Bucculentum sp.

Krzemińska, Ewa, Starzyk, Natalia, Fraaije, René H. B., Schweigert, Günter & Lukeneder, Alexander, 2021, Jurassic brachyurans of the genus Bucculentum, Zootaxa 5032 (3), pp. 395-410 : 404

Bucculentum sp.

Fig. 8

An interesting specimen of Bucculentum has been found in the Plettenberg quarry. Despite the poor state of preservation it shows some peculiar features and deserves to be presented here.

Material examined. Specimen # MAB 3581 (coll. RHB Fraaije), Germany: Plettenberg quarry n. Balingen. Age: Late Oxfordian, Planula Zone ( Schweigert & Callomon 1997; Jantschke & Schweigert 2020).

Description. This is one of the two smallest specimens of the genus ever found; length from the preserved tip of rostrum to the distal margin is 3.9 mm. The carapace is slightly eroded; the apices of tubercles are rounded and smoothed, and all lateral margins are only partially preserved, so that the full reconstruction is not possible to accomplish. Nevertheless, the left metabranchial and the right hepatic regions are almost completely preserved and show that these regions must have been equally wide, or even the metabranchial region was wider. The tubercles surrounding the augenrest are particularly large. Augenrest is laterally flanked by a short ridge, as in B. bucculentum .

The preserved part of the rostrum shows a different shape than in all other species with known rostra. The lateral lobes are not divergent, but distinctly convergent ( Fig. 8A–C ); in contrast to the divergent lobes in B. bucculentum ( Fig. 8E ). The lobes seem to be especially large when compared to remainder of the body. The cardiac region has a large distal tubercle and an axial row of 2–3 small tubercles diminishing in size towards epibranchial region.

Remarks. The small size of this specimen raises a question whether it can be a juvenile form of other species, e.g., Bucculentum plettenbergense , n. sp., from the same locality. Although both species/specimens share some characters: very broad hepatic regions and large tubercles on the cardiac regions, their augenrests are quite different. Such a great change in shape during ontogenic growth does not seem plausible, therefore the identity of MAB 3581 with B. plettenbergense , n. sp., is rejected.

In conclusion, the specimen MAB 3581 may represent a new species, but its poor state of preservation hinders us from description until specimens in better state are found.

Figures

FIGURE 8. Bucculentum sp. MAB 3581, Plettenberg quarry, Lower Kimmeridgian (A–D): A, dorsal view, large tubercles are arrowed; lateral lobes of rostrum are convergent (highlighted); B, partial reconstruction; the concave fragment between lobes of rostrum is marked; C, frontal view, lateral lobes of rostrum are convergent (highlighted); D, lateral view. E. B. bucculentum, I-F/MP/4648/1534/08, frontal oblique view: lateral lobes of rostrum are divergent (highlighted). Bars 1 mm.