Colubotelson edgarensis Wilson

Wilson, George D. F., 2012, Two new species of Colubotelson Nicholls, 1944 in Tasmania's Lake Pedder: persistence of Phreatoicidae (Crustacea, Isopoda) in therein, Zootaxa 3406, pp. 1-29 : 4-15

Colubotelson edgarensis Wilson , sp. nov.

( Figs 2–9 )

Type material. Holotype male, here designated, bl 10.1 mm, QVM:10:51197, 43°0.925’S, 146°20.743’E, depth 9.2 m, hand operated dredge, A. Osborn & N. Forteath, 15.ii.2010. Paratypes, same data as for holotype: male, bl 11.2 mm, dissected for SEM, QVM:10:51198; male, 8.7 mm, QVM:10:51200, SEM entire; female, bl 7.8 mm, dissected for SEM, QVM:10:51199; 14 ind. QVM 10:51195.

Type locality. Australia, Tasmania, Lake Pedder, submerged bed of the former Lake Edgar.

Other material examined. Australia, Tasmania, Lake Pedder in its original extent before inundation, col. A. Neboiss, 10.iii.1972: juvenile male NMV J44909 ; 2 males, 1 juvenile male, 3 preparatory females, NMV J44908 .

Diagnosis. Head lateral margin with only several setae, lacking fringe of elongate setae. Pleotelson lateral length subequal to depth; dorsal surface in lateral view proximal to distal tip with anterior inflection, margin below dorsal inflection concave; posterior apex length less than width, forming angle between 81–85° with adjacent dorsal surface, posterior apex in lateral view distinctly broadening distally, proximally shallower than distal tip; posterolateral margin dorsal lobe with one robust seta; ventral margin anterior to uropods with one row of distally denticulate robust setae. Antenna article 5 shorter than article 4. Mandible molar process left triturating surface ridges directed diagonally to mandibular axis, in line with dorsal condyle. Pereopod I propodus dorsal margin with few short setae in 1 group between proximal and distal margin in addition to single group at distal margin. Pereopod IV propodus palm in male gracile, smoothly convex, without ventral projection. Pleopod II appendix masculina distal tip broadly rounded, with 4 stiff straight setae on apex. Uropod protopod ventral margin with 3 transverse rows of simple setae; endopod shorter than protopod.

Description. Body pigmentation light brown-beige throughout body; head with distinct colour pattern with groups of cream coloured globules set amongst white/semi-translucent background. Dark brown band between eyes (width approximately eye diameter).

Head ( Fig. 2 , 8 ). Length shorter than width in dorsal view; lateral profile of dorsal surface smoothly curved; width 0.93 pereonite 1 width; surface smooth and shiny; setae tiny and sparse, fine. Eyes fully sessile; maximum diameter 0.13 head depth; dorsal margin convex, ventral margin straight; orientation of longest axis vertical; ocelli distinguishable (in transmitted light images) as individual units, pigmentation dark. Cervical groove straight, extending nearly to dorsal margin of head. Mandibular (genal or cheek) groove smoothly indented. Mandibular notch present. Clypeal notch present. Antennal notch shallow, without posterior extension.

Pereon ( Fig. 2 ). Width exceeding head width; surface smooth; setae on dorsal surface absent. Pereonite 1 in dorsal view wider than medial length, width 0.48 length. Pereonites 2–7 in dorsal view wider than long, length:width ratios 0.53, 0.59, 0.53, 0.5, 0.43, 0.26, respectively. Coxal articulation to pereonites 2–4 nearly fused, 5–7 free.

Pleonites ( Fig. 2 ). In lateral view much deeper than pereonites, with large pleurae, basal region of pleopods not visible; pleonite 1 pleura distinctly shallower than pleurae of pleonites 2–5. In dorsal view pleonite 2 length less than 0.5 pleonite 5 length, pleonite 3–4 respective lengths more than 0.5 pleonite 5 length, pleonite 1–4 relative lengths unequal, increasing in length from anterior to posterior, 1–4 width 0.77 composite length in dorsal view; pleonites 1–5 dorsal length:width ratios 0.27, 0.34, 0.3, 0.38, 0.59, respectively; depth:pereonite 7 depth ratio: 1.3; 1.7; 1.8; 1.7; 1.5, respectively. Typhlosole ( Fig. 8 H) minimal, ventral invagination forming laminar projection in cross-section; hindgut caecae present (4 pairs in pleonites 1–2).

