Mollusks from Pliocene and Pleistocene seep deposits in Leyte, Philippines

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Introduction
Deep-water methane-seep faunas have a decent Cenozoic fossil record (Majima et al. 2005;Campbell 2006;Kiel 2010b) providing insights into the paleoecology and evolutionary history of these ecosystems (Campbell and Bottjer 1995;Amano and Jenkins 2007;Amano et al. 2010;Kiel 2010aKiel , 2015;;Kiel et al. 2016).Seep fossils of Plio-Pleistocene age, however, are relatively rare, probably because there has not been enough time for their uplift (Oppo et al. 2020).A few occurrences of chemosymbiotic bivalves are known from Plio-Pleistocene strata along the American Pacific coast and from Taiwan (Olsson 1942;Squires 1991;Campbell 1992;Wang et al. 2006), the late Pliocene Stirone river seep complex in northern Italy has a diverse fauna of around ten mollusk species (Cau et al. 2015;Kiel and Taviani 2018), and the richest Plio-Pleistocene record is that of Japan, with around 15 mollusk species (Majima et al. 2005;Amano et al. 2019).
A few Plio-Pleistocene seep deposits are known from the Philippines (Majima et al. 2007(Majima et al. , 2010) ) but their fauna has never been described in detail, save for one large species of the vesicomyid genus Wareniconcha (Kase et al. 2019).The Philippines are part of the Indo-Australian Archipelago biodiversity hotspot and hence play an important role in generating biodiversity in the Indo-Pacific region (Ellison et al. 1999;Bellwood and Hughes 2001;Jablonski et al. 2006;Renema et al. 2008).Indeed, the species-rich chemosymbiotic bivalve family Lucinidae appears to have its center of biodiversity in the Philippines (Taylor and Glover 2006;Cosel and Bouchet 2008;Taylor et al. 2014;Glover and Taylor 2016).The Philippines might therefore also be significant for the diversity of deep-water methane-seep faunas.Here we provide a detailed taxonomic account on the mollusk fauna of these seep deposits, which includes a remarkably high diversity of lucinid bivalves.

Material and methods
The specimens reported here were collected from four localities on the west coast of the northwestern tip of Leyte Island, Philippines (Fig. 1) (Majima et al. 2007(Majima et al. , 2010)).Deep-water strata of the Visayan back-arc Basin crop out in this area and are mapped as Bata Shale (Corby et al. 1951) or Bata Formation (Porth et al. 1989).Due to submarine slumping during the deposition and the extensive reworking of the micro-and nannofossils, the beds including the seep fauna described here are difficult to date.Ongoing stratigraphic and micropaleontologic work suggests that of the major four sampled localities, the seep deposits at Liog-Liog Point is of late Pliocene age, while the others are of early Pleistocene age.
Liog-Liog Point.-Thissite has been described in detail before (Kase et al. 2019).At least four very large calcareous concretionary blocks are scattered in the property of Douglas Pastor at Liog-Liog Point between Tabango and Campopo Bays (11°17'37.7"N,124°21'57.5"E).The blocks are densely packed with Archivesica pastori sp.nov.and Conchocele majimai sp.nov., and are most probably derived from the semi-consolidated mudstone horizon well below the Pliocene-Pleistocene boundary, as indicated by microfossil analyses (Kase et al. 2019).One of the very large blocks was extensively sampled and this block is meant when we refer to Liog-Liog Point as type locality; however, a few specimens were also collected from smaller, scattered blocks.
Buhoc Point.-Thissite is located south of Buhoc Point in Tabango (11°18'49"N, 124°20'39"E; Loc. 2 in Majima et al. 2007).The beds exposed at this site consist of semi-consolidated, tuffaceous, fine-grained sandstone.Huge float concretions derived from the sandstone are scattered on the intertidal platform and are often densely packed with articulated lucinid bivalves.Our microfossil analyses were not successful to date these beds in detail.We consider the beds as being of Pleistocene age because Majima et al. (2007) correlated the beds to the uppermost part of the Bata Formation exposed on the intertidal shore at the tip of Liog-Liog Point, which include the planktonic foraminifer Globorotalia truncatulinoides diagnostic for the Pleistocene.
Antipolo Point.-Thissite is Loc.7 (11°15'28"N, 124°22'55"E) in Majima et al. (2007).Variable-sized and complex concretions resulting from the precipitation of authigenic carbonate around burrows cover the beach and sea cliff at Antipolo Point, and contain a swarm of articulated shells of Lucinoma spp.and Meganodontia acetabulum.The matrix surrounding these concretions consists of semi-consolidated and unconsolidated muddy sandstone that also yields chemosynthetic bivalves as well as normal deep-water mollusks.The beds in this site have been definitely dated as Pleistocene by planktonic foraminifer and nannofossil analyses.
Cambantug Point.-Thissite has been described in detail by Majima et al. (2007).It is located at the western corner of Cambantug Point (11°26'55.7"N,124°18'18.1"E),where massive semi-consolidated mudstone beds are exposed on the beach and in the beach cliff.Abundant bivalves are found in several calcareous concretions of variable size and also in mudstone around the concretions.The bivalves are mostly articulated and densely packed, keeping their original life orientations.The dating of the mudstone beds remains somewhat questionable: nannofossils provided a middle Pliocene age (NN15), whereas planktonic foraminifers point to an early Pleistocene age.This might indicate reworking of the nannofossils and hence we consider the age of the calcareous concretions as early Pleistocene.
