Politolana Bruce, 1981

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 : 64-71

Politolana Bruce, 1981 .

Synonymy. Bruce (1981a): 958–959, Figs 1 (j), 1(k), 2(g), 2(h), 3(g), 3(h), 4(d), 5(g,h); Kensley & Schotte (1989): 140–143, Figs 63, 64; Wetzer et al. (1987): 1–11.

Type species. Aega polita Stimpson (1853) (by original designation).

Diagnosis. Long and cylindrical, 3–6.5Ⅹ longer than wide, with unornamented and highly polished cuticle. Frontal lamina narrow, 4–5Ⅹ longer than wide, greatly reduced in one species ( P. polita ). Antennules short, just reaching eyes. Antenna peduncle articles 3–5 subequal or progressively longer. Mandible molar process with submarginal row of lightly plumose setae on dorsal surface. Penes long (relative to most other genera in the family), slightly flattened, not fused basally. Pleonites 2–4 with fringe of fine biplumose setae along lateral margin of epimeres; pleonites with produced ventral flanges. Pereopods 1–3 robust and ambulatory, with superior distal angles of merus and carpus moderately or greatly produced; highly setose. Dactyl with small blunt secondary unguis. Pereopods 4–7 strongly flattened. Pereopod 7 with merus and carpus distally expanded, bearing dense clusters of setae. Pleopod 1 peduncle subquadrate, or with length slightly less than width, wider than long in P. eximia ; pleopod 1 endopod width less than exopod width. PMS present on all pleopod rami except endopod of pleopod 5. Uropod peduncle medial margin produced distally; lateral margin with setal fringe; uropod endopod of adults with notch in distolateral margin, notch lacking PMS but housing a small palmate seta.

Description. Body 3–6.5Ⅹ longer than wide, generally of long cylindrical form with lateral margins subparallel in dorsal view; cuticle highly polished, without spines, tubercles or setae; with or without scattered chromatophores on pereon and pleon.

Cephalon: Cuticle polished or lightly textured, sometimes minutely punctate; wider than long, laterally enclosed to eyes by pereonite 1; anterior margin medially concave, convex or straight; with or without distinct rostral point; with cuticle of frontal margin raised into thickened ridge, lateral margins reaching or dividing eyes. Interocular furrow present, not always complete. Eyes present or reduced to remnant ommatidia; cuticle overlying eyes typically without facets or with slight facets marking ommatidia; eyes usually darkly pigmented. Frontal lamina narrow, typically 4–5Ⅹ longer than wide, or highly reduced ( Figs 5 and 6D ); not fused to rostrum; with or without raised margins; posterior margin abutting clypeus, not projecting. Clypeus not projecting; subtriangular, width greater than length; with or without raised lateral margins; curved around lateral margins of labrum. Labrum wider than long, posterior margin slightly concave.

Antennule: Short, usually reaching eyes. Peduncle of four articles: articles 1 and 2 short, article 3 longest; article 4 minute with one or few anterolateral setae; article 2 posterior distal angle usually bearing short palmate setae. Flagellum length subequal to peduncle length, of 8–15 articles, each with numerous aesthetascs; first flagellar article longest.

Antenna: Peduncle of five articles, articles 1 and 2 shortest, wider than long, articles 3–5 subequal or progressively longer; posterior distal margins of peduncle articles 4 and 5 with or without long stiff simple setae; flagellum of 10–22 articles, with clusters of short fine setae on distal angles.

Mandible: Incisor teeth of left mandible less robust than on right mandible. Molar process and setal row well developed; setal row with about 12–16 robust setae; molar process with short spines along entire anterior margin; with submarginal row of lightly plumose setae on dorsal surface; molar process surface typically covered with short fine setae. Palp article 2 longest, with dense row of simple and serrate setae; article 3 shortest, narrowing distally, with simple and slender serrate setae.

Maxillule: Lateral lobe with minute bifid setae along medial margin; gnathal surface with approximately 11 heavily sclerotized robust setae, several anterior ones with notched surface. Medial lobe with three giant circumplumose setae and smaller robust plumose seta between two proximal-most giant setae.

Maxilla: Middle and lateral lobes free and articulating, with long simple and lightly plumose setae; medial lobe with long plumose setae.

Maxilliped: Endite with robust circumplumose setae; with 1–3 coupling hooks, typically two on each endite. Palp of five articles, lateral and medial margins with simple setae, medial margins of distal articles also with serrate setae.

