The new genus is erected by Suarez-Morales & McKinnon (2014, p.315) to accomodate a male specimen with a remarkable combination of important genus level characters not present in any other genus of the Monstrilloida.
It has a 5-segmented geniculate A1 that resembles that of Monstrillopsis in its general structure and armature, particularly in the presence of an inner protuberance of the last segment and the structure of the apical elenents. Setal element 2 (sensu Huys & al., 2007) forms a distinctive sabre-like structure in males of Monstrillopsis (Suarez-Morales & al., 2006) and element 1 is relatively short (as in M. fosshageni, M. chathamensis, M. cahuitae). In the new genus element 2 is short, curved and only slightly longer than element 1. This character is not present in males of Monstrillopsis. Another unique character present is the peculiar cuticular processes of the cephalothorax, forming sac-like protuberances on the anteroventral surface but also dorsal folds.
An important apomorphy found in this genus is the absence of an inner seta on the 1st segment of the exopods of P1-P4. The absence of such a seta is shared only with Maemonstrilla (Grygier & Ohtsuka, 1008).
Type species: Australomonstrillopsis crassicauda.
Total 1 sp.

Type species: Caromiobenella castorea. 3 sp. + 8 sp. (comb. nov.).
Diagnosis male from Jeon & al. (2018,: p.47) :
- Cephalothorax not exceeding half of total body length (caidal rami excluding).
- Forehead margin generally round, lacking 2 usual short sensilla.
- Body segmented: cephalothorax with incorporated 1st pedigerous somit, free pedigers 1-3, 1st urosomal somite, genital somite, postgenital somite, penultimate somite, anal somite.
- A1 5-segmented with modified 5th segment (inner distal margin formed into several comb-like rows of spinules).
- Oral papilla on anterior ventral surface of cephalothorax, low, somewhat inconspicuous.
- Genital apparatus consisting of robust genital shaft pmus 2 short, subtriangular genital lappets diverging from distal posterior end of shaft.
- Branced setae of distal A1 segment replaced by unbranched, wello-developed simple setae in most species (branched setae reportedly in Caromiobenella arctica comb. nov.).
- Spine 2d, on 2nd segment elongated, biserially plumose, or both depending on species.
- Distal end of genital shaft with deep notch or medial protrusion.
- 3 or 6 caudal setae on each caudal ramus, depending on species.
- Two pairs of prominent crater-like depression on anterior dorsum of cephalothorax.
- Posterior dorsum of cephalothorax (i.e. incorporated 1st pediger) with 2 longitudinal rows of 4 pores each, arranged in pairs across midline.

Cruz Lopes da Rosa J. da & al (2021) new zooplankton collections in coastal waters and intertidal rocky pools of the SWA yielded several male and female monstrilloid copepods tentatively identified as Monstrilla brasiliensis. their results of both morphologic and molecular (mtCOI) analyses allowed them to confirm that these males and females were conspecific. They also found evidence suggesting that Caromiobenella is not a monophyletic taxon. Their male specimens are morphologically assignable to Caromiobenella, therefore, females of the nominal species Monstrilla brasiliensis, are matched here with the aforementioned males and, thus, the species should be known as C. brasiliensis comb. nov. (Dias and Suárez-Morales, 2000).

After these authors the species included in this new genus will be (comb. nov.): C. helgolandica (Claus, 1863); C. serricornis (Sars, 1921); C. arctica (Davis & Green, 1974); C. hamatapex (Grygier & Ohtsuka, 1995); C. pygmaea (Suarez-Morales, 2000); C. patagonica (Suarez-Morales, Ramirez & Derisio, 2008); C. humesi (Suarez-Morales, 2001); C. brasiliensis Dias & Suarez-Morales, 2000 and Caromiobenella sp. [= Monstrilla sp. in Huys & Boxshall, 1991].

The new genus displays a unique set of characters, but some ambiguity is present in the generic assignment of all species Caromiobenella mentioned, including the three new species C. castorea, C. ohtsukai and C. polluxea. For example, the numbers of urosomal somites and caudal setae match those of Monstrilla, whereas the modifications of setal element 2d 2 involving elongation and plumosity, are more like those in some species of Cymbasoma.
Molecular analysis provides an alternative means of compensating for uncertainties and defects caused by insufficient morphological information. The molecular evidence strongly supports the separation of caromiobenella from Monstrilla, with an about two-fold difference between the within-genus and between-genera divergences for genes mtCOI and for genes 28S rRNA (see in Table 2)

type: Cymbasoma rigidum Thompson,1888. 41 species in Suarez-Morales, 2011 (p.4) + 25 species in Suarez-Morales & McKinnon, 2016 (p.3). Total: 71 species + 1 undet.