All measurements are given in mm rounded to the nearest first decimal place.

Unidentified bathymodiolin
Remarks.-The single available right valve experienced a shell injury about at its midline, resulting in a deformation that makes the identification of this specimen difficult.Bathymodiolus hirtus, B. japonicus and B. platifrons possess a similar low, subterminal umbo, but those species have a more drawn-out posterior margin that is acutely rounded posteroventrally (Hashimoto and Okutani 1994;Okutani et al. 2004;Sasaki et al. 2005).Bathymodiolus securiformis has a similar narrow posterior margin and long posterodorsal margin, but also a much more elongate anterior margin.Two taxa associated with wood and bones in the Westpacific Ocean are also similar: "ESU D" from the Philippines and Japan, and "Idas sp.SAL 4" from Vanuatu and Philippines (Lorion et al. 2010).
Conchocele majimai sp.nov.Description.-Large,well-inflated shells, W/H ratio of one valve 0.30-0.33,umbones terminal, blunt, prosogyrate; anterior margin long, slightly concave; anterodorsal area broad with blunt internal ridge starting at umbo, ending at 2/3 of length anterodorsal area; anterior half of ventral margin straight, then turning dorsally in broad curve until reaching posterior end of shell; dorsal margin evenly and slightly convex, transition to posterior margin marked by distinct corner; posterodorsal area broad, bordered by deep, sulcus that is curved on first half of shell, nearly straight on second half, and causes an indentation on the posterior shell margin; outer surface with fine, irregular growth lines.
Remarks.-For differences to Conchocele majimai see above.Compared to Conchocele visayaensis, Conchocele sp. from Papua New Guinea (Samadi et al. 2015: fig.2F) has a curved rather than angular transition from posterodorsal to posterior margin, and the posterior sulcus in a more dorsal position, resulting in a smaller posterodorsal area and in a broader and more curved posteroventral margin.The same applies to extant North Pacific shells typically identified as Conchocele bisecta (Coan et al. 2000;Kamenev et al. 2001;Khar la menko et al. 2016)  Remarks.-Wefollow the revised diagnosis for Chan nelaxinus provided by Oliver and Frey (2014: 466) and the provisional assignment of Thyasira excavata Dall, 1901, and  Prothyasira adelaideana Iredale, 1930 to Channelaxinus (Oliver and Frey 2014;Oliver 2015).
Channelaxinus antipoloensis sp.nov.Diagnosis.-Shell of average size for genus; median ridges on shell surface developed as angulations rather than distinct ridges; lunule small for genus, comprising less than half of anterior shell margin; submarginal sulcus distinct but short.
Description.-Shellpolygonal, umbones elevated, prosogyrate, rather blunt; short but distinct posterior submarginal sulcus; posterodorsal area of moderate height, rather short, bordered by distinct sulcus and sharp ridge; shell surface with two low angulations running from umbo to ventral shell margin; anterior margin straight to slightly concave; lunule deep, length slightly less than half of anterior margin; hinge plate narrow, edentulous; ligament nymph short.
Remarks.-Channelaxinus antipoloensis sp.nov. is here placed in Channelaxinus based on its deeply impressed lunule and flattened median slope that is bounded by low ridges.With these two characters, C. antipoloensis clearly differs from members of Conchocele, a genus of large thyasirids that is often found at fossil seep deposits (see above).Ascetoaxinus Oliver and Frey, 2014, with its type species Ascetoaxinus quatsinoensis Oliver and Frey, 2014, has a similar overall shell shape, but C. antipoloensis differs from Ascetoaxinus by lacking the rounded projections that scallop the lunule edge in Ascetoaxinus, and by having a small lunule.Thyasira Lamarck, 1818 differs by having shells that are less angular and thinner, and the posterior and submarginal sulci of C. antipoloensis are deeper and sharper than in Thyasira.
The most similar extant species is Channelaxinus adelaideanus (Iredale, 1930); the original illustration is a sketch (Iredale 1930: pl. 63: 6, 7) and photos of the holotype were provided by Oliver (2015: figs. 3E, F).They show a specimen with a more pronounced median ridge compared to the median angulation of C. antipoloensis; also the less distinct radial ridge ventral to the median ridge is more pronounced in C. adelaideanus than in C. antipoloensis.Channelaxinus excavata (Dall, 1901) has a larger lunule and a more elongate submarginal sulcus than C. antipoloensis.The only fossil so far assigned to Channelaxinus is Chan nelaxinus sp.from the middle Miocene (Langhian) Ca' Cavalmagra seep deposit in northern Italy (Kiel and Taviani 2017: 450, fig. 5); the illustrated specimens differs slightly from C. antipoloensis by having a longer posterodorsal area, which is particularly well-seen in Kiel and Taviani (2017: fig. 5.4).The early Miocene Thyasira minoensis Itoigawa, 1960 from the Mizunami Group in central Honshu, Japan is also similar and might belong to Channelaxinus but appears to have a more defined median ridge (Itoigawa 1960: pl. 2: 1) compared to the median angulation C. antipoloensis.Another potential fossil Channelaxinus is the early Miocene (Altonian, ~late Burdigalian) Thyasira (Prothyasira) bartrumi Powell, 1935 from a deep-water faunule found near Auckland, New Zealand, which is smaller (L = 15 mm, H = 15 mm), and is more elongate and has a shorter anterior margin than C. anti poloensis (Powell 1935: 332, pl. 76: 5, 6).
