List species and varieties by family
Ridgewayiidae M.S. Wilson, 1958 ( Epacteriscoidea )
(1) Badijella Krsinic, 2005
Rem.: Sp. type: Badijella jalzici (from anchialine cave). 1sp.

[1] Badijella jalzici  Krsinic, 2005   (F,M)    [Figs]
(2) Brattstromia Fosshagen, 1991
Rem.: sp. type: Brattstromia longicaudata . 1 sp.

[1] Brattstromia longicaudata  Fosshagen, 1991   (F,M)    [Figs]
(3) Exumella Fosshagen, 1970
Rem.: Coastal forms, anchialine, epibenthic. Type: Exumella polyarthra Fosshagen,1970. 4 spp.

Definition after Bradford-Grieve (1999 b, p.24) :
- As in the familly.
- Head and 1st pediger separated, 4th and 5th pedigers separate.
- Urosome 3-segmented in female; 4-segmented in male.
Genital segments asymmetrical, produced on right side in female, and on left side in male.
- Rostrum downturned, rounded plate with 2 filaments at its tip.
- A1 26-segmented in female; male right A1 20-segmented.
- A2 exopod slightly longer than endopod; endopod segment 2 elongated with no distinct inner lobe.
- Md bears a well-developed masticatory blade with sharp teeth; endopod reduced in size with 0, 6 setae on segments 1 and 2, respectively.
- Mx1 well-developed.
- Mx2 short, compact, with anterior margin of proximal joints produced into large lappets.
- Mxp strong, with a reflexed terminal part; 2 proximal segments of endopod elongated and distal segments short; endopod carries some modified setae, distal ones of which are long.
- Both rami of P1-P4 3-segmented similar in most resêcts to Ridgewayia, but without extra processes on P1 outer distal margin of exopod segments 1 and 2.
- P5 of female with both rami 3-segmented; last segment of exopod of exopod arises from the middle of inner margin of preceding segment.
- Male P5 exopods 2-segmented and elongate, its terminal segment carrying long spines and modified processes.
- Basipod 2 of P5 in both sexes carries a long seta on its outer margin.

[1] Exumella mediterranea  Jaume & Boxshall, 1995   (F,M)    [Figs]

[2] Exumella polyarthra  Fosshagen, 1970   (F,M)    [Figs]

[3] Exumella tsonot  Suarez-Morales & Iliffe, 2005   (F,M)    [Figs]

[4] Exumella tuberculata  Grahame, 1979   (F,M)    [Figs]
(4) Exumellina Fosshagen, 1998
Rem.: 1 sp.

[1] Exumellina bucculenta  Fosshagen, 1998   (F,M)    [Figs]
(5) Hondurella Suarez-Morales & Iliffe, 2007
Rem.: Type: Hondurella verrucosa Suarez-Morales & Iliffe, 2007. Total: 1 sp.

Diagnosis from Suarez-Morales & Iliffe (2007, p.340):
- Female: body slender, not compressed laterally.
- Head and Pedigerous somites 1 fused, 4th and 5th pediger somites fused.
- Posterior corners of prosome smooth, rounded.
- Urosome 4-segmented;
- Genital double-somite asymmetrical, left margin modified; somite projected ventrally.
- Caudal rami relatively short, slightly shorter than anal somite. Seta V symmetrical on both caudal rami.
- Rostrum pointed, strong, with single lobe, filaments absent.
- A1 relatively short, reaching 4th prosome somite, 26-segmented.
- A2 with exopod longer than endopod; exopod plesiomorphic, 8-segmented.
Md basis with 4 setae; endopod 2-segmented, with distal segment having 9 setal elements.
- Mxp with 5-segmented endopod bearing some modified setae.
- P1 with long spiniform expansions on 2nd exopodal segment; outer spines on 3rd exopodal segment with subterminal filament; endopod with reduced number of setae (7).
- P1-P4 with 3-segmented endopods and exopods.
- 3 outer spines on exopods of P3 and P4.
- P5 with 3rd exopodal segment apparently unmodified except for articulated setae and slight asymmetry of insertion and moderate lateral expansion on 2nd exopod; endopod 1-segmented, represented by elongated rod-like structure sdistally acute.
- Male : body smaller and slenderer than female;
- Urosome 5-segmented.
- Caudal rami and setae symmetrical.
- Right A1 23-segmented, geniculated, with spines on segments 11 and 12.
- Mouthparts and P1-P4 similar to female.
- P5 with both endopods reduced, 1-segmented; right exopod reduced, 1-segmented, left exopod highly modified.

