Politolana polita, (Stimpson, 1853)

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 : 88-96

Redescription of P. polita ( Stimpson, 1853)

( Figs 23–27 )

Synonymy. Aega polita: Stimpson (1853) : 41–42; Lütken, 1859: 77 (not seen); Verrill (1873): 16. Conilera polita: Harger (1874) (not seen): 3, 22; Verrill (1874a): 411. Cirolana polita: Harger (1879) : 161 1880: 381–382; Richardson (1900): key, 217 1901: 511 1905: 99–101; Schultz (1969): 182; Verrill (1885): 559; Watling et al. (1974): 347–349. Politolana polita: Bruce (1981a) : 959. Not Politolana polita ( Stimpson 1853) : 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.

Type material. Nongravid female neotype, 14 mm long, herein designated. Col. by M.J. Rathbun, 8 August 1898, USNM # 25150 .

Original type locality. High Duck Island , New Brunswick, low water mark .

Neotype locality. Off Long Beach, Grand Manan , New Brunswick, 1.83 m.

Additional material examined. MCZ # 8433 : Ipswich , MA; 5 females, 3 males. MCZ # 6944 : locality unknown; 10 females, 4 gravid females, 5 males. MCZ # 8435 : Woods Hole , MA, collected on the beach; 1 female. USNM # 25150 : off Long Beach , Grand Manan, Canada, 1.8 m, col. by M.J. Rathbun, 8 August 1898; 1 female. USNM # 35485 : off Cape Cod , MA, 12.8 m, col. by USFC, R/V Speedwell, sta. 354 1879; 2 females (also examined by Harger). USNM # 41870 : Barrington Pass, Nova Scotia, 9.2 m, col. by Geol Sur. of Canada, 1 July 1910; 2 males, 1 gravid female. USNM # 191808 : off NJ, 38°48.30 N, 73°36.36 W, 57 m, col. by VIMS, MMS/NEBP, sta. Ef1, 10 November 1976; 1 damaged female.

Series of specimens from off NJ, col. by VIMS, MMS/NEBP — USNM # 191877 : 39°07.06 N, 73°49.36 W, 32.5 m, sta. D2, 17 August 1976; 1 gravid female, 10 mancas /juveniles. USNM # 191879 : 39°06.36 N, 72°59.00 W, 77 m, sta. I1, 23 August 1976; 1 damaged spec. USNM # 191880 : 39°04.36 N, 73°51.12 W, 31 m, sta. D1, 16 June 1976; 2 mancas. USNM # 191881: 39°02.54 N, 73°47.06 W, 51 m, sta. D4, 17 June 1976; 1 manca. USNM # 191883 : 39°06.36 N, 73°45.54 W, 36 m, sta. D3, 17 June 1976; 3 females, 1 male, 1 damaged. USNM # 191884 : 39°06 36 N, 73°45.54 W, 36 m, sta. D3, 17 June 1976; 1 male. USNM # 191885 : 39°06.36 N, 73°45.54 W, 36 m, sta. D3, 17 June 1976; 1 spec. USNM # 191886 : 38°41.24 N, 73°32.24 W, 56 m, sta. E3, 18 June 1976; 1 spec. USNM # 191887 : 38°44.06 N, 73°25.00 W, 73 m, sta. E2, 18 June 1976; 1 spec.

Series of specimens from Georges Bank , col. by MMS/NEBP — USNM # 214240 : 40°52.59 N, 68°00.00 W, 52 m, sta. 12, 8 May 1977; 1 gravid female, many mancas. USNM # 214241 : 40°49.20 N, 68°11.13 W, 57 m, sta. 9, 8 May 1977; 1 male (+ 1 P. concharum male). USNM # 214242 : Nantucket Shoals of Georges Bank , 41°07.54 N, 70°33.15 W, 40 m, sta. 1, 21 May 1977; 2 gravid females.

Series of specimens from outer Sheepscot Bay , ME, col. by L. Watling — USNM # 288420 : 43°43.4'N, 69°43.6'W, 29 m, sta. B3, 9 August 1988; 1 female, 1 manca. Research Collection of L. Watling (University of Maine): 43°43.4'N, 69°43.6'W, 29 m, sta. B3, 13 June 1988; 1 male, 1 female (+ 1 P. impostor). Research Collection of L. Watling (University of Maine): 43°33.3'N, 69°43.5'W, 31.5 m, sta. B5, 27 June 1988; 1 female .

