In a genus revision, Steuer in 1915 establishes two subdivisions based on the presence/absence of rostral filaments (Arostratae et Rostratae), but later Bowman (1965) when studying a population of A. liljeborgi demonstrates that the rostral filaments can be present or absent. The environmental conditions, notably the salinity, could be responsable for this fact.
It is probable that other morphological characters show a certain variability like the spinulation of the abdomen, the structure of the P5. Various anomalies have been shown by Brylinski (1984, p. 961) .

The genus divides currently into 6 sub-genera: Acartia (Planktacartia ), Acanthacartia , Acartiura , Euacartia , Hypoacartia , Odontacartia, contested by Barthélémy (1999, p.868; 1999 a, p.59, scheme 9) after analysis of the genital structures. Among the majority of species, we can distinguish two main groups, based on the external morphology of the genital area on one hand, and the seminal duct morphology on the other. The first group includes ten species, viz., A. clausi, A. hudsonica, A. omorii, A. longiremis of the subgenus Acartiura, A. bifilosa, A. chilkaensis, A. italica, A. levequei, A. tonsa of the genus Acanthacartia, and A. lilljeborgi of the subgenus Odontacartia, exhibing a compact external area, with well-defined structure for each of them. All exhibit a very homogeneous configuration of their internal area with seminal ducts in characterisytic loop-like form. According to Steuer (1923), this loop is visible in ventral view after clearing the specimens. The duct seems less voluminous only in the subgenus Acanthacartia species. The similitude in the organization of the genital structures af all these species confirms the closerelationship between the subgenera Acartiura and Acanthacartia. Thus, the morphology of the genital complex does not justify the distinction of two subgenera. The second group comprises A. danae, A. negligens of the subgenus Acartia, A. amboinensis, A. japonica of the subgenus Odontacartia and A. southwelli of the subgenus Euacartia; these species offer a fragmented external area with ventrolateral genital slits, and seminal ducts, simple bend-shaped opening in the proximal zone of the egg-laying ducts, as in the precedent group. Therefore, the genital anatomy does not justify the distinction between the different subgenera.

Total: 63 spp. + 2 undet. + 3 n. nudum.

Diagnosis from Bradford-Grieve (1999, p.3): As for the family, with the following additional characters.
- Anal somite is without an anal operculum, as anus opens between last two urosomites into a dorsal grove on anal somite.
- Caudal rami short, separated from anal somite.
- A2 basis fused with endopodal segment 1, which is long and slender and bears 9 setae; exopod shorter than endopodal segment 1.
- P1 exopodal segment 1 and 2 each with a long slender outer distal spine, and with 2 spines on exopodal segment 3.
- Female P5 3-segmented , uniramous, with last segment modified into a long, slender spine.
- Male P5 larger on right, exopodal segment 2 with a large inner lobe, and exopodal segment 3 in the form of a clasper.

Genus defined by Sewell (1914) with for species type: Acartia kempi Sewell, 1914. Considered by various authors as a sub-genus or a new family. According to Sewell (1914) the female P5 ''possesses both an exopodite and an endopodite, and in the male the right leg forms a well-developed clasping apparatus: in both species the rostrum is absent.
For Barthélémy (1999 a, p. 59) this genus has to constitute to him only a family. The species present a genital area of diaptomoid type deprived by opercule and by receptacle seminal, which distinguishes them from all other species of the family of Acartiidae possessing a genital model of area characterized well by the constant presence of receptacles and pores copulators neighboring to gonopores. We can also observe the other morphological characters: the length of the branches of the caudal rami, the shape flattened by the antennula, the biramous P5. These characters differentiate all the species of the genus of the other Acartiidae, with the exception of Acartiella kempi, only species of the genus presenting an antennule similar to that of Acartia (Sewell, on 1918).
According to Barthélémy (1999, p.868) the morphology of the external genital area and the absence of seminal receptacles very clearly isolate species of the genus Acartiella Sewell (1914), the validity of which is thus confirmed. Bradford (1976) pointed out that Acartiella should remain in the Acartiidae family especially because the exopods of P2-P4 are devoid of articulated outer edge spines, as in the other Acartiidae.
Total: 11 spp.

