Colubotelson pedderensis 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 : 15-27

Colubotelson pedderensis Wilson , sp. nov.

( Fig. 10–18 )

Type material. Holotype male, here designated, bl 10.0 mm, QVM:10:51201, 43°57.771’S, 146°03.06’ E, depth 14.2 m, hand operated dredge, A. Osborn, N. Forteath, 14.ii.2010. Paratypes, same data as for holotype: male, bl 10.2mm, dissected for SEM, QVM:10:51202; male bl 10.1 mm, SEM entire, QVM:10:51204; female, bl 8.7 mm, QVM:10:51203; 3 inds, QVM:10:51205.

Type locality. Australia, Tasmania, Lake Pedder.

Diagnosis. Head lateral margin with fringe of closely-spaced elongate setae. Pleotelson lateral length less than depth; dorsal surface in lateral view proximal to posterior apex without anterior inflection, margin below dorsal inflection linear in lateral view; posterior apex length less than width, forming angle between 91°–106° with adjacent dorsal surface, apex in lateral view weakly narrowing distally, dorsal and ventral surfaces approximately parallel; ventral margin anterior to uropods with one row of distally denticulate robust setae; posterolateral margin dorsal setal position with multiple robust setae, ventrolateral setae subequal to dorsomedial setae. Antenna article 5 shorter than article 4. Mandible molar process left triturating surface ridges directed transversely to mandibular axis, originating distally to dorsal condyle; Pereopod I propodus dorsal margin elongate setae in several groups between proximal and distal margin. Pereopod IV propodus palm in male robust, with ventral projection. Pleopod II appendix masculina distal tip broadly truncate, with 3 stiff straight setae on apex. Uropod protopod ventral margin with 2 transverse rows of simple setae; endopod shorter than protopod.

Description. Body pigmentation brown, irregular white bars laterally extending along pereonites.

Head ( Fig. 10 , 17 ). Length shorter than width in dorsal view; lateral profile of dorsal surface smoothly curved; width 0.8 pereonite 1 width; surface smooth; setae scattered, fine. Eyes fully sessile; maximum diameter 0.2 head depth (female, QVM:10:51203); dorsal margin convex, ventral margin straight; orientation of longest axis vertical; ocelli distinguishable 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. 10 ). Width near head width; surface smooth; setae on dorsal surface absent. Pereonite 1 in dorsal view wider than medial length, 0.3 (H). Pereonites 2–7 in dorsal view wider than long, Length: width, respectively: 0.42, 0.37, 0.41, 0.4, 0.38, 0.26. Coxal articulation to pereonites 2–4 nearly fused, 5–7 free.

Pleonites ( Fig. 10 ). 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, 3–4 respective lengths more than 0.5 pleonite 5 length, 1–4 relative lengths unequal, increasing in length from anterior to posterior, 1–4 width 0.93 composite length in dorsal view; length:pleon length ratios 0.22. 0.23. 0.33. 0.34. 0.53, respectively. Pleonites 1–5 depth ratio with pereonite 7 depth, respectively: 1.3; 1.6; 1.7; 1.7; 1.5. Typhlosole minimal, ventral invagination forming laminar projection in cross-section; hindgut caecae present (4 pairs in pleonites 1–2).

