Mesamphisopus kensleyi, Gouws, 2008

Gouws, Gavin, 2008, New species of Mesamphisopus, an endemic South African freshwater isopod genus (Isopoda: Phreatoicidea: Mesamphisopidae), Zootaxa 1690, pp. 1-62 : 29-36

Mesamphisopus kensleyi n. sp.

Figures 9–12

Material examined. Holotype: SAM A45152, ♂ (9.0 mm), along stream, trail above Aurora Drive (off Chapman’s Road), Gordon’s Bay, South Africa (34°09.82’S 18°52.63’E), coll. S. R. Daniels and G. Gouws, 17 November 2000.

Paratypes: SAM A44940, ♂ (8.9 mm, dissected) and ♀ (preparatory 7.7 mm, dissected) parts slide mounted and in microvials, additional 4 ♂, 4 ♀, collection details as for holotype .

Other material: SAM A45153, ♂, ♀, 2 juv., stream above Chapman’s Road , Gordon’s Bay, South Africa (34°08’S 18°52’E), coll. C.L. Griffiths and P. le Roux, 19 October 1989 .

Etymology. Named for Brian Kensley, in recognition of his contribution to the systematics and taxonomy of southern African Isopoda .

Diagnosis. Mandibular groove smoothly indented. Pleonites 1–4 width 1.18–1.21 composite length in dorsal view. Pleotelson dorsal surface covered with abundant elongate setae; ventral margin anterior to uropods with single row of 4 simple RS; lateral uropodal ridge terminating at pleotelson margin above uropods; posterior apex with 1 pair of RS. Mandibular palp article 3 with 19–21 finely setulate setae. Maxilliped palp insertion on basis ventral surface with 3 or 4 SS subdistally near mesial margin. Pereopod I dactylus ventrodistal margin smooth in male; propodal palm with 4 stout denticulate bifid setae, 3 basally-inflated stout RS, 2 elongate broad-based setae; ischium dorsal margin with single RS, 7 SS lateral to margin. Pereopod II and III carpus length:width <1.25. Pereopod II basis length:width <2.00. Pereopods II and III basis dorsal ridge in cross-section rounded. Pereopods II–IV ischium dorsal margin with 13–16 SS, 1 RS on pereopod II. Pereopod IV propodus ventral margin with 2 broad-based setae. Penes with single seta below tip. Pleopodal endopods III–V shallowly cleft distomesially. Distal articles of pleopodal exopods long (distal article length:exopod length> 0.36 for pleopods II, IV and V in male).

Descriptions. Male. Coloration. Body pigmented, slate grey to dark brown grey, fades to brown or almost completely to light brown, yellow-brown upon preservation. Unpigmented parts white to off-white, turning off-white to yellow-brown upon preservation. Darker pigmentation forms longitudinal dorsal band along pereon. Unpigmented parts give mottled appearance to lateral parts of pereon, and dendritic pattern to head and pleotelson. Pereopods generally unpigmented, bases may be lightly pigmented. Uropods lack pigmentation. Pleonites lightly pigmented towards ventral extent of pleura, more heavily coloured along posterior margins of pleonites.

Head setae common, fine. Eyes projecting anteriorly, bulging slightly dorsolaterally; maximum diameter 0.11 head depth; approximately round.

Pereon width exceeding head width; length of setae on dorsal surface 0.16–0.24 body depth. Pereonite 1 length:width in dorsal view 0.36–0.40. Pereonite 2 length:width 0.42–0.45. Pereonite 3 length:width 0.44. Pereonite 4 length:width 0.39. Pereonite 5 length:width 0.40–0.42. Pereonite 6 length:width 0.37–0.39. Pereonite 7 length:width 0.25–0.27.

Pleonites 2–4 respective lengths in dorsal view less than half the length of pleonite 5, 1–4 relative lengths unequal, increasing in length from anterior to posterior. Pleonites 1–5 dorsal length:maximum width of pleo- nites 1–5 respectively 0.16, 0.19, 0.22, 0.27 and 0.58. Pleonites 1–5 depth:pereonite 7 depth respectively 1.47, 1.94, 2.09, 2.06 and 1.85.

Pleotelson dorsal surface in lateral view inflected ventrally, length 0.99–1.02 width; lateral length less than (0.75–0.84) depth; depth 1.35–1.68 pereonite 7 depth. Posterior apex with additional RS pair more laterally.

Antennula ( Fig. 9) length 0.15 body length, with 7 or 8 articles. Antepenultimate article may be divisible into 1 large or 2 small articles. Three fine aesthetascs, 5 SS on terminal article, single aesthetasc and 2 SS on subterminal article distal margin. Terminal article length:width 0.36. Penultimate article distinctly longer than other articles. Distal articles circular to oval in cross-section.

