Politolana eximia, (Hansen, 1890)

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 : 114-118

Redescription of P. eximia ( Hansen, 1890)

( Figs 39–43 )

Synonymy. Cirolana eximia: Hansen (1890) . Politolana eximia: Bruce (1981a) : 159; Riseman et al. 2000.

Type material. Male lectotype, female paralectotype, herein designated from syntype series, ZMUC # CRU591 , Col. 25 May 1890.

Type locality. Brazil.

Additional material examined. Research Collection of A.M. Pires (Universidade de São Paulo): Brazil, 300–350 m, col. by A.M. Pires; 3 females (form a). Research Collection of A.M. Pires (Universidade de São Paulo): Brazil, 350–380 m, col. by A.M. Pires; 2 females (form a). Research Collection of A.M. Pires (Universidade de São Paulo): south-eastern Brazilian shelf, 30°S, 48°W, 50 m, col. by A. M. Pires: 1 male, 1 female (form a). NMB # MNRJ 3690 : North of Sant’Ana Island , 22°25'S, 40°43'W; 1 male (form a). Series of specimens from Uruguay, offshore from Punta del Diablo, from stomach contents of La Plata dolphin ( Pontoporia blainvillei ), col. by R.L. Brownell Jr. — USNM # 211081 : 25 May 1971; 1 female (form b). USNM # 211082 : 25 May 1971; 1 female (form a). USNM # 211083 : 18 March 1971; 2 females, 1 male, 1 damaged (form b). USNM # 243772 : Uruguay, off dolphin; 1 male (form b).

Diagnosis. Body typically broad, pereon loosely articulating with and overlapping pleon. Coxae 4–7 with distinct oblique impressions. Pereonite 1 anterolateral margins slightly sinuate, forming acute anterior point. Cephalon frontal margin medially concave without rostral point; lateral margins of raised frontal ridge dividing eyes. Antenna reaching middle of second pereonite. Eyes large, round and darkly pigmented. Pereopods 1–3 with ischium and merus superior distal angles greatly produced, meral lobe reaching midpoint of propodus; inferior margin of merus with row of broad subacute robust setae. Pereopod 7 superior distal angle of merus with dense slender plumose setae; carpus distal margin greatly expanded with width subequal to length. Appendix masculina broad and lanceolate. Uropod exopod longer than both endopod and pleotelson posterior margin, apex with cluster of long simple setae. Pleotelson posterior margin broadly convex, medially produced into small acute point.

Description of lectotype. Male, 21 mm long; body broad with length about 3.5 Ⅹ width. Pereon cuticle highly polished; cream colour in alcohol with small, scattered chromatophores on pereon, pleon and pleotelson.

Cephalon: Minutely punctate, cuticle less polished than pereon due to fine texturing. Anterior margin medially concave without rostral point; lateral margins of raised frontal ridge dividing eyes. Interocular furrow complete. Eyes large, round, darkly pigmented. Frontal lamina narrow, length about 5.5 Ⅹ greatest width, with 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 several short palmate setae. Flagellum composed of 14 articles, each bearing 4–8 aesthetascs; first flagellar article longest, with length subequal to width; width of subsequent articles about twice length.

Antenna: Reaching middle of second pereonite. Peduncle articles 3–5 progressively longer; article 3 length subequal to width, widening distally; article 4 longer than wide, posterior distal angle bearing row of approximately 12 long stiff simple setae; article 5 approximately 3 Ⅹ longer than wide, with width about half basal width of article 4, posterior distal angle bearing about three long stiff simple setae and 2–3 short circumplumose setae. Flagellum with 23 articles.

Mandible: Molar process dorsal surface covered with fine setae; anterior margin with spines widely spaced, not touching at their bases; submarginal setal row dense, with approximately 20 long lightly plumose setae extending from proximal cluster.

Maxilliped: Endite with distal cluster of approximately eight robust circumplumose setae; right and left endites with two coupling hooks. Basis and palp articles 1 and 2 with submarginal cluster of simple setae on distomedial angle.

Pereon: Body highly vaulted. Medially pereonite 2 slightly shorter than pereonite 1, pereonites 3–7 subequal in length, 5 and 6 slightly longer. Pereonite 1 narrowing anteriorly, with impression along lateral margin, anterolateral margins sinuate, forming acute anterior point. Coxae 2 and 3 with impression parallel to lateral margin; coxae 4–7 broadening posteriorly, with distinct oblique impressions; coxae 4 posterior margins subquadrate, coxae 5 and 6 posterior margins rounded and slightly sinuate, forming small posteroventral points; coxae 7 largest, broader and longer than coxae 6, posterior angle blunt. Posteroventral angle of pereonite 7 extending beyond posterior margin of respective coxae.

Pleon: First two pleonites loosely overlapped by pereonite 7. Pleon cuticle less polished than pereon cuticle; dorso-ventrally narrower than pereon. Pleonites 1–4 with epimeres produced posteriorly and flared laterally; epimeres 2– 4 bearing dense lateral setal fringe which thickens posteriorly. Ventral flanges visible with ventral posterior angles rounded.

Pereopods 1–3: Ischium superior distal angle produced into large scoop-shaped lobe; posterior face of ischium with three oblique rows of simple setae; anterior face of ischium with two rows of transverse setae extending from inferior margin, middle of face with separate row of simple setae. Merus with superior distal angle produced into broad 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 blunt robust setae and row of adjacent short acute robust setae. Carpus of P2 and P3 subquadrate. Distal superior margin of propodus with short row of simple setae. Dactyl length subequal to propodal length.

