Politolana concharum, (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 : 96-110

Redscription of P. concharum ( Stimpson, 1853)

( Figs 28–33 )

Synonymy. Aega concharum: Stimpson (1853) : 42. Conilera concharum: Harger (1874) : 572 (278) (not seen); Verrill (1874b): 459 (165) (not seen). Cirolana concharum: Harger (1879) : 161 1880: 378–381, pls. IX–X, Figs 58–63 1883: pl. 1, Fig. 4 , pl. 2, Figs 4, 4 (c); Hansen (1890): 333–336, Table 2, Figs 4, 4 (f); Richardson (1900): 216 1901, 513 1905: 83, 95, Fig. 75; Schultz (1969): 181–182, Figs 282, 283; Watling et al. (1974): 347–348; Jones (1979): 318; Kussakin (1979): 206–211, Figs 85–87. Politolana concharum: Bruce (1981a) : 959, Figs 1 (j)–(k), 2(g)–(h), 3(g)–(h), 4(d) and 5(g)–(h); Rachlin & Warkentine (1997): 368–379.

Type material. Nongravid female neotype, herein designated, 19 mm long, MCZ # 6797a .

Original type locality. Charleston Harbor , SC.

Neotype locality. Charleston , SC.

Additional material examined. MCZ # 8436 : Woods Hole , MA; 2 females . MCZ # 8437 : Vineyard Sound , MA; 4 females . MCZ # 8439 : off Block Island , RI; 5 females . MCZ # 6797 : Charleston , SC; 16 females, 3 males . MCZ # 8431 : Albatross IV cruise 72–3, sta. 52; 7 females, 1 male, 1 manca . NMB # 6708 : 3 specimens . USNM # 2971 : off New Shoreham , Block Island , RI, 27 m, col. by USFC, 19 August 1874; 1 female . USNM # 2970 : Eel Pond , Woods Hole , MA, col. by USFC, 23 July 1875; 4 females, 1 male . USNM # 6352 : Halifax , Nova Scotia, 95 m, col. by Stimpson, USFC, 1877; 1 female . USNM # 35315 : off Montauk Point , Long Island, from surface, col. by USFC, R/V Albatross, 7 August 1883; 1 male . USNM # 35316 : off Fishers Island , Long Island Sound, in lobster pots, col. by J.H. Latham, USFC, May 1875; 1 male, about 19 females . USNM # 43204 : Monroe County, so. of Key West , FL, on edge of Pourtoles Plateau , 24°34 N, 81°48 W, 183 m, col. by J.B. Henderson; 1, female . USNM # 106186 : Cape May County, Wildwood , NJ, from mammary slits of finback whale, col. by F.A. Ulmer, 6 March 1955; 2 females; 1 male . USNM # 191792 : off NJ, 39°53.24 N, 72°43.06 W, 55–56 m, col. by VIMS/CABP, sta. G4, 27 August 1976; 2 males, 2 juveniles, 6 females (+ 2 P. polita) . USNM # 211103 : South-east Brown’s Bank , Nova Scotia, in lobster trap, col. by D.S. Pezzack, 21 July 1983; 2 males . USNM # 253289 : Woods Hole , MA; 1, female (+ 1 P. impostor) .

Series of specimens from MA, col. by V.N. Edwards, USFC— USNM # 2968 : Vineyard Sound, May 1874; 3 females, 1 male . USNM # 2969 : Vineyard Sound , from stomach of Peak Nosed Skate, 14 May 1874, 2 spec. USNM # 3871 : Woods Hole , 1881; 20+ spec. USNM # 38224 : Woods Hole; 26 females, 4 males .

Series of specimens from outer Sheepscot Bay , ME, col. by L. Watling — USNM # 288411 : 43°43.0'N, 69°43.3'W, 37 m, sta. B1, 30 March 1988; 2 females, 2 males. USNM # 288412 : 43°43.0'N, 69°43.3'W, 37 m, sta. B1, 28 April 1988; 1 male. USNM # 288413 : 43°43.0'N, 69°43.3'W, 37 m, sta. B1, 7 June 89; 1 female, 2 mancas. USNM # 288414 : 43°33.3'N, 69°43.5'W, 31.5 m, sta. B5, 3 March 88; 1 gravid female, 1 male. USNM # 288415 : 43°43.2'N, 69°43.4'W, 39 m, sta. B7, 28 February 1988; 2 females. USNM # 288416 : 43°43.2'N, 69°43.4'W, 38 m, sta. B7, 10 January 1989; 1 gravid female, 1 female, 3 mancas, 1 male. USNM # 288417 : 43°43.2'N, 69°43.4'W, 38 m, sta. B7, 7 June 1989; 1 female. USNM # 288418 : 43°42.8'N, 69°43.7'W, 37 m, sta. B9, 9 August 88; 1 female. Research Collection of L. Watling (University of Maine): 43°42.8'N, 69°43.7'W, 37 m, sta. B9, 10 January 1989; 1 male, 3 females, 3 mancas.

