Acila (Truncacila) interferencia, Kiel & Fernando & Magtoto & Kase, 2022

Kiel, Steffen, Fernando, Allan Gil S., Magtoto, Clarence Y. & Kase, Tomoki, 2022, Mollusks from Miocene hydrocarbon-seep deposits in the Ilocos-Central Luzon Basin, Luzon Island, Philippines, Acta Palaeontologica Polonica 67 (4), pp. 917-947 : 920-922

Acila (Truncacila) interferencia sp. nov.

Fig. 3 .

Zoobank LCID: urn:lsid:zoobank.org:act:215BA2D8-5F8A-42D1-A54C-D2E66CE97C37

Etymology: For the sculpture on the anterior shell portion, where the typical divaricate pattern in Truncacila turns into some interferencelike pattern.

Type material: Holotype: NIGSPAL-004, articulated specimen with preserved shell material, from block I. Paratype: NRM Mo 192694 ,

tral margin convex, posterior margin concave; escutcheon broadly oval, with distinct groove and ridge subparallel to margin, ridge with nodular, commarginal ribs, inner part of escutcheon elevated toward ventral side. Line of primary divarication of external sculpture displaced toward anterordorsal shell margin; two secondary lines of bifurcation, one close and subparallel to anterordorsal margin, one posterior at about one third of shell length, divaricate sculpture becomes irregular on anterior third of shell. Anterior adductor muscle scar near anterior end of dorsal margin, nearly round, bounded posteriorly by strong ridge; posterior adductor scar at posterior end of escutcheon, elongate-oval, bounded anteriorly by distinct ridge; pallial line distinct, entire, parallel to ventral shell margin; inner ventral shell margin crenulated. Hinge with up to 20 anterior teeth and nine posterior teeth.

articulated specimen with shell partially broken off, from block G from the type locality and horizon.

Type locality: The “shale quarry” within the Northern Cement Corporation quarry in Pangasinan province, Luzon, Philippines .

Type horizon: Seep carbonate blocks enclosed in the Amlang Formation (Upper Miocene) .

Material.— Five specimens from block B ( NRM Mo 192589–192593) , one specimen from block G (paratype NRM Mo 192694) , two specimens from block I (holotype NIGSPAL-004, NRM Mo 192659). All from the type locality and horizon .

Dimensions ( in mm).— Holotype NIGSPAL-004: L = 23.7, H = 16.0, W = 11.7; NRM Mo 192659: L = 23.4, H = 15.0, W = 12.0; NRM Mo 192592: L = 21.4, H = 13.6; NRM Mo 192694: L = 27.0, H = 15.0, W = 13.0.

Diagnosis.—Average sized shell for the genus; dorsal and ventral margins evenly convex, subparallel; rostral sinus indistinct; escutcheon broad, wide, oval, lunule very narrow; line of primary divarication displaced toward anterordorsal shell margin, divaricate sculpture disintegrates in anteroventral third of shell.

Description.—Shell subquadrate to elliptical; height/length ratio ~0.65, width/height ratio ~0.8. Anterodorsal shell margin evenly convex, anterior margin acutely rounded, ven- Remarks.—With its elongated shell with nearly parallel dorsal and ventral margins, a very indistinct rostral sinus, and rather unordered sculpture on the anterior half of the shell, this species is quite distinct from other species of Acila and Truncacila . Similar regarding the elongation is a specimen reported as “ Acila divaricata (Hinds) ” from the Miocene Kabeya Formation in Fukushima prefecture, Japan ( Aoki 1954: pl. 1: 17), but that specimen widens anteriorly (rather than narrowing as in A. [T.] interferencia ) and has a deeper rostral sinus than A. (T.) interferencia . The late Oligocene to Early Miocene Acila vigilia var. elongata Nagao and Huzioka, 1941 , from Hokkaido, Japan, has a more distinct and broader escutcheon and a better defined rostrum than A. (T.) interferencia , and has finer sculpture without the interference-like pattern ( Nagao and Huzioka 1941).