Diagnosis after Vives & Shmeleva (2010, Vol. 33, p.157) :
Female :
- Abdomen 2-segmented.
Male :
- Abdomen 2-segmented.
For Jeo,g & al. (2018, p.61) the number of caudal setae 3 or 4 occurs in Cymbasoma including between two sexes of C. rigidum, C. longispinosum, C. tumorifrons, C. quintanarooensis, C. chelemense.

Type: Maemonstrilla hyottoko. With 2 species-groups: kyottoko Group (Grygier & Ohtsuka, 2008, p.463) and turgida Group Grygier & Ohtsuka, 2008, p.492). Total: 11 species.

Diagnosis for females after Grygier & Ohtsuka (2008, p.462) :
- Ovigerous spines pointing forward between thoracopods.
- P1 to P4 widely separated across midline; intercoxal of legs 1-4 low and approximately as wide as legs themselves.
- Cephalothorax bulbous, about half of body length, with often very prominent oral papilla in anterior third of length and 2-4 (usually 3) small scars clustered behind base of each A1.
- Naupliar eye well developed; hyaline bodies absent in front of the widely separated lateral cups.
- Dorsal surface of metasomal pedigers and all urosomal segments except telson (for the so-called 'anal somite') occupied by extensive, more or less rectangular patches of denticles or spinules.
- A1 with branched outer distal b-setae.
- Single pore on anterior face of 3rd segment of each ramus in P1-P4.
- P5 either a long, narrow rod with 2 distal setae and at most a tiny, unarmed endopodal lobe, or bilobed with 3 setae on exopodal lobe and 1 (or supposedly 2 in one instance) on endopodal lobe.
- Urosome 4-segmented.
- Genital compound somite usually with obvious dorsal suture, lacking dorsal pores.
- Caudal rami with 6 setae and ventral pore.

This genus represents the only example of subthoracic brooding among planktonic copepods: Unusual direction of the ovigerous spines (foreward), the shape of the intercoxal sclerite, very low and very wide, and probably the loss of the inner seta of the 1st segment of each leg ramus (see remarks in Monstrillidae concerning the subthoracic egg brooding in copepods).

Males unknown (or unrecognized).
In the samples examined, monstrillid specimens and species of various genera were usually abundant, and up to three species of Maemonstrilla females co-occurred in samples; matching sexes by co-occurrence cannot be done in these circumstances.
Ohtsuka & Nishida (2017, p.574) underline a peculiar characteristic in this genus, which bears anteriorly directed genital spines on the genital compound somite of the female, which are posteriorly directed in other monstrilloids. Because egg masses attached to the spines are positioned in a space surrounded by the right and left legs, Grygier & Ohtsuka (2007) regarded it as a kind of brood chamber.

Maemonstrilla hyottoko species-Group :
- Cephalothorax with reticulate pattern of cuticular ridges.
- A1, lateral sides of metasomal somites and urosomal segments, dorsum of telson, and caudal rami ornamented (except in M. simplex).
- Dorsal surface of metasomal pedigers and first three urosomal segments, as well as outer face of thoracods (coxa and exopod), densely denticulate or spinulose (except in M. simplex).
- No spine-like scales posteriorly near dorsal midline on 1st and 2nd free pedigers.
- Outer basis seta of P3 at least as long as exopod.
- No inner seta of 1st exopodal segment of P1-P4; inner seta of 1st endopodal segment of these legs absent or represented by socket-like or button-like structure;
- P5 a long, thin rod with 2 distal setae, 1 apical and 1 slightly subapical; endopodal lobe absent (or reportedly tiny and unarmed in one instance).
- Posterior part of genital compound somite with ventral protrusion.
5 species: M. hyottoko, M. simplex, M. okame, M. polka, M. spinicoxa.

Maemonstrilla turgida species-Group : Monotypic. See diagnosis to the species Maemonstrilla turgida (A. Scott, 1909) comb. nov. from Grygier & Ohtsuka, 2008 (p.492); distinguished from the former species-Group by the cephalothorax non-reticulated.

Type: Monstrilla viridis Dana, 1849, but the genus concept needs to be clarified by designation and detailed description of a neotype. Total: 52 species + 2 uncertained (of which several doubtful). Provisional number, the species of the genus Monstrillopsis should no doubt be incorporated in this genus (Davis, 1949 a; Davis & Green, 1974).