[1] Hondurella verrucosa  Suarez-Morales & Iliffe, 2007   (F,M)    [Figs]
(6) Normancavia Fosshagen & Iliffe, 2003
Rem.: 1 sp.

[1] Normancavia minuta  Fosshagen & Iliffe, 2003   (F,M)    [Figs]
(7) Placocalanus Ohtsuka, Fosshagen & Soh, 1996
Rem.: type: Placocalanus insularis Fosshagen, 1970. Total: 5 spp.
For Fosshagen (1970 b, p.55) this genus seems to be a true bottom-living calanoids. The small, compressed and slender body-shape, the short, modified A1, and the unusual P1 seem to indicate this way of life. The function of the large process on A1 is not obvious, but it may be related to the bottom-living habits of the species; it may act as a shield protecting the mouthparts when the animal forces its way through loose sediment, or as a device for stirring up particles and for digging. It is to notice characters in common with several harpacticoids, such as the large single aesthetasc in the middle of A1, the modified P1, and the outer setae on the coxa of P1, P3 and P4. The structure of P1 suggests that this limb has other than a purely swimming function, perhaps being used for digging or holding fast to the substrate.

Diagnosis from Ohtsuka & al. (1996, p.248) :
- Body compressed laterally.
- Cephalosome and pedifgerous somite 1 separate, 4th and 5th pedigerous somites fused.
- Urosome elongate, slender, 4-segmented in female and 5-segmented in male.
- Genital double-somite of female with single genital operculum ventromedially.
- 3rd urosomal somite in female and 4th in male longest in urosome.
- Anal somite small, partly or almost completely covered by the preceding somite ;
- Subterminal outermost caudal seta spiniform.
- Rostrum bluntly or sharply poited at tip without terminal filaments.
- A1 of both sexes unique in having 1st segment with posterior distal margin expanded and produced into flattened, triangular process, reaching, ar most, to the end of cephalosome, 22- or 23-segmented in female and 20- or 21-segmented in right geniculate A1 in male ; compound segment XV-XVI with large aesthetasc in both sexes. Sheath present between segments XIV and XV-XVI in right A1 of male.
- Mouthpart appendages showing neither extreme modification nor reduction in any sex.
- P1 conspicuously modified : basis with or without anvil-like process ; endopod 1- to 3-segmented, tapering distally ; exopod slender, 3-segmented.
- Both rami of P2 - P4 usually 3-segmented, but proximal two endopod segments of P4 may be fused.
- Second endopod segments of P2 – P4 sharply produced at outer distal corner, with 1 or 2 inner setae.
- P5 female : endopod 1- or 3-segmented, 3rd segment originating from halfway along inner margin of second, as in other ridgewayiids.
- P5 male endopod 1- or 2 segmented, second segment unarmed or bearing several elements terminally ; right exopod 2-segmented, furnished with 2 or 3 spines and 1 inner seta ; left exopod 3-segmented, 1st segment with outer distal spine, 2nd bearing outer distal spine and expanded process or foliaceous spine or process on inner distal corner, 3rd segment tapering distally to acute process or ending in spine

[1] Placocalanus brevipes  Ohtsuka, Fosshagen & Soh, 1996   (M)    [Figs]

[2] Placocalanus inermis  Ohtsuka, Fosshagen & Soh, 1996   (F,M)    [Figs]

[3] Placocalanus insularis  Fosshagen, 1970   (F,M)    [Figs]

[4] Placocalanus longicauda  Ohtsuka, Fosshagen & Soh, 1996   (F,M)    [Figs]

[5] Placocalanus nannus  Fosshagen, 1970   (F,M)    [Figs]
(8) Ridgewayia Thompson & Scott, 1903
Rem.: Type: Ridgewayia typica I.C. Thompson & A. Scott, 1903. 14 spp. + 1 variety + 3 unident.
Epibenthic forms, coastal.

