Politolana wickstenae, Wetzer et al., 1987

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 : 125-127

Redescription of P. wickstenae Wetzer et al., 1987

Type material examined. Series of specimens from Gulf of Mexico, col. by M.K. Wicksten, R/V Citation— LACM # 3008 : female holotype, 17 May 1985. LACM # 3009 : 28°22.89'N, 86°14'W, 488 m, 17 May 1985; 2 females, 1 gravid female (Paratypes). LACM # 3010 : May 1985; 2 females (Paratypes). LACM # 3011 : 28°22.89'N, 86°25.20'W, 500–600 m, June 1985; 4 females (Paratypes). LACM # 3012 : September 1986; 2 males, about 33 females (Paratypes). USNM # 235303 : 28°22'N, 86°25'W, 500–600 m, June 1986; 1 female (Paratype).

Type locality. Gulf of Mexico, 28°22.89'N, 86°14'W, 488 m.

Diagnosis. Body narrow and tubular, length 5–6 Ⅹ width. Pereonal segments loosely articulated, pereon loosely articulated with and overlapping pleon. Cephalon subquadrate, slightly wider than long. Eyes absent or with remnant pigmented ommatidia.

Description of paratype (LACM#3012). Female, 29 mm long; body narrow with length about 5–6 Ⅹ width. Pereonal segments loosely articulated; pereon cuticle highly polished; with scattered, darkly pigmented chromatophores on pereon, pleon and pleotelson.

Cephalon: subquadrate, slightly wider than long, lightly minutely punctate. Anterior margin medially concave or straight, without distinct rostral point, margins of raised frontal ridge extending laterally over region where eyes would be. Interocular furrow complete. Eyes absent or only with remnant pigmented ommatidia; cuticular ommatidial facets absent. Frontal lamina narrow, length about 3.1 Ⅹ greatest width, with slight hourglass shape, reaching middle of antennule peduncles. Frontal lamina and clypeus with lateral margins raised as thickened ridges.

Antennule: Peduncle article 2 posterior distal angle with 1–2 short palmate setae. Flagellum composed of 11 articles, each with 4–7 long aesthetascs; first flagellar article longest, with length subequal to width; width of subsequent articles about twice length. In dorsal aspect, antennule peduncles proximally separated with frontal lamina usually visible between them.

Antenna: Reaching middle of second pereonite; peduncle articles 3–5 progressively longer; article 3 length subequal to width, widening slightly distally; article 4 longer than wide, subquadrate, posterior distal angle bearing about three long stiff simple setae; article 5 approximately 2.5Ⅹ longer than wide, with width about half the basal width of article 4, posterior distal angle bearing one long stiff simple seta and about four short circumplumose setae. Flagellum composed of 22 articles.

Mandible: Molar process dorsal surface with fine setae, concentrated in distinct patch on distal posterior margin; anterior margin with spines widely spaced, not touching at their bases; molar process submarginal setal row with long lightly plumose setae extending from proximal cluster.

Maxilliped: Endite with distal cluster of approximately three robust circumplumose setae; right and left endites with two coupling hooks.

Pereon: Body long and narrow. Medially, pereonite 2 shorter than pereonite 1, pereonites 3–7 subequal in length, 5–7 slightly longer; in dorsal aspect pereonite 1 narrows slightly anteriorly, encompassing cephalon; with distinct impression along lateral margin, anterolateral margins straight forming blunt anterior angle. Coxae narrow; coxae 2 and 3 with impression parallel to lateral margin; coxae 4–6 narrow, with faint oblique impressions, impressions residual on coxae 6, posterior margins rounded forming blunt angles; coxae 7 extended past posterior margin of pereonite 7, posterior angle slightly acute, with or without residual oblique impressions, length subequal to length of coxae 6.

Pleon: First pleonite completely and loosely overlapped by pereonite 7; pleon cuticle less polished than pereon cuticle; dorso-ventrally narrower than pereon. Pleonites 1–4 with epimeres that are produced posteriorly and flared laterally; epimeres 2–4 bearing dense lateral setal fringe, 2 and 3 with faint notch in posterior margin. Ventral flanges visible, not hidden by dorsal epimeres, with ventral posterior angles rounded.

