Mesamphisopus baccatus, Gouws, 2008

Gouws, Gavin, 2008, New species of Mesamphisopus, an endemic South African freshwater isopod genus (Isopoda: Phreatoicidea: Mesamphisopidae), Zootaxa 1690, pp. 1-62 : 22-29

Mesamphisopus baccatus n. sp.

Figures 5–8

Material examined. Holotype: SAM A45151, ♂ (9.0 mm), above dam, east of Silvermine Nature Reserve , Western Cape, South Africa (34°05.55’S 18°25.37’E), coll. S. R. Daniels and G. Gouws, 10 November 2000.

Paratypes: SAM A44937, ♂ (8.6 mm, dissected) and ♀ (preparatory 7.5 mm, dissected) parts slide mounted and in microvials, additional 3 ♂, 3 ♀, collection details as for holotype .

Etymology. From the Latin adjective “baccatus”, meaning “adorned, ornamented or set with pearls”, in reference to the distinct round or globular flagellar articles of the antenna, which resemble a string of pearls.

Diagnosis. Mandibular groove smoothly indented. Pleonites 1–4 width 1.28–1.46 composite length in dorsal view. Pleotelson dorsal surface covered with abundant elongate setae; ventral margin anterior to uropods with single row of (2 or 3) simple RS; posterior apex with 1 pair of RS. Antennula distal articles rounded and inflated, oval in cross-section. Antenna flagellum articles broad, rounded and globular. Mandibular palp article 3 with 19 setulate setae on mesiodistal margins; 7 or 8 additional setae on mesial surface. Maxillula mesial lobe width 0.77 lateral lobe width; lateral lobe distal margin with 2 smooth RS, 10 denticulate RS. Maxilla outer lateral lobe distal margin with 23 long bidenticulate setae. Maxilliped palp insertion on basis ventral surface with 8 subdistal SS towards mesial margin; palp article 4 length:width 0.85. Pereopod I propodal palm with 1 bifid and 3 serrate denticulate stout setae, 4 basally-inflated stout RS, 8 elongate broad-based setae present along or lateral to margin. Pereopods II and III basis dorsal ridge in cross-section rounded. Pereopod IV carpus with 3 broad-based setae on ventral margin in male. Pereopods V–VII with PNS distodorsally on carpus, dorsally on basis. Pereopod VII ischium dorsal ridge forming flange subequal to shaft width. Penes with setae on shaft and tip. Uropod total length 1.34 pleotelson length in male; protopod ventral margin with long laterally projecting setae; exopod length 1.21 endopod length.

Descriptions. Male. Coloration. Body strongly pigmented, brown/slate-grey to black-grey; dorsal band most strongly pigmented, lighter pigmentation towards ventral margins of pleonites; unpigmented patches give mottled appearance to lateral cephalon, pereonites and pleotelson; slight pigmentation on uropodal protopods; pereopods generally lack pigmentation, white to off-white; pigmentation fades to lighter brown-grey upon preservation.

Head setae sparse, fine. Eyes projecting anteriorly, bulging slightly dorsolaterally; maximum diameter 0.14–0.16 head depth; round to oval, longest axis horizontal or oblique.

Pereon width exceeding head width; setae on dorsal surface concentrated along posterior pereonite margins, length of setae 0.18–0.21 body depth. Pereonite 1 length:width in dorsal view 0.33. Pereonite 2 length:width 0.32–0.39. Pereonite 3 length:width 0.45–0.55. Pereonite 4 length:width 0.43. Pereonite 5 length:width 0.47. Pereonite 6 length:width 0.41. Pereonite 7 length:width 0.20–0.24.

Pleonites 2–4 respective lengths in dorsal view less than half the length of pleonite 5, 1–4 relative lengths unequal, pleonite 4 length greater than pleonites 1–3. Pleonites 1–5 dorsal length:maximum width of pleonites 1–5 respectively 0.12–0.16, 0.16, 0.17, 0.23 and 0.49. Pleonites 1–5 depth:pereonite 7 depth respectively 1.19–1.40, 1.59–1.89, 1.75–2.07, 1.73–2.06 and 1.47–1.74.

Pleotelson dorsal surface in lateral view inflected ventrally, length 1.07–1.10 width; lateral length less than (0.86–0.88) depth; depth 1.46–1.53 pereonite 7 depth.

Antennula ( Fig. 5) length 0.17 body length, with 6–9 articles. Articles 4 and 5 divisible into 1 large or 2 small articles (articles 4 and 5, 6 and 7 potentially single articles). Article 3 with rudimentary antennular scale. Tiny aesthetascs, 3 or 4, around terminal article. Terminal article length:width 0.25–0.33. Penultimate article distinctly longer than other articles.

Antenna ( Fig. 5) length 0.54 body length. Flagellum length 0.62 total antenna length, with 18 articles. Article 5 length subequal to article 4.

