Politolana impostor, Riseman & Brusca, 2002

Riseman, Sarah F. & Brusca, Richard C., 2002, Taxonomy, phylogeny and biogeography of Politolana Bruce, 1981 (Crustacea: Isopoda: Cirolanidae), Zoological Journal of the Linnean Society 134 (1), pp. 57-140 : 71-83

Description of P. impostor n.sp.

( Figs 10–15 )

Synonymy. Cirolana polita of: Harger (1883): pl. 1, Figs 1, 1 (c), pl. 2, Figs 2, 2 (b); Richardson (1905): Figs 80, 81; Menzies & Frankenberg (1966): 18, 50–51, Fig. 26 ; Schultz (1969): Fig. 285; Kussakin (1979): 205–206, Figs 83, 84; Kensley & Schotte (1989): 140–143, Figs 63, 64.

Holotype. Female, USNM # 288404 : col. by L. Watling, sta. B2, 27 June 1988.

Type locality. Outer Sheepscot Bay , ME, 43°43.2'N, 69°43.5'W, 33.5 m.

Paratypes. MCZ # 6853 : Provincetown, MA; 1 female. USNM # 34512 : off Newport, RI, 24–35 m, col. by Usfc, R /V Fishhawk, sta. 793–799; 3 females (1 gravid). USNM # 63743 : Aspy Bay , Nova Scotia, col. by Biol. Board of Canada, Cheticamp Ex., 27 July 1917; 2 females, 2 males. USNM # 236219 : Gulf Stream , otter trawl, col. by J.A. Musick, R/V Eastward, sta. 31, May 1972; 1 male. USNM # 253289 : Woods Hole , MA; 1 spec.

Series of specimens from off NJ, col. by CABP/VIMS — USNM # 191818 : 39°24.12 N, 73°06.12 W, 66 m, sta. Bs6, 15 November 1976; 1 male. USNM # 191873 , 38°45.12 N, 73°25.12 W, 76 m, sta. E2, 11 August 1977; 4 spec.

Series of specimens from Georges Bank , col. by NEEB/Mms/BLM — USNM # 214321 : 40°41.05 N, 67°35.27 W, 86 m, sta. 13, 30 August 1977; 1 spec. USNM # 214322 : 40°41.24 N, 67°35.58 W, 84 m, sta. 13, 30 August 1977; 1 spec .

Series of specimens from outer Sheepscot Bay , ME, col. by L. Watling — USNM # 288405 : 43°43.2'N, 69°43.5'W, 33.5 m, sta. B2, 27 October 1988; 1 spec. (missing posterior half). USNM # 288406 : 43°33.3'N, 69°43.5'W, 31.5 m, sta. B5, 9 August 1988; 1 juvenile. Additional material examined. Research Collection of L. Watling (University of Maine): outer Sheepscot Bay, ME, 43°43.4'N, 69°43.6'W, 29 m, col. by L. Watling, sta. B3, 13 June 1988; 1 juvenile (+ 2 P. polita).

Diagnosis. Body vaulted, pereon and pleon convex and tightly articulated. Coxae broad, lacking oblique or lateral impressions; length of coxae 7 slightly less than length of coxae 6. Frontal lamina narrow, usually spatulate: widened anteriorly, visible in dorsal aspect projecting between antennular peduncles. Lateral margins of frontal ridge reaching but not dividing eyes. Interocular furrow medially incomplete. Eyes subquadrate, darkly pigmented. Antennae reaching middle of second pereonite. Mandible molar process with numerous spines on anterior margin, touching at their bases. Pleon ventral flanges with ventral posterior angles produced into fine points. Pereopods 1–3 with superior distal angles of ischium and merus moderately produced; inferior margin of merus with long blunt robust setae; ischium superior margin with sparse simple setae. Pereopod 4 propodus with sparse simple setae on superior margin. Uropod peduncle ventral distolateral angle with acute robust seta; endopod distal margin broadly truncate; exopod shorter than endopod, peltate in shape, apex with robust seta and one or two short simple setae. Pleotelson posterior margin narrowly convex, with PMS and four small robust setae.

