Mesamphisopus tsitsikamma, Gouws, 2008

Gouws, Gavin, 2008, New species of Mesamphisopus, an endemic South African freshwater isopod genus (Isopoda: Phreatoicidea: Mesamphisopidae), Zootaxa 1690, pp. 1-62 : 51-58

Mesamphisopus tsitsikamma n. sp.

Figures 21–24

Material examined. Holotype: SAM A45154, ♂ (10.2 mm), stream near “Big Tree”, Tsitsikamma forest , Eastern Cape, South Africa (33°57.95’S 23°53.80’E), coll. S. R. Daniels and G. Gouws, 21 February 2000.

Paratypes: SAM A44935, ♂ (11.1 mm, dissected) and ♀ (preparatory 8.9 mm, dissected) parts in microvials, additional 3 ♂, collection details as for holotype .

Other material: SAM A40957, near “Big Tree” on N2 freeway, Storms River Forest , coll. C.L. Griffiths, December 1992 .

Etymology. The epithet (a noun in apposition) is the Khoi-San name, “Tsitsikamma” (place of many waters), for the area of temperate forest along the South African south coast in which the type locality is situated.

Diagnosis. Mandibular groove smoothly indented. Pereon width in dorsal view near head width. Pleonites 2 and 3 lengths in dorsal view less than half the length of pleonite 5, pleonite 4 more than half the length of pleonite 5; 1–4 width 0.89 composite length in dorsal view; 1–5 dorsal length:maximum width of pleonites 1– 5 respectively 0.32, 0.28, 0.34, 0.32 and 0.31. Pleonites deep, pleonites 1–5 depth:pereonite 7 depth respectively 1.60, 2.35, 2.73, 2.79 and 2.40. Pleotelson dorsal length 1.15–1.35 width; depth 2.02 pereonite 7 depth; ventral margin anterior to uropods with single row of 4 simple RS; lateral uropodal ridge curving strongly and extending posteriorly from uropods on pleotelson margin; posterior apex with 2 pairs of RS and 1 subapical pair dorsally. Antennula distal articles oval in cross-section. Mandibular palp article 3 with 9–11 smooth setae. Maxillula mesial lobe width 0.64–0.80 lateral lobe width. Maxilla mesial lobe wider (1.08–1.11) than outer lateral lobe; outer lateral lobe width subequal to inner lateral lobe; few long bidenticulate setae on distal margins of inner (9 or 10) and outer (9–13) lateral lobes. Maxilliped palp insertion on basis ventral surface with 7 subdistal elongate SS. Pereopod I propodal palm with 5 stout denticulate bifid setae, 5 basally-inflated

stout RS, 12 elongate broad-based setae. Pereopods II and III propodus length:width 2.52–2.84. Pereopod VII ischium dorsal ridge forming flange subequal to shaft width. Pereopod V basis length approximately twice width. Pleopod I exopod broadest at midlength; mesial margin convex; protopod longer than wide, longer than other protopods. Pleopod II endopod appendix masculina length 0.53 pleopod length. Uropod protopod dorsomesial ridge scarcely produced.

Descriptions. Male. Coloration. Darkly coloured from dark brown to dark slate-grey, fading to much lighter brown upon preservation, with eyes remaining black. Where unpigmented, white to off-white, turning darker yellowish-white upon preservation. Unpigmented patches give body slight mottled appearance. Pigmentation darkest in longitudinal dorsal band; lateral cephalon, pereon, pleon and pleotelson more lightly pigmented. Pereopods lightly coloured, mottled; pigmentation concentrated along dorsal portions of limbs. Infrequently, individuals may lack pigmentation.

Head with sparse, fine setae. Eyes bulging dorsolaterally to projecting anteriorly; maximum diameter 0.17–0.22 head depth; approximately round.

Pereon. Length of setae on dorsal surface 0.16 body depth. Pereonite 1 length:width in dorsal view 0.39. Pereonite 2 length:width 0.37–0.56. Pereonite 3 length:width 0.41–0.59. Pereonite 4 length:width 0.43–0.45. Pereonite 5 length:width 0.42–0.52. Pereonite 6 length:width 0.36. Pereonite 7 length:width 0.25.

Pleonites 1–4 relative lengths unequal, pleonite 4 length greater than pleonites 1–3.

Pleotelson dorsal surface in lateral view inflected ventrally, sparsely covered with fine setae; lateral length less (0.79) than depth.

Antennula ( Fig. 21) length 0.16–0.18 body length, with 7 or 8 articles. Single tiny aesthetascs, 4 or 5 on terminal and penultimate articles. Terminal article length:width 0.55. Penultimate article distinctly longer than other articles.

