Species Card of Copepod
Calanoida ( Order )
    Clausocalanoidea ( Superfamily )
        Aetideidae ( Family )
            Gaetanus ( Genus )
Gaetanus simplex  Brodsky, 1950   (F,M)
Syn.: Gaetanus intermedius Campbell, 1930 (p.178, figs.F); Brodsky, 1950 (1967) (p.165, figs.F); Park, 1973 (p.1597, figs.F,M); Coyle & al., 1990 (p.763); Hattori, 1991 (tab.1, Appendix); Razouls & al., 2000 (Appendix); Hernandez- Trujillo & Esqueda-Escarcega, 2002 (in Appendix); Park, W & al., 2004 (p.464, tab.1); Kosobokova & al., 2007 (p.929: Tab.7); Andronov, 2014 (p.36, fig.: A2);
Gaetanus campbellae Park, 1975 a (p.12, 13)
Gaetanus armiger : Davis, 1949 (p.28, figs.F)
Brodsky, 1950 (1967) (p.164, figs.F,M); Vervoort, 1963 b (p.129-130: Rem.); Vaupel-Klein, 1970 (p.13, figs.F,M); Morris, 1970 (p.2300, 2304, Rem.); Minoda, 1971 (p.24); Park, 1975 a (p.10); Bradford & Jillett, 1980 (p.48: Rem.); Markhaseva, 1996 (p.196, figs.F,M, Rem.)
Species Gaetanus simplex - Plate 1 of morphological figuresissued from : E.L. Markhaseva in Proc. Zool. Inst. RAN, St. Petersburg, 1996, 268. [p.199, Fig.156].
Female (from Kuril Trench); Male (idem). Ce: forehead (lateral).

Species Gaetanus simplex - Plate 2 of morphological figuresissued from J.C. von Vaupel-Klein in Zool. Verh. Leiden, 1970, 110. [p.14, Fig.3].
Female (from NE Pacific: Station \"P\"); a-c, dorsal view of the last thoracic somite and urosome of three specimens; d-f, forehead (right lateral view of three specimens)

Species Gaetanus simplex - Plate 3 of morphological figuresIssued from : J.C. von Vaupel-Klein in Zool. Verh. Leiden, 1970, 110. [p.16, Fig.4, a-e];
Male: a, last thoracic segment and urosome (dorsal, specimen 1); b, idem (specimen 2); c, serrated caudal margin of the 2nd thoracic somite; d, forehead (specimen 1, lateral view); e, idem (specimen 2).
Nota: The caudal margins of the urosomal somites, with exception of the genital somite, are minutely serrated; In the female the caudal margins of the genital, as well as of the 2nd and 3rd urosomal somites, are serrated, but much less distinctly.

Species Gaetanus simplex - Plate 4 of morphological figuresIssued from : K.A. Brodskii in Calanoida of the Far Eastern Seas and Polar Basin of the USSR. Opred. Fauna SSSR, 1950, 35 (Israel Program for Scientific Translations, Jerusalem, 1967) [p.165, Fig.77].
Female (from NW Pacif.): habitus (dorsal and lateral right side); forehead (lateral); urosome (ventral); S1, P1; S5B1, distal inner margin of basipodal segment 1 of P4.

male: S2, P5.

Species Gaetanus simplex - Plate 5 of morphological figuresissued from : T. Park in J. Fish. Res. Board Can., 1973, 30. [p.1598, Fig.1]. As Gaetanus intermedius.
Female (from Washington Sound): A-B, habitus (dorsal and lateral, respectively); C, forehead (lateral); D, rostrum); E, A1; F, A2; G, Md; H, Mx1; I, Mx2.
Nota: Proportional lengths of prosome and urosome about 81:19. Forehead with a small cephalic spine. Frontal eminence bearing suprafrontal sensilla small. Rostrum simple, with a minutely bifurcated tip. 1st metasomal segment and cephalosome fused, Th4 and Th5 fused. Posterolateral corner of metasome with a spiniform process, extending a little beyond middle of genital segment; A1 reaching to about distal end of genital segment. 2nd exopodal segment of A2 with a large internal process carrying 1 seta. basis of Md with 2 subequal setae. Mx1 with 14 setae on 1st, 4 each on 2nd and 3rd inner lobes, 5 on basis; 14 on endopod; 11 on exopod; 9 on outer lobe. Coxa of Mxp without a lamelliform outgrowth.