Diagnosis. Cephalon anterior margin convex, indented at bases of antennules with small medial point; interocular furrow complete. Lateral margins of frontal ridge reaching but not dividing eyes. Eyes large, subquadrate, darkly pigmented; with rows of short simple setae fringing eyes ventrally. Frontal lamina greatly reduced to small ridge sitting deep between antennae. Antennae very short, just reaching beyond posterior margin of cephalon; with dense setation on peduncle articles 4 and 5. Coxae without lateral or oblique impressions; coxa 7 narrow with acute posterior angle. Pereopods 1–3 robust and highly setose, with superior distal angle of ischium and merus only moderately produced; merus and carpus with very numerous short blunt robust setae scattered on posterior face of articles; inferior margin of merus with row of short, distally blunt robust setae. Pereopods 5 and 6 with short studded-serrate robust setae on merus and carpus anterior distal margins. Uropod endopod apex subacute with large apical robust seta; exopod shorter than endopod, reaching beyond endopodal notch, narrow and curved medially, apex with large robust seta. Pleotelson narrowly convex or subtriangular, without robust setae.

Description of male (MCZ#8433). Eighteen millimetres long, body narrow with length about 4 Ⅹ width. Pereon cuticle highly polished; cream colour in alcohol, with remnants of numerous pigmented chromatophores on pleotelson and concentrated on posterior region of pereonal and pleonal segments.

Cephalon: Polished, without strong minute punctation. Anterior margin convex, indented at bases of antennules with small medial point. Lateral margins of raised frontal ridge reaching, but not dividing eyes. Interocular furrow complete. Eyes large, subquadrate, darkly pigmented; with rows of short simple setae fringing eyes ventrally ( Fig. 23F ). Frontal lamina greatly reduced to small ridge deep between antennae, broadening anteriorly; not extending far between peduncles of first antennae. Clypeus without distinctly raised lateral margins.

Antennule: Peduncle cuticle with microscopic ovate macula; peduncle article 2 posterior distal angle with 2–3 short circumplumose setae. Flagellum composed of 13 articles, each with 2–9 short aesthetascs; first flagellar article longest, wider than long; width of subsequent articles about 3 Ⅹ length.

Antenna: Only slightly longer than first antenna, just reaching beyond posterior margin of cephalon. Peduncle articles 3–5 subequal in length; article 3 length subequal to width, article 4 wider than long, widening slightly distally, posterior margin and distal angle bearing dense cluster of more than 20 long stiff simple setae and some short circumplumose setae; article 5 slightly longer than wide, with width about 2/3 width of article 4, posterior distal angle bearing more than 15 long stiff simple setae. Flagellum composed of nine subquadrate articles.

Mandible: Molar process surface with fine setae organized into small shingle like rows; anterior margin with spines widely spaced, not touching at their bases; submarginal setal row with long lightly plumose setae extending from proximal cluster.

Maxilliped: Endite with approximately 6–8 robust circumplumose setae; right endite with two coupling hooks, left endite with three coupling hooks. Palp articles 1 and 2 with submarginal cluster of simple setae on distomedial angle.

Pereon: Medially, pereonite 2 shortest, 3 and 4 subequal in length, 5 and 6 longest, 7 slightly shorter than pereonite 6; pereonite 1 with impression along lateral margin and small faint oblique impression on midlateral surface; anterolateral margins straight forming a rounded angle. All coxae without lateral or oblique impressions; coxae 2–4 posteriorly rounded; coxae 5 and 6 posterior margins oblique and slightly sinuate, progressively more extended posteriorly; length of coxae 7 subequal to coxae 6 length, with very acute posterior angle, extended to pleonite 4.

Pleon: Pereonite 7 overlapping most of first pleonite. Dorso-ventrally vaulted similar to pereon. Epimeres ventrally produced, but not laterally flared, posteriorly produced; epimeres 2–4 bearing sparse lateral setal fringe. Ventral flanges partially obscured by dorsal epimeres, ventral posterior angles rounded.

Pereopods 1–3: Basis superior submarginal setal row dense, with more than 15 setae. Ischium only moderately produced into scoop-shaped lobe. Meral lobe short, just reaching base of propodus, with one (P1 and P2) or two (P3) giant apical setae; inferior margin of merus with row of distally blunt, flattened and textured setae and row of adjacent short acute robust setae. Ischial and meral lobes of P1–P3 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 without simple setae. Merus and carpus with numerous short blunt robust setae scattered on posterior face of articles, remaining dense through P6; inferior margins with long and short blunt robust setae; anterior distal margins with medial row of 4–5 short studded-serrate robust setae (P5 and P6); P4 carpus length subequal to width, longer than wide on P5 and P6. Propodus without simple setae on superior margin.

Pereopod 7: P7 similar to P6 except: slightly longer, with slender distally biserrate setae on superior distal angles of merus, carpus and propodus; posterior face of merus and carpus less setose and with setae more organized into rows.

