Calanoida ( Order )
    Ryocalanoidea ( Superfamily )
Ryocalanidae Andronov, 1974 ( Ryocalanoidea )
Ref.: Andronov, 1974 a (p.1005); Razouls, 1982 (p.136); Bowman & Abele, 1982 (p.10); Park, 1986 (p.191, 194); Huys & Boxshall, 1991 (p.419); Andronov, 1991(p.133); Razouls, 1993 (p.309); Chihara & Murano, 1997 (p.898); Ohtsuka & Huys, 2001 (p.445, 461); Boxshall & Halsey, 2004 (p.15; 49; 182: Def.); Vives & Shmeleva, 2007 (p.995): Markhaseva, 2012 (p.148, Rem.); Renz & al., 2013 (p.247, 257); Renz & al., 2018 (p.30: phylogenetic relationships)
Bradford-Grieve J.M., (2002 onwards). Key to calanoid copepod families. Version 1 : 2 oct 2002.
Rem.: Andronov created the family Ryocalanidae for the monotypic genus Ryocalanus infelix. The family can be defined by the fused segments 8 and 9 of the A1, the structure and segmentation of the legs as in the Spinocalanidae family, the articulation of the geniculated antennula between the segments 22 and 23 (and not between the segments 18 and 19 as in the majority of the other genera).
Renz & al. (2013 (p.257) define the new genus Yrocalanus including four species: Ryocalanus admirabilis, R. asymmetricus, R. bicornis, R. antarcticus.
2 G.: Ryocalanus, Yrocalanus.

Diagnosis from Bradford-Grieve (1994, p.74) :
- Head and pediger 1 separate, pedigers 4 and 5 seperate.
- Rostrum stout, 1-pointed, may be bifurcate at the tip.
- Urosome female 4-segmented.
- Urosome male 5-segmented.
- A1 24-segmented, segments 8 and 9 fused
- Male right A1 transformed into a grasping organ with segments 23 and 24 fused and the hinge between segments 22 and 23, also the terminal part bends out and backwards.
- Mouth parts and swimming legs generally similar in both sexes.
- A2 with 3 setae on the inner margin of exopod segment 2.
- Md with a relatively slender palp, endopod 2-segmented and shorter than the exopod.
- Mx1 exopod, basis, and inner lobes 2 and 3 relatively slender.
- Swimming legs as in Spinocalanus except that exopodal segment 3 of P1 with 2 outer-edge spines.
- Female P4 coxa with very large spines as well as small spinules.
- Male P5 uniramous or with very reduced endopods, asymmetrical, longest on the left.
Family Ryocalanidae - Plate 1Issued from : J. Renz, E.L. Markhaseva & K. Schulz inZoosyst. Evol., 2013, 89 (2). [p.248, Fig.1]
Distribution of Ryocalanidae species in the world oceans.
1 - Ryocalanus infelix; 2 and 2a - Yrocalanus admirabilis; 3, 4, 5 - Yrocalanus asymmetricus, Yrocalanus bicornis, Ryocalanus bowmani; 6 - Ryocalanus spinifrons; 7 - Yrocalanus antarcticus; 8 - Ryocalanus brazilianus.

Family Ryocalanidae - Plate 2Issued from : G.A. Boxshall & S.H. Halsey in An Introduction to Copepod Diversity. The Ray Society, 2004, No 166, Part. I. [p.182].
Armature formula of swimming legs P1 to P4.
- Female P5 absent. Male P5 asymmetrical; with coxae and intercoxal sclerites fused to form posteriorly bilobed transverse plate; right leg uniramous, comprising basis and 1-segmented exopod, both unarmed; left leg twice as long as right, biramous with 3-segmented exopod and minute, knob-like endopod; exopodal segments lacking spines and setae.
Nota: Proximal outer spine of 3rd exopodal segment of P1 often lost, as in Ryocalanus bicornis Markhaseva & Ferrari, giving formula I, I, 4. Inner margin of coxa of P4 ornamented with pair of large spinules (possibly spines) near base of inner seta.