Pleotelson ( Fig. 10 , 11 , 18 ). Dorsal surface in lateral view inflected ventrally, sparsely covered with short setae, length 1–1.3 width (H; male, QVM:10:51202), lateral length 0.13–0.14 body length (male, QVM:10:51202), 0.82–0.83 depth (male, QVM:10:51202), depth 1.2–1.4 pereonite 7 depth (female, QVM:10:51203; H). Ventral surface anterior to uropods lateral margin convex, margin anterior to uropods length subequal to width of uropodal insertion. Ventral margin anterior to uropods 1.7 width of uropodal insertion (male, QVM:10:51202; female, QVM:10:51203), with one row of distally denticulate robust setae, including 7 robust setae altogether (with medial row of 3 half size distally denticulate setae at posterior end), robust setae on medial side medial to main row distally denticulate, 3 altogether, posterior seta longer than anterior adjacent setae. Postanal ventral surface unelaborated, lateral uropodal ridge present, terminating at pleotelson margin above uropods, with 4–7 fine setae (male, QVM:10:51202; female, QVM:10:51203). Posterolateral margin forming rounded lobe, curving dorsally; medial length 0.13–0.14 pleotelson length (male, QVM:10:51202; female, QVM:10:51203), with one position defined by major robust setae; dorsal setal position with multiple robust setae, ventrolateral setae subequal to dorsomedial setae (2 robust setae); dorsal setal position with 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, 0.16 pleotelson length, width 0.39–0.44 pleotelson width (female, QVM:10:51203; male, QVM:10:51202); forming angle of 91–106° with immediately anterior dorsal surface (female, QVM:10:51203; male, QVM:10:51202), angled 14–23° from horizontal (male, QVM:10:51202; female, QVM:10:51203); with two pairs of robust setae, with numerous fine setae above and below robust setae.

Antennula ( Fig. 13 , 17 ), male and female, respectively (male, QVM:10:51202; female, QVM:10:51203). Length 0.11, 0.12 body length, with 8, 7 articles. Article 5 length:width 1.5–2.1. Article 6 length:width 1.6, 1.7. Aesthetascs (1–2) small occurring on anterior end of distal articles. Terminal article globular, length 1.5–2.1 width, length 0.1–0.14 antennula length. Penultimate article length not greater than other articles; moderately inflated, width greater than ante-penultimate article. Distal articles in cross-section flattened oval.

Antenna ( Fig. 13 , 17 ), male and female, respectively (male, QVM:10:51202; female, QVM:10:51203). Length 0.33, 0.36 body length. Article 5 shorter than article 4. Flagellum length 0.60, 0.61 antenna length, with 17, 20 articles.

Mouthfield ( Fig. 14 , 17 ). Clypeus consisting of broad median bar, angular at mandibular fossae, width 0.52 head width; labrum ventrally semicircular, left half with slight depression at midpoint. Paragnaths with distally rounded lobes.

Mandible ( Fig. 14 , 17 ). Palp length 0.75 mandible length; article 3 setae with more than 5 setae on medial-distal margins, with 16 setae, coarsely spinulate setae in second row behind marginal row, on margin finely spinulate, medial surface additional setae absent, medial surface naked, surface lacking cuticular hairs, 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 12 spines, 8 of which bifurcate, count includes 4 on margin between pedunculate projection and molar. Right spine row with 13 spines, 8 of which bifurcate, count includes 5 on margin between pedunculate projection and molar. Molar process left dorsoposterior margin with spines adjacent to triturating ridges, short fine spines forming dorsal row. Right molar process longer than wide, 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. 15 ). Medial lobe length 0.58 lateral lobe length, width less than lateral lobe, 0.92 lateral lobe width; with 4 pappose setae; with 2 accessory setae, distally denticulate accessory setae, one on distolateral margin and one between central pappose setae; short weakly setulate seta on distal tip absent. Lateral lobe distal margin with 8 denticulate robust setae, with 6 smooth robust setae, distal setal row with 5 robust setae; ventral face with 2–3 plumose setae, ventral face with no simple setae, additional plumose seta among proximal distal robust setae.

Maxilla ( Fig. 15 ). Medial lobe 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 setae with smooth long shaft, setae in distal row 5 robust setae with setules at mid lower shaft and row of teeth (12–16) at distal tip. 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 14 long bidenticulate setae; inner lateral lobe with 10; lateral lobes with bidenticulate setae on distal tips and on medial margin (half of medial margin).

Maxilliped ( Fig. 15 ). Epipod length:width 1.3–1.4. Endite length:basis length 0.45, distal tip rounded, medial margin with 3 coupling hooks on right side, 2 coupling hooks on left side, endite with setulate setae, in fringe; fine cuticular combs present, combs scattered in lateral groups of 2–4 combs, groups at approximately equal distance, shorter towards distal end; ventral surface setae present, short, in medially placed longitudinal rows; distal tip with 9 subdistal biserrate setae on ventral surface; dorsal ridge with 12 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; width across articles 2–3:endite width 2.2; article 4 length:width 1.1–1.3, article 4 shape elongate-oval; article 5 length:width 3.3, article 5 length:article 4 length 1.