Although the extant E. ingens is known only from the holotype and intraspecific variability cannot be assessed, for now we consider the observed differences in deviation of the aams as intraspecific variation.
Elliptiolucina fernandoi sp.nov.Remarks.-Thethree extant species described by Cosel and Bouchet (2008)    Remarks.-Divalucinasoyoae is known from depth of 90 to 200 m in southern Japan (Habe 1952;Dekker and Goud 1994); the genus has not been reported from seep sites before.Extant specimen of Divalucina soyoae are said to reach 47 mm in length (Dekker and Goud 1994), which is only marginally smaller than those reported here.See Dekker and Goud (1994) and Amano ( 2019) for an extensive syno nymy and a summary of fossil and recent occurrence of this species.Remarks.-Overall, the specimens from Liog-Liog Point resemble Lucinoma kastoroae, but differ slightly in being growing to larger size (up to 55 mm length compared to 34 mm in L. kastoroae), by being somewhat taller and by having a slightly less acutely rounded anterior margin.However, we consider these differences too marginal to establish a new species.
Lucinoma canudai sp.nov.Material.-Thetype material only.Diagnosis of single valve = 0.37), greatest width at middle of shell; anterodorsal margin slightly concave, with angulation at transition to broadly rounded anterior margin; posterodorsal margin evenly convex, with slight angulation at transition to broadly rounded posterior margin; ventral margin evenly convex, without distinct transitions to anterior and posterior margins; escutcheon lanceolate, greatest width in posterior half; lunule short, broad, deep; hinge plate broad and thick, two thick and short cardinal teeth in each valve, cardinals 1 and 2 pointing downward, cardinals 3 and 4 pointing toward posteroventral margin; ligament nymph lanceolate, about 2/3 of length of posterodorsal shell margin; anterior adductor muscle scar moderately narrow and of moderate length for genus, reaching down to 2/3 of shell height, detached slightly from pallial for ~70% of its length; posterior adductor muscle scar elongate-oval, its lower end situated at about mid-height of shell; shell interior covered by fine striation, most strongly developed at and beyond pallial line.
Remarks.-Lucinoma velosoi differs from the similarly inflated L. tinagoensis described below by reaching a larger size (Table 1), its more elongated shell (that of L. tinagoensis is taller) and its narrower escutcheon.The Pliocene to Recent Lucinoma galathea Marwick, 1953 from New Zealand has a more pointed umbo than L. velosoi, broader and longer ligament nymph, reaches only about 50 mm in length, whereas L. velosoi reaches 70 mm, and is less inflated than L. velosi (Marwick 1953;Campbell et al. 2010).
Description.-Shellmedium-large for genus, greatest width at middle of shell (W/H ratio of single valve = 0.37); anterodorsal margin straight to sinuous, with angulation at transition to somewhat acutely rounded anterior margin; posterodorsal margin evenly convex, with slight angulation at transition to broadly rounded posterior margin; ventral margin evenly convex, without distinct transitions to anterior and posterior margins; shell surface covered by densely spaced, sharp to cord-like commarginal ribs; escutcheon elongate, broad, greatest width in middle; lunule elongate, heart-shaped.
Anterior adductor muscle scar moderately narrow, of moderate length for genus, reaching down to ~70% of shell height, detached from pallial by ~30° for c. 2/3 its length.
Remarks.-The early Miocene Lucinoma saetheri differs by its smaller and more pointed umbones, narrower escutcheon (Amano et al. 2018).Lucinoma galathea resembles Lucinoma tinagoensis in outline to but is described as "weakly inflated" (Beu and Maxwell 1990: 281) in contrast to the strong inflation of L. tinagoensis.
Lucinoma kosatorea sp.nov.tion at transition to posterior margin; escutcheon lanceolate; lunule long, moderately deep; hinge plate narrow and thick, two thin cardinals in left valve, both pointing downward; thin, elongate anterior lateral tooth in left valve; ligament nymph long, narrow; anterior adductor muscle scar long and narrow, reaching down to 70% of shell height, detached slightly from pallial for c. 70% of its length; posterior adductor muscle scar rounded-oval, its lower end situated at about mid-height of shell; interior of ventral margin marked by two thin ridges with groove in between.
Remarks.-Very similar in shell shape is the Pleistocene Japanese species Lucinoma aokii Hirayama, 1958, but it is larger than L. kosatorea (L = 76.0 mm vs. L = 52.7 mm in L. kosatorea), has a broader lunule with a clearly delimited margin, the hinge plate has an excavated area posterior to the umbo, and the ligament nymph is much narrower than in L. kosatorea (Hirayama 1958).A specimen reported as L. aokii from a Pleistocene seep deposit on the Boso Peninsula in Japan (Shibasaki andMajima 1997: 1068, fig. 4.12): differs from the holotype of L. kosatorea by having a shorter but broader hinge plate, a straighter anteroventral margin, and a distinct external ridge running from the umbo to the anterior shell margin.