Pereopods 4–6: Ischium superior margin with sparse simple setae. Posterior face of merus and carpus with robust setae arranged in transverse rows extending from inferior margin, progressively less setose posteriorly. Carpus longer than wide.

Pereopod 7: Shorter than P6. Ischium width less than meral width, superior distal angle of merus with dense long slender plumose setae, slender distally biserrate setae and short robust acute setae; merus and carpus with distal margins markedly expanded; carpus width subequal to length, at least 3Ⅹ wider than proximal propodal width. Propodus short, length subequal to carpal length.

Pleopods: Pleopod 1 peduncle width 1.5–2 Ⅹ length, with seven plumose coupling hooks; endopod width greater than half of exopod width. Pleopod 2 peduncle with six plumose coupling hooks; endopod greatest width only slightly less than exopod width; appendix masculina lanceolate: broadening from base, medial margin narrows abruptly at apex to fine extended point; reaching slightly beyond apex of exopod. Pleopod 3 with five plumose coupling hooks. Pleopod 4 with four plumose coupling hooks.

Uropods: Peduncle medial production distally acute, with 10–14 PMS on most of medial margin. Endopod distal margin broadly rounded, with PMS and 4–5 small robust setae of equal size; apex with two short simple setae, not much longer than adjacent PMS; exopod long, flat, with straight lateral margins, tapering evenly, reaching beyond both endopod and pleotelson posterior margin; apex with cluster of very long simple setae (abraded off lectotype), without robust setae on apex, medial or lateral margins.

Pleotelson: Posterior margin broadly convex with small medial point; with PMS, without robust setae (see variation section).

Variation. Politolana eximia appears to have two general body forms. One form, that of the type specimens (‘form a’), is broad and slightly more rounded, with length approximately 3.5 Ⅹ width. The second form (‘form b’) is more narrow and tubular, with the length ranging from 4.5–6.0 Ⅹ width. Aside from the difference in length and shape, which upon first inspection cause these two forms to appear quite different, they share all features diagnostic of the species. Other variation, not specifically associated with one form or the other, includes the following: antenna flagellum with 22–32 articles; pleotelson posterior margin usually with 4–6 very small robust setae that appear to be lacking in the type specimens, possibly due to age and damage. Uropod endopod with 4–8 setae on distal margin. Uropod exopod apex may have a very small robust seta in addition to cluster of long simple setae. The pleotelson apex usually has a distinct medial point; however, a few specimens exhibit this shape to a lesser degree.

In addition to the above variation, several very large (27–45 mm) female specimens have been collected from 300 to 380 m in southern Brazilian waters. These specimens differ slightly in the shape of the pleotelson apex, which is more subacute rather than produced into a small medial point, and which has small robust setae (so small as to be difficult to discern); the uropod exopod is of the same form, but is not quite as long; the eyes appear slightly less round, but are still large with many ommatidia; and pereonite 7 does not overlap more than the first pleonite. Aside from these subtle differences, the large females are identical to the smaller specimens in most features, and are clearly P. eximia , ‘form a’.

Sexual dimorphism. Male and female similar.

Size range. 15–45 mm.

Remarks. Hansen’s (1890) description (in Latin) and figures were relatively comprehensive and he identified most of the diagnostic features of this species. However, he did not figure most of the appendages or any of the mouth parts. Politolana eximia is distinctive and easily identified by its long uropod exopods that extend beyond both the uropod endopod and the pleotelson posterior margin. It can also be readily distinguished from the similar P. impressa by the prominent oblique impressions on the seventh coxae, which are absent or residual in P. impressa , and by the lack of studded, distally biserrate setae on the superior margins of P5–P7. Hansen’s original description of P. eximia did not figure most of the appendages, nor any of the mouth parts. In addition, this species has two distinct morphologies, and museum collections are rare (we were able to recover only 15 specimens, aside from Hansen’s original material). For these reasons, we designate and thoroughly illustrate a lectotype for P. eximia .

Distribution. Unfortunately, no detailed locality information was recorded for the type material of P. eximia , and it is known only that it is from the Brazilian coast. Of the seven lots we examined, five were from the gut contents of dolphin, which may have been collected at a distance from where the isopods were consumed. Given this lack of specific locality and depth information, we can provide only a rough distribution for P. eximia , inclusive of the dolphin collection localities. This area includes the south coast of Brazil to northern Argentina, from about 22°S – 35°S. Of the lots available, only three lots had the collection depth recorded. These depths range from 50 to 380 m, with the giant females representing the deepest records. Politolana eximia generally occurs at depths greater than P. tricacrinata , the only other southern hemisphere Politolana species.

Figures

Figure 39. Politolana eximia male lectotype: (A) dorsal aspect; (B) lateral aspect; (C) antenna; (D) antennule; (E) frontal lamina; (F) penes.

Figure 40. Politolana eximia male lectotype: (A) maxilla; (B) maxillule; (C) left uropod; P. eximia typically have long simple setae at apex of uropod exopod that have been abraded off the type specimen and are not figured here. (D) right mandible. Politolana eximia female paralectotype: (E) right maxilliped.

Figure 41. Politolana eximia male lectotype: (A–C) pereopods 1–3, respectively.

Figure 42. Politolana eximia male lectotype: (A, B) pereopods 4 and 5, respectively; (C, D) pleopods 1 and 2, respectively,

Figure 43. Politolana eximia male lectotype: (A) pereopod 6; (C–E) pleopods 3–5, respectively. Politolana eximia female paralectotype: (B) pereopod 7.