Gammarus fasciatus Say, 1818

Gammarus fasciatus Say, 1818 View in CoL

Figs 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4 , 5 View Figure 5 , 6 View Figure 6 , 7 View Figure 7 , 8 View Figure 8

Gammarus fasciatus Say, 1818 p. 874 View in CoL ; 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 View in CoL 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 About USNM (AGC-1096.1) GoogleMaps • topotype female, 5.91 mm; same data as for topotype male; USNM 1694138 About USNM (1096.2) GoogleMaps • 3 topotype males; same data as for topotype male; USNM 1694139 About USNM GoogleMaps • 3 topotype males; same data as for topotype male; USNM 1694140 About USNM GoogleMaps .

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 About USNM (AGC-1065 series) GoogleMaps • 2 males; Spring Creek , Donald R. Taylor Park, Dauphin County, Pennsylvania; 40.25893°N, 86.82501°W; A. G. Cannizzaro leg; USNM 1694141 About USNM (AGC-1093 series) GoogleMaps • 3 males, 2 females; Lake Superior , Ashland, Ashland County, Wisconsin; 26 June 1957; E. L. Bousfield leg.; USNM 191207 About USNM • 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 About USNM GoogleMaps • 5 males; Grand Rapids , Kent County, Michigan; 11 September 1909; R. C. Coker leg.; USNM 41754 About USNM . CANADA • 4 females, 1 male; St. Lawrence River , Beauharnois Power Dam Outlet, Montérégie, Quebec; 1 July 1968; R. K. Lee leg.; USNM 191209 About USNM .

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 View Figure 2 ).

Antennae. Antenna 1 (Fig. 3 A View Figure 3 ): 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 View Figure 3 ): 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 View Figure 3 ): 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 View Figure 3 ): 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 View Figure 4 ): rounded, apical margin of labrum with numerous setules. Lower lip (Fig. 4 B View Figure 4 ): 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 View Figure 4 ): 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 View Figure 4 ): 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 View Figure 4 ): 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 View Figure 5 ): 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 View Figure 6 ): 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 View Figure 5 ): 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 View Figure 6 ): 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 View Figure 6 ): 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 propodus; dactylus approximately 30 % length of propodus, setation as in other pereopods. Pereopod 6 (Fig. 6 C View Figure 6 ): coxal plate weakly bilobate, posterior lobe with 3 setae, increasing in length distally; basis posterior margin weakly convex with 13 shallow serrations bearing setae, posterior face of segment with 9 long setae, distoposterior margin without free lobe and nearly fused to ischium, junction with robust seta and 2 setae, anterior margin with 5 groups of robust setae and 7 anteroproximal setae; merus subequal in length to carpus, densely setose; carpus subequal in length to propodus, densely setose, some setae slightly curled; dactylus approximately 25 % length of propodus, setation as in other pereopods. Pereopod 7 (Fig. 6 D View Figure 6 ): coxal plate small, lobes indistinct, with 5 posterior setae; basis posterior margin convex, with 15 shallow serrations bearing long setae, seta length increasing distally, longest posterior seta 40 % width of segment, face of segment with 28 long setae, distoposterior margin without free lobe, nearly fused to ischium, junction with robust seta and a tuft of setae, anterior margin with 7 robust setae, and 4 anteroproximal setae; merus approximately 80 % length of carpus, densely setose; carpus subequal in length to propodus, densely setose, some setae slightly curled; dactylus approximately 25 % length of propodus, setation as in other pereopods.

Gills (Figs 5 B, C View Figure 5 , 6 A – D View Figure 6 ): coxal gills on somites 2–6, somite 7 with pereopod 7 gill.

Pleon. Pleopod 1 (Fig. 6 E View Figure 6 ): peduncle with 3 outer setae, 7 inner setae, and 3 coupling hooks; outer, inner rami with 19 and 16 segments, respectively. Pleopod 2 (Fig. 6 F View Figure 6 ): peduncle with 14 outer setae, 18 inner setae, and 3 coupling hooks; outer, inner rami with 17 and 14 segments, respectively. Pleopod 3 (Fig. 6 G View Figure 6 ): peduncle with numerous setae and 3–4 coupling hooks; outer, inner rami with 16 and 12 segments, respectively. Epimera (Fig. 7 A View Figure 7 ): first epimeron anterior margin with 6 setae, ventral margin straight, distoposterior corner not produced, posterior margin with 4 short setae; second epimeron anterior margin with 4 setae, ventral margin with 4 setae, 10 additional setae are inserted facially in an oblique row, distoposterior corner produced, posterior margin with 4 setae; third epimeron anterior margin with 8 setae, ventral margin with 7 setae, distoposterior corner produced, posterior margin with 4 setae.