Antenna ( Fig. 21) length 0.62 body length. Flagellum length 0.63 total antenna length, with 28–31 articles. Antenna article 5 longer than article 4.

Mouthfield. Clypeus slightly rounded to truncate at mandibular fossae; width 0.78 head width. Labrum ( Fig. 21) ventrally semi-circular in anterior view, with fringe of fine setae along distal margin; dorsal margin narrower than clypeus. Paragnaths ( Fig. 21) with distally rounded lobes; mesial margins with multiple setal rows, forming dense mat of fine elongate setae; lateral margins with sparse elongate SS and more robust setae.

Mandible ( Fig. 22) palp length 0.87–0.94 mandible length; articles 1 and 2 with elongate SS around entire distal margins, setae longer than respective articles. Left spine row with 11 spines, 3 of which are bifurcate. Right spine row with 9 spines, 4 of which are bifurcate. Molar process longer than wide.

Maxillula ( Fig. 22) mesial lobe length 0.64–0.88 lateral lobe length; with 2 distally denticulate accessory setae, 1 on distolateral margin and 1 between central PPS. Lateral lobe distal margin with 5 smooth RS, 7 denticulate RS, 4 RS form distal setal row.

Maxilla ( Fig. 22) mesial lobe proximal portion smoothly continuous with distal portion; proximal and distal setal rows separated by gap; 9 thickly set elongate setae in single ventral basal row; 29 or 30 closely-set setae with distinct base and long smooth shaft in dorsal basal row; 27–37 elongate, SS or PS and few strongly pectinate (in distal third) setae in distal row. Outer lateral lobe length subequal to inner lateral lobe.

Maxilliped ( Fig. 22) epipod length:width 1.09. Endite length:total basis length 0.44–0.56; mesial margin with 2 coupling hooks on left side, 3 on right side. Palp insertion on basis mesial margin with 1 SS; palp width across articles 2 and 3:endite width 1.36–1.79; article 4 subcircular, length:width 0.92–1.14; article 5 length:width 1.54, article 5 length:article 4 length 0.68–0.83.

Pereopod I ( Fig. 23) length:body length 0.42. Dactylus length subequal to palm or slightly shorter, length:palm length 0.93; ventrodistal margin with thin scale-like spines along 0.10 total length; claw length:dactylus length 0.09; distal accessory claw length 0.33–0.50 primary claw length. Propodus length:width 1.05; dorsal margin with 10 setae (excluding distal group) in several groups between proximal and distal margins. Propodal palm cuticular fringe weakly developed; with low stout cuticular projection distally. Merus distodorsal margin includes 1 or 2 RS. Ischium dorsal margin with 6 SS. Basis length:width 2.15; dorsal margin with 11 or 12 setae along ridge; ventrodistal margin with 6 or 7 elongate setae.

Pereopods II and III ( Fig. 23; Table 1) distal accessory claw length 0.30–0.50 primary claw length. Pereopods II and III with, respectively, 6 and 5 broad-based setae on propodus, most distributed along central third of ventral margin, one more distal, longest setae 0.20 propodus length. Pereopod II carpus with 5 broad-based setae, evenly spaced along ventral margin from proximal margin to midpoint, with distal seta at two-thirds margin length, setae 0.06–0.20 carpus length. Pereopod III carpus with 5 broad-based setae evenly spaced from proximal margin to midpoint of ventral margin and distal seta at three-quarter length, and 3 on lateral ridge distally, setae 0.20–0.48 carpus length. Basis dorsal ridge in cross-section angular and produced but not forming distinct plate, with 9–18 elongate SS along or mesially and laterally to margin, densest proximally. Pereopods II–IV ischium dorsal margin with 7–12 SS, including 3 RS.

Pereopod IV ( Fig. 23) dactylus longer than propodal palm; distal accessory claw length 0.33 primary claw length. Propodus length:pereopod length 0.14; length:width 1.59; distal width:palm width 0.74; with 6 broadbased setae on ventral margin, 2 or 3 distinctly larger than remainder; articular plate subequal in length to dactylar claw. Carpus length:pereopod length 0.13; with 6 broad-based setae on ventral margin, 3 distinctly larger than others. Ischium posterodistal margin with 5 setae, series continuing on anterodistal margin. Basis length:width 2.45; dorsal ridge with 12 setae along ridge and in dense proximal cluster.

Pereopods V–VII ( Fig. 23; Table 2) dactylus distal accessory claw ventrolateral to primary claw, length 0.25–0.66 primary claw length. Propodus distal margins with 3–5 elongate RS. Pereopod VII articular plate lacking in dissected individual. Pereopods V–VII ischium dorsal margin with 1–11 SS, including 1–6 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 ventral ridge.