Definition after Braddord-Grieve (1999, p.25) :
- As in the family.
- Head and pediger 1 indistinctly separated, pedigers 4 and 5 separte.
- Urosome 4-5 segmented in female; 4-5 segmented in male.
- Paired genital openings closely set.
- Caudal rami longer than wide with 4 terminal setae, 1 outer spine may be present.
- Rostrum downturned, broad at its base, rounded or pointed distally, filaments lacking.
- Cephalic appendages all of primitive calanoid type, without reduction, excessive modification, or sexual differentiation.
- A1 extending to end of metasome or to caudal rami; 25-26 segmented in female, the 3 apical segments elongated; left A1 male like that of female, that on right 21-24 segmented, with a moderately developed geniculation, segmentation beyond this specialised joint varying from 3 or 4 segments.
- A2, exopod 7-8 segmented, with apical segment elongate and slightly longer than endopod.
- Md masticatory blade not conspicuously expanded, wiyout gaps between the 7-10 shallowly incised teeth; basipod with 3-4 lateral setae.
- Mx1 with outer lobe 1 (arthrite) with 13 spines and setae ; outer lobe 2 with 0 or 1 seta; inner lobes 2 and 3 each with 4-5 setae; basipod with 4-5 setae; endopod segments 1, 2 and 3 with about 4, 4, 5-7 setae, respectively, and with varying degrees of fusion between segments; exopod lobed and with about 11 setae.
- Mx2 lobes 1-6 with 4, 2-3, 2-3, 3, 3-4, 3-4 setae respectively.
Mxp- basipod 1 with 4 lobes or groups of setae ; endopod shorter than basipod segments 1 and 2, of 5 well-defined segments with about 4, 4, 3, 4, 4 setae respectively.
- P1 basipod 2 (= basis) with 1 inner seta, often with 1 outer seta on P4 and P5.
- Endopod segment 2 on P1-P4 with 2, 2, 2, 1-2 setae respectively; endopod segment 3 on P1-P4 with 6, 8, 5-8, 6-7 setae respectively.
- Female P5 slender, symmetrical, with a well-developed 3-segmented exopod and reduced 2-segmented endopod; exopod modified with segment 3 constricted basally and set into a narrowed, well-defined socket of segment 2, the outer spine-bearing portion of segment 2 enlarged and considerably produced beyond this insertion; exopod segment 3 with 4 spines and 4 setae; endopod segme,t 2 with 6-7 setae.
Male P5 right and left basipod 1 fused; both rami modified and strongly asymmetrical; right exopod 2-segmented, segment 2 tending to elongation with 2 outer marginal spines, or with 1 proximal spine and more distally placed spinous points; left exopod 3-segmented, segment 3 considerably modified with a short but stout basal portion from which may extend spines, complex ornamenied processes, and fragmented membranes of irregular length; endopods unsegmented, right elongate, left much shorter, either endopod entirely unarmed or with setae, spines, or processes.

After Figueroa & Hoefel (2008, p.146) it is presently thought that Ridgewayia is a Tethyan relict (see Ohtsuka & al., 2000). Most members of the marki species-group are found in the Caribbean and they include: R. marki marki, (Bermuda), R. shoemakeri (Dry Tortugas, Florida), R. fosshageni (bahamas, Panama), and R. klausruetzleri (Belize). There is one member from the Mediterranean, R. marki minorcaensis (Minorca) and one from the Indo-West Pacific, R. stygia (Palau). Ohtsuka (2000) points out the faunistic link between the Western Central Pacific and Caribbean, and suggests that the ancestor of R. stygia migrated from the Caribbean into the Western Central Pacific during the Miocene when the Tethys Sea was circumtropical. This is a feasible theory, and the discovery of R. define and R. tunela in the Eastern Pacific can be viewed as further evidence of a westward dispersal of these marki species-group ridgewayiids. The present Galapagos Islands are geologically young, the oldest Islands have been dated to be 4-5 millions years old (Hall, 1983) ; but there is evidence that sea mounts and/or islands have been emerging from the Galapagos hot spot as far back as 75-95 million years ago. Hoernle & al. (2002) show that the entire Caribbean plate originated from the Galapagos hotspot during the Cretaceaos period. This places the emergence of oceanic islands around the Galapagos hot spot well within the time frame needed for a Tethyan dispersal of the ancestors of R. stygia, R. define and R. tunela from the Caribbean into the Pacific. Although this Tethyan hypothesis is one of the favored explanations for the present distribution of anchjaline fauna, it does not exclude the possibility that some of the inhabitants of anchialine systems have colonized these habitats more recently (Boxshall & Jaume, 1999).
The Tethys Sea remained open and circumtropical until about 20 million years ago (Hrbek & Meyer, 2003), but the dispersal of the marki species-group from the Caribbean into the Pacific could have taken place after this period before the closing of the Panama seaway 3.5 million years ago (Nesbitt & Young, 1997). Thus, the colonization of Galapagos by the members of the marki species-group could have come directly from the Caribbean to the present day islands.
Both dispersal scenarios call for the colonization of the marki species-group from the Caribbean into the Pacific, but the possibility remains that members of this group present in the Western Pacific subsequently migrated into the Caribbean. A major argument against a modern day dispersal of ridgwayiids is the 5000 km expanse of deep water separating the Central Pacific and the Eastern Pacific. This marine barrier was first mentioned by Darwin (1859) in The Origin of Species, and it is now referred to as the Eastern Pacific Barrier (EPB). Since there are no islands present across this vast stretch of deep ocean, the EPB acts as a barrier to dispersal of shallow water species. The effectiveness of this barrier has been demonstrated by the large number of shallow species that are not shared by these two regions, in contrast to the very few species that are found on both sides (Lessios & al., 1998 ; Lessios & Robertson, 2006).
There is a debate about the few transpacific species, whether they are the remnants of a previously continuous Tethyan distribution that have not evolved morphological differences since the emergence of the EPB, or whether there is dispersal across the EPB that maintains sufficient gene flow to prevent speciation.
The genetic analysis performed by Lessios & Robertson (2008), concerning transpacific reef fish, demonstrated the dispersal occurred stochastically in time and with respect to species dispersed ; and that gene flow occurred in both directions. Such evidence raises the possibility that the Ridgewayiids from the Galapagos and Palau are the result of post-Tethyan dispersal. Genetic studies of the various Ridgewayia species will be essential for determining the biogeographic history of this genus.

