--------------~--~---.~~---·-~-----4.3 Thysanoessa gregaria Sars, 1883
Thysanoessa gregaria Sars, 1883: p. 26 - Sars,
1885: p. 120, pl. 21 figs. 8-17, pl. 22 - Hansen,
1905a: p. 25 - Hansen, 1905b: p. 28 - Holt and
Tattersall, 1905: p. 115- Zimmer, 1909: p. 20, figs.
32-34- Hansen, 1911: pp. 43, 44, fig. 15- Hansen, 1913: p. 37, pl. 6 fig. la-b- Zimmer, 1914: p.
430- Hansen, 1915: p. 101- Zimmer, 1915: p. 182
- Tattersall, 1924: pp. 27, 28- Tattersall, 1925: p.
9- Tattersall, 1926: p. 22- Tattersall, 1927: p. 22
- Illig, 1930: p. 526- Rustad, 1930: pp. 34, 35, fig.
19- Ruud, 1936: pp. 37-39, fig. 13 - Dakin and
Colefax, 1940: pp. 140, 141, fig. 232, pl. 2 fig. 9Sheard, 1953: p. 17 et seq., fig. 3, tabs. 2, 6, 8, 9 -
Banner, 1954: p. 220, fig. 16a-b- Boden, 1955: p.
344 - Boden et al., 1955: pp. 359-361, fig. 38a-d
- Brinton, 1962b: pp. 146-148, figs. 57,58- Ponomareva, 1963: p. 26 et seq., fig. 9- Sheard, 1965:
p. 240 - Nemoto, 1966: p. 114 et seq., fig. 2 -
Mauchline and Fischer, 1969: pp. 82, 83, fig. 27Mauchline, 197la: p. 7, fig. 9a-d - Mauchline,
197lb: p. 12, fig. IOa-b- Ramirez, 1971: pp. 399,
401, pl. 4 fig. 2, pl. 5 fig. 4, pl. 7 fig. 2, pl. 9- Talbot, 1974: p. 126- Antezana et al, 1976: p. 56, figs.
l-4a- Antezana and Brinton, 1981: p. 689, figs.
231-233.
Body length -
females: 15.2-15.4 mm (2 specimens)
males: 13.5-13.6 mm (2 specimens)
Description
Carapace bearing lateral denticle behind midpoint of lower margin; denticle may be missing
at times (Nemoto 1966). Rostrum long and rather oblong. Dorsal keel with sharp margin extending over rostrum, frontal plate and gastric
region. Eyes very large and transversally strangled in 2 lobes. Upper lobe smaller than lower
one. The difference in size is remarkably greater
in females. Basal segment of antennular peduncle longer than the sum of the following 2 segments. Flagella are extremely short. Antennal
scale reaching about midpoint of 3rd segment of
antennular peduncle. 2nd endopodite considerably elongated. Setae from carpus and propodus
of 2nd - 4th endopodites as long or longer than
those of dactylus. Dorsal keels or epimeral
spines present on every abdominal segment;
spine on 6th segment much smaller than others.
Preanal spine showing sexual dimorphism. In females, it is profusely denticulated and in males it
is usually unarmed or exceptionally provided
with scarce and minute denticles (Nemoto 1966).
Terminal process of petasma broad at base,
curved and narrow at middle, and expanded distally to a broad, truncated, rounded and finely
serrated edge. Proxima! process longer and more
slender than terminal process, ending in a short
and outwardly curved denticle and in a triangular expansion with serrated distal edge. Spiniform process small, frail and moderately curved.
Lateral process somewhat shorter than proxima!
process, more robust at base and slender and
slightly curved at end. Thelycum, only formed
by coxal plates, anteriorly resembles a longitudinal section of a funnel and posteriorly forms 2
cavities for the spermatophores ( Costanzo and
Guglielmo 197 6b).