Pereopod I ( Fig. 12 ), male and female, respectively. Length:body length 0.28, 0.35. Dactylus length subequal to palm, length:palm length 0.96; lateral surface with row of fine setae along axis; ventrodistal margin with row of thin scale-like spines, along 0.42, 0.47 length; claw length:dactylus length 0.19, 0.20, without distal accessory claws; with 1 distal accessory spine, occurring ventrally, 0.42 claw length. Propodus length:pereopod length 0.3, 0.21, length:width 1.4, 1.3; dorsal margin setae in several groups between proximal and distal margin, dorsal margin 5 setae altogether (excluding distal group); dorsal margin proximal region not protruding. Propodal palm in male convex; without simple spines; medial cuticular fringe well developed; stout denticulate setae serrate, 11 altogether; without stout robust simple setae; setal ridge absent. Propodal palm in female convex; simple spines absent; stout denticulate setae present, serrate, 10 altogether; stout robust simple setae absent; setal ridge absent. Merus distodorsal margin with numerous elongate simple setae. Ischium dorsal margin present, with 5, 9 simple setae, none robust. Basis length:width 1.4, 1.9; dorsal setae in male positioned along ridge, 7 altogether, in female positioned along ridge, 17 altogether; ventrodistal margin with 9 elongate setae in male, 9 elongate setae in female, setae longer than ischium.

Pereopods II–III ( Fig.12 , 18 ). Penicillate setae scattered on dorsal ridge. Dactylus with 1 distal accessory spine, ventral to primary claw, length 0.25 primary claw length, without spines on ventral margin. Propodus articular plate present; ventral margin with 4, 2 broad based setae, pereopod II setal length in male ranging 0.14–0.28 propodus length (shortest, longest), 3 proximally, approximately equally spaced, 1 distally, in female 0.21–0.29 propodus, both setae near mid margin. Carpus ventral margin with 6, 5 broad-based setae, pereopod II setal length ranging 0.19–0.74, 0.30–0.59 carpus length. Basis II dorsal ridge in cross-section angular but not forming distinct plate, with 24 simple elongate setae in row along ridge, 3 simple elongate setae forming separate adjacent row at adjacent end. Pereopod II–IV basis lateral face ridge absent; ischium dorsal margin with 11 simple setae, ischium dorsal margin including 1 robust.

Pereopod II ratios ( Fig.12 , 18 ), male and female, respectively. Length:body length 0.33, 0.36. Dactylus length:propodus length 0.76, 0.74; primary claw length:dactylar length 0.32, 0.32. Propodus length:pereopod length 0.16, 0.15; length:width 3, 2.7. Carpus length:pereopod length 0.11, 0.11; length:width 1.5, 1.4. Basis length:pereopod length 0.26, 0.29; length:width 2.2, 2.3. Pereopod III ratios, male and female, respectively. Length:body length 0.3, 0.29. Dactylus length:propodus length 0.67. Propodus length:pereopod length 0.16; length:width 3. Carpus length:pereopod length 0.11; length:width 1.3. Basis length:pereopod length 0.31; length:width 2.2.

Pereopod IV ( Fig. 12 ). In male, subchelate with major hinges on dactylus and propodus. Penicillate setae present in both sexes, in male occurring on dorsal margin of basis and posterolateral surface of propodus, near distal end. Basis dorsal ridge in cross-section angular, not forming distinct plate, with 24 setae, 18 in female. Ischium dorsal margin with 5-10 setae. Carpus ventral margin in male with 5 broad based setae, 3 distinctly larger than others; in female with 3 broad based setae. Propodus articular plate on posterior side of limb shorter than dactylar claw; in male distal width:palm width 0.63, with 3 broad based setae on ventral margin, 2 distinctly larger than remainder, in female with 1 broad based seta on ventral margin. Dactylus in male shorter than propodal palm; ventral claw length approximately 0.25 primary claw length. Pereopod IV ratios, male, female respectively. Length:body length 0.28, 0.31. Basis length:width 2.4, 2.4. Propodus length:pereopod length 0.17, 0.15. Propodus length:width 1.7, 2.5. Carpus length:pereopod length 0.12, 0.11.

