Protomunida spitzbergica ( Gripp, 1927 )

Hryniewicz, Krzysztof, Amano, Kazutaka, Bitner, Maria Aleksandra, Hagström, Jonas, Kiel, Steffen, Klompmaker, Adiël A., Mörs, Thomas, Robins, Cristina M. & Kaim, Andrzej, 2019, A late Paleocene fauna from shallow-water chemosynthesis-based ecosystems, Spitsbergen, Svalbard, Acta Palaeontologica Polonica 64 (1), pp. 101-141 : 125-127

Protomunida spitzbergica ( Gripp, 1927)

Fig. 20 .

1927 Galathea spitzbergica n. sp.; Gripp 1927: 33, pl. 7.16,7.17.

1970 Galathea spitzbergica Gripp, 1927 ; Vonderbank 1970: 78, fig. 25c, pl. 6.1.

2013 Galathea spitzbergica Gripp, 1927 ; Robins 2013: 38, fig. 8.5.

2016 Munididae ; Hryniewicz et al. 2016: fig. 12k.

Material.— Neotype, GPIBo 85 , the sole specimen, available thus far, carapace, from the upper Paleocene , Fossildalen and locality 500 m west from Trigonometric point 25, Hollendarbukta, Spitsbergen, Svalbard.

Measurements.— Lmax (without rostrum) 5.1 mm; Wmax 4.6 mm.

Emended diagnosis.—Carapace ~10% longer than wide, widest at meso-metabranchial regions. Relatively wide central rostral spine at base with tubercles. Spines in oblique rows on epigastric regions, near orbital angle, and on anterior part lateral margin. Cardiac region rectangular, poorly delimited laterally, well delimited anteriorly and posteriorly. Epibranchial regions with tubercles. Area posterior to cardiac region without ornamentation, with two tiny elongated tubercles on either side of axis.

Description.—Carapace ~10% longer than wide (excluding rostral length), weakly convex longitudinally, moderately convex transversely, widest at meso-metabranchial regions. Rostrum triangular, flattened dorsally, with weak axial keel, tip and lateralmost parts not preserved, probably with spines adjacent to central rostral spine ( Gripp 1927: 33, pl. 7: 17). Orbits not exposed. Frontal margin incompletely preserved, with base of spine near outer orbital angle. Lateral margins moderately convex, rounded. Posterior margin moderately concave, with distinct rim. Epigastric regions with oblique row of bases of spines, followed posteriorly by parallel row of granules. Hepatic region small, depressed, with some tubercles. Proto- and mesogastric regions weakly differentiated, with transverse, interrupted ridges. Mesogastric region triangular with convex base and distinct tip. Epibranchial regions triangular, with tubercles dorsally and three bases of spines laterally. Uro-/metagastric region only delimited anteriorly and posteriorly, containing some transversely elongate tubercles. Confluent meso-metabranchial regions containing transverse ridges best connected laterally; lateral sides without spines except perhaps one near epibranchial regions. Cardiac region rectangular, poorly delimited laterally, well-delimited anteriorly and posteriorly by somewhat sinuous grooves. Area posterior to cardiac region without ornamentation, with two tiny elongate tubercles on either side of axis. Cervical groove distinct, widely U-shaped, curving more anterolaterally in lateralmost part. Lateral groove branching off base cervical groove sinuous. Specimen appears to preserve most of cuticle, partially absent from right epibranchial region. No muscle scars visible. Abdomen, venter, and appendages not preserved.

Remarks.—Since the holotype was destroyed during WWII, Vonderbank (1970) correctly designated a neotype for this species. He gave a five-page description of this species in his monograph. However, only the neotype is conspecific with the illustration of the lost holotype by Gripp (1927). All other carapaces figured by Vonderbank (1970) and the specimen illustrated by Hägg (1925: pl. 6.28, 6.28a) are part of a new species described below.

Placement in the Munididae is with little doubt. Munidids typically have spines directly adjacent to the central rostral spine (e.g., Macpherson 1994; Ahyong et al. 2010; Robins et al. 2012), but this part is not preserved in the sole specimen. However, Gripp (1927: 33, pl. 7.17) did illustrate such adjacent spines and mentioned them in the text. The axial part of the rostrum in munidids is usually a narrow spine rather than a somewhat wider, more flattened surface, but there are some exceptions in munidids including Protomunida primeava (personal observation AAK), P. munidoides (see Jakobsen and Collins 1997), and Juracrista spp. (see Robins et al. 2012). Another character suggesting a munidid affinity are the spines interpreted to be present on the epigastric regions, lateral sides of the epibranchial regions, and at the outer orbital angle. This combination of spines is also seen in extant and other fossil munidids such as Munida , Agononida , Juracrista , Sadayoshia , and P. munidoides (e.g., Ahyong et al. 2010; Robins et al. 2012; Robins 2013; personal observation AAK for P. munidoides ), although some galatheids ( Lessinigalathea regalis De Angeli and Garassino, 2002 , and Acanthogalathea spp. ( De Angeli and Garassino, 2002) also exhibit these features.

Whether the ornamentation would look different without the cuticle (see examples in Klompmaker et al. 2015, for various examples and references therein, as well as Robins et al. 2016: 68–70), is difficult to determine as only a minor portion of the cuticle appears gone, exposing the internal mold on the right epibranchial region. In general, however, it appears that differences are limited for galatheoids based on evidence thus far ( De Angeli and Garassino 2002: pl. 4.2; Schweitzer and Feldmann 2008: fig. 2; Klompmaker et al. 2012: figs. 7, 10; Robins et al. 2013: figs. 10, 11; Nyborg and Garassino 2015: figs. 1, 2; Robins et al. 2016: figs. 3, 7, 8, 11, 12, 14).

The neotype originates from locality 500 m west from Trigonometric point 25, Hollendarbukta, and not from Fossidalen, interpreted to be the seep and wood fall community of Gripp (1927) by Hryniewicz et al. (2016). The same species was present at Fossildalen as well given the illustration of the lost holotype by Gripp (1927).

Stratigraphic and geographic range. —Upper Paleocene cold seep carbonates from the Basilika Formation, Fossildalen, and locality 500 m west from Trigonometric point 25, Hollendarbukta, Spitsbergen, Svalbard.

Figures

Fig.20.Munididcrustacean Protomunidaspitzbergica (Gripp,1927) fromtheupper Paleocene,Basilika Formation,locality 500mwest fromTrigonometric point 25, Hollendarbukta, Spitsbergen, Svalbard. Neotype, GPIBo 85, dorsal view of carapace (A1), detailed view of incomplete rostrum (A2), right lateral A3), frontal (A4), and left lateral (A5) views.