Philobrya limoides E.A. Smith, 1907

Urcola, Matias Ricardo & Zelaya, Diego Gabriel, 2024, The Genus Philobrya J. G. Cooper, 1867 (Bivalvia: Philobryidae) In Patagonia And Adjacent Antarctic Waters, Zootaxa 5437 (2), pp. 151-192 : 169-171

Philobrya limoides E.A. Smith, 1907

( Figure 11 )

Philobrya limoides E.A. Smith, 1907: 4 , 5, pl. 3, figs. 2, 2a, 2b.

Philippiella bagei . Hedley, 1916: 20, pl. 1, figs. 5‒7.

Philobrya sublaevis . Lamy 1906a: 51, fig. 5; Lamy 1906b: 18, pl. 1, figs. 17, 18; Nicol 1966 (in part): pl. 4, fig. 5 [not pl. 4, fig. 7 = P. sublaevis ]; Hain 1990: 84, 85, pl. 12, figs. 4a‒d; Choe et al. 1994: 24, fig. 17; Absher & Feijó 1998: 440, fig. 2E; Jackson et al. 2015: figs. 2H, 3H; Osorno Arango & Cantera Kintz 2021: 202, 203, fig. 4a. (Not Philobrya sublaevis Pelseneer, 1903: 25 , 26, 42, 43, pl. 7, figs. 93‒95, pl. 8, figs. 96‒99).

Hochstetteria sublaevis . Egorova 1982 (in part): fig. 258. (Not Philobrya sublaevis Pelseneer, 1903: 25 , 26, 42, 43, pl. 7, figs. 93‒95, pl. 8, figs. 96‒99).

Type localities: Winter Quarters [Ross Sea, 77°50’S 166°39’W], 20‒130 fathoms [36.5‒219.5 m] ( Philobrya limoides ); Commonwealth Bay, [D’Urville Sea, 66°54’S 142°40’E], 3 fathoms [5.5 m], 25 fathoms [45.7 m], 45‒50 fathoms [82.3‒91.4 m] and 55‒60 fathoms [100.6‒109.7 m] ( Philippiella bagei ).

Material examined: Photographs of one syntype of Philobrya limoides ( NHMUK 1905.7.10.73-82), and five syntypes of Philippiella bagei ( AM C.46517). South Orkney: 60°40.99’S 46°14.56’W, 104 m (MACN-In 44443: 1 spec) ; 60°42.33’S 46°01.34’W, 85 m (MACN-In 44444: 3 spec) . South Shetland: Bahía Luna, 62°36’S 59°54’W (MACN-In 35245: 1 spec) . Antarctic Peninsula : Puerto Melchior, [64°19’S 62°58’W] ( MACN-In 35180 : 2 spec) and 25 m (MACN-In 35181: 12 spec) ; Bahía Paraíso , [64°51’S 62°54’W] (MACN-In 35266: 3 spec; MACN-In 35082: 1 spec; Base Brown [64°53.72’S 62°52.25’W] (MACN-In 35283: 1 spec).

Distribution: Antarctic waters, from Ross Sea (E. A. Smith 1907) to Weddell Sea ( Hain 1990), and Davis Sea ( Egorova 1982); South Shetland ( Choe et al. 1994; Absher & Feijó 1998; this study), South Orkney (this study); 5.5‒219.5 m.

Description: Shell large (maximum L = 11.2 mm), ovate to subcircular, high (H/L = 0.99 ± 0.02, n = 18), compressed (W/H = 0.59 ± 0.04, n = 18), delicate; with a wide, ill-defined dorsal slope. Umbo small, narrow, only slightly outstanding from shell outline, located at anterior end. Umbonal angle: 90‒95° (n = 18). Dorsal margin with the anterior portion long, straight, vertical and the posterior portion arched in small-sized specimens but slightly to markedly truncated in larger specimens. Posterior margin somewhat projected in larger specimens, forming a continuous curve with the dorsal margin. Ventral margin long and straight.

Prodissoconch D-shaped, with posterior end higher than anterior end, widely projected ventrally, of 670‒ 750 µm Lp, separated from the dissoconch by a prominent rim. Antero-dorsal and postero-dorsal areas poorly differentiated, sculptured with prominent commarginal folds. Central area sculptured with 42‒47 thin radial ribs. Some ribs extending all along; other (shorter) ribs, appearing distally, intercalated or coalescent to the previous ones.