Species Gaetanus simplex - Plate 6 of morphological figuresGaetanus simplex female:
1 - Anterior part of cephalon with frontal spine.
2 - Exopodal segment 1 of A2 without seta; exopodal segment 2 with 2 setae (1 medial situated and 1 distal). 2nd internal lobe of Mx1 with 4 setae. Exopod of P1 always with 2 external spines.
3 - Mxp protopodite without lateral plate.
4 - Exopod of P1 2-segmented, or indistinctly 3-segmented.

Species Gaetanus simplex - Plate 7 of morphological figuresGaetanus simplex male:
1 - Cephalon with frontal spine.
2 - Exopodal segment 3 of left P5 prolonged, stylet-like, never bilobated. It is always longer than exopodal segment 2.
3 - Frontal spine is in anterior part of cephalon dorsally (lateral view), well visible.
4 - Spines on last thoracic segment long, longer than half length of genital segment.

Species Gaetanus simplex - Plate 8 of morphological figuresIssued from : V.N. Andronov in Russian Acad. Sci. P.P. Shirshov Inst. Oceanol. Atlantic Branch, Kaliningrad, 2014. [p.36, Fig.9, 5]. As Gaetanus intermedius after Park, 1973.
2, distal segment of exopod of A2.

Compl. Ref.:
Björnberg, 1973 (p.324, 386); Peterson & Miller, 1976 (p.14, Table 1, 3, abundance vs interannual variations); Deevey & Brooks, 1977 (p.256, tab.2, Station "S"); Peterson & Miller, 1977 (p.717, Table 1, seasonal occurrence); Hernandez-Trujillo, 1991 (1993) (tab.I); Bragina, 1999 (p.195); Yamaguchi & al., 2002 (p.1007, tab.1); Yamaguchi & al., 2004 (p.479, tab.2); Sedova & Grigoriev, 2005 (p.112); Gaard & al., 2008 (p.59, Table 1, N Mid-Atlantic Ridge); Galbraith, 2009 (pers. comm.); Homma & Yamaguchi, 2010 (p.965, Table 2); Homma & al., 2011 (p.29, Table 2, 4, 5, abundance, feeding pattern: suspension feeders); Abe & al., 2012 (p.100, temporal & vertical changes, gut content); Takenaka & al., 2012 (p.1669, Table 1, bioluminescence assay); Ohashi & al., 2013 (p.44, Table 1, Rem.); Coyle & al., 2014 (p.97, table 3)
NZ: 7

Distribution map of Gaetanus simplex by geographical zones
off Bermuda: Station "S" (32°10'N, 64°30'W) (in Deevey & Brooks, 1977), off S Iceland, Japan Sea, Japan (off Sanriku, off E Hokkaido), Station Knot, Okhotsk Sea, Kuril-Kamchatka, off SE Kuril Is., S Aleutian Is., S Bering Sea, S Aleutian Basin, Aleutian Trench, station "P", G. of Alaska (Auke Bay, Icy Strait), Pacif. (central sub-Arct.), British Columbia, Strait of Georgia, Washington Sound, Oregon (off newport), W Baja California, S Peru (in Björnberg, 1973).

Type locality: Pacific (NW part).
N: 30
(22) F: 3,2; M: 3,1; (37) F: 3,5-3,2; M: 3,1-2,65; (92) F: 3,47-3,15; (205) F: 3,5; M: 3,4; (208) F: 3,64-3,5; M: 3,55; {F: 3,15-3,64; M: 2,65-3,55}
Rem.: epi-abyssopelagic. Sargasso Sea: 500-1000 m (Deevey & Brooks, 1977, station "S");
The indication of this species in Antarctica by Hopkins (1985, p. 167) and Hopkins & Torres (1988, p.82, tab.2) in the Weddell Sea is probably a confusion with Gaidius intermedius Wolfenden,1905 = Gaetanus brevispinus (Sars,1900), as probably in Rau & al., 1991 (p.1, Fig.1);
See remark in Gaetanus armiger.
After Morris (1970, p.2304) this species is very similar to G. armiger Giesbrecht, 1888, and Vervoort (1963) suggested that the two species are synonymous. G. armiger typically has the exopod of P1 trimerous and A1 that reach the middle of the urosome. G. simplex has bimerous exopod of P1 and A1 do not extend past the prosome.
According to Morris it appears that G. simplex inhabits the cold waters north of the subarctic boundary, and the closely related G. armiger occurs in the warmer waters to the south.
Last update : 15/02/2019
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Razouls C., Desreumaux N., Kouwenberg J. and de Bovée F., 2005-2021. - Biodiversity of Marine Planktonic Copepods (morphology, geographical distribution and biological data). Sorbonne University, CNRS. Available at http://copepodes.obs-banyuls.fr/en [Accessed February 24, 2021]

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