Pereopods V–VII ( Fig. 10 , 13 , 18 ). Penicillate setae on dorsal ridge of basis, or dorsodistally on propodus. 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 (Pereopod V). Ischium dorsal margin with 7–12 simple setae (pereopod V, VII, 12 including setae in rows on lateral surfaces immediately adjacent to dorsal margin), including 1 robust seta. Basis dorsal ridge in cross-section, 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. 13 ), male and female, respectively. Length:body length 0.28, 0.33. Dactylus claw length:dactylar length 0.43. Propodus length:pereopod length 0.17, 0.16. Carpus length:pereopod length 0.12, 0.14. Basis length:width 1.9, 2.1. Pereopod VI ratios, male and female, respectively. Length:body length 0.43. Propodus length:pereopod length 0.16. Carpus length:pereopod length 0.16. Pereopod VII ratios, ( Fig. 13 , 18 ) male and female, respectively. Length:body length 0.39, 0.44. Dactylus claw length:dactylar length 0.4. Propodus length:pereopod length 0.16. Carpus length:pereopod length 0.16. Basis length:width 2.2, 2.0.

Penes ( Fig. 13 ). With cuticular hairs on shaft; distally tubular; tip truncate.

Pleopods ( Fig. 16 ). Exopods I lateral proximal lobe absent, medial proximal lobes absent. Protopods medial margin setose projections present. Pleopod I exopod broadest proximally, distal margin rounded, medial margin straight, divergent from lateral margin proximally, dorsal surface lacking setae; protopod longer than wide (ratio 1.3). Pleopod II in male endopod basal musculature not pronounced; appendix masculina length 0.52 pleopod length, proximal half of shaft solid and rod-like, indented in cross-section, distal tip extending near to distal margin of endopod, truncate, 1 seta on margin near proximal end, lateral margin with 1 seta, apex with 4 setae.

Pleopod ratios ( Fig. 16 ), in male only. Pleopod I exopod length:width 2.5; endopod length:width 2.1; endopod length:exopod length 0.73. Pleopod II length:body length 0.13; exopod length:width 2.1, distal article length:exopod length 0.31; endopod length:width 1.8, length:exopod length 0.48. Pleopod III length:body length 0.13; length 1.7 width; exopod length:width 2.1, distal article length:exopod length 0.28; endopod length:width 2.1, length:exopod length 0.48. Pleopod IV length:body length 0.13; exopod length:width 1.9, distal article length:exopod length 0.29, length:width 2.1; endopod length:exopod length 0.59. Pleopod V length:body length 0.11; epipod V length:width 1.5; exopod length:width 1.8, distal article length:exopod length 0.31; endopod length:width 2.1, length:exopod length 0.56.

Uropod ( Fig. 10 , 11 , 18 ). Extending posterior to pleotelson apex; dorsomedial ridge produced, forming bump, margin smooth, setae on margin robust and simple, 3 robust seta (lateral seta thin, half size of central seta); 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. Uropod ratios, male and female, respectively. Length 1.2, 1.2 pleotelson length. Protopod length:width 2.7, 3.2; length 0.46, 0.46 uropod length, dorsomedial ridge length:endopod length 0.54, 0.50. Exopod length 0.84, 0.85 endopod length; dorsal margin with 2, 1 robust seta.

Distribution. Found in current Lake Pedder, (Tasmania, Australia), at the position of its previous pre-inundation extent.

