Politolana micropthalma, (Hoek, 1882)

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 : 111-114

publication ID	https://doi.org/ 10.1046/j.1096-3642.2002.00002.x
DOI	https://doi.org/10.5281/zenodo.14055835
persistent identifier	https://treatment.plazi.org/id/D54B2255-4129-8200-CFE2-FDA3FAE5FB1F
treatment provided by	Carolina
scientific name	Politolana micropthalma
status

Treatment

Redescription of P. micropthalma ( Hoek, 1882)

( Figs 34–38 View Figure 34 View Figure 35 View Figure 36 View Figure 37 View Figure 38 )

Synonymy. Cirolana cranchi: G.O. Sars (1872) (not seen). Cirolana micropthalma: Hoek (1882) : 28, pl. 2, Figs 13–17 View Figure 13 View Figure 14 View Figure 15 View Figure 16 View Figure 17 ; (G).O. Sars (1885); (1899): 71–72, pl. 30, Fig. 1 View Figure 1 ; Dollfus (1903): 9; Hansen (1905): 349–350; Jones (1979): 318–320, Fig. 1 View Figure 1 ; Kussakin (1979): 201–203, Figs 79, 80. Cirolana concharum: G.O. Sars (1885) (not seen). Politolana micropthalma: Bruce (1981a) : 959.

Type material. Hoek’s (1882) holotype was an immature male; col. 8 July 1879: deposition unknown. GoogleMaps

Type locality. 73°13.5'N, 30°42'E, 304 m.

Material examined. ZM # F15280 : Storeggen on western coast of Norway, 92 m; 1 female . ZM # F10220 : col. by Sars; permanent slide of appendages. USNM # 288409–288410 : North Sea, 56°24'N, 02°07'E, 82 m, col. by Shell U.K. Exploration & Production; 1 female, 1 juvenile GoogleMaps .

Diagnosis. Pereon and pleon convex and tightly articulated, all pleonites visible. All coxae without lateral or oblique impressions; coxae 6 and 7 subequal in length. First pereonite with distinct mid-lateral oblique impression. Cephalon anterior margin medially straight with minute medial point; lateral margins of frontal ridge reaching but not dividing eyes; interocular furrow incomplete medially. Eyes small, rounded triangles. Antennae short, reaching anterior region of first pereonite. Mandible molar process with spines on anterior margin touching at their bases. Pereopods 1–3 with superior distal angles of ischium and merus moderately produced; inferior margin of merus with row of robust subacute setae. Uropod endopod distal margin broadly subacute, with PMS and five small robust setae, without giant apical seta; notch on medial margin shallow, not excised. Exopod shorter than endopod flat and peltate. Pleotelson with narrow truncate distal margin, with PMS and four very small robust setae.

Description of female (ZM#F15280). Ten millimetres long; body broad, with length about 3.5 Ⅹ width. Pereon cuticle highly polished; cream colour in alcohol, without any apparent pigment or chromatophores on pereon and pleon.

Cephalon: Minutely punctate. Anterior margin medially straight with minute medial point; lateral margins of raised frontal ridge reaching, but not dividing eyes. Interocular furrow incomplete medially. Eyes small, rounded triangles, slighter wider dorsally than ventrally, lightly pigmented. Frontal lamina narrow, length about 4.5 Ⅹ greatest width, with lateral margins parallel, anteriorly rounded; frontal lamina and clypeus with lateral margins raised as thickened ridges.

Antennule: Peduncle cuticle with microscopic ovate macula; peduncle article 2 posterior distal angle with several short palmate setae. Flagellum composed of eight articles, each bearing 4–5 aesthetascs, some articles with additional cluster of short simple setae; first flagellar article longest, slightly wider than long, width of subsequent articles about 3Ⅹ length.

Antenna: Short, reaching anterior region of pereonite 1; peduncle articles 3–5 subequal in length; article 3 length subequal to width, widening distally; article 4 subquadrate, posterior distal angle bearing row of approximately seven long stiff simple setae; article 5 about 1.5Ⅹ longer than wide, posterior distal angle bearing about five long stiff simple setae; flagellum of 12 subquadrate articles.

Mandible: Molar process medial surface with fine setae; spines on anterior margin numerous, closely spaced, touching at their bases; submarginal setal row with long lightly plumose setae extending from proximal cluster.

Maxilliped: Endite with distal cluster of approximately 10 robust circumplumose setae; right and left endites with two coupling hooks. Palp article 1 with submarginal cluster of long simple setae on dorsal distolateral angle; articles 3–5 with distomedial angle weakly produced.

