1. Introduction

Callianassa s.l. hayanoi^{Karasawa, 2011}, was the first decapod described from the Upper Albian chemosynthetic community of Hokkaido. The purpose of the present note is to describe the goniodromitid crab from the Cenomanian cold seep deposit of Hokkaido. This is the second record of a decapod from the fossil chemosynthetic communities of Japan.

The specimen described herein was collected from limestone of the Cenomanian Tenkaritoge Formation of the Middle Yezo Group exposed at Loc. R3013 (Figure 1A) of ^{Tanabe et al. (1977)} (=Loc. OB42095 of ^{Funaki and Hirano, 2004}) of the Kanajirisawa Creek, Obiracho, north-western Hokkaido. In this locality, ^{Kanie et al. (1996)} first found the chemosynthetic mollusks and ^{Kanie and Kuramochi (1996)} described two chemosynthetic pelecypods, Thracia yezoensis^{Kanie and Kuramochi, 1996} (as Amanocina yezoensis by ^{Kiel, 2013}) and Miltha sp.

Figure 1 Map showing the fossil-bearing localities. (A); Goniodromites sp., (B); Sabellidromites inflata (^{Collins and Karasawa, 1993}). The map is derived from the Geospatial Information Authority of Japan (http://geolib.gsi.go.jp/). 

The subsequent workers (i.e., ^{Kaim et al., 2008}; ^{Kiel et al., 2008}) called it the Kanajirisawa seep and reported additional mollusks representing a cold seep-dependent chemosynthetic community. ^{Ogihara (2005}; ²⁰⁰⁸⁾ recognized the limestones as cold-seep carbonate rocks based upon biomarker analyses and the significant depletion of δ13C values vs PDB (-43.4- -39.9‰).

The stratigraphic horizon of the limestone is the Upper Cretaceous (middle Cenomanian) by the presence of Desmoceras japonicum^{Yabe, 1904}, and Turrilites sp. cfr. T. acutus^{Passy, 1832} (^{Tanabe et al., 1977}; ^{Kanie et al., 1996}; ^{Funaki and Hirano, 2004}).

Furthermore, Sabellidromites inflata (^{Collins and Karasawa, 1993}), a poorly known species of Goniodromitidae ^{Beurlen, 1932}, is redescribed based upon the newly collected specimen as well as the type specimen.

The specimens described herein are deposited in the Mikasa City Museum (MCM) and the Mizunami Fossil Museum (MFM).

2. Systematic paleontology

Type species: Goniodromites bidenatus^{Reuss, 1858}, by subsequent designation of ^{Glaessner (1929)}.

Included species: See ^{Klompmaker et al. (2012)}.

Figure 2 A-D, Goniodromites sp., MCM-M395, carapace, Tenkaritoge Formation (middle Cenomanian). E-J, Sabellidromites inflata (^{Collins and Karasawa, 1993}), MFM247135, carapace, Osoushinai Formation (lower Campanian). A, E, F, oblique-frontal; B, D, H, I, dorsal; C, G, J, lateral view. A-C, F, I, and J are whitening images coated with ammonium chloride sublimate. Scale bars = 5 mm. 

Examined material: MCM-M395, carapace (length, 4.5 mm; width, 4.3 mm) from Loc. R3013 (Figure 1A) of ^{Tanabe et al. (1977)}, Kanajirisawa Creek, Obiracho, Hokkaido; limestone of the Tenkaritoge Formation of the Middle Yezo Group (middle Cenomanian); collected by M. Kano.

Description: Carapace small, pentagonal in outline, about as long as wide, widest at about outer orbital angle, narrowed anteriorly and posteriorly, moderately convex longitudinally and transversely. Fronto-orbital width equal to maximum carapace width. Front downturned, strongly protruded anteriorly; frontal margin about 40% maximum width, composed of two rounded lobes, very weakly notched medially, continuous with upper orbital margin. Upper orbital margin long, nearly straight, oblique to obtuse outer orbital angle. Lateral margins slightly sinuous, tapered posteriorly, with cervical and branchiocardiac incisions. Posterior margin sinuous, weakly concave medially; width about 55% maximum width. Frontal region with shallow median sulcus. Protogastric regions defined by subtle grooves. Pyriform mesogastric region and narrow anterior mesogastric process, separated from protogastric regions by subtle grooves. Hepatic and protogastric regions not differentiated. Cervical groove well defined; axial element broadly V-shaped; lateral elements nearly straight. Cardiac region defined by broad grooves laterally. Branchiocardiac groove well defined, lateral elements nearly parallel those of cervical groove. Meso- and metabranchial regions not differentiated.

Discussion: The studied specimen is assigned to Goniodromites in having a pentagonal carapace being about as long as wide, the well-marked cervical and branchiocardiac grooves, and the posteriorly converged lateral margins.

Detailed characters of the dorsal carapace are not known because of lacking most cuticles of the carapace. Since it is difficult to compare the studied specimen among the known fossil species of the genus, we prefer to leave it in open nomenclature.

The hitherto known species of Goniodromites have been recorded from the Jurassic and Cretaceous deposits of Europe, except for two Jurassic species from Japan (Schweitzer and Feldmann, 2008; ^{Schweitzer et al., 2012}; ^{Klompmaker et al., 2012}); therefore, Goniodromites sp. represents the first record of the genus from the Cretaceous deposits of the North Pacific realm.

The oldest record of decapods from the fossil chemosynthetic communities seems to be part to the Jurassic of France (^{Campbell, 2006}).