Remarks
T. gregaria closely resembles the deep-water
dweller T. parva. Clear diagnostic differences between the two species include the petasma and
setae from the lst to the 3rd thoracic endopodites. Identification of the species may be difficult for juvenile and larval stages, which be-
Thysanoessa gregaria Sars, 1883: p. 26 - Sars,
1885: p. 120, pl. 21 figs. 8-17, pl. 22 - Hansen,
1905a: p. 25 - Hansen, 1905b: p. 28 - Holt and
Tattersall, 1905: p. 115- Zimmer, 1909: p. 20, figs.
32-34- Hansen, 1911: pp. 43, 44, fig. 15- Hansen, 1913: p. 37, pl. 6 fig. la-b- Zimmer, 1914: p.
430- Hansen, 1915: p. 101- Zimmer, 1915: p. 182
- Tattersall, 1924: pp. 27, 28- Tattersall, 1925: p.
9- Tattersall, 1926: p. 22- Tattersall, 1927: p. 22
- Illig, 1930: p. 526- Rustad, 1930: pp. 34, 35, fig.
19- Ruud, 1936: pp. 37-39, fig. 13 - Dakin and
Colefax, 1940: pp. 140, 141, fig. 232, pl. 2 fig. 9Sheard, 1953: p. 17 et seq., fig. 3, tabs. 2, 6, 8, 9 -
Banner, 1954: p. 220, fig. 16a-b- Boden, 1955: p.
344 - Boden et al., 1955: pp. 359-361, fig. 38a-d
- Brinton, 1962b: pp. 146-148, figs. 57,58- Ponomareva, 1963: p. 26 et seq., fig. 9- Sheard, 1965:
p. 240 - Nemoto, 1966: p. 114 et seq., fig. 2 -
Mauchline and Fischer, 1969: pp. 82, 83, fig. 27Mauchline, 197la: p. 7, fig. 9a-d - Mauchline,
197lb: p. 12, fig. IOa-b- Ramirez, 1971: pp. 399,
401, pl. 4 fig. 2, pl. 5 fig. 4, pl. 7 fig. 2, pl. 9- Talbot, 1974: p. 126- Antezana et al, 1976: p. 56, figs.
l-4a- Antezana and Brinton, 1981: p. 689, figs.
231-233.
Body length -
females: 15.2-15.4 mm (2 specimens)
males: 13.5-13.6 mm (2 specimens)
Description
Carapace bearing lateral denticle behind midpoint of lower margin; denticle may be missing
at times (Nemoto 1966). Rostrum long and rather oblong. Dorsal keel with sharp margin extending over rostrum, frontal plate and gastric
region. Eyes very large and transversally strangled in 2 lobes. Upper lobe smaller than lower
one. The difference in size is remarkably greater
in females. Basal segment of antennular peduncle longer than the sum of the following 2 segments. Flagella are extremely short. Antennal
scale reaching about midpoint of 3rd segment of
antennular peduncle. 2nd endopodite considerably elongated. Setae from carpus and propodus
of 2nd - 4th endopodites as long or longer than
those of dactylus. Dorsal keels or epimeral
spines present on every abdominal segment;
spine on 6th segment much smaller than others.
Preanal spine showing sexual dimorphism. In females, it is profusely denticulated and in males it
is usually unarmed or exceptionally provided
with scarce and minute denticles (Nemoto 1966).
Terminal process of petasma broad at base,
curved and narrow at middle, and expanded distally to a broad, truncated, rounded and finely
serrated edge. Proxima! process longer and more
slender than terminal process, ending in a short
and outwardly curved denticle and in a triangular expansion with serrated distal edge. Spiniform process small, frail and moderately curved.
Lateral process somewhat shorter than proxima!
process, more robust at base and slender and
slightly curved at end. Thelycum, only formed
by coxal plates, anteriorly resembles a longitudinal section of a funnel and posteriorly forms 2
cavities for the spermatophores ( Costanzo and
Guglielmo 197 6b).
Remarks
T. gregaria closely resembles the deep-water
dweller T. parva. Clear diagnostic differences between the two species include the petasma and
setae from the lst to the 3rd thoracic endopodites. Identification of the species may be difficult for juvenile and larval stages, which be-