Antenna ( Fig. 9) length 0.51 body length. Flagellum length 0.61 total antenna length, with 16–20 articles. Article 5 length subequal to article 4.

Mouthfield. Clypeus ( Fig. 9) greatly expanded and broadly triangular laterally; width 0.61 head width. Labrum ( Fig. 9) ventrally semicircular in anterior view, with fine fringe of setae distally; dorsal margin same width as clypeus. Paragnath ( Fig. 9) lobes distolaterally rounded to angular, distally more truncate; distomesial margin with dense rows of fine setae projecting inwards; elongate SS scattered distolaterally.

Mandible ( Fig. 10) palp length 1.01 mandible length; article 1 with elongate SS distoventrally; article 2 with numerous elongate SS in longitudinal row along ventral margin or concentrated along mesio-anterior margin, separate distal row of 3 setae dorsolaterally; setae longer than half respective segment lengths. Left spine row with 13 spines, 4 or 5 of which are bifurcate. Right spine row with 11 spines, 4 of which are bifurcate. Molar process length subequal to width or longer than wide; fine simple spines forming posterior row.

Maxillula ( Fig. 10) mesial lobe length 0.70 lateral lobe length; width 0.54 lateral lobe width; with 2 accessory setae, 1 on distolateral margin simple and 1 between distomesial PPS distally denticulate. Lateral lobe distal margin with 5 smooth RS, 7 denticulate RS, with 3 RS placed in distal setal row; ventral face with 1 PS, 2 pectinate-plumose setae, widely spaced.

Maxilla ( Fig. 10) mesial lobe width 0.90 outer lateral lobe width; proximal portion distinctly angled to distal portion; proximal and distal setal rows separated by gap; 13 broad-based, elongate SS in single ventral basal row; 35–45 closely set, elongate setae with distinct base, sparsely plumose shaft in dorsal basal row; setae in multiple distal rows include large number of simple, pectinate or setulate setae and PS. Outer lateral lobe length subequal to inner lateral lobe, wider than inner lateral lobe; distal margin with 17 long bidenticulate setae. Inner lateral lobe distal margin with 13 long bidenticulate setae.

Maxilliped ( Fig. 10) epipod length:width 1.13–1.18; distal margin scattered SS, finer fringe along mesial margin. Endite length:total basis length 0.42; mesial margin with 3 or 4 coupling hooks on left side, 3 on right side; dorsal ridge with 18 large distally denticulate PS. Palp insertion on basis with 2 additional elongate SS ventral subdistal/distolateral; palp width across articles 2 and 3:endite width 1.79; article 4 subcircular, length equals width; article 5 length:width 1.23, article 5 length:article 4 length 0.67.

Pereopod I ( Fig. 11) length:body length 0.49. Dactylus length subequal to palm or longer than palm, length:palm length 1.33–1.42; claw length:dactylus length 0.14; distal accessory claw length 0.30 primary claw length. Propodus length:width 1.16; dorsal margin with 14 setae in several groups between proximal and distal margin, including 9 in distal group. Propodal palm cuticular fringe weakly developed. Merus distodorsal margin includes 1 RS. Basis length:width 1.89; basis dorsal margin with seta proximally; ventrodistal margin with 5 elongate setae.

Pereopods II and III ( Fig. 11; Table 1) dactylus distal accessory claw length 0.33–0.38 primary claw length. Pereopods II and III with, respectively, 5 and 4 broad-based setae on propodus, evenly spaced along ventral margins, setae 0.16–0.40 respective propodus lengths. Pereopod II and III each with 7 broad-based setae on carpus, setae 0.10–0.65 carpus length. Basis dorsal ridge with 11–18 elongate SS along or mesiolaterally to margin. Pereopod III with single PNS on dorsal ridge of basis.

Pereopod IV ( Fig. 11) with PNS on dorsal margin of basis. Dactylus longer than or subequal to propodal palm; distal accessory claw length 0.25–0.33 primary claw length. Propodus length:pereopod length 0.12; length:width 1.36; distal width:palm width 0.82; articular plate subequal in length to dactylar claw. Carpus length:pereopod length 0.13; with 6 broad-based setae on ventral margin, some distinctly larger than others. Ischium posterodistal margin with 7 setae. Basis length:width 2.12; dorsal ridge may appear rounded in crosssection, with 18 setae.

Pereopods V–VII ( Fig. 11; Table 2) with PNS on dorsal ridge of basis. Dactylus distal accessory claw ventrolateral to primary claw, length 0.33–0.43 primary claw length. Propodus distal margins with 5–7 elongate RS, 3–5 more elongate than others. Pereopods V–VII ischium dorsal margin with 8–10 SS, including 2–5 RS. Basis dorsal ridge in cross-section angular on V, produced and forming distinct plate on VI and VII, with elongate fine setae along entire margin; lateral face with central ridge on pereopods VI and VII.

