Alahexapus martini ( Feldmann, Schweitzer & Portell, 2014 )

Alahexapus martini ( Feldmann, Schweitzer & Portell, 2014) n. comb.

( Fig. 20 View FIG ; Appendix 1K, L View APPENDIX )

Stevea martini Feldmann, Schweitzer & Portell, 2014: 142 View in CoL , pl. 3.

TYPE MATERIAL. — Holotype. 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); UF 228988 GoogleMaps .

Paratype. United States • 1 specimen; same as for the holotype; UF 235561 GoogleMaps .

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:5915 GoogleMaps • 1 specimen; idem; ALMNH: Paleo:21464 GoogleMaps • 1specimen; idem; MMNS IP-7939 GoogleMaps • 1 specimen; idem; UF 254040 GoogleMaps • 1 specimen; idem; UF 254041 GoogleMaps • 1 specimen; idem; UF 254042 GoogleMaps • 1 specimen; idem; UF 303801 GoogleMaps .

TYPE HORIZON. — Pine Barren Member of the Clayton Formation, lower middle NP2 nannofossil zone, lower Danian.

TYPE LOCALITY. — ALMNH loc.3: Mussel Creek roadcut ( 31°58’17”N, 86°42’15”W), Lowndes County, Alabama, United States.

DIAGNOSIS. — Carapace length-width ratio c. 0.67, widest about mid-length. Fronto-orbital width c. 50% of maximum carapace width. Orbits of moderate size, oval-shaped. Cervical groove widely U-shaped but diverging, fairly distinct, diminishing near orbits. Branchiocardiac grooves weaker, defining cardiac region laterally. Cuticle of carapace with densely covered fine granules.Pterygostome exhibiting stridulating apparatus with c. 15 striae. Female pleon with unfused, much wider than long somites; triangular telson with rounded tip; with gentle axial keel; pitted cuticular surface. Sternopleonal cavity of female appears to reach distal portion of sternite 3. Male pleon narrow, generally narrowing distally; telson longer than wide with rounded tip; somite 6 slightly wider than long, appears unfused, hexagonal, with rimmed lateral margins; somites 3-5 appear fused but with distinct suture marking boundaries; with pitted cuticular surface. Sternopleonal cavity of male appears to reach distal portion of sternite 4.

MEASUREMENTS. — Maximum carapace width (mm): ALMNH:Paleo:5915: 7.1, ALMNH:Paleo:21464:11.1. UF 228988: 11.1, UF 254041: 8.9, MMNS IP-7939: 11.4.

DESCRIPTION

Referral is made to Feldmann et al. (2014: 142-143). Some additional and revised characters are noted in new specimens. Carapace length-width ratio c. 0.67. Fronto-orbital width c. 50% of maximum carapace width. Sternites with tubercular and pitted cuticular surface; pleonal sternite 2 narrow; sternites 3-4 fused; sternite 4 with curved, anterolaterally directed spine separated by sulcus. Female pleon with unfused, much wider than long somites; triangular telson with rounded tip; maximum width pleon c. 30% of maximum carapace width; with gentle axial keel; pitted cuticular surface. Female pleonal somites 1-3 not preserved. Sternopleonal cavity of female appears to reach distal portion of sternite 3; with small press button on sternite 5 on upper part of slope near sternite 4; with subcircular oviduct on sternite 6, adjacent to base of sternopleonal cavity.

Male pleon narrow, generally narrowing distally; telson longer than wide with rounded tip; somite 6 slightly wider than long, appears unfused, hexagonal, with rimmed lateral margins; somites 3-5 appear fused but with distinct line marking boundaries; with pitted cuticular surface. Sternopleonal cavity of male appears to reach distal portion of sternite 4. Third maxilliped partly preserved, with elongated exopod; boot-shaped, tubercular ischium, and about equally wide and long, rounded merus. Appendages not preserved.

REMARKS

This species is rare with only nine individuals reported herein after c. 15 years of collecting.This rarity is not primarily caused by the small size of the specimens, making them potentially more difficult to find, because many small specimens of other species were found (see above).

Recently, Schweitzer (2024) ascribed four specimens to Stevea martini from a site near Streetman, Freestone County, Texas, United States, originating from the upper Danian-Selandian Wills Point Formation (see Armstrong et al. 2009, for age). However, the tubercles on the dorsal carapace are coarser on average and more uniform in the Texan specimens based on all available specimens; sternite 4 has a wider, hexagonal-shaped extension as preserved rather than anterolaterally directed, curved spines as in A. martini n. comb. (compare Schweitzer 2024: fig. 3.2 vs Fig. 20E View FIG ); and the pterygostome does not appear to bear the stridulating apparatus ( Schweitzer 2024: fig. 3.6) characteristic for A. martini n. comb. ( Fig. 20L View FIG ; Feldmann et al. 2014: pl. 3.2)though differential preservation may play a role here. Thus, the specimens from Texas may represent a different hexapodid species warranting further study.