Knowledge on decapods from the fossil chemosynthetic communities has been poor (see ^{Karasawa, 2011}). Later, new records from the Cenozoic increased (i.e., ^{Kiel and Hansen, 2015}; ^{Hryniewicz et al., 2019}; ^{Kiel et al., 2020}), whereas decapods from the Cretaceous have been extremely rare.

^{Bishop and Williams (2000)} recorded four brachyurans, Heus foeresteri^{Bishop and Williams, 2000}, Heus manningi (^{Bishop and Williams, 2000}), Konidromites bjorki (^{Bishop and Williams, 2000}), and Hoplitocarcinus? punctatus (^{Rathbun, 1917}), from the Campanian (Upper Cretaceous) cold seep sediment of South Dakota and Colorado, U.S.A. ^{Karasawa (2011)} described Callianassa s.l. hayanoi, an axiidean from the upper Albian (Lower Cretaceous) cool seep sediment of Hokkaido. ^{Agirrezabala et al. (2013)} reported Callianassa sp. from the upper Albian methane-seep carbonates of Spain. Goniodromites sp. is the first recognition of the genus and family from the Upper Cretaceous chemo-synthetic communities. However, most species of Goniodromites have been reported from the Jurassic and Cretaceous coral-reefal sediments of Europe (^{Schweitzer and Feldmann, 2007}; ^{Klompmaker et al., 2012}) and only two species have been known from shale of the Upper Jurassic Torinosu Group of Japan (^{Karasawa and Kato, 2007}). Therefore, it is not clear whether Goniodromites sp. represented by only one specimen had been a chemosynthetic-dependent species during the depositional period or the studied specimen had been exceptionally preserved in the sediments.

Type species: Goniodromites scarabaeus^{Wright and Wright, 1950}, by original designation.

Included species: Sabellidromites inflata (^{Collins and Karasawa, 1993}); S. lanae^{Nyborg, Garassino, and Ross, 2020}; S. scarabaea (^{Wright and Wright, 1950}).

Examined material: MFM247135, carapace (length 27.7 mm; width, 24.8 mm) from YEZ-20 (Figure 1B) of ^{Karasawa and Hayakawa (2000)}, Wakkauenbetsugawa, Nakagawa-cho, Hokkaido; Osoushinai Formation (lower Campanian) of the Upper Yezo Group (^{Takahashi et al., 2003}, modified from ^{Osanai et al., 1960}); collected by K. Masuda.

Emended diagnosis: Carapace rounded-pentagonal, slightly longer than wide, strongly vaulted longitudinally and transversely; frontal margin composed of two triangular lobes; lateral margins gently convex, converged posteriorly, with two low, broad teeth anterior to cervical notch and two more between cervical and branchiocardiac notches; dorsal regions with scattered tubercles; anterior mesogastric process well marked; urogastric region quadrate, depressed; cardiac region elongate-pentagonal with weak, transverse, tuberculated ridge anteriorly; cervical groove deep; epibranchial regions with tuberculated ridge parallel to cervical groove; branchiocardiac groove well defined.

Emended description: Carapace rounded-pentagonal in outline, slightly longer than wide, maximum width about 90% maximum length, widest at about midlength, strongly vaulted longitudinally and transversely. Fronto-orbital width about two-thirds maximum carapace width. Frontal margin protruded anteriorly, strongly downturned, rimmed, composed of two triangular lobes, with V-shaped median sulcus. Orbit ovate, oblique; upper orbital margin continuous with frontal margin, nearly straight, rimmed, with blunt outer orbital angle.

Lateral margins gently convex, converged posteriorly; two low, broad teeth present anterior to cervical notch and two more between cervical and branchiocardiac notches. Posterior margin nearly straight, wide, about 60% maximum carapace width. Frontal region with deep median sulcus. Dorsal regions with scattered tubercles. Epigastric regions vaulted, united with protogastric regions. Anterior mesogastric process well defined; mesogastric region kite-shaped, interrupted medially, barely differentiated from protogastric regions. Hepatic and protogastric regions not differentiated. Metagastric region depressed posteriorly. Urogastric region quadrate, depressed. Cardiac region elongate-pentagonal in outline, weakly delimited from meta- and mesobranchial regions, with weak, transverse, tuberculated ridge anteriorly, interrupted medially. Intestinal region small, concave medially. Cervical groove deep; lateral elements nearly straight; axial element concave. Epibranchial regions with tuberculated ridge parallel to cervical groove. Branchiocardiac groove well defined, lateral elements nearly parallel those of cervical groove, weakened medially, deepest laterally. Meso- and metabranchial regions not differentiated.

Discussion: Sabellidromites inflata, a quite rare goniodromitid species has been known by the holotype (TMNH01530 deposited in the Toyohashi Museum of Natural History). ^{Collins and Karasawa (1993)} originally assigned this species to Pithonoton^{Meyer, 1842}. Subsequently, ^{Schweitzer and Feldmann (2007)} moved Pithonoton inflatum to the new genus Sabellidromites. Therefore, the revised diagnosis and description of this species placed in Sabellidromites are provided by examination of the holotype and the additional specimen herein figured.

^{Collins and Karasawa (1993)} supposed that the stratigraphic horizon of this species was the Upper Cretaceous (Cenomanian to Campanian) based upon the co-occurrence of Gaudryceras sp., an ammonoid showing a wide stratigraphic distribution in the Cretaceous deposits of Hokkaido. A discovery of the second specimen from the Osoushinai Formation of the Upper Yezo Group suggests that the stratigraphic range for this species is restricted to the lower Campanian.