Pacifastacus malheurensis Larson, 2025

Pacifastacus malheurensis Larson sp. nov.

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( Fig. 4 View FIGURE 4 , Table 3)

Pacifastacus klamathensis View in CoL .— Miller, 1960:130, 132, 197, 198 pl. VIII fig. 39 [all in part].

Pacifastacus leniusculus klamathensis (Stimpson) View in CoL .— Miller, 1960: 133, 146, 160, 180, 181 [all in part].

Pacifastacus leniusculus View in CoL .— Hobbs, 1972: 21 [by implication].— Larson & Olden, 2011: 64 [in part].

Pacifastacus leniusculus leniusculus View in CoL .— Hobbs, 1972: 21 [in part].— Hobbs, 1974: 6 [in part; neither fig. 5 nor 6, p. 81 = P. okanaganensis sp. nov.].

Pacifastacus leniusculus klamathensis View in CoL .— Hobbs, 1974: 22 [in part].— Larson et al. 2012: 3, 6, 12, fig. 1 [all in part].— Larson & Williams, 2015: 413, 419, 424, fig. 17.2 [all in part].

Pacifastacus (Pacifastacus) leniusculus klamathensis View in CoL .— Bouchard, 1978: 431 [by implication, in part].— Hobbs, 1989: 82 [in part]. Pacifastacus (Pacifastacus) leniusculus leniusculus View in CoL .— Hobbs, 1989: 82 [in part]. Pacifastacus lenisculus lenisculus .— Fitzpatrick, 1983: 155 [erroneous spelling]. Pacifastacus leniusculus (Dana, 1852) View in CoL .— Larson et al., 2012: 2–6 [all in part].— Williams & Weaver, 2019: 286, 287, 291, 296,

297. Pacifastacus klamathensis (Stimpson, 1857) View in CoL .— Larson et al., 2012: 2, 3 [all in part] Central Oregon Group.— Larson et al., 2012: 7, 8, 10, 12 [by implication], 13, fig. 2, table 1, 2.— Larson & Williams, 2015: 419,

426, fig. 17.2.— Larson et al., 2016: 10, 12, fig. 3. Pacifatacus leniusculus klamathensis .— Larson & Williams, 2015: 413 [erroneous spelling]. P. l. klamathensis .—Hart & Hart, 1974: 129. Pacifatacus leniusculus klamathensis .— Larson & Williams, 2015: 413 [erroneous spelling]. Pacifastacus l. klamathensis .— Larson & Williams, 2015: 413, 419, 424, fig. 17.2 [all in part]. Central Oregon Group.— Larson & Williams, 2015: 419, 426, 427, fig. 17.2.— Larson et al., 2016: 10, 12, fig. 3.

Type material. Holotype ( RBCM 012-00086 View Materials - 003 View Materials ) male, South Fork of the John Day River , Oregon (44.3981°, -119.5472°) . Allotype ( RBCM 012-00086 View Materials - 004 View Materials ) female, South Fork of the John Day River , Oregon (44.3981°, - 119.5472°) .

Other material. RBCM 012-00086-001, South Fork of the John Day River, Oregon (44.3981°, -119.5472°); RBCM 012-00093-001, Camas Creek, Oregon (45.0460°, -118.9805°); RBCM 012-00094-001, North Fork of the John Day River, Oregon (44.9979°, -118.9358°); RBCM 012-00095-001, Upper Silvies River, Oregon (44.1941°, -119.1844°). Number of specimens by sex in Table 1.

Type locality. South Fork of the John Day River , Oregon (44.3981°, -119.5472°).

Diagnosis. Pacifastacus with rostrum bearing only single pair of marginal tubercles or spines; acumen length less than 79.4% of anterior rostrum width; rostrum length less than 18.85% of TCL ( Fig. 3 View FIGURE 3 ).

