Heteromesus frigidus Hansen, 1916

Cunha, Marina R. & Wilson, George D. F., 2006, The North Atlantic genus Heteromesus (Crustacea: Isopoda: Asellota: Ischnomesidae), Zootaxa 1192 (1192), pp. 1-76 : 34-37

Heteromesus frigidus Hansen, 1916

( Figs 15–16)

Heteromesus frigidus Hansen 1916: 71–72 , pl. VI, figs 4a–t; Gurjanova 1932: 46, tabl. XVI, 57, 1933: 411, 1964: 259; Menzies 1962: 122; Wolff 1962: 73, 85, 216, 260; Svavarsson 1984: 35; Kussakin 1988: 478–480, figs. 391–392.

Material examined

Syntypes: 12 females, 2 males, 1 manca III male, 6 manca, Norwegian Sea , north of the Faeroes, 63°36’N, 7°30’W, 1895–1896, R / V Ingolf , stn 139, 1322 m (702 Danish fathoms) ( ZMUC CRU­9234 ) ; 1 female, 1 manca III female, 2 manca III males, 11 manca, several fragments, same locality, 63°22’N, 6°58’W, 1895–1896, R / V Ingolf , stn 141, 1279 m (679 Danish fathoms) ( ZMUC CRU­9235 ) ; 1 female, Norwegian Sea , East of Iceland, 66°23’N, 12°05’W, 1895–1896, R / V Ingolf , stn 101, 1012 m (537 Danish fathoms) ( ZMUC CRU­9236 ) . 1 female, 1 manca, same locality, 66°23’N, 10°26’W, 1895–1896, R / V Ingolf , stn 102, 1413 m (750 Danish fathoms) ( ZMUC CRU­6468 ) ; 1 female, same locality, 65°34’N, 7°31’W, 1895–1896, R / V Ingolf , stn 105, 1435 m (762 Danish fathoms) ( ZMUC CRU­3764 ) ; 5 females, 4 manca, 1 fragment (head), Norwegian Sea , North of Iceland, 67º40’N, 15º40’W, 1895–1896, R / V Ingolf , stn 124, 932 m (495 Danish fathoms) ( ZMUC CRU­9233 ) .

Remarks on type material. Numerous syntype specimens, mostly mancae and females and only two males in CRU­ 9234. Several females and mancae were intact but most were mutilated or fragmented specimens. The male illustrated here is lacking part of the left antenna and the right uropod. The other male lacked pleopods; these were possibly removed by Hansen for illustration. An intact female from the same sample ( CRU­ 9234) was selected for the illustration.

Diagnosis

Pereonite 1 in female with no median dorsal tubercles or spines; pereonite 5 in female length 2.2 width. Male with rook spines on peronites 1–4. Pereonite 5 in female length 2.2 width, in male length 4.4 width. Pleotelson posterolateral margin anterior to uropods without spines or tubercles. Antennula with 3 articles altogether. Pereopods II– VII bases denticulate, sometimes sharply toothed. Uropods in male longer than in female, length 0.60 pleotelson length.

Description

Body length in female 3.7 mm; heavy blunt tubercular granulation. Head in female length 0.30 width; dorsal cuticle tubercular granulation. Pereonite 1 in female width 0.25 total body length; with 1 pair of anterolateral simple spines, short to stout, length distinctly less than length of pereonite 1. Pereonite 4 in female length 0.65 width. Pereonite 5 in female length 0.30 total body length. Pleotelson in female length 1.4 width.

Antennula in female article 2 length 0.51 head width, with 3 elongate stiff ventromedial setae, distal tip produced distally beyond insertion of next article, distal article inserting subapically; article 3 terminal, squat, wider than long, aesthetascs absent. Antenna in female length 1.7 anterior body length; article 3 length 0.35 anterior body length, length 3.7 width; article 5 length 0.27 anterior body length; article 6 length 0.34 anterior body length; flagellum with 11–12 articles, flagellum length 0.31 total antenna length.

Labrum knobs present, distally truncate, denticulate.

Pereopod I carpus palm length near proximal region length, with 3 robust setae on palm distal to elongate seta; propodus ventral margin with 2 robust setae. Pereopods II– VII bases denticulate, sometimes sharply toothed.

Uropods in female length 0.35–0.4 length of pleotelson.

Male specific characters. Body length 3.6 mm. Head length 0.45 width. Pereonite 1 width 0.20 total body length; with median rook spine, 3–4 pairs of dorsal rook spines, 1 pair of anterolateral simple spines, short to stout, length distinctly less than pereonite 1 length. Pereonite 2 with median rook spine, 2 pairs of dorsal rook spines, 1 pair of lateral rook spines. Pereonite 3 with median rook spine, 3 pairs of dorsal rook spines. Pereonite 4 length 0.70 width; with 1 pair of dorsal rook spines, 1 pair of posterolateral rook spines. Pereonites1–4 with heavy granulations arranged in rosettes developing into stout rook spines. Pereonite 5 length 0.30 total body length. Pleotelson length 1.3 width. Antennula article 2 length 1.1 head width. Antenna article 3 length 0.50 anterior body length, length 4.5 width; article 5 length 0.38 anterior body length; article 6 length 0.48 anterior body length; flagellum with 10–11 articles. Pleopod I distal tip without lateral horns. Pleopod II protopod apex narrow, tapering; stylet thick and blunt, heavily calcified, extending beyond distal margin of protopod.

Distribution

Norwegian Sea, north of the Faeroes, east and north of Iceland, North Polar Sea, 539–2024 m ( Hansen 1916; Gurjanova 1964; Svavarsson 1984; Ólafsdóttir & Svavarsson 2002), epibenthic ( Svavarsson 1984; Ólafsdóttir & Svavarsson 2002).

Remarks

Heteromesus frigidus Hansen shows high sexual dimorphism, males having several rook spines (sets of 4–5 large tapering granulations or short spines arranged in the shape of a star or flower with one seta in the centre) on pereonites 1–4, uropods much longer than in females and juveniles and propodus of pereopods with 5–6 robust setae (3–4 in female). The material from Ingolf stations labelled as H. frigidus by Hansen is abundant and the specimens show some morphological variability. Among these, some manca III male specimens have developing spines (anterolateral on pereonites 1–3 and one additional lateral pair on pereonite 1); one female with oostegites (smaller than the other females) has 1 additional pair of lateral spines on pereonite 1 and one pair of anterolateral spines on pereonite 2.

This species is similar to H. granulatus , H. inaffectus and H. schmidti in having 3 antennular articles altogether, in having one pair of anterolateral spines only on pereonite 1 and by the tubercular granulation and inconspicuous ornamentation (few spines) of the body. The male differs from these species in having dorsal rows of rook spines on pereonites 1–4. The female differs from H. inaffectus and H. schmidti in having short uropods and from H. inaffectus and H. granulatus by the different proportion of pereonite 5.