Pereon: Pereonites with dorsal medial pore pair, usually set in small round depression in textured cuticle ( Fig. 6C ). Pereonite 1 anterolaterally produced and encompassing head, with impression along lateral margin; lateral margins of pereonites 4–7 with small medial excision. Coxae not forming sternal plates; coxae 2 and 3 posteriorly rounded, not extending past posterior margins of respective pereonites; coxae 4–7 with posterior margins increasingly acute and extended, with or without oblique impressions ( Fig. 6A,B ).

Pleon: Of five free segments, posterolateral angles of pleonite 5 covered by pleonite 4, or slightly visible; cuticle often more textured than pereon; pleonite epimeres laterally and posteriorly produced to varying degrees; pleonites 2–4 with fringe of fine biplumose setae along lateral margin of epimeres ( Fig. 7 ); pleonites with produced ventral flanges.

Pleotelson: Length usually subequal to width, surface without setae, tubercles, pits or ridges; posterior margin with PMS, with or without robust setae, without spines.

Pereopods 1–3: Ambulatory, robust, highly setose. Basis with long simple setae on distal inferior angle and in submarginal row extending proximally from superior distal angle; superior margin with at least a few palmate setae ( Fig. 8C ). Ischium with 1–3 oblique rows of simple setae on posterior face; inferior margin with long simple setae; superior distal angle produced as scoop-shaped lobe with long simple marginal setae, degree of production varies. Merus superior distal angle moderately to greatly produced, with giant robust apical setae and marginal row of long simple or robust setae; inferior margin of merus and carpus setose. Propodus with row of simple setae on superior margin. Dactyl with small, blunt secondary ungui. Pereopod 1 propodus with simple seta inserted on midanterior face ( Fig. 9 ).

Pereopods 4–7: Longer and more slender than P1–P3, flattened on anterior-posterior plane. Posterior face of merus and carpus with numerous short robust setae ( Fig. 8A ). Pereopod 7 with distal angles of merus and carpus expanded, bearing dense clusters of setae; P7 propodus shorter than P6 propodus.

Pleopods: Pleopod 1 peduncle subquadrate, or with length only slightly less than width (except P. eximia ); endopod width less than exopod width, PMS on distal margin only; exopod with PMS on distal and lateral margins, medial margin bare. Pleopods 2–4 peduncle wider than long; endopod width less than exopod width, with PMS on distal margin, medial and lateral margins bare (males with PMS on medial margin of pleopod 2); exopod with PMS on entire margin or with medial margin bare. Appendix masculina arising subbasally on endopod of pleopod 2, reaching to or beyond distal margin of exopod; narrow and evenly tapering or lanceolate in form. Pleopod 5 with reduced peduncle, without coupling hooks; endopod with large proximomedial lobe, without PMS; exopod large, with PMS on entire margin.

Uropods: Peduncle with lateral setal fringe extending onto ventral distal margin; medial margin produced distally. Endopod of adults with notch in distolateral margin, shallow or deeply excised, usually housing short palmate seta, with short robust seta lateral to notch; endopod with PMS except in region of medial notch, shape and additional setation varies; with palmate setae on proximal dorsal surface. Exopod with PMS; shape and additional setation varies.

Remarks. The lateral setal fringe on the pleon is a synapomorphic feature unique to Politolana sensu stricto and is in itself diagnostic. This setation pattern has been figured and mentioned by some authors although its potential as a diagnostic feature of the genus had not been recognized. While some other species of Cirolanidae exhibit setation on one or more pleonal segments, these conditions are not homologueous with the lateral setal fringe of Politolana . The other setation occurs on a different area of the epimere (such as the ventral margin), is not biplumose and/or does not occur as a continuous fringe extending through the fourth pleonite. Politolana can also be identified by the unique combination of characters given in the diagnosis. Among these additional characters, the excision or notch in the distolateral margin of the uropod endopod is quite distinct in adult Politolana specimens, but less developed in juveniles. While the notch is less excised in P. polita and P. micropthalma , the uropod setation pattern is identical, with PMS present proximal and distal to the notch but absent in the region of the excision, and with a palmate seta set within the notch. This notch and associated setation pattern are present in all Politolana species , but are not unique to the genus and also occur in at least some species of Orphelana and Natatolana . The presence of small secondary ungui and the varying lengths of the antennal peduncle articles disagree with the diagnosis given for subfamily Conilerinae in which Politolana was included ( Kensley & Schotte, 1989).

The phylogenetic analysis, discussed in the previous section, revealed three species as not belonging to the clade containing the rest of the Politolana species. These outlying species are not described here, but are included in the key for the sake of completeness. Couplets that distinguish phylogenetic clades are noted within the key. Brusca & Wilson (1991) suggested that the minute fourth article of the antennule might not be peduncular, but on the basis of its setation pattern we herein regard it as part of the peduncle.