Pleotelson ( Fig. 2–3 , 9 ). Dorsal surface in lateral view inflected ventrally, covered with abundant elongate setae, length 1.4 width, lateral length 0.13 body length, 0.95 depth, depth 1.2 pereonite 7 depth. Ventral surface anterior to uropods lateral margin convex, margin anterior to uropods length subequal to width of uropodal insertion, with one row of distally denticulate robust setae, including 9 robust setae altogether (with 4 half-size distally denticulate setae at anterior end), robust setae on medial side medial to main row distally denticulate, posterior seta longer than anterior adjacent setae; 4 robust setae medial to main row. Postanal ventral surface unelaborated; lateral uropodal ridge present, terminating at pleotelson margin above uropods, with 4 fine setae (male, QVM:10:51198, female, QVM:10:51199). Posterolateral margin forming rounded lobe, curving dorsally, medial length 0.15–0.17 pleotelson length (female, QVM:10:51199; male, QVM:10:51198); with dorsal position defined by major robust setae; dorsal setal position with one robust seta and 2 setae; with robust seta on dorsolateral surface adjacent to margin. Posterior apex projecting in dorsal view, visible in lateral view, length less than width, 0.15–0.17 pleotelson length (female, QVM:10:51199; male, QVM:10:51198), width 0.4–0.42 pleotelson width (male, QVM:10:51198; female, QVM:10:51199), forming angle of 81–85° with immediately anterior dorsal surface (male, QVM:10:51198; female, QVM:10:51199), angled 27–38° from horizontal (female, QVM:10:51199; male, QVM:10:51198); with two pairs of robust setae, with numerous fine setae above and below robust setae.

Antennula (Fig. 6, 8), male and female, respectively (male, QVM:10:51198; female, QVM:10:51199). Length 0.12, 0.10 body length, with 8, 7 articles. Article 5 length:width 1.8, 1.4. Article 6 length:width 1.8, 1.4. Aesthetascs (1–2) occurring on anterior end of all distal articles. Terminal article globular, length 1.5–1.7 width, length 0.10–0.15 antennula length. Penultimate article length not greater than other articles. Distal articles in cross-section flattened oval.

Antenna ( Fig. 2 , 8 ), male and female, respectively. Length 0.40, 0.43 body length. Article 1 absent. Article 5 shorter than article 4. Flagellum length 0.7 antenna length, 0.66 antenna length, with 17–27 articles.

Mouthfield ( Fig. 5 , 8 ). Clypeus consisting of broad median bar, angular at mandibular fossae, width 0.48 head width (female, QVM:10:51199); labrum ventrally semicircular, left half with slight depression at midpoint. Paragnaths with distally rounded lobes, having medial and lateral setal rows and thickened medial base covered with cuticular spinules, medial setae thicker and denser than lateral setae.

Mandible ( Fig. 5 , 8 ). Palp length 1 mandible length; article 3 setae with more than 5 setae on medial-distal margins, with 18 setae, coarsely spinulate setae in second row behind marginal row, on margin finely spinulate, medial surface additional setae absent, medial surface naked, surface covered with cuticular hairs (except on medial ridge), cuticular combs absent; article 2 longitudinal row of setae present, separate distal group of setae present; articles 1–2 group of long setae at distal end of dorsolateral margin. Left incisor process with 2 distal and 2 dorsal cusps. Right lacinia mobilis indistinctly separated from remainder of spine row but with bifurcate plate on side distal to spine row. Spine rows on linear pedunculate projection between incisor and molar, distal margin in line with proximal margin in ventral view, basal insertions in line between incisor and molar processes. Left spine row with 15 spines, 9 of which bifurcate, count includes 6 on margin between pedunculate projection and molar. Right spine row with 15 spines, 9 of which bifurcate, count includes 6 on margin between pedunculate projection and molar. Molar process left triturating surface posterodorsal ridge projecting; dorsoposterior margin with spines adjacent to triturating ridges, short fine spines forming dorsal row. Molar process right longer than wide, right row of complex spines adjacent to triturating ridges absent, dorsal side ciliated spine row present, dorsal surface ciliated spine row 2 members altogether, dorsal surface cuticular hairs sparse.