Family Ryocalanidae - Plate 3Issued from : G.A. Boxshall & S.H. Halsey in An Introduction to Copepod Diversity. The Ray Society, 2004, No 166, Part. I. [p.183, Fig.43].
Ryocalanidae: A, Ryocalanus admirabilis, habitus female; B, habitus male; C, distal tip of male A1. D,Ryocalanus spinifrons, female P1. E, Ryocalanus bowmani, male P5. F, Ryocalanus bicor,nis, coxa of female P4. [Andronov, 1992: A-C; Shimode, Toda & Kikuchi, 2000: D. Markhaseva & Ferrari, 1996: E-F]
(1) Ryocalanus Tanaka, 1956
Ref.: Tanaka, 1956 b (p.1); 1956 c (p.404); Razouls, 1982 (p.136); Razouls, 1993 (p.309); Bradford-Grieve, 1994 (p.93, Def.); Chihara & Murano, 1997 (p.898); Mauchline, 1998 (p.78: F; p.80: M); Shimode & al., 2000 (p.133: clι spp.); Bradford-Grieve, 2004 (p.287); Boxshall & Halsey, 2004 (p.184: Def., spp. Key); Vives & Shmeleva, 2007 (p.995); Markhaseva, 2012 (p.149, Rem.: 2 groups); Renz & al., 2013 (p.255, Rem.); Renιz & al., 2018 (p.11-12, Rem.)
Rem.: Brodsky (1980: pers. comm.) indicates that Ryocalanus should be spelled as Riocalanus.
Type: Ryocalanus infelix Tanaka,1956.
Following the redefinition of the genus by Renz & al (2013) the number of species is 4 . Total (2018): 5 spp.

Diagnosis after Renz, Markhaseva & Schulz (2013, p.255) :
- Body length > 1.6 mm.
- Urosome very short.
- Rostrum 1-pointed.
- P1 endopod with proximal inner wedge-shaped projection.
- Male right A1 moderately modified.
- Male P5 uniramous, containing terminal spines on the distal exopod segments.

Key oto species after Boxshall & Halsey (2004, p.184) (modified, Ryocalanus brasilianus not included) :
1- Rostrum simple, tapering to point …….. 2.
1’ – Rostrum bifid …….. other genus (Yrocalanus.
2 - Lateral margins of 5th pedigerous somite rounded ; 1st exopodal segment of male P5 armed with 1 outer spine and ornamented with several fine hair-like setules …….. R. bowmani.
2’ - Lateral margins of 5th pedigerous somite produced into posteriorly directed spinous processes, readily visible in lateral view ……3 ;
3 – 5th pedigerous somite of female ornamented ventrally with 12 long spinules on each side ; Mx1 with 9 setae on coxal epipodite and 4 setae on coxal endite ; female P4 with 9 large robust spinules on posterior surface of coxa …… R. spinifrons.
3’ – 5th pedigerous somite of female ornamented ventrally with row of short spinules on each side ; Mx1 with 6 setae on coxal epipodite and 5 setae on coxal endite ; male P5 without external spine on 1st exopodal segment ……R. infelix.

Nota: The A2 exopod to endopod ratio is 0.82 in R. squamatus (Renz & al., 2018, p.12), while in all other species it is close to 1, a character hypothesized to be diagnostic for the genus Ryocalanus (Renz & al., 2013).
(2) Yrocalanus Renz, Markhaseva & Schulz, 2013
Ref.: Renz & al., 2013 (p.257, Def., Rem.); Renz & al., 2018 (p.23: Rem.)
Rem.: Type: Ryocalanus admirabilis Andronov, 1992. Total: 5 spp.
Species included: 4.
Diagnosis after Renz, Markhaseva & Schulz (2013, p.257):
Body length < 1.6 mm.
Urosome relatively long.
Rostrum bifid.
P1 endopod proximal inner part smooth.
Male right geniculated A1 is of highly complex structure.
Male P5 indistinctly biramous with small endopodal buds and with distal exopod segments lacking spines.
Key to species after Boxshall & Halsey (2004, p.184) (modified, Yrocalanus antarcticus not included) :
1- Rostrum simple, tapering to point …….. other genus (Ryocalanus).
1’ – Rostrum bifid …….. 2
2 – Genital double-somite of female strongly asymmetrical in dorsal view …….. Y. asymmetricus.
2’ – Genital double-somite of female more or less symmetrical in dorsal view ……… 3.
3 – Posterolateral angles of 5th pedigerous somite produced posteriorly into pointed lobes …… Y. bicornis.
3’ – Posterolateral angles of 5th pedigerous somite triangular in lateral view : segment 21 of male A1 with 1 long, robust spine on anterior margin ……Y. admirabilis.

 Any use of this site for a publication will be mentioned with the following reference :

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 [Accessed July 07, 2022]

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