Diagnosis. Body narrow, with pereon and pleon convex and tightly articulated, pereonite 7 overlapping most of first pleonite. All coxae without lateral or oblique impressions. Pleon ventral flanges with ventral posterior angles produced into fine points. Cephalon anterior margin convex, with small medial rostral point; lateral margins of frontal ridge reaching but not dividing eyes. Eyes large, triangular, darkly pigmented. Antennae short, reaching middle of first pereonite. Pereopods 1–3 with ischium and merus only moderately produced; inferior margin of merus with row of short molariform setae or distally blunt, textured setae. Pereopods 4–6 ischium superior margin with dense simple setae. Pereopod 4 merus and carpus with numerous scattered short robust on posterior face; propodus with sparse simple setae on superior margin. Uropod peduncle ventral distal lateral corner with robust seta in lateral setal row; endopod apex triangular, with large apical robust seta; exopod shorter than endopod, but reaching beyond endopodal notch, narrow and rounded, curved medially, apex with single large robust seta. Pleotelson posterior margin convex with posterior emargination flanked by two large robust setae on each side.

Description of neotype. Female, 19 mm long; body length about 4.5 Ⅹ width. Pereon cuticle highly polished; cream colour in alcohol; with numerous darkly pigmented chromatophores, concentrated in posterior region of pereonal and pleonal segments, and covering pleotelson.

Cephalon: Cuticle polished, without strong minute punctation. Anterior margin convex, with small medial rostral point; lateral margins of raised frontal ridge reaching, but not extending over and dividing eyes. Interocular furrow incomplete medially. Eyes large, subtriangular, wider dorsally than ventrally, darkly pigmented; cuticular ommatidial facets distinct. Frontal lamina narrow, length about 5 Ⅹ greatest width, with slight hourglass shape, reaching middle of antennule peduncles. Frontal lamina and clypeus with lateral margins raised into thickened ridges.

Antennule: Peduncle cuticle with microscopic ovate macula; article 2 posterior distal angle with 4–5 short palmate setae. Flagellum composed of 15 articles, each with about 6–7 short aesthetascs; first flagellar article longest, wider than long, width of subsequent flagellar articles about 3 Ⅹ length.

Antenna: Reaching middle of first pereonite. Peduncle articles 3–5 subequal in length; article 3 length subequal to width, widening slightly distally; article 4 subquadrate, posterior distal angle bearing about 20 long stiff simple setae; article 5 only slightly longer than wide, with width about 2/3 width of article 4, posterior distal angle bearing five long stiff simple setae. Flagellum short, length subequal to peduncle length; composed of about 15 subquadrate articles.

Mandible: Molar process dorsal surface with fine setae, posterior surface with scattered larger setae ( Fig. 29E ); anterior margin with spines widely spaced, not touching at their bases; submarginal setal row with long lightly plumose setae extending from proximal cluster.

Maxilliped: Proximolateral angle of basis bearing cluster of about 10 short simple setae. Endite with distal cluster of approximately 6–8 robust circumplumose setae; right and left endites with two coupling hooks.

Pereon: Medially, pereonite 1 slightly longer than 2 and 3, pereonites 4 and 5 longest, pereonite 7 shorter than 6. In dorsal aspect, pereonite 1 narrowing only slightly anteriorly to encompass cephalon; first pereonite with faint impression along lateral margin; anterolateral margins straight, forming rounded anterior angles. All coxae without lateral or oblique impressions; coxae 2–4 posteriorly rounded; coxae 5 posterior margins subquadrate, forming slight posterior point; posterior margin of coxae 6 suboblique, forming acute posterior angle; length of coxae 7 subequal to 6 with acute posterior angle, extended to pleonite 3 or 4.

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

Pereopods 1–3: Robust and highly setose. 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 pereopods 1–3 equally produced, but with inferior face of merus broadening into distinct ‘palm’ fringed with robust and simple setae. Pereopod 3 carpus 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 dense simple setae; P4 merus and carpus with many short robust setae scattered on posterior face, progressively less numerous and more organized into transverse rows on P5–P7; inferior margins of merus and carpus with long and short robust setae. Carpus length subequal to width (P4) or longer than wide (P5 and P6). Propodus with simple setae on superior margin.

Pereopod 7: Length subequal to P6. Similar to P6 except: with slender distally biserrate setae on superior distal angles of merus and carpus; posterior face of merus and carpus less setose.

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. Pleopods 3 and 4 each with four plumose coupling hooks.

Uropod: Peduncle medial production distally blunt or truncate, with seven long plumose setae confined to apex; peduncle ventral distal lateral corner with robust acute seta in lateral setal row. Endopod apex triangular or subacute, with large apical robust seta, distal margin with 3–4 slightly smaller robust setae and PMS. Exopod shorter than endopod, but reaching beyond endopodal notch, narrow and rounded, curved medially; apex with one large robust seta, distal lateral margin with small robust seta.