Pereopods 1–3: Ischium superior distal angle produced into large scoop-shaped lobe; posterior face of ischium with 2–3 oblique rows of simple setae. Merus with superior distal angle produced into large recurved lobe reaching midpoint of propodus, with one (P1) or two (P2 and P3) giant apical setae; inferior margin of merus with row of long acute robust setae and row of adjacent short acute robust setae. Ischial and meral lobes of pereopods 1–3 progressively less produced. Carpus of P3 subquadrate. Distal superior margin of propodus with short row of simple setae.

Pereopods 4–6: Ischium superior margin with sparse simple setae; distal margin of ischium with studdedbiserrate setae (absent on P4). Merus and carpus with robust setae arranged in transverse rows extending from inferior margin, progressively less setose on P5–P7. Carpus longer than wide. Pereopod 6 with distal angles of merus and carpus bearing long distally biserrate setae. Propodus without simple setae on superior margin; P6 propodus inferior margin with short acute distally biserrate setae and a robust studded-serrate seta on inferior distal angle.

Pereopod 7: Subequal in length to P6. Like P6 except: ischium width less than meral width; superior distal angle of merus with dense long slender plumose setae, long slender distally biserrate setae, and short acute robust setae; carpus distal margin expanded, about twice as wide as proximal propodal width.

Pleopods: Pleopod 1 peduncle subquadrate, or with length only slightly less than width, with six plumose 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 coupling hooks.

Uropod: Peduncle medial production distally acute, with seven long plumose setae. Endopod apex truncate, with 3–4 small robust setae, PMS, and apical cluster of short simple setae. Exopod shorter than endopod, not reaching endopodal notch, peltate: broad and flat, with lateral margins convex; apex, distal medial and lateral margins with small robust setae.

Pleotelson: Posterior margin narrowly convex or subacute, with PMS, without apparent robust setae.

Sexual dimorphism. Wetzer et al. (1987) remarked on the near absence of males in the collections of P. wickstenae and the small size of the only two males collected. They illustrate a long, narrow, evenly tapering appendix masculina, reaching slightly beyond the pleopod rami.

Variation. The absence of eyes in this species varies from no visible signs of ommatidia to the presence of a few darkly pigmented remnant ommatidia. The distal patch of setae on the mandible molar process is not always distinct. Setation is more dense in larger individuals.

Remarks. This species is so similar to P. impressa that we question its status as a distinct species. None of the diagnostic characters given by Wetzer et al. (1987) are unique to this species: the short ovate uropod exopod is identical to that of P. impressa , and a variation in the length of this ramus is seen in both species; the slender appendix masculina is typical of most Politolana species ; the compact coxae and the shape of the pleotelson margin are similar to those of P. impressa . The only differences that we observe between P. wickstenae and P. impressa are: (1) the near absence of pigmented ommatidia in the eyes; (2) the ‘loosely articulated’ nature of the pereonal segments in the former; and (3) the presence of simple setae along the entire distal margin of the maxillipedal palp (ventral face). All existing P. wickstenae specimens were collected on the same expedition and show poor preservation. Without these distinctions no reliable characters separate the two species other than length–width ratio, which has been seen to vary within P. impressa as well as within another species, P. eximia .

While we question the status of P. wickstenae as a distinct species, we cannot at this point rule out the possibility that those P. impressa specimens with a body form similar to P. wickstenae are a result of hybridization between these two species. We thus leave P. wickstenae with valid species status, using the absence of eyes and ‘loose’ nature of the pereonal segments as key diagnostic characters. Politolana wickstenae also differs subtly from P. impressa in the following ways: the coxae appear smaller in relation to the pereonites; the pereon overlaps pleon less markedly; the cephalon is longer in relation both to its width and to the length of the first pereonite; in dorsal aspect, the antennules are more distinctly separated and the frontal lamina is usually visible between them. However, within both species these additional characters show enough variation that they cannot be easily quantified or considered reliably diagnostic. Additional collections or molecular work will be necessary to determine the actual status of, and relationship between P. wickstenae and P. impressa .

Distribution. Known only from the Gulf of Mexico: 28°N, 86°W, at depths of 488– 600 m. Politolana wickstenae appears to be syntopic with P. impressa , collected from the same general localities and from the same depth range.