Diagnosis after Vives & Shmeleva (2010, Vol. 33, p.157) :
Female :
- Abdomen 3-segmented.
- Oral papilla located approximately more than 1/4 of the ventral length of the cephalothorax (mainly at half length).
- Eyes absent or small.
Male : Abdomen 4-segmented
- Eyes not prominent.
- P5 absent or very small.
With the creation of the new genus Caromiobenella Jeon, Lee & Soh, 2018) the number of the species is at the present time 50.

type: Monstrilla dubia T. Scott,1904. The authors do not agree on the validity of this genus, in spite of the arguments of Davis (1949 a) : ? Cf. Monstrilla.
Total: 20 species (some probably doubtful).
Suarez-Morales & al. (2006, 2013) included the following nominal ten species in the genus Monstrillopsis: M. dubia (Scott, 1904) from Scotland (60°N), M. zernowi from the Black Sea (43°N), M. sarsi Isaac, 1974 from England (54°N), M. fosshageni from Brazil (20°S), M. dubioides Suarez-Morales, 2004 from Norway (62°N), M. ferrarii Suarez-Morales & Ivanenko from the White Sea (66°N), M. chilensis from off Chle (33°S), M. igniterra from the Southern Ocean (55°S), M. chathamensis from the Eastern Pacific, M. cahuitae from the Costa Rica (Caribbean Sea (9°45'N).
For Delaforge & al. (2017, p.11), several authors have questioned the validity of the genus Monstrillopsis Sars (1921) whereas others have accepted ir (Huys & Boxshall, 1991; Boxshall & Halsey, 2004; Suarez-Morales & al., 2006). The argumentation against it has relied on the presumed mixed characters shown by males of the Arctic species M. bernardensis (Willey, 1920); as in Monstrillopsis, these specimens have 4 caudal setae and the oral papilla is located anteriorly on the cephalothorax, but the specimens examined by Davis & Green (1974) from Resolute Bay have a rudimentary P5 as in Monstrilla; they explicitly state that the differ from Willey's population. The specimens of M. bernardensis from Resolute Bay should be redescribed. For instance, the number of caudal rami should be confirmed, some species of Monstrilla have a small, inconspicuous caudal seta V (i.e., M. elongata Suarez-Morales, 1994; M. gracilicauda Giesbrecht (1892). Also, the A1 segmentation and armature, particularly of the distal segment, should be examined to determine if it has the characters relatable to Monstrillopsis. Huys & Boxshall (1991) strengthened the genus concept by assigning to the males of Monstrillopsis a particular antennular type, different from those recognized in Cymbasoma and Monstrilla. With regard to the females of species of Monstrillopsis, little evidence contrary to the validity of the genus has been presented. The other Arctic species described by Davis & Green (1974), M. arctica and M. nasuta are clearly species of Monstrilla.
The distribution of the genus seems to be largely restricted to temperate and cold latitudes.

Diagnosis of the the genus Monstrillopsis owing to its possession of the combination of characters noted by Sars (1921) :
- 2 free somites posterior to the genital double-somite;
- Eyes fully developed;
- 4 segmented A1 in the female;
- Oral papilla occurring near the anteriormost part of the cephalothorax (< 20 % of way back along cephalothorax);
- P5 bilobed in female , outer lobe armed with 3 setae;
- Caudal rami with 4 setae.
For Delaforge & al. (2017, p.8), some species can have more caudal setae (i.e. M. reticulata (Davis, 1949), M. zernowi Dolgopolskaya, 1948), but except for the aberrant M. zernowi with 5 caudal setae, also present in the females.

Diagnosis after Vives & Shmeleva (2010, Vol. 33, p.157) :
Female :
- Abdomen 3-segmented.
- Eyes well developped.
- Oral papilla located 1/4 length of the ventral cephalothorax.
Male : Abdomen 4-segmented
eyes very prominent.

lee J. & al. (2016, p.421), in Monstrillopsis the number of caudal setae is generally 4 in both sexes; however, some congeneric species have more caudal setae (see Suarez-Morales & al., 2006), and are distinguished from the Korean species: in the male, 6 setae in M. cohuitae and 5 setae in M. reticulata and M. zernowi.
After Jeon (2018, p.62) the genus Haemocera Malaquin, 1901, should be a senior synonym of Monstrillopsis.

Remarks from Suarez-Morales & al. (2006, p.101)combination of characters defined by Sars (1921) in his diagnosis of this genus concerning females:
- 1: A1 4-segmented.
- 2: Oral papilla occurring near anteriormost part of cephalothorax.
- 3: zyzs fully developed.
- 4: Urosome with 3 somites including genital double-somite.
- 5: P5 of female bilobed, and outer lobe armed with 3 setae.
- 6: Caudal rami with 4 setae. Sars (1921) mentioned also unusually produced caudal rami; this character is not constant in the members of the genus.
- Additional characters proposed later for this genus are the absence or armament on the inner lobe of the female P5; a modified distal segment and a curved terminal spine in the male A1, and absent or reducted P5 in the male (character shared with Cymbasoma (Suarez-Morales, pers. obs.).

Total : 1 sp.
This genus, created to understand an entirely original species (Thaumatohessia armoricana (Hesse,1868) does not correspond to the diagnosis of the family, but may belong to a neotenic form of a species of the preceding genera. This atypic form, presenting rudimentary mouth parts, has never been re-encountered in Brest (among the corals: Griffithsia corallina)