The North Atlantic genus Heteromesus (Crustacea: Isopoda: Asellota: Ischnomesidae)
Author
Cunha, Marina R.
Author
Wilson, George D. F.
text
Zootaxa
2006
2006-05-04
1192
1192
1
76
journal article
11755334
D14EC3CD-E581-4263-81EF-656B7574C846
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.
FIGURE 15
.
Heteromesus frigidus
Hansen, 1916
. Syntype female, ZMUC CRU9234: habitus dorsal and lateral; antennula; pleotelson dorsal, lateral and ventral. Syntype male, ZMUC CRU 9234: habitus dorsal and lateral; detail on head cuticular structure and rook spines; antennula; anterolateral spine on pereonite 1; pleotelson dorsal and ventral. Scale bars: habitus 1.0mm; pleotelson 0.5mm.
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.
FIGURE 16
.
Heteromesus frigidus
Hansen, 1916
. Syntype female, ZMUC CRU9234: head ventral; maxilliped; pereopods I and IV. Syntype male: pereopod IV. Scale bar 0.5mm.
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.