Lucinoma canudai, L. velosoi, and L. tinagoensis are much more inflated than Lucinoma kosatorea.A similarly acutely rounded anterior margin is seen in the extant Lucinoma anemiophila Holmes, Oliver, and Sellanes, 2005 from methane seeps off of central Chile.But L. anemiophila has a truncated, angular posterior margin and a more distinctive posterior ridge than Lucinoma kosatorea (Holmes et al. 2005).
Vesicomya margotae Beets, 1953  species is Vesicomya katsuae Kuroda, 1952  Remarks.-Thedifferences between Isorropodon and Vesicomya were defined as follows: "Isorropodon is distinguished from Vesicomya by the much larger and more oval to oval-oblong shell, the poorly developed to missing lunular incision and the smooth valve margins without an incision.Vesicomya is smaller, the shells are very tumid to nearly spherical, the general hinge teeth configuration however is the same in both" (Cosel and Salas 2001).
Isorropodon cf.perplexum Sturany, 1896 Remarks.-Theavailable specimens are virtually indistinguishable from the syntypes of I. perplexum as illustrated by Cosel and Salas (2001: figs. 33-35), but with the hinge dentition of the Philippine specimens unknown, we only hesitantly assign them to the extant Mediterranean species I. perplexum.
Description.-Largeelongate-oval shell, umbones blunt, elevated, slightly prosogyrate, situated anterior at c. 26-31% of total shell length; anterodorsal margin straight; anterior margin acutely rounded, anterior-most point somewhat above midline of shell; ventral margin straight or slightly concave; posterior margin broadly rounded; posterodorsal margin gently sloping.Hinge plate strong, broad, with three relatively thick cardinals in each valve, radiating outward from underneath umbo; right valve: cardinal 1 elongate, protruding, pointing anteroventrally, 3a elongate, subparallel to shell margin, reduced, 3b elongate-triangular, pointing posterodorsally; left valve: cardinal 2a moderately thin and of same length or longer as 2b, pointing anterorventrally, 2b triangular, thick, occasionally bifid, pointing to center of ventral margin, cardinal 4 short, narrow, pointing posterior, with shallow, elongate posterior depression; nymph plate elongate, about ½ of total shell length, starts tapering posteriorly after about half its length.Outer shell surface with faint, irregular growth increments.
Remarks.-Very similar regarding hinge dentition are the extant Japanese species Archivesica similaris (Okutani et al. 1997) and Archivesica tsubasa (Okutani et al. 2000), but both are more elongate than Archivesica pastori.As a result of being more elongate, their dorsal and ventral margins are more parallel than in A. pastori.However, this feature shows some variability in A. pastori, for example the specimen shown on Fig. 21B 1 has rather parallel dorsal and ventral margins, but is not as elongate as A. similaris and A. tsubasa.Another extant species with similar hinge dentition is Archivesica ochotica Scarlato, 1981, which is less elongate compared to A. pastori and has a proportionally shorter ligament nymph (Scarlato 1981).The early Miocene Japanese Archivesica sakoi Amano, Jenkins, Ohara, and Kiel, 2014 also shows a similar hinge dentition and overall shape, but its cardinal 3b in the right valve is more elongate and subparallel the shell margin unlike the shorter and oblique tooth of A. pastori, and A. sakoi also has more prominent and more prosogyrate umbones (Amano et al. 2014), and is much smaller (L = 80 mm in A. sakoi compared to L = 143 mm in A. pastori).
The hinge dentition of A. pastori is also somewhat similar to that of Archivesica magnocultellus (Okutani et al. 2002) except that A. pastori lacks the large pit posterior to the cardinals seen in A. magnocultellus.Archivesica pastori differs from the type species of Archivesica, A. gigas (Dall 1896), by having a short cardinal 2a and a strong, thick cardinal 2b in the left valve, whereas A. gigas has a very elongate 2a and a narrow 2b.Furthermore, A. pastori has a long ligament nymph (c.½ of shell length), whereas the ligament nymph is short in A. gigas.
When Boss (1968) described "Pliocardia" cordata, he considered it "remarkably similar, and probably most closely related, to V. ticaonica Dall" (Boss 1968: 735).The two shells are indeed very similar, and we concur with this view.Boss (1968)   Waisiuconcha alberdinae Beets, 1942 from Buton Island, Sulawesi, Indonesia, as a precursor or possibly even as a synonym of V. ticaonica.However, whether the much smaller (23 mm) and thin-shelled W. alberdinae is indeed closely related to the thick-shelled "P." ticaonica and "P." cordata remains to be tested.

also considered the late Miocene
Stratigraphic and geographic range.-EarlyPleistocene, Leyte, Philippines.Recent: Philippines and Indonesia.