Description. Body and eyes pigmented. Eyes not reduced. Rostrum deflected ventrally, base and anterior broad, margins parallel to sub-parallel, non-serrate; median carina subtle; acumen strongly converging, not separated from remainder of rostrum by spines; acumen length 68% of anterior rostrum width (11% sd). Rostrum length including acumen 145% of basal rostrum width (15% sd) and 19% of TCL (2% sd); anterior rostrum width 82% of posterior rostrum width (6% sd). Cephalothorax subcylindrical; postorbital ridge not terminating in spine, occasionally terminating in tubercle; TCL 203% of carapace width (11% sd); areola length 273% of areola width (44% SD), 34% of TCL (1% sd), width 26% of TCL (5% sd). Third pereopods without hook on ischium. Chelae without tubercles; palm length 82% of maximum chela width at palm (5% sd); palm length 35% of propodus length (2% sd); chela height 63% of maximum chela width at palm (2% sd). First pleopod (gonopod) of males nondescript, typical for genus. Annulus ventralis lacking, typical for genus.

Holotypic male. Body compressed dorsoventrally ( Fig. 4A View FIGURE 4 ). Carapace slightly wider (102%) than abdomen. Rostrum broad, margins parallel to sub-parallel, anterior width 85% of posterior width, without spines or tubercles, deflected ventrally; with weak median carina ( Fig. 4B View FIGURE 4 ). Rostrum length 139% of posterior width, 18% of TCL; acumen 30% of rostrum length. Carapace maximum depth less (85%) than carapace width; TCL 25.1 mm; areola 200% longer than wide, 32% of TCL ( Fig. 4B View FIGURE 4 ); short postorbital ridges terminating in small tubercle; surface otherwise lacking tubercles or spines. Abdomen slightly shorter than carapace (97%). Palm length 87% of palm width; palm depth 64% of palm width (all measurements and counts from right chela; Fig. 4C View FIGURE 4 ). Gonopod nondescript, typical for genus ( Fig. 4D, E View FIGURE 4 ). Epistome with semi-circular anterior lobe, lacking setae ( Fig. 4F View FIGURE 4 ). Right antennal scale 4.1 mm long and 2.0 mm wide (Fig. H). Third pereopods without hook on ischium.

Allotypic female. Differing from holotype in following respects: TCL 33.9 mm; areola 286% longer than wide, length 35% of TCL; anterior rostrum width 69% of posterior rostrum width; rostrum length 133% of posterior width and 17% of TCL; acumen 34% of rostrum length; palm length 81% of palm width, depth 59% of palm width (all measurements and counts based on right chela). Antennal scale 5.0 mm long, 2.2 mm wide. Annulus ventralis absent ( Fig. 4G View FIGURE 4 ).

Size. The largest individual measured was 37.6 mm TCL.

Color. Olive brown ( Fig. 5 View FIGURE 5 ) to yellow or orange. The white mark at the joint of the dactyl and propodus in P. leniusculus is generally absent or reduced.

Etymology. For the Malheur region of eastern Oregon, including the Malheur National Forest and Malheur Lake, from the French “malheur” meaning misfortune. We propose the common name the “Misfortunate Crayfish” due to its discovery while studying spread of invasive F. rusticus throughout the John Day River watershed in Oregon, which has displaced P. malheurensis sp. nov. from a substantial proportion of its former distribution.

Geographic distribution and habitat. Pacifastacus malheurensis sp. nov. occurs in the John Day River watershed of central Oregon and its tributary streams, as well as over a watershed divide into the endorheic Harney Basin of southeastern Oregon ( Fig. 6 View FIGURE 6 ). Populations visualized in Fig. 6 View FIGURE 6 are vouchered at the RBCM except the most downstream location in the John Day River and the East Canal at Page Springs Dam population reported in Larson et al. (2016). Harney Basin tributaries include the upper Silvies River and East Canal at Page Springs Dam, an irrigation-modified tributary of the Donner und Blitzen River. Both the Silvies and Donner und Blitzen rivers drain to the saline Malheur Lake. Whether P. malheurensis sp. nov. occurs in other rivers of the Blue Mountains in northeast Oregon, or other endorheic watersheds of the Great Basin of California, Idaho, Oregon, or Nevada, is unknown. Pacifastacus malheurensis sp. nov. has never been detected west of the Cascade Mountains in coastal California, Oregon, or Washington. Pacifastacus malheurensis sp. nov. has not been collected from lentic ecosystems, but natural lakes are scarce within its distribution excluding saline lakes of endorheic basins that are unlikely to be viable for these crayfish.

