material is larger in shell size than those forms and should be assigned to A. barrettiana . There is no record of A. cuneata nor A. jacksoni from the Colombian Caribbean so far. The only brachiopod species reported in both the Colombian Caribbean and the Mediterranean Sea, is the cosmopolitan Platidia anomioides . This form was recorded in Punta Piedras, Magdalena Province, approximately 200 km north of the San Bernardo Archipelago ( Cooper 1977).

Figures

FIGURE 2. Brachiopods off the San Bernardo Archipelago, Colombian Caribbean. A – E. Tichosina plicata Cooper, 1977. A – D. INV BRA 5 conjoined shell. A. Dorsal view. B. Lateral view. C. Ventral view. D. Anterior view. E. INV BRA 6, inner view of dorsal valve showing the loop and broad transverse band. 2 F – I. Terebratulina latifrons Dall, 1920. INV BRA 8 conjoined shell. F. Dorsal view. G. Lateral view. H. Ventral view. I. Anterior view. 2 J – K. Terebratulina cailleti Crosse, 1865. INV BRA 9. J. Inner view of ventral valve. K. Inner view of dorsal valve showing the loop. L – Q. Argyrotheca barrettiana (Davidson, 1866). INV BRA 7. L. Conjoined shell, dorsal view. M. Lateral view. N. Ventral view. O. Anterior view. P. Oblique inner view of ventral valve showing the depressions near to the anterior end of the ventral septum. Q. Inner view of dorsal valve. P – Q. SEM photographs. All scales 5 mm.