Remarks. Colubotelson pedderensis sp. nov. can be distinguished from C. edgarensis sp. nov. by the following features, with the latter species indicated in parentheses and order of value for identification. The pleotelson posterodorsal margin in lateral view is linear (concave), posterior apex is weakly narrowing distally (broadening, with a proximal constriction), forming an angle subequal or greater than 90°, range 91°–106° (less than 90°, range 73°–83°). The lateral margin of the head has a fringe of closely-spaced elongate setae (only a few short setae). Pereopod IV propodus palm of the male is robust, with a weak inflection at the position of the robust setae (palm not robust, smoothly concave); in other species of Colubotelson , the male propodal palm is even more robust with a larger inflection and larger setae. The uropodal protopod ventral margin has 2 transverse rows of simple setae (3 rows). The male pleopod II appendix masculina has a truncate distal tip, with 3 stiff straight setae on apex (rounded, with 4 setae). The DELTA database includes 182 characters that differ (list available from first author), although many differences are small, and undoubtedly not significant.

Figures

FIGURE 10. Colubotelson pedderensis sp. nov. Lateral views, with enlargements of anterior and posterior parts of the body. A – C, holotype male (QVM: 10: 51201). E – F, paratype male (QVM: 10: 51204). Scale bars 5.0 mm.

FIGURE 11. Colubotelson pedderensis sp. nov. Paratype male (QVM: 10: 51202), 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, ventral margin anterior to uropods, distally denticulate robust setae. F, medial view of ventral margin, showing group of medial group of small distally denticulate robust setae. G, posterior margin of pleotelson, ventral view. H, distal group of robust setae on ventral margin of uropodal protopod. I, left uropod, lateral view. Small globular objects are epizoic peritrichs. Scale bar 1.0 mm.

FIGURE 12. Colubotelson pedderensis sp. nov. Paratype male (QVM: 10: 51202), pereopods. A – D, pereopod I, lateral view, with enlargements of dactylus and palm, and setation of palm, lateral and medial views. E – F, pereopod II, lateral view, with enlargement of dactylus, propodus and carpus. G – H, pereopod IV, lateral view, with enlargement of dactylus, propodus and carpus. Small globular objects are epizoic peritrichs. Scale bars 1.0 mm.

FIGURE 13. Colubotelson pedderensis sp. nov. Paratype male (QVM: 10: 51202). A – B, pereopod V, lateral view, with enlargement of dactylus and propodus, medial view. C, pereopod VII, segments distal to merus lost, lateral view. D, penes, posterior view. E, antennula, in situ, with enlargement of distal tip. F, antenna, in situ, with enlargement of distal tip. Scale bars: A, C, F 1.0 mm; D, E 0.5 mm.

FIGURE 14. Colubotelson pedderensis sp. nov. Paratype male (QVM: 10: 51202), anterior mouthparts. A, labrum, anterior view, small globular objects are epizoic peritrichs. Scale bar 1 mm. B – D, left mandible medial view, palp distal articles with enlargement of setae (scale bar 0.05 mm), and ventral view of distal gnathal margin. E – F, right mandible, dorsal view and medial view of incisor and spine row. A, B, E scale bars 0.5 mm.

FIGURE 15. Colubotelson pedderensis sp. nov. Paratype male (QVM: 10: 51202), mouthparts. A – D, maxillula: ventral view, enlargement of lateral and medial lobe, lateral lobe, medial view. E – F, maxilla: medial and ventral views. G – I, maxilliped: ventral view, medial view of endite, enlargement of endite distal tip setae. Scale bars 0.5 mm.

FIGURE 16. Colubotelson pedderensis sp. nov. Paratype male (QVM: 10: 51202), pleopods, light micrographs in ventral view: A, I; B – D, II with SEM enlargements of appendix masculina and distal tip; E, III with enlargement of setae on exopod distal article; F – G, IV – V. Scale bar 1.0 mm.

FIGURE 17. Colubotelson pedderensis sp. nov. Paratype female (QVM: 10: 51203), head. A, lateral view. B, dorsal view. C – D, antennula with enlargement of distal tip. E – F, mandibular palp with enlargement of denticulate seta on palp article 3. G, ventral view. Scale bar 1 mm.

FIGURE 18. Colubotelson pedderensis sp. nov. Paratype female (QVM: 10: 51203). A – B, pereopod I, with enlargement of palm. C, pereopod II, lateral view. D, pereopod VII, lateral view. E – H, pleotelson: lateral view, uropod, dorsal view, posterior margin. Scale bars 1 mm.