[1] Ridgewayia boxshalli  Barthélémy, Ohtsuka & Cuoc, 1998   (F,M)    [Figs]

Ridgewayia canalis    Gurney, 1927   (M)
Syn.: Suezia canalis Gurney, 1927 d (p.457, Descr.M, figs.M)
Ref.: M.S. Wilson, 1958 (p.145, Rem.)
Rem.: Cf. Ridgewayia typica

[2] Ridgewayia delfine  Figueroa & Hoefel, 2008   (F,M)    [Figs]

[3] Ridgewayia flemingeri  Othman & Greenwood, 1988   (M)    [Figs]

[4] Ridgewayia fosshageni  Humes & Smith, 1974   (F,M)    [Figs]

[5] Ridgewayia gracilis  M.S. Wilson, 1958   (F,M)    [Figs]

[6] Ridgewayia klausruetzleri  Ferrari, 1995   (F,M)    [Figs]

[7] Ridgewayia krishnaswamyi  Ummerkutty, 1963   (F,M)    [Figs]

[8] Ridgewayia marki  (Esterly, 1911)   (F,M)    [Figs]

[9] Ridgewayia marki minorcaensis  Razouls & Carola, 1996   (F,M)    [Figs]

[10] Ridgewayia shoemakeri  M.S. Wilson, 1958   (F,M)    [Figs]

[11] Ridgewayia stygia  Ohtsuka, Kase & Boxshall, 2000   (F,M)    [Figs]

[12] Ridgewayia tortuga  Figueroa, 2011   (F,M)    [Figs]

[13] Ridgewayia tunela  Figueroa & Hoefel, 2008   (F,M)    [Figs]

[14] Ridgewayia typica  Thompson & Scott, 1903   (F,M)    [Figs]

[15] Ridgewayia wilsonae  Fosshagen, 1970   (F,M)    [Figs]

[16] Ridgewayia sp.  (Krishnaswamy, 1953)   (M)    [Figs]

[17] Ridgewayia sp.  M.S. Wilson, 1958   (M juv.5)    [Figs]

[18] Ridgewayia sp.  Yeatman, 1969   (M)    [Figs]

Ridgewayia sp.    Fosshagen, 1970   (F)
Ref.: Fosshagen, 1970 b (p.34, figs.F); Humes & Smith, 1974 (p.126, 130, Rem.)
Loc: Bahamas
Rem.: Cf. Ridgewayia fosshageni
(9) Robpalmeria Fosshagen & Iliffe, 2003
Rem.: Total: 1 sp.

[1] Robpalmeria asymmetrica  Fosshagen & Iliffe, 2003   (F,M)    [Figs]
(10) Stargatia Fosshagen & Iliffe, 2003
Rem.: Total: 1 sp.

[1] Stargatia palmeri  Fosshagen & Iliffe, 2003   (F,M)    [Figs]

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Razouls C., Desreumaux N., Kouwenberg J. and de Bovée F., 2005-2021. - Biodiversity of Marine Planktonic Copepods (morphology, geographical distribution and biological data). Sorbonne University, CNRS. Available at [Accessed August 04, 2021]

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