Maxillula ( Fig. 5 ). Medial lobe length 0.5 lateral lobe length, width less than lateral lobe, 0.45 lateral lobe width; with 4 pappose setae, with 2 accessory setae, distally denticulate accessory setae present, 1 on distolateral margin and 1 between central pappose setae, short weakly setulate seta on distal tip absent. Lateral lobe distal margin with 9 denticulate robust setae, with 5 smooth robust setae, distal setal row with 5 robust setae; ventral face with 2 plumose setae, ventral face with no simple setae, additional plumose seta among proximal distal robust setae.

Maxilla (Fig. 6). Medial lobe width 1.5 outer lateral lobe width, proximal portion smoothly continuous with distal portion, proximal and distal setal rows continuous, setae in ventral basal rows with single row of fine setules, setae in dorsal basal row plumose with smooth long shaft. Outer lateral lobe length subequal to inner lateral lobe, wider than inner lateral lobe, distal margin setal row approximately linear and diagonal to lobe axis, with 10 long bidenticulate setae; inner lateral lobe with 6 long bidenticulate setae; lateral lobes with bidenticulate setae on distal tips and on medial margin (half of medial margin).

Maxilliped (Fig. 6). Epipod length:width 1.4; endite length:basis length 0.45–0.46, distal tip rounded. Endite with 3 coupling hooks on right side, 2 on left side, with setulate setae, in fringe, fine cuticular combs scattered in lateral groups of 2–4 combs, groups at approximately equal distance; combs shorter towards distal end, ventral surface setae present; endite short, distal tip with 9 subdistal biserrate setae on ventral surface; dorsal ridge with 13 large distally denticulate plumose setae. Palp insertion on basis without lateral margin plumose setae, with medial margin plumose setae, with 1 simple seta, ventral surface with 3 subdistal smooth setae, without ventral surface subdistal biserrate setae, length:basis length 1–1.1; article 4 length:width 1.4, shape elongate-oval; article 5 length:width 2.7, length:article 4 length 1.0.

Pereopod I ( Fig. 4 ), male and female, respectively (male, QVM:10:51198; female, QVM:10:51199). Length:body length 0.28, 0.26. Dactylus projecting beyond palm, length:palm length 1.06; lateral surface with row of fine setae along axis; ventrodistal margin with row of thin scale-like spines, along 0.39 length; ventrodistal margin with row of thin scale-like spines, along 0.4 length; claw length:dactylus length 0.17, 0.16, without distal accessory claws; with 1 distal accessory spine, occurring ventrally, length 0.42 claw length. Propodus length:pereopod length 0.22, 0.19; length:width 1.1, 1.3; dorsal margin setae in 1 group between proximal and distal margin in addition to single group at distal margin, dorsal margin 2 setae altogether (excluding distal group); dorsal margin proximal region recurved and protruding to distodorsal margin of carpus, dorsal margin proximal region not protruding. Propodal palm in male convex to straight; without spines; cuticular fringe well developed; stout denticulate setae serrate, 12 altogether; without stout robust simple setae; setal ridge absent. Propodal palm in female straight; simple spines absent; stout denticulate setae serrate, 9 altogether; stout robust simple setae present; stout robust simple setae conical, 2 altogether, setal ridge absent. Merus distodorsal margin in cross-section spinelike and pointed, with numerous elongate simple setae in male and female. Ischium dorsal margin with 3, 1 simple setae, none robust. Basis length:width 2.4, 2.9; dorsal setae in male positioned along ridge, 7 altogether, in female positioned along ridge, 6 altogether; ventrodistal margin with 7 elongate setae in male, 2 elongate setae in female, setae longer than ischium.