Wareniconcha guineensis (Thiele and Jaeckel, 1931)   Wareniconcha aff.winckworthi (Prashad, 1932)  Remarks.-Wareniconchaaff.winckworthi is slightly more inflated and has broader umbones than the extant Wareniconcha winckworthi from Indonesia (Prashad 1932).Furthermore, it has a truncate posterior margin (see Fig. 26B 2 ) whereas it is more obliquely truncated in Wareni concha winckworthi; however, this difference might not be a distinguishing character but instead a case of intraspecific dimorphism, as reported for example for the vesicomyid genus Calyptogena (see Krylova and Sahling 2006).The recently described Wareniconcha mercenarioides Kase, Isaji, Aguilar, and Kiel, 2019 from the same seep deposit is much larger (up to 120 mm) and has a roundish-triangular outline, whereas W. aff.winckworthi has an oval outline.
Remarks.-Compared to the holotype of Waisiuconcha alberdinae Beets, 1942(Beets 1942: figs. 147-151), Waisiuconcha sp. 1 from Liog-Liog Point has a more acutely rounded posterior margin, the anterior adductor muscle scar is more elongate than the diamond to drop-shaped scar of W. alberdinae, the pallial line starts at the base of the anterior adductor scar rather than on its posteroventral side, and the pallial line is closer to the shell margin as in W. alberdinae.The two extant species W. surugensis Habe, 1976a andW. haekeli Cosel andSalas, 2001 have shorter shells than Waisiuconcha sp. 1 from Liog-Liog Point (Habe 1976a;Cosel and Salas 2001;Hoffman et al. 2019).Remarks.-Theearly Pleistocene Waisiuconcha sp. 2 has a more distinctive lunular incision and more elevated umbones than the late Pliocene Waisiuconcha sp. 1 reported above from Liog-Liog Point.

Class Gastropoda Cuvier, 1795 Limpets of uncertain affinities
Remarks.-In the absence of data on shell microstructure and protoconch, the four species reported below are difficult to place.Serradonta Okutani, Tsuchida, andFujikura, 1992 andBathyacmaea Okutani, Tsuchida, andFujikura, 1992 (Pectinodontidae) have been shown to vary greatly in outline (from oval to pointed egg-shaped), in the position of the apex (subcentrally to displaced anteriorly) and surface sculpture (from nearly smooth to having strong beaded ra-dial ribs), both within genera as well as within species (Chen et al. 2019).Very similar external morphologies are for example also found among member of the paralepetopsids and neolepetopsids (McLean 1990, 2008, Warén and Bouchet 2009).
Limpet gastropod sp. 1 Description.-Moderatelyelevated limpet (H/L ratio ~0.46), apex displaced slightly toward the anterior, outline oval with anterior side slightly narrower than posterior side, flanks more-or-less straight; external surface with concentric growth rings only, or with numerous narrowly spaced, tuberculate radial ribs; base straight or slightly convex.
Remarks.-Similar species can be found among the pectinodont patellogastropod genus Serradonta Okutani, Tsuchida, and Fujikura, 1992, which is a morphologically variable genus that includes axially ribbed as well as smooth species, with a fossil record ranging back into the Cretaceous (Okutani et al. 1992;Jenkins et al. 2007;Chen et al. 2019).Neolepetopsids such as Neoplepetopsis McLean, 1990 andParalepetopsis McLean, 1990 are another group of patellogastropods with similar shells (McLean 1990(McLean , 2008)).Cocculiniform limpets with oval, radially ribbed shells with subcentral apex are known from the genera Coccocrater Haszprunar, 1987and Coccopigya Marshall, 1986(Marshall 1986;Haszprunar 1987;McLean and Harasewych 1995); the latter has a fossil record ranging back to the early Oligocene (Kiel et al. 2020).
Limpet gastropod sp. 2 Description.-Low to moderately elevated limpet (H/L ratio ~0.4), outline irregularly-round, apex displaced anteriorly; anterior slope straight, posterior slope slightly convex; pallial attachment line close to base; two elongate, slightly curved muscle scars at about 1/3 of shell height, one on each lateral side of shell, tapering slightly anteriorly, posterior end broadened.Remarks.-Theouter shell surface is missing in both specimens; hence the external sculpture is unknown.Compared to limpet sp. 1, these specimens are generally smaller, have a lower elevation and the apex in a more central position.Such shells are often found among the cocculiniforms, such as Coccocrater portoricensis (Dall and Simpson 1901) from the western Atlantic Ocean (McLean and Harasewych 1995), or Cocculina tenuitesta Hasegawa, 1997, a species associated with sunken wood in Suruga Bay, Japan (Hasegawa 1997).
Remarks.-Tall, roundish limpets of the size of these two specimens are common among the genus Pectinodonta; however, all Pectinodonta species show distinct axial ribbing (Marshall 1985(Marshall , 1998;;Marshall et al. 2016;Zhang and Zhang 2018), which is lacking in the two Philippine specimens reported here.
Remarks.-Shells of the heterobranch genera Hyalogyra and Hyalogyrina are quite similar, but the "archaegastropod"-type protoconch (Fig. 29D 3 ) makes affinities with the neomphaline Planorbidella more likely.However, the protoconch lacks the irregular net sculpture typical for Planorbidella, but this might be an artefact of preservation.
Dillwynella sp.Remarks.-Species of Dillwynella can be variable in the height of the spire, as shown for Dillwynella vitrea Hasegawa, 1997 from wood-falls in Japanese waters (Hase gawa 1997).Two species with a similar spire and a similarly narrow umbilicus as the specimen reported here are D. haptricola Marshall, 1988 living on algal holdfasts, andD. ingens Marshall, 1988 living on wood falls in New Zealand waters (Marshall 1988).