The mean female size is 1.166 mm (n = 18), and for male 1.062 mm (n = 19). The size ratio male/female is 0.911.

Considered as a subgenus by T. Scott, Steuer, then later as a genus by Sars (1904b).
For Barthélémy (1999 a, p. 59) the organization of the external genital area , separated, in very lateral side and posterior genital splits, could constitute an important characteristic of the genus.
Type: Acartia dubia T. Scott,1894. Total: 5 spp.

Diagnosis from Bradford-Grieve (1999, p.14):
- Rostral filaments present.
- Sexual dimorphism strongly marked.
- Ovaries paired.
- Last prosomite of female usually strongly spread into wing-shaped extensions on each side, that of the male simple with lateral parts not expanded.
- Urosome of female comparatively short, 3 free somites with genital double-somite expanded laterally, may be asymmetrical, genital pores laterally placed on somite.
- Caudal rami broad and 1 of apical setae may or may not be transformed into a thickish spine.
- Urosome of male slender, of 5 somites, with caudal rami of normal shape.
- Female A1 as in Acartia.
- Right geniculate A1 of male may be expanded.
-A2 mouth parts, and swimming legs similar to those of Acartia.
- Female P5 with both basis fused, terminal spine, if present, is heavily built, and lateral seta is usually much shorter than terminal spine.
- Male P5 powerfully developed; right leg much larger and terminates in a very long slender incurved claw, basis with a conspicuous inner projection which is sometimes very large; left exopodal segments 2 + 3 usually wider than long, bearing at least 2 spines which oppose each other to make segment resemble a chela.
- The spermatophore, fixed to genital-double-somite of female is accompanied by a complicated thin plate which may curve around female genital double-somite.

Type: Paracartia antarctica Thompson,1898. Total: 3 spp.
For Barthélémy (1999, p.869) the sole examined species presents a fragmented area with two lateral genital slits, but internally there is no seminal duct and the receptacle seems to open distally in the egg-laying duct. The presence of paired genital orifices situated on both side of the genital segment is a constant character of the genus. The three species of the genus therefore present genital structures clearly differing from those of the Pontellidae. Thus, in spite of the resemblance with the genus Labidocera (Pontellidae), the comparison with the genital structures in Pontellidae (Barthélémy & al., 1998) confirms that the genus Paralabidocera must be referred to Acartiidae.

Diagnosis from Bradford-Grieve (1999 b, p.227): As for the family definition with the following additional charaters.
- 2 rostral filaments present.
- Posterior metasomal corners rounded.
- Female genital segment swollen and may be asymmetrical.
- Anal operculum absent.
- Female P5 with fused 1st basal segments, an endopod, and a bifurcate 1-segmented exopod.
- Male P5 generally as in other Acartiidae but much more powerfully built.
- The spermatophore has a larger coupler which wraps around both sides of the female genital segment.

type: Acartia josephinae. Total: 1 sp.

Diagnosis from Bradford-Grieve (1999, p.15), after Belmonte, 1958 :
- Rostral filaments present.
- Sexual dimorphism marked.
- Last prosomite of female and male rounded.
- Urosome of female comparatively short, of 3 free somites with genital double-somite asymmetrical, longer than half the urosome, genital pores paired, laterally placed, withot opercula; fin-like expansion on right side of genital double-somite.
Male urosome slender, of 5 free somites, caudal rami short.
- Female A1 22-segmented.
- Right geniculate A1 of male without swollen segments.
- Female P5 reduced to small knob, each with 1 long seta.
- Male P5 right leg much larger than left leg and terminates in a long claw which is curved inwards; exopodal segment 2 of right leg with a long finger-like protrusion originating from the distal half of the segment; left leg exopodal segments 2 + 3 half-moon shaped with spines at either end.
- The spermatophore is fixed by a gelatinous 'apron' to the ventral surface of female genital double-somite.