Pygolabis humphreysi, Wilson, George D. F., 2003

Wilson, George D. F., 2003, A new genus of Tainisopidae fam. nov. (Crustacea: Isopoda) from the Pilbara, Western Australia, Zootaxa 245, pp. 1-20 : 13-19

Pygolabis humphreysi sp. nov. ( Figs. 1­7 )

Type fixation. Holotype male, WAM C33562, here designated.

Etymology. The species is named in honour of Dr William F. Humphreys, whose exploration and biological study of the Western Australian calcrete aquifers has discovered many new taxa, including this new genus and species.

Type Material: Holotype male, body length 14.2 mm, pleopod II separate and photographed, WESTERN AUSTRALIA: Pilbara Region: Newman Borefield: 23°20’S 119°51’E, fld.no. BES4836 trap 24.vii.1997 (W.F. Humphreys, S.M. Eberhard) ( WAM C33562). Paratypes: female, body length 14.6 mm, pleopods dissected, same data as holotype, (AM P64992), 2 males, same data as holotype ( WAM C33563); 1 male, body length 11.9 mm, dissected for SEM, Bore W29, 23°24’S 119°47’E, fld.no. BES5496 19.xi.1998 (S.M. Eberhard) (AM P64993); female, 23°20’S 119°51’E, fld.no. BES4801 Haul net 22.vii.1997 (W.F. Humphreys, S.M. Eberhard) ( WAM C33564); male, 23°19’S 119°51’E, fld.no. BES4826 Haul net 23.vii.1997 (W.F. Humphreys, S.M. Eberhard) ( WAM C33565); female, 23°19’S 119°51’E, fld.no. BES4838 Haul net 24.vii.1997 (W.F. Humphreys, S.M. Eberhard) ( WAM C33566); 2 males, Bore W135, 23°17’S 119°52’E, fld.no. BES6377 20.xi.1998 (S.M. Eberhard) ( WAM C33567); 1 spm., Bore W256, 23°12’S 119°53’E, fld.no. BES3515 11.xi.1998 (S.M. Eberhard) ( WAM C33568); male and female, Bore W157, 23°13’S 119°54’E, fld.no. BES3535 12.xi.1998 (S.M. Eberhard) ( NMV J52441 ); female, Bore W28, 23°24’S 119°47’E, fld.no. BES5499 19.xi.1998 (S.M. Eberhard) ( WAM C33569); 1 spm., 23°19’S 119°51’E, fld.no. BES4816 Haul net 22.vii.1997 (W.F. Humphreys, S.M. Eberhard) ( WAM C33570).

Diagnosis. Body medial length 7–8.2 (H) width at pereonite 3. Head dorsal surface distinctly convex in lateral view. Pleopod II appendix masculina rounded cup on distal tip narrow, cup width subequal to groove width proximal to distal tip, teeth on lateral margin barely projecting from lateral margin, proximal teeth subequal to lateral teeth in middle of ridge, ~23–29 (H) teeth altogether.

Description. Head length 0.77 width, 1.4 pereonite 1 medial length; dorsal surface covered with scattered fine setae; antennal notch present; clypeus rounded, proximal width 0.46 head width, extending between antennal insertions; mandibular articular fossa narrower than clypeal height; labrum distally rounded, without setae, symmetrical.

Pereonites total medial length 0.49–0.54 body length; dorsal surfaces with scattered fine setae, setae density dorsally uniform, with 1–2 thin transverse cuticular ridges.

Pleonites with scattered sparse fine setae; total medial length 0.26–0.28 (H) body length; pleonites 1–4 relative lengths subequal, all shorter than pereonite 7, medial lengths 0.05, 0.05, 0.05, 0.05, 0.06­0.07 (H) body length, respectively; pleonite 5 subequal in length to pereonite 7.

Pleotelson medial length 1.14–1.41 (H) width in adults, 0.47 pleon length; with scattered simple setae; posterolateral margins without robust sensillate setae, with ~20 small non­sensillate simple setae (including several submarginal setae).

Penes oval in cross­section, with elongate thin­walled and tapering extension.

Antennula length 0.17–0.24 (H) body length, with 22–26 (H) articles; article 1 with few simple setae, surface with cuticular scales on medial margin; article 2 subequal to article 1; article 3 shorter than article 1, without penicillate setae; secondary flagellum on article 3 with several large simple setae and at least 1 penicillate seta; distal flagellar articles with simple setae and aesthetascs on distal margins, most articles only with 1 aesthetasc, none with more than 2, each aesthetasc consisting of narrow proximal peduncle, enlarged thin distal section and distal tip with tiny pore.

Antenna 0.31–0.40 (H) body length; with 48–54 (H) articles; articles 1–3 increasing in length distally, surface with cuticular combs or scales, with few simple setae; article 4 subequal to article 3; articles 5–6 longer, increasing in length distally; flagellum length 0.63– 0.72 (H) antenna total length.