Solariella sp.Remarks.-Thisspecimen is identical to an extant shell identified as Solariella tobaruensis Noda, 1988, collected in c. 520 m depth off Omami-oshima island (Ryukyu Islands, southern Japan) and illustrated in Hasegawa (2005) and Sasaki (2017).However, the name Solariella tobaruensis is based on a Plio-Pleistocene fossil from Okinawa, Japan (Noda 1988: 33, pl. 5: 5, 6), which has a more distinct shoulder and a deeper suture than both the extant specimen just mentioned and the Philippine specimen reported here.
Margarites hayashii sp.nov.Diagnosis.-TrochiformMargarites with weakly convex whorls, sculptured by six spiral cords and a finer spiral between cords; umbilicus narrow, base with fine spiral lines.
Description.-Shelltrochiform, at least five whorls with convex profile, sculpture of up to six low, widely spaced cords crossed by strongly prosocline growth lines, some interspaces with fine cord; basal margin marked by another cord; base sculptured by finer and more densely spaced spiral lines than whorl flanks; umbilicus conical, width about 1/3 of shell diameter; aperture circular, strongly inclined.
Description.-Minute,turbiniform shell, protoconch about 0.4 mm across, teleoconch of 3¼ whorls, last whorl very large; whorls strongly convex, sculptured by ~20 very distinct, oblique axial ribs reaching into umbilical area, their interspaces about twice of rib width; ribs and interspaces crossed by ~10 very fine spiral threads.
Remarks.-Vetulonia philippinensis sp.nov.differs from the known species of Vetulonia as follows: Vetulonia galapagana is the most similar species but has fewer axial ribs per whorl (Dall 1913); Vetulonia densilirata Dall, 1927 has  a flat spire according to Dall (1927: 120) in contrast to the trochiform shell of Vetulonia philippinensis; Vetulonia giacobbei Renda and Micali, 2016 has much stronger spiral ornament, giving the whorls an angular appearance; Vetulonia parajeffreysi Absalão and Pimenta, 2005 has a lower spire, and fewer and more oblique axial ribs; and Vetulonia phalcata Warén and Bouchet, 1993 has finer and more numerous axial ribs (Dautzenberg 1889;Dall 1927;Warén and Bouchet 1993, Absalão and    Diagnosis.-Average-sizedCataegis with four distinct spiral cords per whorl, third spiral forming distinct shoulder; base with two strong spiral cords, one of them forming basal margin, and seven finer, equally strong spiral lines; aperture with apical notch, inner lip callused.
Description.-Trochiformshell with up to five whorls, suture deeply incised; whorls sculptured by four spiral cords, first two thin, closely spaced and close to upper suture, third cord strong, marking whorl's shoulder, fourth of same strength as third, situated vertically below third close to lower suture; entire whorl surface covered by finely spaced, distinct, oblique growth increments; basal margin marked by two cords of equal strength; base rather straight with seven densely spaced, beaded spiral cords; umbilical slit covered by callus; aperture circular inclined backwards, inner lip callused with groove between umbilical and lip callus.Subclass Caenogastropoda Cox, 1960Family Provannidae Warén and Ponder, 1991Genus Provanna Dall, 1918 Type species: Trichotropis lomana Dall, 1918, by monotypy; Recent, off California, USA.
Provanna azurini sp.nov.Diagnosis.-Smallfor genus; tall, slender shell, whorls angular, with two equally strong spiral cords per whorl, no axial sculpture; three spiral cords of decreasing strength on base, upper one marking basal margin; aperture slightly oval.
Description.-Tall,slender shell composed of at least 3 whorls, reaching at least 4 mm in height; whorls profile angular, shoulder nearly straight and smooth, two distinct spiral cords per whorl, with broad, smooth interspace; base with three further spiral cords of decreasing strength and beaded appearance, the uppermost marks the basal margin; aperture slightly oval with small, short siphonal notch, columellar and parietal lip callused.
Remarks.-Provanna species having exclusively spiral ornament are rare.The most similar extant species are Provanna macleani Warén and Bouchet, 1989 from seeps off of Oregon, USA (Warén and Bouchet 1989), and Provanna cingulata Chen, Watanabe, and Ohara, 2018, from the Shinkai seep field in the southern Mariana Trench (Chen et al. 2018).Provanna macleani differs from Provanna azurini by having four to five spiral cords per whorl, whereas Provanna azurini has only two.Provanna cingulata has an increasing number of spiral cords per whorl, starting with two spiral cords on very early whorls.However, the whorls of Provanna cingulata are more angular and the species is overall less slender than Provanna azurini.Among fossil species, Provanna antiqua Squires, 1995 from Oligocene seeps in Washington state, USA, and northern Peru (Squires 1995;Kiel et al. 2019), has very variable sculpture including specimens with almost exclusively spiral ornament.But as in the extant P. macleani, these are more numerous (3-4) than in Provanna azurini.
Genus Desbruyeresia Warén and Bouchet, 1993 Type species: Desbruyeresia spinosa Warén and Bouchet, 1993, by original designation;Recent, North Fiji Basin.Desbruyeresia? sp.Material.-Onefragment from Liog-Liog Point (NMNS PM 28457, H = 3.8 mm, W = 3.9 mm).It consists of about one convex whorl sculptured by four equally spaced spiral cords, crossed by equally strong axial ribs; the lowermost spiral cord forms the basal margin, and the base bears about five smaller cords.