Life history. Life history of P. malheurensis sp. nov. has not been studied, and berried or ovigerous individuals are not included among the RBCM vouchers. Pacifastacus malheurensis sp. nov. life history might be expected to broadly resemble other crayfishes of the genus Pacifastacus , as slower-growing and with lower fecundity proportional to carapace length relative to members of the family Cambaridae native to eastern North America ( Momot 1984).

Conservation status. Pacifastacus malheurensis sp. nov. has likely been displaced from much of its native range in the John Day River of Oregon by ongoing spread of invasive F. rusticus ( Messager & Olden 2018; Olden et al. 2009). Urgent conservation attention is needed, with an emphasis on preventing invasive crayfish introductions to isolated P. malheurensis sp. nov. populations in the Silvies River and Donner und Blitzen River. The rapid pace of the spread of F. rusticus , and associated displacement of P. malheurensis sp. nov. from the John Day River, suggests an International Union for the Conservation of Nature (IUCN) status of globally Endangered due to likely range declines of ≥70% over 10 years or three generations ( IUCN 2012). As only six occurrences of P. malheurensis sp. nov. are known ( Fig. 6 View FIGURE 6 ), an Oregon natural heritage ranking of Imperiled is recommended (https://inr.oregonstate. edu/orbic/rare-species/ranking-definitions).

Crayfish associates. Faxonius rusticus is now the dominant crayfish throughout much of the John Day River and its tributaries in Oregon ( Messager & Olden 2018; Olden et al. 2009). Pacifastacus malheurensis sp. nov. was not collected in sympatry with F. rusticus by Larson et al. (2012) or Larson et al. (2016). Pacifastacus leniusculus was collected from the mainstem John Day River in the town of John Day by Larson et al. (2012) and included in phylogenetic and morphological analyses here ( Table 1). These P. leniusculus did not co-occur with P. malheurensis sp. nov. and mtDNA haplotypes of the two lineages have never been recovered from the same location. Pacifastacus connectens is also known from some locations in the Harney Basin of eastern Oregon, which constitutes its western range boundary, but P. connectens has not been collected with P. malheurensis sp. nov. and is known instead from isolated springs in the vicinity of Harney Lake ( Egly & Larson 2018; Principe et al. 2021).

Relationships and comparisons. Pacifastacus malheurensis sp. nov. is morphologically similar to P. okanaganensis sp. nov. and P. l. klamathensis crayfishes of coastal, southwestern Oregon and northwestern California. Pacifastacus malheurensis sp. nov. generally has an acumen length less than 79.4% of anterior rostrum width, whereas P. leniusculus generally has an acumen length greater than 79.4% of anterior rostrum width ( Fig. 3 View FIGURE 3 ). Pacifastacus malherensis sp. nov. generally has a rostrum length less than 18.85% of TCL, whereas P. okanaganensis sp. nov. has a rostrum length greater than 18.85% of TCL ( Fig. 3 View FIGURE 3 ). Pacifastacus l. leniusculus in particular are easy to differentiate from P. malheurensis sp. nov. by the long, spiny rostrum and chelae with short, convex palms ( Hobbs 1972). Pacifastacus malheurensis sp. nov. has not been collected in sympatry with P. okanaganensis sp. nov. or coastally distributed P. l. klamathensis and may be differentiated by geographic range. Pacifastacus connectens can be differentiated from P. malheurensis sp. nov. by a serrated rostrum with many pairs of marginal tubercles or spines and the presence of patches of setae on the dorsal margins of the chelae. Pacifastacus connectens in the Harney Basin often has a distinctive color pattern of orange or red mottling on a yellow background ( Principe et al. 2021).