Mandible articular axis approximately at right angles to incisor; incisor broader than molar process in medial view; left lacinia mobilis large, flattened and cuspidate, distinctly separated from spine row; right lacinia mobilis indistinctly separated from remainder of spine row, bifurcate with two dentate plates (smaller plate on anterior surface of larger plate); spine row on ridge between incisor and molar, with remaining spines other than lacinia mobilis not bifurcate, left side with 4 denticulate spines, right side with 3 denticulate spines. Palp length 0.71 mandible length; article 1 with 2 distal simple setae; article 2 with 2 longitudinal rows of setae (1 setulate setae and 1 simple setae), additional distal transverse row of simple setae present, medial cuticular surface forming combs; article 3 weakly curved, with 12 setae, setae finely setulate, coarsely spinulate setae absent.

Maxillule medial lobe with 4 pappose setae; with 2 additional small simple accessory setae on distolateral margin and between medial pappose setae. Lateral lobe with 12 distal robust setae, including 7 denticulate; ventral face setae absent.

Maxilla outer lateral lobe with 9 comb setae. Medial lobe medial margin slightly concave distally; extent of setae confined to distal half of medial margin past insertion of lateral lobes; with 2 large medial pappose setae; ~5 setae in ventral row (obscured in SEM); 12 setae in dorsal row; setae in ventral and dorsal rows with spinules and setules.

Maxilliped epipod length 1.2 width, distal margin narrowly rounded; palp basal width 0.23 length; endite with 3 coupling hooks on both sides.

Pereopod I propodus and carpus ventral margins with robust bidenticulate sensillate setae, 6, 1 (5 robust setae present but only 1 bidenticulate) respectively. Pereopods II­III carpus and I­III merus ventral margins with smooth robust sensillate setae, carpus with 16–20, 16–18 (H) respectively (distally in two rows), lateral setal row with 5–6 (H) robust setae. Coxae II lateral sutures indistinct; III­VII well indented laterally, with broad medial extension toward midline, pereopod III triangular; IV­VII elongate, covering entire lateral margin.

Pleopods lying flat on ventral surface of pleon, weakly enclosed laterally by respective pleonites, II­IV each weakly overlapped by preceding pleopod (i.e., by about half­length); protopods medial margin with curved serrate robust setae; exopods with fewer than 27 marginal plumose setae (21–26). Pleopod I endopod thin and flattened; in female length 0.53 exopod length; distal margin rounded, with only 2–3 small plumose setae. Pleopod II male endopod appendix masculina lateral margin proximally concave; medial margin cuticular combs absent; teeth barely projecting from lateral margin, separated by at least tooth width for only part of length, with 3 distal elongate spine­like teeth; distal segment length 1.52 width (light microscope measurements), not projecting ­ forming smoothly rounded arc. Pleopod II female endopod without setae. Pleopod III­V endopods without setae.

Uropods length 0.24 body length, 0.94 pleotelson length. Protopod extending beyond pleotelson distal margin, length between insertions and distal margin 1.1 length of pleotelson posterior margin (between insertions and pleotelson distal tip); medial margin with 20 small tooth­like setae; ventrolateral margin with abundant long thin laterally­projecting setae. Endopod length 0.70 protopod length, 1.4 exopod length; medial margin with proximal and distal penicillate setae, medial margin with 12–14 (h) small tooth­like setae. Exopod length 0.43 protopod length.

Distribution. Calcrete aquifers of the upper Fortescue River, near Newman, Western Australia (Pilbara Region).

Discussion. Although Pygolabis gen. nov. is currently monotypic, at least three undescribed species of this genus inhabit other borefields of the Pilbara region (research in progress). These species occur at Hardey River (a tributary of the Ashburton River), Paraburdoo and Weeli Wolli. They differ in the relative shapes of the head in lateral view, length of the body compared to width, and in details of the male pleopod II endopod, (particularly number and size of denticles that line the dorsal margin of groove and size of the distal cup of the appendix masculina). The diagnosis for P. humphreysi sp. nov. was constructed using these comparisons. The species also differ in the lengths of the limbs compared to the body, although this feature is not fully assessed.

The narrow terminal projection of the pleotelson of P. humphreysi shows considerable variability in its length, apparently correlated with body length. The smallest specimens examined had a short pleotelson tip well anterior to the distal margin of the uropodal protopod, while the tip in the largest specimens reached nearly to this point. The undescribed species of Pygolabis also vary in the form of the pleotelson tip, although their allometries have not been examined.

Figures

FIGURE 1. Pygolabis humphreysi gen. nov., sp. nov (holotype male WAM C 33562, light micrographs): A, C. Body, dorsal and lateral; B, D. Head, dorsal and lateral. (scale bars 1 mm)