Pleotelson: Posterior margin broadly convex, posteromedial region truncated or emarginate, with PMS; flattened or emarginate region flanked on each side by two large robust setae set in distinct marginal scallops.

Sexual dimorphism. Males and females similar. Males with appendix masculina of relatively constant width, narrow, tapering evenly to slightly curved apex, extending beyond distal margins of endopod and exopod.

Variation. One of the distinctive characters of this species is the truncated or emarginate posterior margin of the pleotelson. However, the degree of emargination varies such that in some individuals it is only barely truncated. If viewed in the dorsal aspect, these specimens have a slight longitudinal depression in the posteromedial pleotelson, distinguishing them from specimens of P. impostor . On larger animals the distal emargination of the pleotelson becomes distinct. In all cases, four robust setae are present on the pleotelson distal margin and are large compared with those of other species. The interocular furrow varies from almost absent to complete. Most specimens have two coupling hooks on both maxilliped endites; however, larger animals may have three coupling hooks on each.

Size range. Adults: 9.5–32 mm.

Remarks. Politolana concharum is easily distinguished from other Politolana by the triangular shape of the eyes and the narrow uropod exopod (more than 5Ⅹ longer than wide). Politolana polita has a similar uropod exopod, but can be easily recognized by its reduced frontal lamina and short antennae, which only reach the posterior margin of the cephalon.

A recent study by Rachlin & Warkentine (1997) evaluated the population structure of P. concharum by examining specimens collected from Atlantic sturgeon gut contents. The area where the study was conducted supports four very similar species of Politolana , one of which was undescribed before now. The authors did not provide any definitive features by which they identified the specimens, but report to have used Smithsonian Institution specimens as vouchers. Our examination of Smithsonian Institution material shows a high percentage of Politolana material to be misidentified. However, some of the literature they report using for species identification has accurate figures of P. concharum in which key diagnostic features can be seen. Therefore it is possible (although not certain) that the animals were correctly identified. They report a sex ratio of 1:1.68 female:male among their samples. This skewed sex ratio is consistent with our observations. They observed a size range of 8–31 mm, close to the range we observed.

As with P. polita , Stimpson’s original description of this species was brief and lacked figures. Because of the inadequate description, and the subsequent loss of type material, there has been confusion regarding this species since its original description (see Remarks section for P. polita ). Polita concharum often co-occurs with P. polita and P. impostor , and museum specimens are frequently misidentified among these three species. Thus there is a need to define P. concharum objectively and we herein designate a neotype to do so, and to clarify the taxonomic status of this species.

Distribution. Along the Atlantic coast of North America from about 22°N to 44°N, generally at depths of 25– 90 m. While Stimpson described this species from Charleston, SC, the majority of P. concharum specimens have been collected from New England waters, especially in the regions of Cape Cod, Martha’s Vineyard and Georges Bank. In these areas P. concharum has been collected at depths of 0–121 m, but has been typically found between 25 and 90 m and has occasionally been collected together with P. polita and P. impostor . Politolana concharum records south of Cape Hatteras are rare, and many of these specimens were collected at significantly greater depths (183– 317 m) than is typical in the northern portion of the range, suggesting a trend of latitudinal or isothermal submergence in this species.

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 4. (A, B) Right pereopod 1 and right pereopod 4, respectively, showing orientation terminology used in the species descriptions and character list: sm, superior margin; im, inferior margin; pdm, posterior distal margin; adm, anterior distal margin; pf, posterior face; ida, inferior distal angle; sda, superior distal angle (produced into ‘meral lobe’ on pereopod 1). Pleon (C) showing terminology used to describe the different regions: e, epimeres; lsf, lateral setal fringe; vf, ventral flanges.

Figure 28. Politolana concharum female neotype: (A) dorsal aspect; (B) lateral aspect; (C) antenna; (D) pleon detail; (E) frontal lamina; (F) antennule. Politolana polita male: (G) penes.

Figure 29. Politolana concharum female neotype: (A) right maxilliped; (B) right mandible; (C) maxilla; (D) maxillule; P. concharum female (MCZ#6797a): (E) mandible molar process posterior surface.

Figure 30. Politolana concharum female neotype: (A–C) pereopods 1–3, respectively.

Figure 31. Politolana concharum female neotype: (A, B) pereopods 4 and 5, respectively.

Figure 32. Politolana concharum female neotype: (A, B) pereopods 6 and 7, respectively.

Figure 33. Politolana concharum female neotype: (A–E) pleopods 1–5, respectively. Politolana concharum male (MCZ#6797): (F) pleopod 2. Politolana concharum female (USNM 288411): (G) uropod.