Orconectes macrus Williams, 1952

Morehouse, Reid L. & Tobler, Michael, 2013, Crayfishes (Decapoda: Cambaridae) of Oklahoma: identification, distributions, and natural history, Zootaxa 3717 (2), pp. 101-157 : 129-130

Orconectes macrus Williams, 1952 : Neosho Midget Crayfish

General charateristics. Adults rarely exceed 50 mm in total length. The carapace is nearly equal in length to the abdomen. The rostrum is narrow with a well-developed trough-like depression. Chelae are short, broad, and look oversized relative to body size. In form I males, gonopods have two long, slender, and slightly curved processes that reach the base of the first pair of pereiopods. In females, the annulus ventralis has a deep fossa (Pflieger, 1996).

Life coloration. The background color is uniform olive-tan to brown without any colorful markings. There is typically a dark brown to black saddle on the conjunction of the carapace and abdomen ( Figure 55 ). The ventral side is light yellow to white.

Similar species. In Oklahoma, O. macrus closely resembles O. meeki brevis and O. nana . O. macrus does not have black speckling on its chelae like O. meeki brevis . It differs from O. nana in the length of the gonopods in form I males, which reach the base of the first pair of pereiopods as opposed to the second pair of pereiopods in O. nana . Furthermore, the two species have an allopatric distribution, with O. nana occurring in the upper Illinois River drainage, while O. macrus occurs in the Neosho River, Spavinaw Creek, and Spring Creek drainages.

Distribution and habitat. Orconectes macrus occurs in the Neosho River Drainage including southwestern Missouri, southeastern Kansas, northwestern Arkansas, and northeastern Oklahoma. In Oklahoma, O. macrus is found predominantly in small tributaries of the Neosho River and Spavinaw Creek. Our ecological niche model shows that O. macrus appears to be confined to the tributaries of the Neosho River and Spavinaw Creek, although there are areas scattered throughout the southern portions of the Neosho River drainage that have suitable environmental conditions ( Figure 56 ). The species inhabits clear, permanently flowing Ozark streams over gravel substrate in fast shallow water and is a tertiary burrower. It usually digs under large rocks or constructs short tunnels under smaller pieces of gravel.

Life history. Pflieger (1996) documented form I males from September through March, suggesting a fall and winter breeding season as observed in other stream crayfish in the Ozark region. Ovigerous females were collected in late March and early April. We collected one ovigerous female in April and form I and II males and nonovigerous females throughout the year. The ovigerous female only had five relatively large eggs attached to her abdomen. It is suggested that O. macrus reaches sexual maturity within the first year of life (Pflieger, 1996). We conducted stomach content analyses and found that the majority of the individuals contained macroinvertebrates, which could be due their small body size and ability to get into the substrate.

Syntopic species. Orconectes meeki brevis and Orconectes neglectus neglectus .

Conservation status. AFS: Currently Stable; Heritage Rank: Apparently Secure (G4); IUCN: Least Concern; ODWC: Not Listed.

Additional resources. Crandall (1998); Dillman et al. (2010); Taylor & Knouft (2006).

Figures

FIGURES 53 – 60. 53. Orconectes leptogonopodus 54. Potential distribution of Orconectes leptogonopodus 55. Orconectes macrus 56. Potential distribution of Orconectes macrus 57. Orconectes menae 58. Potential distribution of Orconectes menae 59. Orconectes meeki brevis 60. Potential distribution of Orconectes meeki brevis.