Dissoconch whitish, glossy. Sculpture cancellate, consisting of 17‒25 primary radial ribs, irregularly distributed commarginal folds, and intercalated radial ribs and commarginal treads.

Periostracum thick, pale yellow to yellowish brown, extending up to 2 mm beyond calcified shell margin; forming delicate radial folds, thin and raised commarginal lamellae, and long, thin setae. Commarginal lamellae extending up to the tip of the setae, with straight margin between contiguous setae.

Inner shell margins strongly crenulated; radial folds absent. Posterior adductor muscle scar located in the anterior half of the valves, dorsally displaced.

Hinge: Anterior and posterior series of G1b teeth forming an angle of 165‒170° (n = 10). Distal teeth of the posterior series partially disintegrated, forming pustules, in specimens longer than 2mm. Distal teeth of the anterior series also forming pustules in specimens longer than 6.4 mm. Resilifer long and wide.

Remarks: Dell (1964) included Philobrya limoides in the synonymy of P. sublaevis , a criterion followed by all subsequent authors, in the last 60 years (e.g., Dell 1990; Huber 2010). However, the present study of a large series of specimens from the Scotia Arc islands and the Antarctic Peninsula, and of the syntypes of P. limoides ( Fig. 11A, B ) reveals that this synonymy is wrong, and most probably originated in the previous misinterpretation of the concept of P. sublaevis . The latter is a species described in detail below, where a comparison with P. limoides is also provided. Philobrya limoides also resembles P. multistriata ( Fig. 13 ; see comparison under that species and Appendix 1).

Our current concept of Philobrya limoides is in agreement with descriptions and figures provided by Lamy (1906a: fig.5; 1906b: figs. 17, 18), Nicol (1966: fig. 5), Hain (1990: figs. 4a‒d), Choe et al. (1994: fig. 17), Absher & Feijó (1998: fig. 2E), Jackson et al. (2015: figs. 2H, 2H), and Osorno Arango & Cantera Kintz (2021: fig. 4a).

Figures

FIGURE 11. Philobrya limoides. A, B: syntypes of P. limoides (NHMUK 1905.7.10.73-82), C: syntype of Philippiella bagei (AM C.46517), D, O, P: specimens from South Orkney (D: MACN-In 35245, O, P: MACN-In 44444), E, F, H‒L, N, Q‒T: specimens from Puerto Melchior (MACN-In 35181), G, M: specimen from Bahía Paraíso (MACN-In 35081). A, D, E: outer views left valve (A, D: without periostracum, E: with periostracum), B, J: inner views left valve, C, F‒I: outer views right valve (C: with periostracum, F‒I: without periostracum), K‒N: inner views right valve, O: brooded embryo removed from the demibranch of an adult specimen, P‒R: hinge plates left valve (P: specimen of 10.2 mm L, Q: specimen of 6.4 mm L, R: specimen of 2.7 mm L), S, T: hinge plates right valve (S: specimen of 6.4 mm L, T: specimen of 2.7 mm L). Scale bars A‒N: 1 mm; O: 100 µm; P‒T: 500 µm.

FIGURE 13. Philobrya multistriata. A, I: syntype (MNHN-IM-2000-34158), B, G, H, N: specimens from Tierra del Fuego (MLP-Ma 7459), C‒F, J, K, O‒Q: specimens from Burdwood Bank (C‒F, Q: MACN-In 44468, J, K, O, P: MLP-Ma 7460), L, M: specimen from Isla de los Estados (MACN-In 44466). A‒G: outer views right valve (A, B: with periostracum, C‒G: without periostracum), H, L: outer view left valve (without periostracum), I, J: inner views left valve, K: inner view right valve, M: detail of prodissoconch (slightly tilt), N, O, Q: hinge plates right valve (N: specimen of 5.1 mm L, O: specimen of 3.4 mm L, Q: specimen of 7.1 mm L), P: hinge plate left valve (specimen of 3.4 mm L). Scale bars A‒K: 1 mm; L, N‒Q: 500 µm; M: 100 µm.