Pereon: Body highly vaulted. Medially, pereonite 1 longest, 2 and 3 slightly shorter than 4–6, 7 shortest; in dorsal aspect pereonite 1 narrows markedly anteriorly to encompass cephalon; with distinct impression curving to lateral margin and distinct mid-lateral oblique impression; anterolateral margins straight forming blunt anterior angles. All coxae without lateral or oblique impressions; coxae 4 posterior margin subquadrate; coxae 4–7 posterior margins oblique, progressively more extended posteriorly, coxae 6 and 7 subequal in length, with acute posterior angles, coxae 7 extended to pleonite 4.

Pleon: Pereonite 7 tightly overlapping only anterior portion 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 posteriorly obscured by dorsal epimeres, ventral posterior angles rounded.

Pereopods 1–3: Basis with 3–4 stout flexible circumplumose setae on proximal superior margin. Ischium only moderately produced into scoop-shaped lobe; posterior face of ischium with one submarginal and one oblique row of simple setae; inferior margin with long simple setae. Meral lobe short, just reaching base of propodus, with two giant apical setae; inferior margin of merus with row of robust subacute setae and adjacent row of short acute robust setae. Ischial and meral lobes of pereopods 1–3 equally produced. 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 without setae; P4 merus and carpus with robust setae in clusters on posterior face, arranged in transverse rows on P5–P7. Pereopod 4 carpus slightly longer than wide, lengthening on posterior pereopods. Propodus without simple setae on superior margin.

Pereopod 7: Similar to P6 except: longer, superior distal angle of merus with long slender plumose setae and short robust acute setae.

Pleopods: Pleopod 1 peduncle subquadrate, with six coupling hooks; endopod width about one-half of exopod width. Pleopod 2 peduncle with five plumose coupling hooks; endopod width less than exopod width. Pleopod 3 with five plumose coupling hooks. Pleopod 4 with four plumose coupling hooks.

Uropod: Peduncle medial production distally truncate, apex with 4 PMS. Endopod distal margin broadly subacute, with PMS and five small robust setae, without giant apical seta; notch on medial margin shallow, not excised. Exopod shorter than endopod, reaching endopodal notch; flat, peltate: lateral margins convex; apex with very small robust seta, medial and lateral margins without robust setae.

Pleotelson: Narrowing to truncate posterior margin, with PMS and four very small robust setae confined to narrow posterior margin.

Variation. Most of the variation observed (density of setation, pronunciation of cuticular sculpting, etc.) is likely due to size and age differences, as the three available specimens differ significantly in this regard. The largest female has the cephalon more encompassed by the first pereonite, and the cuticular ridges on the cephalon, first pereonite and lateral margins of the pereonites are more pronounced. In addition, the cephalon frontal margin is slightly more concave medially, the eyes are smaller in relation to the cephalon, and the cuticular ommatidial facets are absent. Maxilliped endites with 1–2 coupling hooks.

Sexual dimorphism. We examined only females. Hoek’s (1882) and Kussakin’s (1979) figures and descriptions of male specimens agree with our description of the female. Sars (1899) figures the appendix masculina as narrow, tapering evenly and extending beyond the distal margin of endopod.

Size range. Adults: 10–33 mm.

Remarks. The most recent treatment of this species ( Jones, 1979) provides a short review of the previous literature and the first description providing characters separating P. micropthalma from the similar west Atlantic species, P. concharum and P. impressa . While P. micropthalma was figured by Hoek (1882), Sars (1899), Kussakin (1979) and Jones (1979), many of the appendages have remained unfigured until now.

We have been unable to locate Hoek’s original specimen, an immature male, and no reference to this specimen has been made other than in the original description. This species appears to be rare with only seven specimens ever referred to in the literature. Of these seven, we have only been able to locate and examine the two specimens Jones described, and a single female Sars examined. Hoek noted in his original description that some specimens of P. micropthalma may have been recorded as Cirolana borealis prior to 1882.

Of the three specimens available to us, we chose to figure the small female that Sars had examined because the other two specimens are gravid or immature. It should be noted, however, that this specimen is the smallest recorded adult, much smaller than Hoek’s 23 mm type, and it was collected from less than 100 m, which is one of the shallower recorded depths for this species.

Distribution. Eastern Atlantic upper boreal species. Found off the Norwegian coast, from 56°24'N to 73°13'5'N and 02°07'E to 36°15'E, at depths of 82– 440 m. Politolana micropthalma is the only Politolana species found in the east Atlantic.