Remarks.-A similar species is D. chamorrensis from South Chamorro Seamount on the southeastern Mariana Forearc (Chen et al. 2016).But with only a fragment consisting of one whorl with concealed aperture available, and similar shells known from deep-water rissoids (Warén 1996;Okutani 2000), this specimen is only hesitantly placed in Desbruyeresia.
A comparison of the Leyte seep faunas to Plio-Pleistocene to Recent Japanese seep faunas is interesting.Of the five extant species from Japanese waters reported here from the late Pliocene and early Pleistocene of the Philippines (Bathymodiolus securiformis, Elliptiolucina ingens, Vesi comya nakaii, Pliocardia kuroshimana, Archivesica kawa murai), only the widespread Archivesica kawamurai has a fossil record in Japan (Amano et al. 2019).Thus it appears that a remarkable portion of the extant Japanese seep mollusks originated around the Philippines and spread to Japanese waters only recently.Furthermore, Amano et al. (2019) pointed out that the present-day distribution of vesicomyid bivalves in Japan is probably related to temperature.Whereas Calyptogena originated in colder waters and today inhabits the colder North Pacific waters of Japan, Archivesica has a warmer-water origin and today inhabits the warmer waters of southern and southeastern Japan (Amano et al. 2019).This argument could possibly be extended to a wider range of the seep fauna because all five extant Japanese taxa with a Philippine origin mentioned above presently live in areas of southern Japan influenced by the warm-water Kuroshio Current that originates around the Philippines and flows toward Japan (Saito 2019).
Another remarkable feature of the Philippine Plio-Pleistocene seep mollusks reported here is the high number of lucinids.More than one third (12 out of 30) of all bivalve species are lucinids, and nearly two thirds of the new bivalve species (7 out of 11) are lucinids.Such a large proportion of lucinids is unusual for extant seep faunas (Sibuet and Olu 1998;Sasaki et al. 2005;Olu-Le Roy et al. 2007;Cordes et al. 2010) but is more commonly seen in the fossil record.For example, in the Pliocene Stirone river seep complex, five out of seven chemosymbiotic bivalve species are lucinids (Kiel and Taviani 2018).This discrepancy might relate to the infaunal mode of life of the lucinids, due to which they are rarely found on video observations or in surface collections at modern seeps (Glover et al. 2004;Taylor and Glover 2010;Kiel 2010b).

Conclusions
We report the most diverse Plio-Pleistocene seep faunas to date; the late Pliocene Liog-Liog Point deposit alone yielded 27 species, followed by the Pleistocene Cambantug Point site (14 species) and the Antipolo Point site (9 species).Most species either belong to extant species living in the western Pacific Ocean, or are closely related to them.Remarkable is that several species occur in Japanese waters today, especially the Okinawa Trough, but those species are absent from the well-studied fossil record of seeps in Japan.The only exception is the widespread species Archivesica kawamurai, for which a warm-water origin has been suspected (Amano et al. 2019).
have a narrower posterodorsal area than Conchocele majimai.A specimen illustrated as Conchocele sp. from Broken Water Bay in Papua New Guinea (Samadi et al. 2015: fig.2F) has a more rounded ventral margin and a narrower posterodorsal area than Conchocele majimai.The Miocene holotype of Conchocele bisecta has a much more rounded outlined and a more acutely rounded anterior margin than both Conchocele maji mai and Conchocele visayaensis described below.Stratigraphic and geographic range.-LatePliocene, Leyte, Philippines.Conchocele visayaensis sp.nov.

Fig. 5 .
Fig. 5.The thyasirid bivalve Channelaxinus antipoloensis sp.nov.from the Pleistocene Antipolo Point seep deposit in Leyte, Philippines.A. Paratype NMNS PM 28178, disarticulated right valve embedded in rock matrix; exterior of shell with the light coming from two different angles, emphasizing the posterodorsal sulcus (A 1 ) and the median angulation (A 2 ), and view on dorsal margin (A 3 ).B. Holotype NMNS PM 28177, articulated specimen; views on right (B 1 ) and left (B 2 ) valves, the dorsal margin (B 3 ) and the anterior margin showing the lunule (B 4 ).C. Paratype NMNS PM 28179, articulated specimen with displaced valves; view on exterior of right valve (C 1 ), close-up on edentulous hinge of left valve (C 2 ).Note the frequent repaired shell injuries on all specimens.

Fig. 10 .Fig. 9 .
