Markhaseva & al., 2008 (p.2421); Markhaseva & al., 2014 (p.63, 67, 77, Table 1, 2, 3, 4, Rem., Def.); Laakmann & al., 2019 (p.330, Table 1, fig.1, 2, 3, 4, Table A, phylogenetic relationships)

Type genus: Rostrocalanus Markhaseva, Schulz, Martinez Arbizu, 2009. 1 G

For Markhaseva, Laakmann & Renz (2014, p.77) the diagnosis is based on the following combination of characters: the apomorphies for the family within the ''Bradfordians'' are: Md exopod 4-segmented, bearing 4 setae; Mxp praecoxal endites setal formula: 0, 1, 2, with praecoxal setae as: 0 + 1sc + 2sc; Mxp basis without distal setae.

General characters :

1 - A2 coxa without seta; basis with 1 seta; endopodal segment 1 with 1 seta; setal formula of exopod: 0, 0-1-1-1, 1, 1, 1, 0, 3.

2 - Md endopodal segment 2 with 6 setae; gnathobase with hump/crest (see table 2).

3 - Mx1 setal formula: 9, 2, 2, 5 (at fused distal basal endite and endopod), 5-6, 0 (or 3-4) (see table 3).

4 - Mx2 endites setal formula: 1-2, 3, 3, 3, 4; endopod with 6 worm-like sensory setae (see table 4).

5 - Mxp basis with 2 proximal setae.

For Markhaseva & al. (2008, p.2438) Rostrocalanus could be considered an early offshoot of the Tharybidae lineage.
Markhaseva & al. (2014, p.77) note that this genus shows a similarity to Brodskius Markhaseva & Ferrari, 2005; Undinella Sars, 1900 and some species of Tharybis, since the coxa of A2 lacks a seta. Rostrocalanus shares with some species of Ubdibella and Parkius 2 proximal setae at the Mxp basis, and with Brodskius, Bradfirduiella Andronov (2007) and some species of Rythabis Schulz (1995) a fused distal endite and endopod of the Mx1 (see Table 1, 3 and 5).