Mouthfield. Clypeus rounded laterally, asymmetrically at mandibular fossae; width 0.72 head width. Labrum ( Fig. 5) oblong along dorsoventral axis, semi-circular to broadly triangular (pointed ventrally) in anterior view, with fringe of fine setae along distal margin; dorsal margin same width as clypeus. Paragnaths

( Fig. 5) with distally rounded lobes; dense mats of fine setae on distomesial margins and in multiple rows on surfaces; lateral margins of lobes with scattered SS.

Mandible ( Fig. 6) palp length 1.10 mandible length; article 1 with elongate SS distomesially; article 2 with elongate SS scattered along length of mesial margin, separate distal row of 4 closely-set elongate SS distally on both mesial and lateral surfaces. Left spine row with 11–13 spines, 4 of which are bifurcate. Right spine row with 8 spines, 5 of which are bifurcate. Molar process longer than wide or length subequal to width.

Maxillula ( Fig. 6) mesial lobe length 0.85 lateral lobe length; with 2 distally denticulate accessory setae, 1 on distolateral margin and 1 at base of mesial central PPS. Lateral lobe with 3 RS in distal setal row; ventral face with 2 widely spaced PS.

Maxilla ( Fig. 5) mesial lobe width 0.80 outer lateral lobe width; proximal portion smoothly continuous with distal portion; proximal and distal setal rows separated by gap; 13 fairly broad-based elongate SS in single ventral basal row; 40–42 elongate, closely-set setae, with distinct base, smooth shaft, slightly plumose distally in dorsal basal row; 16 or 17 broad-based, distally plumose elongate setae with distinct base and smooth shaft grade into apical cluster of multiple pectinate, SS and PS (24) in 3 distal rows. Outer lateral lobe length subequal to inner lateral lobe, wider than inner lateral lobe. Inner lateral lobe distal margin with 14 long bidenticulate setae.

Maxilliped ( Fig. 6) epipod length:width 1.28; SS scattered along mesiodistal margin. Endite length:total basis length 0.44; mesial margin with 3 coupling hooks on left side, 2 on right side; dorsal ridge with 19 or 20 large distally denticulate PS. Palp insertion on basis lateral margin with 3 elongate fairly stout SS; palp width across articles 2 and 3:endite width 1.75; article 4 subcircular; article 5 length:width 1.25, article 5 length:article 4 length 0.91.

Pereopod I ( Fig. 7) length:body length 0.53. Dactylus length subequal to palm or longer than palm, length:palm length 1.10–1.82; ventrodistal margin with thin, fine scale-like spines along 0.05 total length; claw length:dactylus length 0.10; distal accessory claw length 0.25–0.33 primary claw length. Propodus length:width 1.14; dorsal margin with 8–15 setae in several groups between proximal and distal margin, including 4 in distal group. Propodal palm cuticular fringe weakly developed. Ischium dorsal margin with 7 or 8 SS, including 1 RS. Basis length:width 2.08; 2–7 dorsal setae along ridge; ventrodistal margin with 3 elongate setae.

Pereopods II and III ( Fig. 7; Table 1) dactylus distal accessory claw length 0.25–0.33 primary claw length. Pereopod II and III each with 5 broad-based setae on propodus, evenly spaced along ventral margin, setae 0.17–0.19 and 0.08–0.27 respective propodus lengths. Pereopod II and III each with 6 broad-based setae along carpus ventral margin, additional 2 setae distolaterally on pereopod II carpus, setae 0.20–0.54 respective carpus length. Basis dorsal ridge with 9 or 10 elongate SS along margin, some clustering in proximal group. Pereopods II–IV ischium dorsal margin with 8–11 SS, including 1–3 RS.

Pereopod IV ( Fig. 7) dactylus longer than propodal palm; distal accessory claw length 0.33 primary claw length. Propodus length:pereopod length 0.12; length:width 1.41; distal width:palm width 0.70; with 4 broadbased setae on ventral margin, 2 distinctly larger than remainder; articular plate longer than dactylar claw. Carpus length:pereopod length 0.15. Ischium posterodistal margin with 5–8 setae. Basis length:width 2.54; dorsal ridge may appear rounded, with 8 setae.

Pereopods V–VII ( Fig. 7; Table 2) dactylus distal accessory claw ventrolateral to primary claw, length 0.33–0.45 primary claw length. Propodus distal margins with 4–6 elongate RS. Pereopods V–VII ischium dorsal margin 5–10 SS, including 2–4 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.

Penes length 0.32 body width at pereonite 7; distal tip rounded.

Pleopods ( Fig. 8; Table 3). Pleopod I–V endopod margins with PS. Protopod mesial margins/epipods I–IV with 4, 3, 2 and 2 coupling hooks, respectively; II–V with 4, 7, 6, and 6 elongate SS, respectively. Protopod lateral epipod III length 2.25–2.29 width, lateral epipod V length 1.64–1.93 width. Protopod lateral margin of pleopod I with 2 elongate SS; lateral epipods III–V with 28, 25 and 20 elongate 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 basal musculature pronounced; with 24 setae occurring along lateral margin and proximally and most distally along mesial margin; length 0.38 pleopod length; distal tip extending to distal margin of endopod.

