Planoprosopon, Schweitzer, Feldmann, and Lazar, 2007

Klompmaker, Adiël A., Starzyk, Natalia, Fraaije, René H. B. & Schweigert, Günter, 2020, Systematics and convergent evolution of multiple reef-associated Jurassic and Cretaceous crabs (Decapoda, Brachyura), Palaeontologia Electronica (a 32) 23 (2), pp. 1-54 : 18-19

Planoprosopon aff. P. hystricosus Schweitzer and Feldmann, 2009a

Figure 9

2009a Planoprosopon hystricosus Schweitzer and Feldmann , p. 219, fig. 4.4-4.6.

Diagnosis. See Schweitzer and Feldmann (2009a,

p. 220).

Material studied. NHMW 1990/0041/0805, 1990/ 0041/1614, 1990/0041/4221b, 2017/0089/0034.

Occurrence. Coral reef Ernstbrunn Limestone of the Ernstbrunn quarries (Google Earth coordinates: 48.54, 16.35), Austria, Late Jurassic (Tithonian) (Schweitzer and Feldmann, 2009d; Schneider et al., 2013).

Dimensions. (In mm) NHMW 2017/0089/0034: max. length excl. rostrum (L)=3.0, max. width excl. projections (W)=2.7; 1990/0041/0805: L=-, W=3.3; 1990/0041/1614: L=~ 2.0, W=~1.8; 1990/0041/ 4221b: L=~3.0, W=~2.5.

Description. See Schweitzer and Feldmann (2009a, p. 220-221).

Remarks. This species has been figured only in dorsal view; we here provide frontal and lateral views for the first time using a newly discovered specimen. Schweitzer and Feldmann (2009a) provided images of three specimens of this species measuring 2.8, 3.7, and 11.8 mm in length excluding the rostrum. The differences from the smallest two figured versus the largest specimen include: (1) change in the course of the cervical groove from broadly V-shaped to more sinuous with a middle segment, (2) development of large tubercles in the hepatic-protogastric region, (3) increase of the proportional length of the meta/urogastric region, (4) the epibranchial region becomes less swollen laterally, (5) position of maximum width becomes located more anteriorly, and (6) the length-width ratio increases. These changes were attributed to allometric growth (Schweitzer and Feldmann, 2009a). The number and types of changes are quite remarkable for crabs, however. For example, brachyuran carapaces usually become proportionally wider instead of longer through ontogeny as shown quantitatively (e.g., Barnes, 1968; Davidson and Marsden, 1987; Negreiros-Fransozo et al., 2003; Klompmaker et al., 2012, 2015b; Gómez-Cruz et al., 2015; but see Finney and Abele, 1981, for the opposite). A change from a carapace with small tubercles to a combination of small and large tubercles is uncommon in crabs. More specimens of intermediate size are needed to confirm whether all specimens of the type series are truly conspecific. The specimens under study resemble the paratypes more closely than the holotype, so we questionable assign these specimens to Planoprosopon aff. P. hystricosus .

One of the three studied specimens contains a swelling in the right branchial region ( Figure 9C, E ), almost certainly caused by an epicaridean isopod parasite, as seen in modern decapods (e.g., Williams and Boyko, 2012; An et al., 2015). Such swellings are referred to the ichnotaxon Kanthyloma crusta Klompmaker, Artal, Van Bakel, Fraaije, and Jagt, 2014 [see also Klompmaker and Boxshall (2015)]. This is the first record of Kanthyloma in this species.

Figures

FIGURE 9. Specimens of the crab Planoprosopon aff. P. hystricosus Schweitzer and Feldmann, 2009a, from the Late Jurassic (Tithonian) of Ernstbrunn, eastern Austria. A, C, dorsal views of carapace (NHMW 2017/0089/0034 and 1990/0041/0805). B, right-lateral view (2017/0089/0034). D, E, frontal views (2017/0089/0034 and 1990/0041/0805). Note the presence of an epicaridean parasite swelling (ichnotaxon Kanthyloma crusta Klompmaker et al., 2014) in the right branchial region in 1990/0041/0805. Scale bar width equals 1.0 mm.