Species included in Politolana sensu stricto:

Politolana concharum ( Stimpson, 1853) . North-west Atlantic

Politolana eximia ( Hansen, 1890) . South-west Atlantic

Politolana haneyi n.sp. Gulf of Mexico and Gulf of California

Politolana impostor n.sp. North-west Atlantic

Politolana impressa ( Harger, 1883) . North-west Atlantic, Gulf of Mexico

Politolana micropthalma ( Hoek, 1882) . North-east Atlantic, Barents Sea

Politolana polita ( Stimpson, 1853) . North-west Atlantic

Politolana tricarinata Riseman et al., 2001 . Southwest Atlantic

Politolana wickstenae Wetzer et al., 1987 . Gulf of Mexico

Species excluded from Politolana sensu stricto:

Politolana crosnieri Bruce, 1996 . New Caledonia

Politolana dasyprion Bruce, 1991 . Bass Strait, Australia

Politolana obtusispina ( Kensley, 1975) . Still Bay, South Africa

Key to the species of Politolana

1. Frontal lamina wide and pentagonal; without lateral fringe of biplumose setae on the pleonite epimeres, but may have simple setae on ventral margins of epimeres, or setae confined to the third pleonite (non- Politolana sensu stricto)........... 2

— Frontal lamina narrow and blade-like (length about 4–5 Ⅹ width), or highly reduced; with lateral fringe of biplumose setae on the pleonite epimeres ( Politolana sensu stricto)..................... 4

2. Antennule flagellum longer than peduncle, reaching fifth pereonite; ventral margins of coxal plates and pleonite epimeres with short stiff simple setae; antennule peduncle article 2 length 2 Ⅹ width .. P. crosnieri

— Antennule flagellum shorter than, or subequal to peduncle length, usually reaching eyes; ventral margins of coxal plates and pleonite epimeres without short stiff simple setae; antennule peduncle article 2 length subequal to width.................... 3

3. Dorsal surface of pereonites with medial transverse cuticular ridge; with complete interocular furrow; pereopod dactyls with small blunt secondary ungui; uropod exopod flat and broad, length about 2 Ⅹ width, shorter than endopod; pleotelson posteriorly acute.............................. P. obtusispina

— Dorsal surface of pereonites without transverse cuticular ridges; without interocular furrow; pereopod dactyls with long narrow secondary ungui; uropod exopod narrow, length more than 5 Ⅹ width, subequal in length to endopod, curving laterally; pleotelson posterior margin narrow and emarginate............................... P. dasyprion

4. Pereopods 1–3 with superior distal angle of merus produced into a large recurved lobe reaching beyond midpoint of the propodus and equal to half length of article; coxae 4–6 with distinct or weak oblique impressions; cuticular ridge of cephalon frontal margin laterally reaching and dividing eyes (clade

3)...................................... 8

— Pereopods 1–3 with superior distal angle of merus produced into a small lobe just reaching base of the propodus and only 1/4 length of entire article; coxae

4–6 without oblique impressions; cuticular ridge of cephalon frontal margin laterally reaching, but not dividing eyes (clade 2)...................... 5

5. Frontal lamina greatly reduced to small ridge sitting deep between the antennae; ventral margin of eyes with fringe of simple setae; setation of antenna 2 peduncle dense, article 5with cluster of about 15 stiff simple setae......................... P. polita

— Frontal lamina narrow, length about 4–5 Ⅹ width; ventral margin of eyes without fringe of simple setae; antenna 2 peduncle article 5 with cluster of about six or fewer stiff simple setae.................... 6

6. Pleotelson posterior margin broadly convex and posteriorly emarginate (except in smallest individuals), with four robust setae (two on each side of emarginate region); uropod exopod length subequal to endopod length, narrow and rounded, with large apical seta...................... P. concharum

— Pleotelson posterior margin evenly convex, or narrowly truncate, without large robust setae; uropod exopod shorter than endopod, flattened with convex lateral margins............................ 7

7. Antennae 2 reaching middle of pereonite 2; pleon ventral epimeres with ventral posterior angle produced into a fine point; pleotelson posterior margin evenly convex; pereopod 4 propodus with sparse setae on superior margin............. P. impostor n.sp.