Uropod ( Fig. 7) protopod length:width 2.90; length 0.44 uropod total length; extending posteriorly subequal to pleotelson apex; dorsomesial ridge produced, plate-like, ridge length:endopod length 0.50. Rami (in cross-section) flattened on dorsal surface only. Endopod dorsal margin with 6 RS along length and apically. Exopod with 4 RS along dorsal margins and apically.

Female. Head. Mandibular groove more acutely indented than in male.

Pereon. Pereonite 2 length:width in dorsal view 0.41–0.43. Pereonite 3 length:width 0.38–0.46. Pereonite 5 length:width 0.36–0.40. Pereonite 7 length:width 0.17.

Antennula length 0.13 body length. Penultimate article subequal in length to other articles.

Antenna flagellum with 16 articles.

Pereopod I length:body length 0.42. Dactylus ventrodistal margin with thin scale-like spines along 0.31 total length; claw length:dactylus length 0.13. Propodus length:width 1.23. Propodal palm concave; cuticular fringe well developed; with 7 stout denticulate bifid setae, 7 elongate broad-based setae, additional broadbased SS lateral to margin. Ischium dorsal margin with 3–6 SS. Basis length:width 2.00; 6–8 dorsal setae clustered proximally and positioned along ridge.

Pereopods II and III ( Table 1). Pereopod II propodus broad-based setae 0.20–0.43 propodus length; carpus with 4 broad-based setae on ventral margin, 3 on distolateral surface. Pereopod III propodus broad-based setae up to 0.33 propodus length; evenly spaced from proximal third to distal margin; carpus with additional 2 broad-based setae on distolateral surface, setae reach 0.71 carpus length. Pereopod II basis dorsal ridge setation includes 2 PS.

Pereopod IV propodus length:width 1.80; with 3 broad-based setae on ventral margin; articular plate shorter than dactylar claw. Carpus length:pereopod length 0.11; with 5 broad-based setae on ventral margin and 3 on posterolateral surface. Ischium posterodistal margin with 4 setae. Basis length:width 1.78; dorsal ridge with 10 setae.

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

Pleopods ( Table 3). Endopod I–IV margins with PS and SS, V with SS only. Protopod mesial epipod IV with single coupling hook; epipods II–V with 4, 6, 6, and 7 elongate SS, respectively. Protopod lateral margin of pleopod I with 3 elongate SS; lateral epipods III–V with 21, 19 and 18 elongate SS on margins, respectively.

Uropod total length 1.64 pleotelson length. Protopod length:width 3.25.

Distribution. Known only from the type locality, a marshy area about 30 m north of the dam, to the east of Ou Kaapse Weg, Silvermine Nature Reserve. Individuals were taken from peaty, acidic (pH 4.0), black mud at the base of a shrub. Individuals were abundant, but appeared to have a patchy distribution within only the immediate area.

Remarks. Mesamphisopus baccatus is identified by the characteristic globular or inflated bulbous antennal and antennula flagellum articles of the short antennae and antennula. The antennal flagellum is short (<20 articles) compared to that of M. capensis (20 to 30 articles) and most other species (24 to 36 articles). However, other species, including those with short antennae (e.g., M. kensleyi and M. capensis ), have antennal and antennular flagellum articles that are more rectangular or more slender than those of M. baccatus .

Mesamphisopus baccatus is also unusual in having plumose setae on the endopods of all five pleopods. This is only encountered in M. tsitsikamma and the examined female M. albidus individual (this sexual dimorphism giving an indication of a possible inherent variability in pleopodal setation).

In terms of the extent of setation of the pleon and pleotelson, M. baccatus is similar to M. abbreviatus , M. depressus and M. kensleyi . Mesamphisopus baccatus is similar to M. kensleyi in setation of the pleon and ple- otelson, and also M. depressus and M. abbreviatus . However, Mesamphisopus baccatus lacks the sub-apical pair of robust setae found dorsally on the pleotelson of M. abbreviatus , M. depressus and M. penicillatus ( Kensley 2001) .

Mesamphisopus baccatus and M. paludosus are unique among the six species described herein in lacking a well-developed lateral uropodal ridge on the pleotelson. Amongst the already-described species, the ridge has been documented or figured for M. abbreviatus , M. depressus and M. capensis ( Barnard 1914, 1927; Nicholls 1943; Kensley 2001).

The type locality of Mesamphisopus baccatus lies within the geographic range of M. capensis across the Cape Peninsula, but M. baccatus is further distinguished from M. capensis by the more abundant setation of the pleon and the elongate setae on the pleotelson.