Martesia fragilis Verril and Bush 1898

Delfino, Marina & Signorelli, Javier H., 2021, Fig. 13 in Fig. 12. Majella pristis n in Periclimenaeus djiboutensis Bruce 1970, Zoological Studies 60 (28), pp. 1-20 : 14

Martesia fragilis Verril and Bush 1898 ( Fig. 7 )

Martesia (Martesiella) fragilis Verrill and Bush, 1898: 777 , pl. 79, fig. 10.

Pholadidea (Penitella) minuscula Dall, 1908: 425 .

Martesia (Diploplax) exquisita Bartsch and Rehder, 1945: 10 .

Martesia (Diploplax) bahamensis Bartsch and Rehder, 1945: 11 .

Martesia (Martesia) fragilis – Turner 1955: 111, pl. 65–66, figs. 1–9; Daniel and Srinivasan 1956: 59; Srinivasan 1959: 107; Klappenbach 1967: 167; Bernard 1983: 60; Turner and Santhakumaran 1989: 161, fig. 4; Rios 1994: 296: pl. 100, fig. 1440; 2009: 593, fig. 1635; Huber 2010: 476; Coan and Valentich-Scott 2012: 894, pl. 279.

Martesia fragilis – Olsson 1961: 446; Keen 1971: 276; Hoagland and Turner 1981: 130; Díaz Merlano and Puyana Hegedus 1994: 101, pl. 30, fig. 288; Scarabino 2003: 242; Turgeon et al. 2009: 737; Dias Passos and Magalhães 2011: 148; Scarabino et al. 2016: 7; Velásquez et al. 2017: 252, figs. 9–10.

Type locality: 360 miles Off Charles cape, Virginia, United States, Station N° 2566 R/V Albatross in a floating piece of wood, lat. 37°23'N, long. 68°8'W.

Ty p e m a t e r i a l: M a r t e s i a f r a g i l i s: USNM 614180, lectotype, two valves; Martesia (Diploplax) bahamensis : USNM 573549, holotype, collected at Est side of Hudros Island, Andros Light, South Bight, Bahamas; Martesia (Diploplax) exquisita : USNM 573548, holotype, collected at Stony Cove, St. Mary Parish, Jamaica; Pholadidea (Penitella) minuscula : USNM 122946, syntypes, seven valves, collected at Azuero Peninsula, Punta Mala, SE of Gulf of Panama, Panama in 1891.

Description: Shell: small, fragile, thin, equivalve, inequilateral; length up to 10 mm; anterior end rounded and short; pedal aperture closed by the callum in adults; dorso-anterior margin rounded toward the umbos; posterior end elongated, rounded, less developed in juveniles, laterally compressed in adult specimens; external surface with a deep sulcus that goes from the umbos to the ventral margin dividing the external sculpture in two areas; thin and concentric imbricate ribs over the anterior side of the sulcus; sculpture curved downward and form a distinct angle in line with the antero-ventral margin; concentric ribs crossed by fine radial lines; irregular growth lines on the posterior side of the sulcus; mesoplax thick, relatively large, and usually heart-shaped, ovate-elongate with a dorsal depression and concentric sculpture; metaplax long, narrow, placed above the dorsal margin, with free edges under the posterior end of mesoplax and the anterior end narrow.

Distribution: Martesia fragilis was recorded from floating woods in the Northwestern Atlantic, USA ( Turner 1955), in the southwestern Atlantic ( Klappenbach 1967, Díaz Merlano and Puyana Hegedus 1994; Rios 2009), in the Eastern Pacific from Mexico to Panama ( Díaz Merlano and Puyana Hegedus 1994), in the Indian and eastern Pacific Oceans ( Daniel and Srinivasan 1956; Srinivasan 1959); and in the United Kingdom ( Holmes et al. 2015).

Remarks: Martesia fragilis had been occasionally recorded in fixed wooden substrates. It was first reported by Klappenbach (1967) for Uruguayan waters (Natural History National Museum, Montevideo, N° 1313). Nevertheless, it was widely registered in floating pieces of wood of different trees such as Myristica fragrans and Mangifera indica in the Indo Pacific; coconuts in the United Kingdom or the cork Quercus suber in the western Atlantic ( Turner 1955; Srinivasan 1959; Klappenbach 1967; Holmes et al. 2015). It is considered a pelagic species ( Turner 1955) with a wide geographical distribution suggesting the presence of an ocean traveler. However, more studies must be carried out to understand this process. Three species have been mentioned as synonym of Martesia fragilis in the literature. They are and Pholadidea (Penitella) minuscula ( USNM 122946) ( Fig. 7D–H ), Martesia (Diploplax) bahamensis ( USNM 573549) ( Fig. 7I–L ), Martesia (Diploplax) exquisita ( USNM 573548) ( Fig. 7M–P ). The description of these three nominal species were based on very small specimens, juveniles ( Fig. 7D–P ) with equal external sculpture in comparison with the types of M. fragilis . The synonyms listed above were described from the Caribbean Sea. The morphology of M. fragilis was studied by Holmes et al. (2015) who distinguished it from M. striata and M. cuneiformis by mesoplax morphology. The type species has a mesoplax large, circular with irregular wrinkles and without concentric sculpture as in M. fragilis and without a longitudinal groove and growth lines as in M. cuneiformis . In addition, Martesia fragilis can be distinguished from M. striata by the thinnest umbonal reflection, most elongated anterior adductor muscle, longest anterior part of the shell, lanceolate hypoplax and largest metaplax ( Srinivasan 1959).

Figures

Fig. 7. Martesia fragilis. A−C, USNM 614180, lectoype. D−H, Pholadidea minuscula Dall, 1908, USNM 122946, syntypes. I−L, Martesia (Diploplax) bahamensis Bartsch and Rehder, 1945, USNM 573549, holotype. M−P, Martesia (Diploplax) exquisita Bartsch and Rehder, 1945, USNM 573548, holotype. Scale bars: A−C, E = 2 mm; D = 1 mm; F−G, I−P = 5 mm; H = 500 µm.