Pleopods: Pleopod 1 peduncle subquadrate, with six plumose coupling hooks; endopod width about one-half of exopod width. Pleopod 2 peduncle with five plumose coupling hooks; appendix masculina narrow, of relatively constant width, tapering evenly to slightly curved apex, extending slightly beyond distal margins of exopod; exopod distal margin broadly rounded. Pleopods 3 and 4 with four plumose coupling hooks.

Uropod: Peduncle medial production distally blunt or truncate, with 13 long plumose setae confined to apex. Endopod apex triangular or subacute, with large apical robust seta; distal margin with two smaller robust setae and PMS; medial notch shallow, without palmate setae set in notch or robust seta lateral to notch. Exopod shorter than endopod, reaching beyond endopodal notch, narrow and rounded, curved medially, apex with large robust seta, medial and lateral margins without additional robust setae.

Pleotelson: Posterior margin narrowly and evenly convex, minutely scalloped, with fine plumose setae, without robust setae.

Variation. The pleotelson apex varies from narrowly rounded to more subtriangular ( Fig. 23H ).

Sexual dimorphism. Males and females similar.

Size range. Adults 9–18.5 mm.

Remarks. Stimpson’s original description of this species was brief and lacked figures. Because of the inadequate description, and the subsequent loss of the type material, there has been much confusion over the past 145 years regarding this species. This confusion stems partly from the fact that there are at least four very similar species in the vicinity of the type locality: P. polita , P. impressa , P. concharum and P. impostor n.sp. Most commonly P. impostor has been identified, figured and described as P. polita , or descriptions of P. polita have erroneously combined unique characters of several species into a single species description.

In his 1883 paper, Harger figured P. impostor as P. polita . In 1901, Richardson provided a key including P. polita and among the characters she used to identify this species were an elongate frontal lamina (characteristic of P. impostor ) and short antennae (characteristic of P. polita ). In her 1905 monograph, Richardson again failed to discriminate these two species and described them as one. In the key (p. 83), she used an ‘elongate frontal lamina’ to distinguish P. polita , yet in her description of the same species she described the frontal lamina as ‘small and almost inconspicuous’. She also described the antennal flagellum as being short, composed of 10 articles, yet the figure (taken from Harger, 1883) shows an antenna with a flagellum of about 22 articles. Harger (1883: 382) provided a table of the ‘ P. polita ’ material examined and among these the following two lots are actually P. impressa : George’s Bank, 150 fms (USNM#35930), and East Quereau, 190 fms (USNM#35321). Menzies & Frankenberg (1966), Schultz (1969) and Kussakin (1979) all figured P. impostor specimens as P. polita .

While Stimpson’s description was quite brief, it contains clues as to which of the two forms he was describing, notably his description of the antennae: ‘Antennae small but rather stout at base, placed transversely, curving backward, the superior ones being three-fifths as long as the inferior ones, which reach the middle of the first thoracic segment at its lower edge.’ The form we have identified as P. polita has the short antennae Stimpson noted and this character is unique among the west Atlantic Politolana species. On the other hand, the length of the antennae in P. impostor is markedly longer, reaching the second pereonite. Given this clear difference, we can confidently identify the species that Stimpson described in 1853. Stimpson stated that the animals were deposited at USNM, and ‘in the cabinet of Professor Agassiz, at Cambridge’. We have searched these and other possible collections, and again have not been able to locate Stimpson’s type specimens. Because of the past confusion regarding this species, and for nomenclatural stability, it is necessary to erect a neotype in accordance with article 75 of the International Code for Zoological Nomenclature (1999). Of the available material, we have chosen the lot that was collected closest to the original type locality to provide a neotype. This monograph provides the first figures of P. polita , 145 years after its description. Distribution. Politolana polita is a western Atlantic , cold temperate species known from Nova Scotia, Georges Bank, around Cape Cod, Massachusetts, and south to about 38°N. It has been taken at depths of 0– 86 m, with the majority of animals collected between 30 m and 60 m. Harger (1880) suggested that this species replaces P. concharum to the north. However, the ranges of these two species overlap significantly and P. polita has been collected together with P. concharum , as well as P. impostor , on the Georges Bank and in the Gulf of Maine.

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 23. Politolana polita male (MCZ#8433): (A) dorsal aspect; (B) lateral aspect; (C) antenna; (D) penes; (E) antennule. Politolana polita female neotype: (F) cephalon, ventral aspect; (G) pleon detail. Politolana polita female (MCZ#6944): (H) pleotelson.

Figure 24. Politolana polita male (MCZ#8433): (A) maxilla; (B) right mandible; (C) right maxilliped; (D) maxillule; (E) right uropod.

Figure 25. Politolana polita male (MCZ#8433): (A–D) pereopods 1–4, respectively.

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

Figure 27. Politolana polita male (MCZ#8433): (A–E) pleopods 1–5, respectively.