— Antennae 2 reaching middle of pereonite 1; pleon ventral epimeres with ventral posterior angle blunt or rounded; pleotelson posterior margin narrowly truncate; pereopod 4 propodus without setae on superior margin...................... P. micropthalma

8. Pereon-pleon articulation loose, with pereonite 7 overhanging and overlapping first and sometimes second pleonites; dorso-ventrally narrower than pereon such that epimeres are laterally flared and do not obscure the ventral flanges; uropod endopod apex broadly rounded or truncate, apex with or without cluster of long simple setae; pleotelson posterior margin slightly subacute or medially produced into an acute point............................... 9 — Pereon-pleon articulation tight, with first pleonite visible, not completely overlapped by pereonite 7; pleon dorso-ventrally vaulted similar pereon such that ventral flanges obscured by dorsal epimeres; uropod endopod apex subacute, with distomedial margin slightly concave, apex with cluster of long simple setae; pleotelson posterior margin evenly and narrowly convex................... P. haneyi n.sp.

9. Uropod exopod long, reaching beyond endopod, lateral margins relatively straight, tapering evenly; pereonite 1 anterolateral margin sinuate, forming acute anterior point; pleotelson posterior margin medially produced into acute point; P5–P7 with posterior distal margin of ischium bearing simple acute robust setae; pleopod 1 peduncle width nearly twice length; pleopod 1 endopod width greater than half the width of exopod..................... P. eximia

— Uropod exopod shorter than or subequal to endopod, with lateral margins slightly convex; pereonite 1 anterolateral margin straight, forming rounded or blunt anterior angle; P5–P7 with posterior distal margin of ischium bearing studded-biserrate setae; pleopod 1 peduncle subquadrate, or with length only slightly less than width; pleopod 1 endopod width about one half width of exopod............... 10

10. Cephalon with additional transverse cuticular ridge between frontal ridge and the interocular furrow; pereopod 7 coxae with distinct oblique impressions; antennae 2 not reaching second pereonite; frontal lamina narrow, usually spatulate (anteriorly widened); pleotelson posterior margin with PMS and four small robust setae; P4–P7 with posterior distal margin of ischium bearing studded-biserrate setae.............................. P. tricarinata

— Cephalon without transverse cuticular ridge between frontal ridge and the interocular furrow; pereopod 7 coxae with or without residual oblique impressions, never complete and distinct; antennae

2 reaching second pereonite; frontal lamina narrow with slight hourglass shape or evenly wide; pleotelson posterior margin with PMS, with or without minute robust setae; studded-biserrate setae absent on posterior distal margin of P4 ischium, present on ischia of P5–P7..................................11

11. Eyes present, darkly pigmented P. impressa

— Eyes absent................... P. wickstenae

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 5. Scanning electron micrographs showing frontal lamina morphologies: (A) P. impostor (USNM#34512, female); (B) P. wickstenae (LACM#3012, female); (C) P. impressa (GCRL#1354, male); (D) P. polita (USNM#191877).

Figure 6. Scanning electron micrographs showing coxae with and without lateral oblique impressions: (A) P. concharum without impressions (USNM#38224, male); (B) P. haneyi with impressions (USNM#288403); (C) frontal lamina of P. concharum (USNM#3871, male); (D) scanning electron micrograph of P. polita showing detail of the dorsal medial depression housing two minute pores with sensilla (MCZ#6944).

Figure 7. Scanning electron micrographs showing the synapomorphic fringe of biplumose setae present on the lateral margins of the pleon. (A) Politolana impressa (GCRL#1354, male); (B, D) P. haneyi (USNM#288403); (C) P. concharum (USNM#38224, male), showing a less dense setal row on pleonites 4 and 5 (the setae shown in this SEM are damaged, but remnants of the plumosity can be seen on the posterior-most setae of the fringe).

Figure 8. Scanning electron micrographs showing pereopod and cuticle morphology. Ventral aspect of P. concharum (USNM#3871, male) showing (A) pereopods 4–7 and (D) detail of cuticle on ventral mid-line; (B) P. polita pereopod 2 merus (MCZ#6944, male); (C) palmate setae on superior margin of pereopod 2 basis in P. concharum (USNM#38224, male).

Figure 9. Scanning electron micrographs of some different types of pereopod setae. Distally blunt, flattened and textured setae on inferior margin of merus of pereopods 1–3 in (A) P. polita (P2, USNM#191877) and (D) P. concharum: (P2, USNM#38224); (B) blunt robust setae on inferior margin of merus of pereopods 1–3 in P. impostor (P3, USNM#34512); (C) P. haneyi pereopod 6 showing studded-biserrate setae on posterior distal margin of ischium (USNM#288304).