Also similar regarding elongation are several specimens reported as A. (T.) nehalemensis Hanna, 1924, from the Eocene Keasey Formation in Oregon ( Schenck 1936: pl. 5: 6, 8), and as A. (T.) conradi ( Meek, 1864) from the Early Miocene Astoria Formation in Oregon and Washington ( Schenck 1936: pl. 8: 2, 3, 5–10, 12, 13), but the ribs on the anterior side of these shell radiate in an orderly way toward the shell margin, quite distinct from the granular pattern of A. (T.) interferencia . All other species reported by Schenck (1936) are shorter and/or more oval, or have a more distinct posterior projection, and more ordered divaricate sculpture.

Stratigraphic and geographic range. —Upper Miocene of Luzon, Philippines.

Family Mytilidae Rafinesque, 1815

Genus Gigantidas Cosel and Marshall, 2003

Type species: Gigantidas gladius Cosel and Marshall, 2003 , Recent from the southern Kermadec Ridge in 360–750 m depth.

Gigantidas coseli Saether, Little, Campbell, Marshall, Collins, and Alfaro, 2010b

Fig. 4 .

2010 Gigantidas coseli sp. nov; Saether et al. 2010b: 21 , figs. 4B, C, 8–10, 17.

2016 Gigantidas coseli Saether et al. 2010 ; Saether et al. 2016: 7 , fig. 4.

Material.— One specimen from block A (NIGSPAL-039), seven specimens from block E ( NRM Mo 192454–192462) , two specimens from block I ( NRM Mo 192668, 192669). Upper Miocene of the “shale quarry” within the Northern Cement Corporation quarry in Pangasinan province, Luzon, Philippines .

Dimensions (in mm).— NRM Mo 192454, L = 113.0, H = 28.3, W = 27.3; NRM Mo 192455, L = 60.7, H = 16.2, W = 12.4; NRM Mo 192456, L = 43.0, H = 13.8, W (single) = 0.4; NRM Mo 192668, L = 26.0+, H = 12.8, W (single) = 7.6; NRM Mo 192669, L = 45.8, H = 18.4, W (single) = 7.5.

Remarks.—The New Zealand specimens of Gigantidas coseli show some variation regarding the expansion of the posterior shell portion, ranging from being almost straight to bending and expanding ventrally ( Saether et al. 2010b),

which is also seen among the specimens from the Northern Cement Corporation quarry.

Stratigraphic and geographic range. —Middle Miocene of New Zealand (North Island) and Upper Miocene of Luzon, Philippines.

Genus Bathymodiolus Kenk and Wilson, 1985

Type species: Bathymodiolus thermophilus Kenk and Wilson, 1985 , by original designation; Recent, Galapagos Ridge.

Figures

Fig. 3. The nuculid bivalve Acila (Truncacila) interferencia sp. nov. from Upper Miocene seep deposits of the Amlang Formation in Pangasinan province, Luzon, Philippines. A. NIGSPAL-004, holotype, an articulated specimen showing external sculpture; view on RV (A1), dorsal view on anterodorsal margin (A2) and on posterior margin (A3). B. NRM Mo 192694, paratype, specimen with most of the shell material removed, revealing internal features; view on LV (B1), dorsal view on anterodorsal margin (B2) and on posterior margin (B3). Abbreviations: aams, anterior adductor muscle scar; pams, posterior adductor muscle scar.

Fig. 4. The bathymodiolin bivalve Gigantidas coseli Saether, Little, Campbell, Marshall, Collins, and Alfaro, 2010, from Upper Miocene seep deposits of the Amlang Formation in Pangasinan province, Luzon, Philippines. A. NRM Mo 192455, articulated specimen, view on LV (A1) and dorsal view (A2). B. NRM Mo 192456, internal mold, view on LV showing posterior adductor muscle scar (pams). C. NRM Mo 192668, isolated LV, view on exterior (C1) and on dorsal side (C2). D. NRM Mo 192669, isolated LV, view on exterior. E. NRM Mo 192454, large, articulated, and slightly distorted specimen, view on RV.