Fig. 10.Zoobank LSID: urn:lsid:zoobank.org:act:6A60B3D8-F57F-498C-9E7D-895ADB4496FC Etymology: In honour of Allan Gil S. Fernando (Quezon City, Philippines), for his invaluable help in dating the Bata Formation.Type material: Holotype NMP-2163, an articulated specimen with the depth in the central Philippines is smaller than E. fernandoi (44.1 mm vs. 68.0mm maximum length) and it possesses a prominent anterior lateral tooth in the right valve that is missing in E. fernandoi.The extant E. ingens Okutani, 2011 from 576-594 m depth on the slope of the East China Sea(Okutani 2011), growth to bigger size (up to 90.7 mm) and is more inflated than E. fernandoi.Three fossil species of Elliptiolucina are described to date.The late Oligocene E. washingtonia Kiel, 2013 from western Washington state, USA, is more elongate and has a straighter posterodorsal margin than E. fernandoi.The middle Miocene E. neozelandica Amano, Little, and Campbell, 2018 from the Moonlight North seep deposit in New Zealand(Amano et al. 2018) is much smaller and has more elevated umbones than E. cambantugensis.The late Miocene Elliptiolucina hetzeli(Martin, 1933) from asphalt deposit on Buton Island, Indonesia(Martin 1933;Kiel 2013) is more elongate and has more narrowly rounded anterior and posterior margins compared to E. fernandoi.Stratigraphic and geographic range.-LatePliocene to early Pleistocene: Leyte, Philippines.Genus DivalucinaIredale, 1936 Type species: Lucina cumingi Adams and Angas, 1864, by original designation; Recent, Australia and New Zealand.

Fig. 10 .
Fig. 10.The lucinid bivalve Elliptiolucina fernandoi sp.nov.from the Pliocene Liog-Liog seep deposit in Leyte, Philippines.A. Holotype NMP-2163, articulated specimen; view on left (A 1 ) and right (A 2 ) valves, view on the dorsal side (A 3 ), close-up on hinge of right valve (A 4 ).B. Paratype NMNS PM 28119, slightly damaged, articulated specimen; view on exterior of right valve and hinge of left valve (B 1 ), view on exterior of left valve (B 2 ), close-up on hinge of left valve (B 3 ).
Remarks.-KanoiaWarén and Rouse, 2016 was separated from Cataegis based on radula characters(Warén and Rouse 2016), which are typically not preserved in fossils.Based on a comparison of the known species of Kanoia and Cataegis, the latter appears to have a higher, more conical spire whereas the spire of Kanoia appears somewhat dome-shaped (seeMcLean and Quinn 1987;Fu and Sun  2006, Warén andRouse 2016;Vilvens 2016).Based on these shell characters we place C. ramosi in Cataegis rather than Kanoia.The type species C. toreuta differs from C. ramosi by having fewer and stronger spiral cords on the base and a less distinct whorl's shoulder(McLean and Quinn 1987).Also C. celebesensis McLean and Quinn, 1987 has fewer spiral cords on the base than C. ramosi.Cataegis leucogranulatus(Fu and Sun 2006) from the South China Sea has more granular sculpture than C. ramosi and it also has secondary, fine spiral lines between the main spiral cords, a feature not seen in C. ramosi.Among the three species of Cataegis described byVilvens (2016) from the deep waters around the Solomon Islands, C. stroggile Vilvens, 2016 is most similar to C. ramosi but differs from it by having a more convex whorl profile with three main spiral cords instead of two, and by having fewer spiral lines on the base.Stratigraphic and geographic range.-LatePliocene, Leyte, Philippines.
. Shells identified as "Conchocele bisecta Conrad" dredged from Sagami Bay, Japan, in the collection of the National Museum of Nature and Sciences in Tsukuba (T.Haga coll.) are very similar, if not identical, to Conchocele visayaensis.

Table 1 .
(Amano et al. 2018)Campbell, 2018outline angular, umbones blunt, surface sculpture of numerous densely spaced, sharp commarginal ribs, several smaller sharp ridges in interspaces; distinct anterior ridge; posterior sulcus well-developed, lunule long, narrow; ligament long, deeply sunken.Lucinoma saetheriAmano, Little, and Campbell, 2018from the lower Miocene of New Zealand differs from L. canudai by lacking lamellar sculpture and by having smaller umbones(Amano et al. 2018).Overview of the characteristics of Lucinoma species discussed here.Abbreviations: H, height; L, length; W, width.Measurements without decimal point were taken from the literature.
-Cosel and Salas (2001)s (2001)considered V. nakaii as belonging to Isorropodon, but the species has a distinct lunular incision and hence belongs to Vesicomya.The specimen illustrated here from Cambantug Point has the posterior ridge and truncate posterior margin of V. nakaii, whereas V. margotae from Liog-Liog Point is posteriorly more elongated.The specimen clearly shows a lunular incision.Unfortunately, the hinge of our specimen is concealed in rock matrix.Stratigraphic and geographic range.-EarlyPleistocene: Leyte, Philippines.Recent: west coast of Kyushu, Japan.Genus Isorropodon Sturany, 1896 Type species: Isorropodon perplexum Sturany, 1896, by monotypy; Recent, eastern Mediterranean Sea.
Margarites hayashii by having a more angular whorl profile, more numerous spiral cords on the whorls and narrower umbilicus.M. similis has a lower spire and more conical base than Margarites hayashii, and more densely spaced spiral cords.In reference to its origin, the Philippines.Holotype: NMNS PM 28447, specimen with the apertural area concealed by sediment.Type locality: Liog-Liog Point, Leyte, Philippines.Type horizon: Upper Pliocene part of the Bata Formation.

Table 2 .
The species reported here and their occurrences.* from early Pleistocene non-seep sediments at the tip of Liog-Liog Point.