Species Card of Copepod
Cyclopoida ( Order )
    Oithonidae ( Family )
        Oithona ( Genus )
Oithona fragilis  Nishida, 1979   (F)
Ref.:
Nishida, 1979 (p.89, Descr.F, figs.F); 1985 a (p.45, 136)
Species Oithona fragilis - Plate 1 of morphological figuresIssued from Nishida, 1979 [p.90, fig. 1].
Female: a, lateral view; b, dorsal view; c, rostrum, lateral view; d, mandible; e, first maxilla.

Nota:
- Prosome elongate, oval, 2.7 times as long as wide.
- Proportional lengths of prosomal segments 53.5 : 14 : 10.5 : 11 : 11.
- Head rounded (in dorsal view), in lateral view bent ventrally into sharply pointed rostrum with small swelling at the base of rostrum, anteriorly.
- Proportional lengths of urosomal segments including caudal ramus 13.5 : 28.5 : 14 : 13 : 16 : 15.
- Genital segment nearly rectangular and slightly swollen laterally toward anterior end, having greatest width between a pair of genital openings located at about 1/4 of length of genital segment from anterior margin.
- Caudal ramus with 1 stout dorsal seta, 1 stout and 3 finer apical setae, and 1 outer marginal seta located at 1/2 of length of inner margin of caudal ramus from distal end of outer margin.
- Md with 2 hook-like spines with spinules on distal end of 2nd basal segment, the longer one of which is 1.7 times as long as the shorter. Endopod with 4 setae, outermost one long and stout with setules. Exopode with 5 setae, outermost one very slender. 2nd basal segment with 1 minute seta in the middle of inner margin.
- Mx1 armed on distal end of 2nd basal segment with 1 short seta and 2 strong spines (the2 spines with spinules and about equal in length). Endopod swollen posteriorly, terminating in 1 seta (1.3 times as long as endopod). Setation of exopod not exactly made out, but at least 2 stout setae present on distal end.


Species Oithona fragilis - Plate 2 of morphological figuresIssued from Nishida, 1979 [p.91, fig. 2].
Female: a, first antenna; b, second antenna; c, second maxilla; d, maxilliped; e, first swimming leg; f, second swimming leg; g, third swimming leg; h, fourth swimming leg.

Nota:
- A1 0.7 times as long as total length, extending to anterior end of genital, segment. Posterior margin of 1st to 6th segments armed with a row of small teeth.
- A2 4-segmented. Posterior margin of 1st and last segments with a row of fine setae.
- Mx2 5-segmented, armed with stout spines.
- Mxp 5-segmented, 3rd segment with 2 stout spines armed with spinules and 2 short spines without spinules. Other segments as in figure.
- P1 with inconspicuous articulation between 2nd and terminal segments of exopod. 1st basal segment with 1 thick and plumose seta at distal end of inner margin. Inner marginal seta of 1st segment of exopod very minute. Outer margin of 1st and 2nd segments of both rami armed with fine setae.
- P2 and P3 with a row of small teeth on outer margin of exopod.
- P4 with 1st endopodal segment armed with thick and plumose seta. Outer marginal spine of exopod minute. Connecting plate with a V-shaped row of setae on posterior side.

Important structural formula of the swimming legs:
- 1 outer marginal seta on 2nd basal segment (basis).
- Endopod and exopod of P1 to P4 3-segmented.
- Exopod with 1, 1, 2; 1, 1, 2; 1, 1, 2; 1, 1, 2 outer marginal spines and 1, 1, 4; 0, 1, 5; 0, 1, 5; 0, 1, 5 inner marginal setae.
- Proportional length of terminal spine to exopod 1,9, 1.7, 1.8 and 1.7, respectively.
Endopod with 0, 0, 1; 0, 0, 1; 0, 0, 1; 0, 0, 1 outer and 1, 1, 5; 0, 1, 5; 0, 1, 5; 1, 2, 4 inner marginal setae.


Species Oithona fragilis - Plate 3 of morphological figuresFemale: 1, dorsal view; 2, Rostrum (lateral); 3, P1; 4, P4; issued from : Nishida, 1985. 5, dorsal view; issued from : Tanaka, 1960.
Male: 6, dorsal view; 7, Urosome (dorsal); 8, P4; issued from : Rosendorn, 1917 [doubtful].

Compl. Ref.:
Hsieh & al., 2004 (p.398, tab.1)
NZ: 4

Distribution map of Oithona fragilis by geographical zones
Species Oithona fragilis - Distribution map 2Issued from : S. Nishida in Bull. Ocean Res. Inst., Univ. Tokyo, 1985, No 20. [p.136, Fig.87].
Indo-Pacific geographical distribution of Oithona fragilis.
Loc:
Indian, China Seas (East China Sea), W Taiwan, off E Ogasawara Is., off Marquesas Is., Pacif. (tropical central & E)

Type locality: 24°58' N, 155°00' W.
N: 2
Lg.:
(636) F: 0,5-0,46; {F: 0,46-0,50}
Prosome length female: 0.25-0.28.
Rem.: After Nishida (1979) the swelling of the anterior part of genitalsegment is incouspicuous as compard with that of the other species, such as O. plumifera, O. similis, O. brevicornis, O. tenuis (Cf. Giesbrecht, 1892, pl.34, figs.3, 6, 21, 22; Rosendorn, 1917, p.14, fig.3-a). The setae on the connecting plate (intercoxal sclerite) of P4 have not been taken into account as a diagnostic character of Oithona.
Last update : 15/06/2021
    to add or edit your remark
  
By Shuhei Nishida 2021-05-29 04:53:32    ( Citation of this remark )
The figure indicated for Oithona fragilis is incorrect (not from Nishida, 1979).
Should be replaced with Figs 1 & 2 of Nishida (1979).

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Razouls C., Desreumaux N., Kouwenberg J. and de Bovée F., 2005-2022. - Biodiversity of Marine Planktonic Copepods (morphology, geographical distribution and biological data). Sorbonne University, CNRS. Available at http://copepodes.obs-banyuls.fr/en [Accessed August 08, 2022]

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