Pereopods II–III ( Fig. 4 , 9 ). Penicillate setae scattered on dorsal ridge. Dactylus with 1 distal accessory spine, ventral to primary claw, length ratio to that of primary claw 1:4, without spines on ventral margin. Propodus articular plate present; male pereopod II ventral margin with 3 broad based setae, length 0.22–0.28 propodus length, equally spaced along margin; female pereopod II broad-based setae length 0.25 propodus length, occurring at mid margin. Carpus ventral margin setae broad-based, 4–7 (female, QVM:10:51199; male, QVM:10:51198); male pereopod II setal length 0.15–0.48 carpus length, evenly spaced along margin, female pereopod II setal length 0.36–0.93 carpus length, evenly spaced along margin, central 2 setae with larger gap remaining setae. Basis dorsal ridge in cross-section angular and produced but not forming distinct plate, with 18 simple elongate setae in row along ridge, 4 widely spaced setae forming separate adjacent row on lateral surface, of which proximal two simple elongate, distal two penicillate. II–IV basis lateral face ridge absent; ischium dorsal margin with 9 simple setae, none robust.

Pereopod II ratios, ( Fig. 4 , 9 ) male and female, respectively. Length:body length 0.29, 0.25. Dactylus length:propodus length 0.75, 0.58. Dactylus primary claw length:dactylar length 0.32, 0.35. Propodus length:pereopod length 0.14, 0.16; length:width 2.4, 3.3. Carpus length:pereopod length 0.14, 0.11; length:width 1.4, 1.4. Basis length:pereopod length 0.29, 0.32; length:width 2.5, 3. Pereopod III ratios, male and female, respectively. Length:body length 0.29, 0.26. Dactylus length:propodus length 0.55; primary claw length:dactylar length 0.46. Propodus length:pereopod length 0.15; length:width 2.9.

Pereopod IV ( Fig. 4 , 9 ). In male, subchelate with major hinges on dactylus and propodus. Penicillate setae present in both sexes, occurring on dorsal margin of basis. Basis dorsal ridge in cross-section angular and produced but not forming distinct plate; dorsal ridge with 8 setae in male, with 7 setae in female. Ischium dorsal margin with 7 setae in male, 6 setae in female. Carpus in male ventral margin with 5 broad based setae, 2 distinctly larger than others; in female ventral margin with 3 broad-based setae. Propodus articular plate on posterior side of limb shorter than dactylar claw; in male distal width:palm width 0.39, setae on ventral margin broad-based, with 2 broad based setae on ventral margin, none distinctly larger than others; in female, with 1 broad based seta on ventral margin. Dactylus in male shorter than propodal palm. Pereopod IV ratios, male and female, respectively. Length:body length 0.25, 0.24. Basis length:width 2.6, 2.6. Carpus length:pereopod length 0.11, 0.10. Propodus length:pereopod length 0.16, 0.14, length:width 1.9, 2.6. Dactylus distal accessory claw length 0.27, 0.30 primary claw length.

Pereopods V–VII ( Fig. 4 ). Penicillate setae dorsodistally on carpus. Dactylus accessory claw ventral to primary claw absent (spine not claw). Propodus articular plate on posterior side of limb present; distal margins with 2 elongate robust setae and 3 broad based setae. Ischium dorsal margin with 7–17 simple setae (pereopod V, VII), none robust. Basis dorsal ridge in cross-section angular, not distinctly separated from basis shaft, with elongate fine setae, positioned along entire margin; lateral face central ridge absent; ventral ridge absent.

