Gammarus fasciatus Say 1818

Gammarus fasciatus Say, 1818 Figs 2, 3, 4, 5, 6, 7, 8 Gammarus fasciatus Say, 1818 p. 874; Smith, 1874 p. 653; Weckel, 1907 p. 48; Huntsman, 1911 p. 151; Pentland, 1930; Hubricht & Mackin, 1940 p. 193; Hubricht, 1943 p. 6; Clemens, 1950; Bousfield, 1958 p. 69; Cole, 1970 p. 338; Cole, 1980 p. 72; Bousfield, 1973 p. 53; Holsinger, 1972 p. 21. Gammarus nr. fasciatus Beckett, 1998. Gammarus sp. Nicholson, 1873, p. 500. Material examined. USA • topotype male, 13. 12 mm; Schuylkill River at Flat Rock Park, Montgomery County, Pennsylvania; 40.04379°N, 75.2527°W; 6 June 2024; A. G. Cannizzaro leg.; USNM 1694137 (AGC-1096.1) • topotype female, 5.91 mm; same data as for topotype male; USNM 1694138 (1096.2) • 3 topotype males; same data as for topotype male; USNM 1694139 • 3 topotype males; same data as for topotype male; USNM 1694140. Additional material examined. USA • 3 males; Ohio River, Gallipolis, Gallia County, Ohio; 38.80599°N, 82.20491°W; 21 April 2024; A. G. Cannizzaro leg.; USNM 1694140 (AGC-1065 series) • 2 males; Spring Creek, Donald R. Taylor Park, Dauphin County, Pennsylvania; 40.25893°N, 86.82501°W; A. G. Cannizzaro leg; USNM 1694141 (AGC-1093 series) • 3 males, 2 females; Lake Superior, Ashland, Ashland County, Wisconsin; 26 June 1957; E. L. Bousfield leg.; USNM 191207 • 2 males, 2 females; Lake Champlain, Burlington, Chittenden County, Vermont; 44.75°N, 73.33°W; 19 July 1956; E. L. Bousfield leg.; USNM 191214 • 5 males; Grand Rapids, Kent County, Michigan; 11 September 1909; R. C. Coker leg.; USNM 41754. CANADA • 4 females, 1 male; St. Lawrence River, Beauharnois Power Dam Outlet, Montérégie, Quebec; 1 July 1968; R. K. Lee leg.; USNM 191209. Diagnosis. distinctly banded, setiferous species; antenna 1 0.9–1.5 × length of antenna 2; antenna 2 setiferous, lacking calceoli in males; mandibular palp with C-setae on third segment, C-setae 2–2.5 × D-setae in length; mandibular palp α-setae inserted parallel to margin; B-setae on mandibular palp longer than A-setae; coxal plates 1–4 with numerous long facial setae; pereopods setiferous, pereopod 7 basis posterior margin convex, posterior setae 35–40 % length of basis width; second and third epimera lacking or with limited robust setae, facial surface of epimeron 2 and ventral margin of epimera 2 + 3 with long setae; uronites distinctly humped; uropod 3 of male inner ramus 75–80 % length of outer ramus. Description. Male: 13.12 mm in length. Eyes reniform, integumentary pigment present when alive and in freshly preserved specimens (Fig. 2 A). Antennae. Antenna 1 (Fig. 3 A): approximately 40 % body length, subequal in length to antenna 2; peduncle segment 1 with 1 marginal ventral seta and 3 robust setae on distoventral corner; peduncle segment 2 with 3 clusters of marginal ventral setae; primary flagellum with 23 segments, aesthetascs present on all but proximal segments, aesthetascs shorter than respective segments; accessory flagellum with 5 segments, approximately 20 % length of primary flagellum. Antenna 2 (Fig. 3 B): gland cone developed; peduncle approximately 1.4 × length of flagellum, peduncular segment 4 with 6 clusters of ventral setae, 6 clusters of lateral setae, and 6 clusters of submarginal ventral setae; peduncular segment 5 subequal in length to segment 4 with 6 clusters of submarginal ventral setae and 5 clusters of dorsal setae, and an additional 3 clusters of submarginal setae inserted laterally near the dorsal margin; flagellum with 9 segments, dorsal and ventral setae decreasing in length distally, all segments lacking calceoli. Mouthparts. Left mandible (Fig. 3 C): incisor 5 - dentate, lacinia mobilis 4 - dentate; accessory setae row with 5 plumose setae; molar process well developed, cylindrical triurative with plumose seta; palp 3 - segmented, second segment approximately 1.2 × length of third segment, with 7 α-setae, 6 β-setae, and 6 γ-setae; third segment weakly rounded distally, inner margin straight, with 8 A-setae set in two rows, 3 B-setae, 2 C-setae, 18 D-setae, and 5 E-setae; E-setae 1.25 × length of longest α-seta, C- setae 2 × D-setae in length, longest A-seta approximately 60 % length of B-setae; distal face of segment covered in numerous fine pubescent setules. Right mandible (Fig. 3 D): incisor 4 - dentate, lacinia mobilis bifurcate, lobes with numerous fine dentations; accessory setae row with 6 plumose setae; molar similar in form to left mandible, palp as in left mandible. Upper lip (Fig. 4 A): rounded, apical margin of labrum with numerous setules. Lower lip (Fig. 4 B): inner lobes indistinct, outer margin of inner, outer lobes covered in setules; face of lip covered in pubescent setules. Maxilla 1 (Fig. 4 C, D): inner plate with 13 pappose setae and numerous fine pubescent setules covering entire plate; outer plate with 11 apical serrate setae, pubescent setules covering plate, decreasing laterally and proximally; right palp with 2 segments, subapical margin of distal segment with 1 long seta, apical margin with 6 robust setae; left