Eucalliaxiopsis alabamensis ( Rathbun, 1935a ), 2025

Eucalliaxiopsis alabamensis ( Rathbun, 1935a) n. comb.

( Figs 8-10 View FIG View FIG View FIG )

Callianassa alabamensis Rathbun, 1935a: 70-71 , pl. 15.7-15.10.

TYPE MATERIAL. — Holotype. United States • Alabama, Wilcox County, Prairie Creek and Pine Barren section; Porters Creek Formation ; Paleocene (upper Danian); USNM MO 371505 About USNM .

Paratypes. United States • 1 specimen; same as for the holotype; USNM PAL 327231 A • 5 specimens; idem; USNM PAL 327231 About USNM .

ADDITIONAL MATERIAL EXAMINED. — United States • 1 specimen; Alabama, Lowndes County, Mussel Creek roadcut ( 31°58’17”N, 86°42’15”W), ALMNH loc. 3; Clayton Formation, Pine Barren Member , lower middle NP2 nannofossil zone; Paleocene (lower Danian); ALMNH: Paleo:21509 (partial propodus) GoogleMaps • 1 specimen; idem; ALMNH: Paleo:21510 (base fixed finger) GoogleMaps • 1 specimen; idem; MMNS IP-7251 (cheliped) GoogleMaps • 1 specimen; idem; ALMNH: Paleo:21549 (fixed finger and dactylus) GoogleMaps • 1 specimen; idem; ALMNH: Paleo:21552 (fixed finger and dactylus) GoogleMaps • 2 specimens; idem; ALMNH: Paleo:21548 (dactyli) GoogleMaps • 16specimens; idem; ALMNH: Paleo:21551 (dactyli) GoogleMaps • 22 specimens; idem; ALMNH: Paleo:21554 (dactyli) GoogleMaps • 1specimen; idem; MMNS IP-7256.3 (dactylus) GoogleMaps • 8specimens; idem; MMNS IP-7256.6-13 (dactyli) GoogleMaps • 1 specimen; idem; UF 303824 (dactylus) GoogleMaps • 1 specimen; idem; UF 303829 (dactylus) GoogleMaps • 1 specimen; idem; UF 303830 (dactylus) GoogleMaps • 1 specimen; idem; UF 303832 (dactylus) GoogleMaps • 1 specimen; idem; UF 303833 (dactylus) GoogleMaps • 1 specimen; idem; UF 303834 (dactylus) GoogleMaps • 1 specimen; idem; UF 303835 (dactylus) GoogleMaps • 1 specimen; idem; UF 303836 (dactylus) GoogleMaps • 1 specimen; idem; UF 303837 (dactylus) GoogleMaps • 1 specimen; idem; UF 303840 (dactylus) GoogleMaps • 1specimen; idem; UF 303841 (dactylus of?minor) GoogleMaps • 1 specimen; idem; UF 303842 (dactylus) GoogleMaps • 1 specimen; idem; UF 303843 (dactylus) GoogleMaps • 1specimen; idem; UF 303844 (dactylus) GoogleMaps • 1 specimen; idem; UF 303845 (dactylus) GoogleMaps • 1 specimen; idem; UF 303847 (dactylus) GoogleMaps • 1 specimen; idem; UF 303848 (dactylus) GoogleMaps • 1 specimen; idem; UF 303849 (dactylus) GoogleMaps • 1 specimen; idem; UF 303850 (dactylus) GoogleMaps • 1 specimen; idem; UF 303851 (dactylus) GoogleMaps • 1 specimen; idem; UF 303853 (dactylus) GoogleMaps • 1 specimen; idem; UF 303856 (dactylus) GoogleMaps • 1 specimen; idem; UF 303857 (dactylus) GoogleMaps • 1 specimen; idem; UF 303862 (dactylus) GoogleMaps • 1 specimen; idem; UF 303863 (dactylus) GoogleMaps • 1 specimen; idem; UF 303864 (dactylus) GoogleMaps • 1 specimen; idem; UF 303865 (dactylus of?minor) GoogleMaps • 7 specimens; idem; ALMNH: Paleo:21550 (fixed fingers) GoogleMaps • 6 specimens; idem; ALMNH: Paleo:21553 (fixed fingers) GoogleMaps • 2 specimens; idem; MMNS IP-7256.4-5 (fixed fingers) GoogleMaps • 1 specimen; idem; UF 303823 (fixed finger) GoogleMaps • 1 specimen; idem; UF 303825 (fixed finger) GoogleMaps • 1 specimen; idem; UF 303826 (fixed finger) GoogleMaps • 1specimen; idem; UF 303827 (fixed finger) GoogleMaps • 1 specimen; idem; UF 303828 (fixed finger) GoogleMaps • 1 specimen; idem; UF 303831 (fixed finger) GoogleMaps • 1specimen; idem; UF 303838 (fixed finger) GoogleMaps • 1 specimen; idem; UF 303839 (fixed finger) GoogleMaps • 1 specimen; idem; UF 303846 (fixed finger) GoogleMaps • 1specimen; idem; UF 303852 (fixed finger) GoogleMaps • 1 specimen; idem; UF 303854 (fixed finger) GoogleMaps • 1 specimen; idem; UF 303855 (fixed finger) GoogleMaps • 1 specimen; idem; UF 303858 (fixed finger) GoogleMaps • 1specimen; idem; UF 303859 (fixed finger) GoogleMaps • 1 specimen; idem; UF 303861 (fixed finger) GoogleMaps .

TYPE HORIZON. — Porters Creek Formation (Sucarnoochee beds in Rathbun 1935a), upper Danian.