Pereopod V ratios, ( Fig. 4 ) male and female, respectively. Length:body length 0.25, 0.24. Dactylus claw length:dactylar length 0.36. Propodus length:pereopod length 0.13–0.16 (male, QVM:10:51200; male, QVM:10:51198), 0.15. Carpus length:pereopod length 0.11–0.16. Basis length:width 1.9–2.2. Pereopod VI ratios, male and female, respectively. Length:body length 0.39. Propodus length:pereopod length 0.15, 0.17. Carpus length:pereopod length 0.15, 0.16. Pereopod VII ratios, ( Fig. 4 ) male and female, respectively. Length:body length 0.35–0.4 (male, QVM:10:51198; male, QVM:10:51200). Dactylus claw length:dactylar length 0.3. Propodus length:pereopod length 0.15–0.16 (male, QVM:10:51200; male, QVM:10:51198). Carpus length:pereopod length 0.15–0.16 (male, QVM:10:51200; male, QVM:10:51198). Basis length:width 1.8, 2.1.

Penes ( Fig. 4 ). With setae on shaft; distally tubular, tip truncate.

Pleopods ( Fig. 7 ). Pleopod I exopod broadest proximally, distal margin rounded, medial margin straight, divergent from lateral margin proximally, dorsal surface lacking setae. Pleopod II in male endopod basal musculature not pronounced; appendix masculina length 0.51 pleopod length, proximal half of shaft solid and rod-like, indented in cross-section, distal tip extending near to distal margin of endopod, broadly rounded, 4 setae on apex with large gap medial to lateral margin setae, lateral margin with 3 setae, medial margin with 2 setae, apex with 4 setae.

Pleopod Ratios. ( Fig. 7 ). Pleopod I, male and female, respectively. Length:body length 0.11. Exopod length:width 2.5, 2.6. Endopod length:width 3.4, 3.2. Endopod length:exopod length 0.79, 0.83. Pleopod II, male and female, respectively. Length:body length 0.15, 0.14. Exopod length:width 3.3, 2.6. Exopod distal article length:exopod length 0.28, 0.27. Endopod length:width 2, 2.3. Endopod length:exopod length 0.49, 0.57. Pleopod III, male and female, respectively. Length:body length 0.15, 0.15. Exopod length:width 2.5, 2.2. Exopod distal article length:exopod length 0.28, 0.3. Endopod length:width 2.3, 1.9. Endopod length:exopod length 0.45, 0.51. Pleopod IV, male and female, respectively. Length:body length 0.13, 0.14. Exopod length:width 2.2, 2.8. Exopod distal article length:exopod length 0.32, 0.25. Endopod length:width 2, 2.2. Endopod length:exopod length 0.5, 0.44. Pleopod V, male and female, respectively. Exopod length:width 2.1. Exopod distal article length:exopod length 0.26. Endopod length:width 2. Endopod length:exopod length 0.5. Exopods I lateral proximal lobe absent, medial proximal lobes absent. Protopods medial margin setose projections present. Protopods epipod III length 1.7 width, epipod V length 1.9 width.

Uropod ( Fig. 2 , 3 , 9 ) Extending posterior to pleotelson apex; dorsomedial ridge produced, forming bump, margin smooth, dorsomedial ridge length:endopod length 0.59, dorsomedial ridge length:endopod length 0.52, setae on margin robust and simple; 3 robust seta (lateral seta thin, half size of central seta), spinose setae present, distoventral margin with 3 robust spinose setae, without robust simple seta; ventral ridge with rows of long laterally projecting setae. Rami distal tips pointed; cross-sectional shape round. Endopod dorsal margin in male with 1 robust seta, placed midlength, in female with 1 robust seta. Ratios, male and female, respectively. Uropod Length 1.3, 1.1 pleotelson length. Protopod length:width 3.5, 3.7; length 0.45, 0.46 uropod length. Exopod length 0.72, 0.81 endopod length; dorsal margin with 2, 2 robust setae.

Distribution. Found in current Lake Pedder, (Tasmania, Australia), at least at position of old Lake Edgar but probably more widely occurring because it was collected in the original Lake Pedder in 1972 by A. Neboiss.