Penes length 0.47 body width at pereonite 7; distally tapering slightly; distal tip rounded.

Pleopods ( Fig. 12; Table 3). Endopod I–IV margins with PS and SS, V with SS only. Protopods mesial margins/epipods I–IV with 4, 2, 1 and 1 coupling hooks, respectively; I–V with 4, 3, 4, 5 and 4 elongate inflexible SS, respectively. Protopod lateral epipod III length 1.75 width, lateral epipod V length 1.37 width. Protopods lateral epipods III–V with 19, 21 and 20 elongate inflexible SS on margins, respectively. Pleopod I exopod broadest proximally, mesial margin straight to slightly convex, dorsal surface with setae; protopod length subequal to that of other pleopods, width subequal to length. Pleopod II endopod appendix masculina with 32 setae on margin; length 0.43 pleopod length; distal tip extending beyond distal margin of endopod.

Uropod ( Fig. 12) total length 1.79 pleotelson length. Protopod length:width 3.22; length 0.43 uropod total length; extending posteriorly subequal to pleotelson apex; dorsomesial ridge produced, plate-like, ridge length:endopod length 0.56. Rami (in cross-section) flattened on dorsal surface only. Endopod dorsal margin with 6 RS along length and apically. Exopod length 0.82 endopod length; with 4 RS along dorsal margins and apically.

Female. Pereon. Pereonite 1 (length:width in dorsal view 0.31), pereonite 5 (0.34–0.37) and pereonite 7 (0.21) relatively shorter and wider than in male.

Antennula with 4 fine aesthetascs on terminal article or terminal article periphery, 2 along subterminal article distal margins; 5 SS on terminal article and subterminal article distal margins.

Pereopod I length:body length 0.38. Dactylus length:palm length 1.24; ventrodistal margin with thin scale-like spines along 0.26 total length; claw length:dactylus length 0.17–0.21. Propodus length:width 1.29. Propodal palm concave; with 7 serrate and bifid denticulate stout setae, 3 elongate broad-based setae. Ischium dorsal margin with 7 SS. Basis with 4 or 5 dorsal setae positioned proximally; ventrodistal margin with 3 or 4 elongate setae.

Pereopods II and III ( Table 1). Pereopod II with 3 broad-based setae, proximal pair closely set, distal seta at midpoint of ventral margin; carpus with 6 broad-based setae. Pereopod III propodus with 2 or 3 broadbased setae, evenly spaced from midpoint of ventral margin to distal margin, setae 0.13–0.26 propodus length; carpus with 5 broad-based setae, reaching 0.87 carpus length.

Pereopod IV approaching prehensile state. Propodus length:width 1.60. Propodus with 3 broad-based setae on ventral margin. Carpus with 5 broad-based setae on ventral margin and 4 distolaterally. Ischium posterodistal margin with 8 setae. Basis length:width 1.89; dorsal ridge with 12 setae.

Pereopods V–VII. Consult Table 2 for comparison with male ratios.

Pleopods ( Table 3). Protopods mesial margins/epipods I–IV with 2, 1, 1 and 1 coupling hooks, respectively; I–V with 2, 3, 3, 3 and 5 elongate inflexible SS, respectively. Protopods lateral epipods III–V with 19, 22 and 15 elongate inflexible SS on margins, respectively.

Uropod total length 1.55 pleotelson length. Protopod length:width 2.83; dorsomesial ridge length:endopod length 0.49. Endopod with 8 RS.

Distribution. Known only from the type locality, the stream above Aurora Drive (Gordon’s Bay) on the western slopes of the Hottentots Holland Mountains. Animals were taken along a 50 m length of the narrow stream, in shallow water (2 cm deep) below a small cascade and an exposed ridge. Specimens were found between coarse sand and gravel and among roots of unidentified Restionaceae .

Remarks. Mesamphisopus kensleyi is unique in that the endopods of pleopods III–V (of both males and females) are weakly cleft dorsomesially. The pleopodal endopod margins in other species are entire and only the pleopod V endopod in M. setosus is similarly cleft, albeit more slightly. The setation of the pleopods of M. kensleyi is otherwise typical of Mesamphisopus .

Mesamphisopus kensleyi is most similar to M. baccatus , and also M. depressus and M. abbreviatus , in the setation of the head, pereon and pleotelson. These features are more setose in M. kensleyi than in M. capensis , M. paludosus and M. penicillatus . Mesamphisopus setosus is similarly setose on the pereopods, but its setae are characteristically more robust, and the body and head are less setose.

The absence of a fringe of small cuticular spines on the ventrodistal margin of the dactylus of pereopod I of the male of this species is noteworthy, because this cuticular fringe was previously regarded as common to all species within the genus ( Nicholls 1943).