Description of holotype. Female, 13 mm long; body broad, length about 3.5 Ⅹ width; pereon cuticle highly polished; cream colour in alcohol with chromatophores on pereon, pleon and pleotelson.

Cephalon: Minutely punctate. Anterior margin medially straight with distinct medial point; lateral margins of raised frontal ridge reaching but not dividing eyes. Interocular furrow incomplete medially. Eyes subquadrate, darkly pigmented. Frontal lamina narrow, length about 4 Ⅹ greatest width, anteriorly widened and spatulate, visible in dorsal aspect projecting between antennular peduncles; with lateral margins only slightly or not raised into thickened ridges. Clypeus with lateral margins raised as thickened ridges.

Antennule: Peduncle cuticle with microscopic ovate macula; articles with numerous short palmate setae on distal angles. Flagellum composed of eight articles, each bearing about 3–5 aesthetascs, some articles with additional cluster of short setae; first flagellar article longest, length subequal to width, width of subsequent articles about twice length.

Antenna: Reaching middle of second pereonite; peduncle articles 3 and 4 subequal in length, five longest; article 3 length subequal to width, widening slightly distally; article 4 subquadrate, posterior distal angle bearing row of approximately 10 long stiff simple setae; article 5 length about twice width, posterior distal angle bearing five long stiff simple setae. Flagellum composed of 16 articles.

Mandible: Molar process medial surface and distal posterior margin with fine setae organized into small shingle like rows; spines on anterior margin numerous, closely spaced, touching at their bases; submarginal setal row dense, with long lightly plumose setae extending from proximal cluster.

Maxilliped: Endite with distal cluster of approximately five robust circumplumose setae; right and left endites with two coupling hooks. Basis and palp article 1 with submarginal cluster of 2–3 long simple setae on distolateral angle.

Pereon: Body highly vaulted. Medially, pereonites 2, 3 and 7 slightly shorter than 4–6, which are subequal. Pereonite 1 narrowing anteriorly to encompass cephalon, with impression along lateral margin, and less distinct mid-lateral oblique impression. Coxae 2–5 posterior margins subquadrate, not extending beyond posterior margin of respective pereonite; coxae 6 and 7 posterior margins oblique with acute posterior angles, extending well beyond posterior margin of respective pereonite; all coxae without lateral or oblique impressions.

Pleon: Dorso-ventrally vaulted similar to pereon. Pereonite 7 tightly overlapping anterior portion of first pleonite. Epimeres ventrally and posteriorly produced, not laterally flared; epimeres 2–4 bearing sparse lateral setal fringe. Ventral flanges with ventral posterior angles produced into fine points.

Pereopods 1–3: Basis with 6–7 stout circumplumose setae on superior margin. Ischium only moderately produced into scoop-shaped lobe; posterior face of ischium with one submarginal and one oblique row of simple setae. Meral lobe short, just reaching base of propodus, with one (P1) or two (P2 and P3) giant apical setae; inferior margin of merus with long blunt robust setae and adjacent row of short acute robust setae. Ischial and meral lobes of pereopods 1–3 equally produced, but with inferior face of merus broadening into distinct ‘palm’ fringed with robust and simple setae. Carpus of P2 and P3 wider than long. Superior margin of propodus with long row of simple setae. Dactyl length less than propodal length.

Pereopods 4–6: Ischium superior margin with sparse simple setae. Merus and carpus with short blunt robust setae scattered on posterior face of articles, more organized into transverse rows on posterior pereopods; inferior margins of merus and carpus with long and short robust setae. Carpus longer than wide, lengthening posteriorly; P6 with slender distally biserrate setae on superior distal angles of carpus and propodus. Propodus superior margin with sparse setae (P4 and P5).

Pereopod 7: P7 similar to P6 except longer.

Pleopods: Pleopod 1 peduncle subquadrate, with six coupling hooks; endopod width about one-half of exopod width. Peduncle of pleopods 2 and 3 with five plumose coupling hooks. Pleopod 4 with four plumose coupling hooks.