Remarks. The easiest feature to distinguish Colubotelson edgarensis sp. nov. from its co-occurring congenor C. pedderensis sp. nov. is its more strongly reflexed (in lateral view) and broader (in dorsal view) pleotelson posterior apex or terminal tip, what Nicholls (1944) called the “tailpiece”. The pleotelson dorsal surface just anterior to the posterior apex is concave so that this margin appears to have a posteriorly projecting hump, whereas in C. pedderensis sp. nov. this margin is roughly linear. A more detailed list of differences is included in the remarks for this latter species. Among other Colubotelson species, both species appear to be closely related, as they share several similarities. The pleotelson of both species has a ventral margin anterior to uropods with only distally denticulate robust setae, whereas other species have a mixture of simple setae, robust setae and distally denticulate setae. Both species also share an antennal article 5 shorter than article 4 and an uropodal endopod shorter than protopod, which occurs in other combinations in Colubotelson and related genera. Overall both species share 376 similarities out of 794 characters (INTKEY set to match = exact; list available from first author on request).

Figures

FIGURE 2. Colubotelson edgarensis sp. nov. A – C, holotype male (QVM: 10: 51197), left lateral view, with enlargements of head and pleotelson. D, paratype male (QVM: 10: 51200), right lateral view, SEM. Scale bar 1.0 mm.

FIGURE 3. Colubotelson edgarensis sp. nov. Paratype male (QVM: 10: 51198), pleotelson and uropods. A, right lateral view. B, posterior margin and apex, lateral view. C, dorsal view. D, posterior apex and posterolateral lobes, dorsal view. E, right uropod, lateral view. F, ventral margin anterior to uropods, distally denticulate robust setae. G, medial view of ventral margin, showing group of medial group of small distally denticulate robust setae. H, posterior margin of pleotelson, ventral view. I, distal group of robust setae on ventral margin of uropodal protopod. Scale bar 1.0 mm.

FIGURE 4. Colubotelson edgarensis sp. nov. Paratype male (QVM: 10: 51198), pereopods. A, C, D, pereopod I, lateral view, with enlargements of dactylus and palm, and setation of palm. B, pereopod II, lateral view. E – F, pereopod IV, lateral view, with enlargement of dactylus, propodus and carpus. G, pereopod V, lateral view. H, pereopod VII, medial view. I, penes, posterior view. Scale bars 1.0 mm.

FIGURE 5. Colubotelson edgarensis sp. nov. Paratype male (QVM: 10: 51198), mouthparts. A – D, left mandible. A, dorsal view. B, lacinia and spine row. C, medial view. E, right mandible, gnathal margin, dorsal view. F, paragnaths, ventral view. G – I, maxillula, ventral view, enlargement of gnathal margin, and medial view of lateral lobe. Scale bars 0.2 mm.

FIGURE 7. Colubotelson edgarensis sp. nov. Paratype male (QVM: 10: 51198), pleopods. A, B, E, F, pleopods I – IV, ventral view, scale bars 0.5 mm. C – D, pleopod II appendix masculina dorsal view with enlargement of distal tip, scale bar 0.2 mm.

FIGURE 8. Colubotelson edgarensis sp. nov. Paratype female, (QVM: 10: 51199). A, anterior part of body, lateral view. B, mandibular palp showing distal setae, lateral view. C, mouthfield, anterior view. D, head, dorsal view. E – F, antennula in situ, dorsal view, with enlargement of distal tip. G, pereopod I, dactylus and propodus palm. H, posterior section of hindgut from pleonites 1 – 2, ventral view, showing indented groove of the typhlosole (typh) and 4 pairs of hind gut caecae (hg caecae); posterior sections of the midgut caecae (mg caecae) shown. Scale bars 1.0 mm.

FIGURE 9. Colubotelson edgarensis sp. nov. Paratype female, (QVM: 10: 51199), pereopods (A – D) and pleotelson (E – I). A, C, pereopod II, lateral view. B, D, pereopod IV, lateral view. E, right lateral view. F, uropod, lateral view. G, ventral margin anterior to uropods, medial view, showing posterior group of 3 distally denticulate setae. H – I, posterior margin and apex, lateral and dorsal views. Scale bars 1.0 mm.