palp with 2 segments, subapical margin of distal segment with 3 long setae, apical margin with 7 robust setae, weaker than those of left palp. Maxilla 2 (Fig. 4 E): both inner and outer plates covered in pubescent setules; outer plate approximately 1.1 × length of inner plate, with numerous apical setae; inner plate narrowing slightly distally with numerous apical setae and 12 pappose facial setae. Maxilliped (Fig. 4 F): inner plate shorter than outer plate, apical margin with 3 naked cuspidate setae, and an additional naked cuspidate seta inserted toward inner margin, surface of plate covered in pubescent setules; outer plate armed with numerous naked cuspidate setae covering inner margin along with setae inserted submarginally, apical margin with 5 plumose setae, increasing in robustness towards inner margin; palp second segment with numerous marginal setae, third segment with numerous marginal / submarginal setae, apical margin with robust serrate setae, distal surface of segment with pubescent setules; dactylus with numerous setae lining inner margin. Gnathopods. Gnathopod 1 (Fig. 5 A): coxal plate with 5 anterior setae, 3 posterior setae, and 4 facial setae, additional smaller, submarginal setae line margin of plate; basis with numerous long setae inserted along anterior and posterior margins, robust, serrate setae on posterodistal corner; ischium with tuft and pubescent setules along posterior margin; merus with 2 anterior setae, setae lining posterior and distal margins, posterior surface of segment with weak pubescent setules; carpus approximately 55 % length of propodus with 3 tufts of setae along anterior margin, posterior margin with numerous setae and 4 submarginal setae directed distally, distal margin with robust, plumose setae; propodus 2 × longer than broad, with 2 tufts of superior medial setae, 5 anterodistal setae, 7 tufts of inferior medial setae, proximal most singly or doubly inserted, and 4 tufts of posterior setae; palm oblique, highly concave with large, robust setae placed medially along margin and numerous inner / outer marginal setae; defining angle with 6 robust setae; dactylus with outer seta, inner setae lacking. Gnathopod 2 (Fig. 6 B): coxal plate with 5 anterior setae, 3 posterior setae, 6 facial setae, and additional smaller, submarginal setae lining margin of plate; basis with numerous long setae inserted along posterior margin, anterior margin with long setae proximally and shorter setae distally; ischium with 2 tufts of posterior setae and sparse pubescent setules along posterior margin; merus with 2 anterior setae, setae lining posterior and distal margins, posterior surface of segment with weak pubescent setules; carpus approximately 50 % length of propodus with 2 tufts of setae along anterior margin, posterior margin with numerous setae, distal margin with plumose setae; propodus 2 × longer than broad, with 3 tufts of anterior setae, 7 anterodistal setae, 2 tufts of superior medial setae with proximal-most singly inserted, 4 tufts of inferior medial setae, and 6 tufts of posterior setae; palm oblique, concave with large, robust setae placed medially along margin and numerous inner / outer marginal setae; defining angle with 7 robust setae; dactylus with outer seta and 4 inner setae. Pereopods. Pereopod 3 (Fig. 5 C): coxal plate with 4 anterior setae, 1 posterior seta, 7 facial setae, and additional smaller, submarginal setae line margin of plate; basis with numerous long setae inserted along anterior and posterior margins; merus approximately 1.5 × longer than carpus, posterior margin heavily setose; carpus approximately 75 % length of propodus, posterior margin heavily setose; dactylus approximately 45 % length of propodus, with plumose seta proximally on anterior margin, stout seta placed distally along posterior margin, proximal to nail, and an additional seta placed medial near base of nail. Pereopod 4 (Fig. 6 A): approximately 90 % of the length of pereopod 3, coxal plate with 4 anterior setae, 7 posterior setae, 11 facial setae, and additional smaller submarginal setae line plate, plate with distinct posteroproximal excavation; basis with numerous long setae inserted along anterior and posterior margins; merus approximately 1.5 × longer than carpus, posterior margin heavily setose; carpus approximately 70 % length of propodus, posterior margin heavily setose; dactylus approximately 50 % length of propodus, setation as in pereopod 3. Pereopod 5 (Fig. 6 B): coxal plate large, bilobate with distinct anterior and posterior lobes, anterior lobe with a seta, posterior lobe with 3 setae; basis posterior margin convex with 11 serrations bearing setae, posterior face of segment with 5 long setae, distoposterior margin without free lobe and nearly fused to ischium, anterior margin with 6 groups of robust setae and 7 anteroproximal setae, anterior face of segment with 8 long setae; merus subequal in length to carpus; carpus approximately 80 % length of pro

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