Uropod: Peduncle medial production distally acute, apex with 3 PMS; peduncle ventral distal lateral corner with robust seta in lateral setal row. Endopod distal margin broadly truncate, with PMS and five small robust setae of relatively equal size, without giant apical seta. Exopod shorter than endopod, reaching endopodal notch; peltate shape: flat with convex lateral margins; apex with robust seta and one or two short simple setae; distal medial and lateral margins with small robust setae.

Pleotelson: Posterior margin narrowly rounded, with PMS and four small robust setae.

Variation. Setation on all appendages, including antennae and mouth parts, becomes more dense with size. Frontal margin of the cephalon is more concave medially in larger animals, and the small rostral point is not always as distinct as on the holotype. Ommatidial cuticular facets range from absent to well developed. This species has two frontal lamina morphologies: the long spatulate form of the holotype, visible in dorsal aspect, and a shorter slight hourglass shape, more typical among Politolana , which is not visible from dorsal aspect. Antenna peduncle article 5 varies in length from slightly longer than wide to almost twice as long as wide. The antenna flagellum can have from 15 to 22 articles. Maxilliped endites have one or two coupling hooks. The oblique impression on the mid-lateral face of pereonite 1 is sometimes absent. The posterior angles of coxae 6 and 7 can be less acute and less posteriorly projected than in the holotype. Pereonite 7 may completely overlap pleonite 1. Pleopod coupling hook numbers increase with size.

Sexual dimorphism. Males and females are similar. Males with appendix masculina long, tapering evenly to narrow point, extending well beyond distal margins of both pleopod rami.

Size range. Adults range from 10.5 mm to 23 mm in length.

Remarks. Politolana impostor has been mistakenly identified as Politolana polita in the past (see remarks section of P. polita description). However, the reduced form of the frontal lamina and the very short antennae of P. polita immediately distinguish it from this species. Politolana impostor is also very similar to P. concharum and P. micropthalma . In most cases, it can be distinguished from these species by the spatulate frontal lamina. In addition, the form of the uropod rami and the inner production of the uropod peduncle also differ from P. concharum and P. micropthalma . The subquadrate eyes of P. impostor also differ from the triangular eyes of P. concharum .

Etymology. Since the late 1800s this species has been figured and described as P. polita . Because this species has for so long remained undistinguished from P. polita , we have given it the name impostor .

Distribution. A west Atlantic lower boreal species, recorded as far north as Aspy Bay, Nova Scotia but more commonly found on the Georges Bank and on the continental shelf south to approximately 38°N. One unusual record, a single specimen collected from the mouth of a fish, exists from Cape Hatteras. Collection depths range from 29 m to about 587 m, but the majority of specimens have been collected between 70 m and 200 m. Politolana impostor has been collected together with P. impressa , P. polita and P. concharum .

Figures

Figure 1. Five equally most parsimonious trees resulting from branch-and-bound search, PAUP version 3.1. For all five trees, length = 158 steps, CI = 0.65, RI = 0.65, RC = 0.43. With six uninformative characters removed, length = 151 steps, CI = 0.63, RC = 0.41.

Figure 2. Strict consensus tree of five most parsimonious trees. Disagreement is confined to the relationships between the out-groups and three Politolana species, P. dasyprion, P. crosnieri and P. obtusispina, that do not belong to Politolana sensu stricto.

Figure 10. Politolana impostor n.sp. female holotype: (A) dorsal aspect; (B) lateral aspect; (C) frontal lamina; (D) antennule; (E) antenna.

Figure 11. Politolana impostor n.sp. female holotype: (A) right maxilliped; (B) maxilla; (C) right mandible; (D) maxillule; (E) right uropod.

Figure 12. Politolana impostor n.sp. female holotype: (A–C) pereopods 1–3, respectively.

Figure 13. Politolana impostor n.sp. female holotype: (A, B) pereopods 4 and 5, respectively.

Figure 14. Politolana impostor n.sp. female holotype: (A, B) pereopods 6 and 7, respectively.

Figure 15. Politolana impostor n.sp. female holotype: (A–E) pleopods 1–5, respectively. Politolana impostor male: (F) pleopod 2.

Figure 26. Politolana polita male (MCZ#8433): (A–C) pereopods 5–7, respectively.