Kellnerius jamacaruensis, Santana, William, Pinheiro, Allysson P., Da Silva, Caroline M. R. & Saraiva, Antônio Álamo, 2013

Santana, William, Pinheiro, Allysson P., Da Silva, Caroline M. R. & Saraiva, Antônio Álamo, 2013, A new fossil caridean shrimp (Crustacea: Decapoda) from the Cretaceous (Albian) of the Romualdo Formation, Araripe Basin, northeastern Brazil, Zootaxa 3620 (2), pp. 293-300 : 296-297

Kellnerius jamacaruensis n. sp.

Figures 3–5

Type material: LPU 648 A and 648 B, holotype.

Type locality: Sítio Pinheira in Distrito de Jamacaru – Município de Missão Velha, estado do Ceará (07º25’18,6”S – 39º07’23”W excavation in fine scale).

Stratigraphic unit: Romualdo Formation, Santana Group, Araripe Basin.

Age: Early Cretaceous – Albian.

Etymology: The specific epithet was derived from the locality where the material was collected. Jamacaru is a district of the Missão Velha municipality where the first fossils of the Araripe basin were cited.

Diagnosis: The same as for the genus.

Description: Total length 18.33 mm, without telson; carapace including rostrum 7.43 mm long; abdomen 10.9 mm long. Carapace length about twice its maximum height, laterally compressed, ventral margin smooth; dorsal margin of carapace straight, posterior margin rounded ventrally, both margins without spines. Rostrum long, 2.4 mm from the posterior margin of orbital cavity to tip, latter pointed and tip slightly upturned, slender in the distal half; rostral blade laterally compressed, with 5 spines, proximal spine longest, ventral margin entire. Antennal spine present. Eye stalks not preserved. Antenna and antennule incompletely preserved and not discernible. Scaphocerite large, lateral margin weakly rounded, longer than rostrum, apparently without ornamentation. Third maxilliped not discernible. Pereiopods scarcely preserved, slender, some relatively long, ornamentation not visible; chela on the first pereiopod not distinguishable; second pereiopod apparently chelate, longer, without sign of subdivisions on carpus; second to fifth periopods slightly decreasing in size progressing posteriorly. Abdomen six segmented, all somites apparently without ornamentation, pleura well developed, second pleura covering first and third; first, second and fourth somites about same in size, third and fifth larger, third being the largest, sixth somite elongated; third somite with a distinct groove in the first third part of tergite, not extending to pleurite. Pleopods, uropods and telson not preserved.

Remarks: While the placement of Kellnerius jamacaruensis n. sp. within the Caridea is clear (vide second pleura overlapping the first and the third), the assignment of K. jamacaruensis n. sp. to the Palaemonidae should be viewed with caution. The family Palaemonidae was established based on very few characters. The diagnostic characters provided by Rafinesque (1815) were concise and focused only on the antennae (Rafinesque 1815: 98). Additional characters that could be diagnostic of this family are: the rostrum is often prominent, possibly toothed, and the first and second pereopods chelated, the second larger, without subdivisions of the carpus (Williams 1984; Wicksten 2005). Although the antennae and the chela of the first pereiopod are not discernible on the material, the other characters cited above are shared by Kellnerius jamacaruensis n. sp. Among the fossil palaemonids, the genus Bechleja Houša, 1957 is typical of freshwater deposits (Garasino and Bravi, 2003) and has four species: B. bahiaensis (Beurlen, 1950) ; B. inopinata Houša, 1957 ; B. robusta Martins-Neto and Mezzalira, 1991 b; and B. rostrata Kellnerius jamacaruensis n. sp. differs from all Bechleja species by having a rostrum with 5 spines (versus a serrated rostrum); and a small chela of the second pereiopod (versus a large chela on the second pereiopod). Additionally, K. jamacaruensis n. sp. can be easily distinguished from B. robusta by the carapace length twice its maximum height, laterally compressed (versus a dorsally triangular cephalothorax); and a long rostrum with pointed, slightly upturned tip (versus a short and large rostrum). Kellnerius jamacaruensis n. sp. can be promptly distinguished from Propalaemon longispinata Martins-Neto and Mezzalira (1991b) , Pseudocaridinella tremenbeensis (Beurlen, 1950) and P. ro x o i (Beurlen, 1950), by a rostrum with a smooth ventral margin and a slender distal portion, that is slightly upturned, laterally compressed, and bears 5 distinct spines proximally on the dorsal margin, of which the first is longer (versus a long, serrated and uncompressed rostrum in P. longispinata , and a smooth rostrum, without spines in P. tremenbeensis and P. ro x o i). Kellnerius jamacaruensis n. sp. is also easily differentiated from Beurlenia araripensis by the distinct five spines on the dorsal margin of the rostrum, with the proximal longest (versus four spines of similar size in B. araripensis ); a large scaphocerite being slightly longer than the rostrum with a weakly rounded lateral margin and apparently without ornamentation (versus a short scaphocerite, slightly acuminated, larger laterally in B. araripensis ); the third abdominal somite with a distinct groove in the first one-third part of the tergite, not extending to the pleurite (versus a smooth third abdominal somite in B. araripensis ).

Figures

FIGURE 3. Reconstitution of Kellnerius jamacaruensis n. gen. n. sp. Dotted lines represent not preserved appendages. Scale bar: 5 mm.

FIGURE 4. Lateral view of the holotype of Kellnerius jamacaruensis n. gen. n. sp. (LPU 648 A) from Romualdo Formation, Araripe basin, Brazil. Scale bar: 5 mm.

FIGURE 5. Kellnerius jamacaruensis n. gen. n. sp. (LPU 648 A). A – B, detail of the carapace showing the rostrum and the scaphocerite (note the five rostral spines and the scaphocerite larger than the rostrum). C – D, detail of the six abdominal somites showing the overlap of the second over first and third (note the groove on the third abdominal somite). B, D, schematic drawing over photo emphasizing the interpretation of the fossil. D, roman numbers indicating the abdominal somites one to six. Scale bars: 3 mm.