Urosome. Uronites (Fig. 7 B View Figure 7 ): first and second uronites strongly humped dorsally; dorsomedial surface of first and second uronites with 3–4 robust setae and 3–6 setae; dorsolateral margins of first and second uronites with a pair of 2–3 robust setae and 2–3 setae; third uronite weakly humped, with 3 robust setae and 1 seta dorsomedially, and 2–3 robust setae and 2–3 setae dorsolaterally. Uropod 1 (Fig. 7 C View Figure 7 ): peduncle 2.4 × rami in length with 8 outer robust setae, 5 inner robust setae, and 2 anteroproximal robust setae; outer ramus subequal in length to inner, with 3 marginal robust setae, 4 apical robust setae, and 1 anteroproximal seta; inner ramus with 2 outer robust setae, 3 inner robust setae, and 5 apical robust setae. Uropod 2 (Fig. 7 D View Figure 7 ): peduncle approximately 85 % length of outer ramus, with 2 outer robust setae and 4 inner robust setae; outer ramus approximately 1.3 × inner ramus in length, with 3 outer robust setae and 5 apical robust setae; inner ramus with 1 inner robust seta, 1 outer robust seta, and 5 apical robust setae. Uropod 3 (Fig. 7 E View Figure 7 ): elongate, biramous; peduncle approximately 40 % length of outer ramus with 4 marginal robust setae; outer ramus 2 - segmented, 1 st segment approximately 7 × length of 2 nd segment, with 4 groups of robust setae on outer margin paired with setae and / or plumose setae, 3 additional robust setae line apical margin; 2 nd segment with apical group of setae and plumose setae; inner ramus 75 % length of outer ramus, 1 - segmented, with 1 robust seta on both outer and inner margins, apical margin with robust seta and setae / plumose setae. Telson (Fig. 7 F View Figure 7 ): cleft to base, apices each with 3 robust setae and 2–3 setae; outer margins with 2–4 robust setae and 3 setae, 2 additional plumose setae arise distally; facial / inner surfaces with a seta.

Female: (Figs 2 B View Figure 2 , 8 View Figure 8 ): 5.91 mm in length. Differing from male in smaller body size, gnathopod 2 shape / setation, pereopod shape / setation, and uropod 3 size / setation. Structures not described below are as in male.

Gnathopods. Gnathopod 2 (Fig. 8 A View Figure 8 ): coxal plate with 4 anterior setae, 2 posteroventral 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, posterodistal margin with 2 serrate robust setae; ischium with 1 tuft of posterior setae and pubescent setules along posterior margin; merus with 1 anterior seta and setae lining the posterior and distal margins, posterior surface of segment with weak pubescent setules; carpus approximately 80 % length of propodus with 2 tufts of setae along anterior margin, posterior margin with numerous setae, distal margin with 6 setae; propodus approximately 2.5 × longer than broad, with 1 tuft of anterior setae, 12 anterodistal setae, 3 tufts of superior medial setae with proximal-most singly inserted, 4 tufts of inferior medial setae with proximal-most singly inserted, and 5 tufts of posterior setae; palm transverse, straight, with 8 setae along inner margin and 6 long setae along outer margin; defining angle with 2 robust setae, a seta on inner margin, and 4 serrate setae on outer margin; dactylus with outer seta, margin at base of nail with 2 seta, and a distinct tooth.

Brood plates (Fig. 8 A View Figure 8 ). Broad, expanding apically with medium-length setae, present on somites 2–5.

Pereopods. Pereopod 7 (Fig. 8 B View Figure 8 ): coxal plate small, lobes indistinct, with 5 posterior setae; basis posterior margin convex, with 11 shallow serrations bearing setae, seta length increasing slightly distally, longest posterior seta 15 % width of segment, face of segment with 17 long setae, distoposterior margin without free lobe, nearly fused to ischium, junction with robust seta and a tuft of setae, anterior margin with 6 robust setae and an anteroproximal seta; merus subequal in length to carpus; carpus approximately 75 % length of propodus; dactylus approximately 30 % length of propodus, setation as in male.

Urosome. Uropod 3 (Fig. 8 C View Figure 8 ): less elongate than in male, biramous; peduncle approximately 40 % length of outer ramus with 1 outer robust seta and 6 marginal robust setae; outer ramus 2 - segmented, 1 st segment approximately 3 × length of 2 nd segment, with 2 groups of robust setae on outer margin paired with setae, 3 additional robust setae line apical margin; 2 nd segment with apical group of setae; inner ramus approximately 66 % length of outer ramus, 1 - segmented, with 1 robust seta on both outer and inner margins, apical margin with robust seta and setae / plumose setae.

Variation.

Individuals examined were shown to vary notably in several morphological characteristics (Tables 2 View Table 2 , 3 View Table 3 ; Fig. 9 View Figure 9 ).

Distribution and ecology.

While Gammarus fasciatus has historically had an uncertain distribution, the core portion of its range is found on the northern Atlantic coastal plain of the United States and southern Canada (Fig. 1 View Figure 1 ). Additional records putatively identified as G. fasciatus are known as far south as South Carolina (Fig. 1 View Figure 1 ). However, critical examination of these populations may prove them to be either similar species, such as G. tigrinus / daiberi , or undescribed species closely related to G. fasciatus sens. str. Furthermore, G. fasciatus has also been recorded from the Laurentian Great Lakes and the Mississippi River drainages; evidence suggests recent dispersal into these regions, either naturally or due to anthropogenic factors (see Discussion).

Gammarus fasciatus has been recorded from a range of habitats, including lakes, rivers, and estuaries, where it appears to prefer slower-moving, turbid water. The species is also known from lower-order habitats such as small streams and even spring runs; this appears to be especially true in the southern portions of its range ( Holsinger 1972). Ovigerous females have been collected from February to September, with populations in the southern portion of the range appearing ovigerous earlier in the year ( Bousfield 1958; Holsinger 1972). Life history information is relatively limited, but two generations have been reported per year, with a life cycle of less than a year in duration ( Bousfield 1958).