Penes length 0.41 body width at pereonite 7; with setae on shaft; distal tip rounded to truncate.

Pleopods ( Fig. 24; Table 3). PS on endopod I–V margins. Protopod mesial margins/epipods I–IV with 4, 2, 2 and 2 coupling hooks, respectively; II–V with 2, 3, 6 and 8 elongate SS, respectively. Protopod lateral epipod III length 1.76–2.26 width, lateral epipod V length 1.67–1.97. Pleopod I exopod dorsal surface with setae. Pleopod II endopod appendix masculina basal musculature pronounced; with 27–34 setae on margin; distal tip extending to distal margin of endopod.

Uropod ( Fig. 21) total length 1.62 pleotelson length. Protopod length:width 4.07; length 0.46 uropod total length; extending posteriorly subequal to pleotelson apex; dorsomesial ridge length:endopod length 0.64. Rami (in cross-section) flattened on dorsal surface only. Endopod dorsal margin with 6 RS along length and apically. Exopod length 0.86 endopod length; with 6 RS along dorsal margins and apically.

Female. Pereon. Pereonite 6 (length:width 0.42) and pereonite 7 (0.36) in dorsal view relatively longer and thinner than in male.

Antennula with 6 articles.

Pereopod I length:body length 0.36. Dactylus ventrodistal margin with thin scale-like spines along 0.49 total length; claw length:dactylus length 0.15–0.19. Propodus length:width 1.24. Propodal palm straight; with 9 stout denticulate serrate setae; 3 or 4 elongate broad-based setae. Ischium dorsal margin with 1 RS. Basis length:width 2.36; dorsal margin with 9 setae; ventrodistal margin with 2 or 3 elongate setae.

Pereopods II and III ( Table 1). Pereopod II propodus with 4 broad-based setae, evenly spaced from quarter to three-quarter length of ventral margin, setae up to 10–0.26 propodus length. Pereopod III propodus with 3 broad-based setae, evenly spaced from one-third to two-thirds ventral margin length. Pereopod II and III each with 4 broad-based setae on carpus, evenly spaced from proximal margin along two-thirds of ventral margin, setae up to 0.46 and 0.65 respective carpus lengths.

Pereopod IV dactylus distal accessory claw half primary claw length. Propodus length:width 1.21; with 2 or 3 broad-based setae on ventral margin. Carpus length:pereopod length 0.11; with 3 broad-based setae on ventral margin. Ischium posterodistal margin with 3 setae, fourth anteriorly. Basis dorsal ridge with 9–11 setae.

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

Pleopods ( Table 3). Endopod I–V margins with PS and SS, V with SS only. Protopod mesial epipods IV and V with 4 and 4 or 5 elongate SS, respectively.

Uropod protopod dorsomesial ridge length:endopod length 0.45. Exopod with 4 RS.

Distribution. Known from the type locality only. The type locality was a broad (> 1 m), almost stagnant section of a slow-flowing stream in the temperate Tsitsikamma Forest. The water was tannin-stained and acidic (pH 4.5). Specimens were collected from amongst the abundant leaf litter and the peaty, humic soil of the bank.

Remarks. The setation of the mouthparts of M. tsitsikamma is unique and distinguishes this species from all others within the genus. The mesiodistal setae of mandibular palp article 3 are few (ca. 10) and smooth in M. tsitsikamma , but abundant (> 20) and finely setulate in the remaining species described here. Fewer of these seta occur in M. depressus ( Nicholls 1943) , with the greatest numbers found in M. setosus (27–32) and M. paludosus (32–38). Fewer setae occur on M. tsitsikamma ’s maxilla than in the above species, particularly distally on the inner and outer lateral lobes, and in the ventral basal row of the mesial lobe (although a similar number occurs in this row in M. paludosus ).

Another unique feature of M. tsitsikamma is the relatively linear dorsomesial margin of the uropodal protopod. This margin is straight, forms a weak ridge and is scarcely produced distally. In all other species of the genus, the dorsomesial margin forms a ridge produced distally to a plate-like projection. This margin has been described as being weakly produced in M. depressus ( Nicholls 1943) , but the extent of the projection figured for M. depressus ( Nicholls 1943: Figs 8.3 and 9.15) still appears to be more pronounced than in M. tsitsikamma .

An additional peculiarity of the species is the presence of plumose setae on all five pleopodal endopods, known otherwise only in M. baccatus .

The pair of sub-apical dorsal robust setae on the pleotelson, recorded for M. abbreviatus , M. depressus , M. penicillatus (see Barnard 1927; Kensley 2001) and M. paludosus , was not present in the dissected and examined M. tsitsikamma individuals, but has been documented in individuals collected from the same locality, included in an earlier genetic analyses ( Gouws et al. 2005).