TYPE LOCALITY. — Prairie Creek and Pine Barren section, Wilcox County, Alabama, United States.

DIAGNOSIS. — Cheliped merus 1.6 times as long as high; outer lateral surface with longitudinal ridge at mid-height; lower margin smooth. Cheliped carpus 1.5 times as high as length at upper margin. Cheliped propodus palm approximately as high as length at upper margin; upper and lower margins carinate, carinae accompanied with rows of setal pores on both sides (inner and outer), carina on lower margin forming microdenticles distally (along fixed finger); distal margin of outer lateral surface with blunt tooth just below articulation with dactylus. Fixed finger approximately as long as upper palm length; outer lateral surface with oblique longitudinal ridge; fixed finger occlusal surface with proximal blunt tooth, entire occlusal surface (incl. proximal tooth) with numerous equally sized denticles. Dactylus upper margin straight, carinate; occlusal surface of robust dactylus morphotype with proximal blunt tooth followed with finely denticulated edge; occlusal surface of slender dactylus morphotype without proximal tooth.

MEASUREMENTS. — Palm length (mm): MMNS IP-7251: 8.9, USNM MO 371505: c. 19.0.

DESCRIPTION

Cheliped merus oval in outline, 1.6 times as long as high; outer lateral surface with longitudinal ridge at mid-height; lower margin distinctly convex, smooth. Cheliped carpus 1.5 times as high as length at upper margin; proximal margin rounded; distolateral margin square at lower angle. Cheliped propodus palm approximately as high as length at upper margin, highest proximally; proximo-lower corner rounded; upper and lower margins carinate, carinae accompanied with rows of setal pores on both sides (inner and outer), carina on lower margin forming microdenticles distally (along fixed finger); inner lateral surface with numerous setal pores concentrated close to distal margin and forming subvertical irregular row; outer lateral surface with setal pores concentrated distally, highest number of pores present close to junction with fixed finger; distal margin of outer lateral surface with blunt tooth just below articulation with dactylus. Fixed finger approximately as long as upper palm length, broadly oval in cross section; outer lateral surface with oblique longitudinal ridge, numerous setal pores scattered below ridge and in row above it along entire fixed finger length; fixed finger occlusal surface with proximal blunt tooth, entire occlusal surface (incl. proximal tooth) with numerous equally sized denticles, tip slightly bent upward. Dactylus upper margin straight, carinate; outer lateral surface with rows of setal pore clusters along upper and occlusal margins; inner lateral surface with several setal pore clusters along mid-length; occlusal surface of robust dactylus morphotype with proximal blunt tooth followed with finely denticulated edge; occlusal surface of slender dactylus morphotype without proximal tooth; dactylus tip slightly bent.

REMARKS

Rathbun (1935a: pl. 15.7-15.10) figured two type specimens, the dactylus paratype, which received a new number subsequently (USNM PAL 327231 A), but she also mentioned the presence of more specimens (20 propodi and three fingers). Five additional specimens (USNM PAL 327231) are listed as paratypes in the Smithsonian Institution database and seen by AAK in 2018, but another catalog number used in Rathbun (1935a) (371504) does not return any match in their database. Thus, the whereabouts of 16 original specimens is uncertain.

Newly collected specimens match the type material in most details. Slight differences relate to the mode of preservation. The type specimens are partly abraded hindering the observation of minute details while the cuticular surfaces are better preserved in the newly collected material. For instance, the development of microdenticles on the lower margin of the propodus, the dentition on the occlusal edges of fingers and morphological details of setal pores are not well observable in the type material. Setal pores are arranged in clusters; the clusters are oval, distinctly elongate or V-shaped. Elongate setal pore clusters, oriented perpendicularly to the occlusal margin, are present especially on the outer lateral surface of dactyli, whereas V-shaped clusters are sometimes present on the outer lateral surface of the fixed fingers. The number of setal pores/setal pore clusters slightly varies when comparing the same parts of various specimens.

There are two morphotypes of dactyli identified in the newly collected material: the robust one, with the proximal tooth on the occlusal surface, and the slender one, without the respective tooth. The slender morphotype is interpreted to belong to a minor claw, whereas the robust morphotype is interpreted to belong to a major claw; such differences in the morphology of cheliped dactyli are known also in extant species of Eucalliacidae ( Poore 2021) . Based on the presence of a proximal tooth on the occlusal surface of the fixed finger, all studied propodi attributed to E. alabamensis n. comb. are interpreted to belong to major claws only; such a proximal tooth is missing in minor claws ofeucalliacid shrimps (Hyžný 2012; Hyžný & Hudáčková 2012; Poore 2021).

Major chelipeds are sexually dimorphic in representatives of Eucalliaxiopsis , with males having the propodus palm proportionally longer than that of females ( Poore 2021). The limited number of complete propodi does not allow an evaluation of this dimorphism in E. alabamensis n. comb., although one propodus ( Fig. 8F, G View FIG ) indeed appears to be proportionally longer than others and might represent a male individual.

The newly presented material of E. alabamensis n. comb. is the second report of the species, originally described nearly a century ago ( Rathbun 1935a). It also adds further details to the description of the species, especially the morphology of the carpus and merus, previously unknown for this taxon. The range of the species is expanded from the late Danian to the early Danian.

From fossil congeners, Eucalliaxiopsis alabamensis n. comb. differs from E. pseudorakosensis mainly in the nature of major dactylus. In E. pseudorakosensis , the occlusal margin of the dactylus is armed with a distal tooth ( Hyžný & Hudáčková 2012), which is entirely missing in E. alabamensis n. comb.