Order Harpacticoida Sars, 1903

Family Cletodidae T. Scott, 1905

Subfamily Cletodinae T. Scott, 1905

 Pseudechinopsyllus andrei sp. nov.

https://zoobank.org/A8715BE5-20F7-4E89-9CED-826540058FDA

Locus typicus.

Grussaí Canyon, Campos Basin, Brazil, geographic position 21°55'S, 39°50'W, 1,300 m depth.

Type material.

Syntypes (ST) 1: female, put on 16 slides, MOUFPE collection no. 22056/1–16; ST2: female, put on 1 slide, MOUFPE collection no. 22057; ST3: female, put on 1 slide, MOUFPE collection no. 22058; ST4: male, put on 1 slide, MOUFPE collection no. 22059; ST5: male, put on 1 slide, MOUFPE collection no. 22060; ST6: female, put on 1 slide, MOUFPE collection no. 22061; ST7: female, put on 1 slide, MOUFPE collection no. 22062; ST8: female, put on 1 slide, MOUFPE collection no. 22063; ST9: female, put on 1 slide, MOUFPE collection no. 22064 (used for CLSM); ST10: male, put on 3 slides, MOUFPE collection no. 22065/1–3; ST11: copepodid CIV, put on 1 slide, MOUFPE collection no. 22066.

Note.

Because all representatives of the type material show damage to different parts of the body or appendages, the description was not based on one but on several individuals. The figure captions refer to the syntype on the basis of which an appendage or body section was drawn.

Description of female.

Habitus (Figs 2A, 3A, B) long and slender, mean body length (R to end of FR) 1,255.9 µm (range 1,155.9–1,400.0 µm; n = 5). Cphth frontally with strongly developed peak, lacking FLH but bearing ACST, and four pairs of long tube pores. CLVPa (Figs 2A, 3A, B, 4A) and CLVPp (Figs 2A, 3A, B) well developed. Rostrum (exemplified in Fig. 5A) small, constricted and almost squarish, apically with pair of sensilla, long tube pore, and RST; previous to the sensillar pedestals, with hyaline outgrowths. CLDP absent. Free thoracic somites bearing P2–P5 laterally with TST1–TST4 and long, unarmed DP1–DP4 that carry sensilla at their tips; somites dorsally and dorsoventrally bearing long tube pores.

Figure 2. 

Pseudechinopsyllus andrei sp. nov. A female habitus, dorsal view (syntype 2) B male urosoma, dorsal view (syntype 5). Scale bar: 100 µm.

Figure 3. 

Pseudechinopsyllus andrei sp. nov., CLSM microphotograph, female habitus A dorsal view B ventral view (syntype 2). Scale bar: 100 µm.

Females with last thoracic and first abdominal somite fused to GDS; former separation still indicated by dorsal suture; GST developed. GDS and remaining abdominal somites except telson also carrying dorsal and dorsoventral tube pores.

Abdominal somites with AST1–AST3, whilst AST4 are missing. Telson (Figs 2A, 3A, B, 4B) at the most as large as the previous somite, laterally with two pairs of tube pores; anal operculum with dense row of fine long spinules on apical margin. FR (Fig. 4C) reaching up to 1/3 of the body length, ~ 15× longer than wide, with long tube pore ventrally, close to proximal margin.

Figure 4. 

Pseudechinopsyllus andrei sp. nov. (syntype 1) A left anterior cephalothoracic lateroventral process (CLVPa), dorsal view B telson, dorsal view C right furcal ramus, dorsal view. Scale bar: 50 µm.

Seven setae present: I and II standing closely together laterally in the middle of FR, III subapically at the outer margin. IV, V and VI terminally, being IV as long as III, VI smaller; V longest and bipinnate. VII biarticulated, inserting dorsally.

A1 (Fig. 5B) four-segmented, all segments covered with long slender spinules. First, third, and fourth segments of nearly the same length, second segment somewhat shorter. First segment apically with one bipinnate seta. Second segment with eight setae (two broken and two bipinnate). Third segment bearing five bare setae at its anterior margin and an acrothek consisting of one aes and two bare setae. Fourth segment with ten bare setae (1 broken), of which two are fused at their bases and arising from a knob together with a small aes. Setal formula: I–1, II–8, III–5 (+ 2 and aes), IV–8 (+ 2 and aes).

Figure 5. 

Pseudechinopsyllus andrei sp. nov. A rostrum, dorsal view (syntype 10) B female A1 (syntype 1). Scale bars: 50 µm.

A2 (Fig. 6A, B) lacking exp. Allobasis with two abexopodal setae (1 seta broken in Fig. 6A). Enp (Fig. 6B) anteriorly with row of spinules, medially with two pinnate and one smaller bare seta. Terminally with six setae, at least three of which long, unipinnate and geniculated, the anterior ones short and bipinnate, the posterior seta bare.

Figure 6. 

Pseudechinopsyllus andrei sp. nov. A A2 basis (syntype 10) B A2 endopod (syntype 1), C, C* Md, showing a semi-schematic contour of the gnathobase plus the detailed md palpus (C) and the detailed gnathobase of the counterpart (C*) (syntype 1). Scale bars: 50 µm.

Md (Fig. 6C, C*) gnathobase strong, with two strongly sclerotised teeth that vary in their shape, one broad brush-like element and one small bare seta. Md palp (Fig. 6C) formed by fused basis, enp, and exp; long and slender, with basal seta no. 2 and endopodal setae nos. 3–5; basal seta no. 1 and exopodal seta no. 6 completely reduced.

Mxl (Fig. 7A) praecoxal arthrite basally with row of spinules; terminally with four bare and two unipinnate strong spines; subapically with two bare setae; additionally, with two bare surface setae, and on the other side with curved row of long spinules. Coxal endite with one bare small seta. Basis fused with enp and exp, forming a single segment that carries two lateral and two apical setae.

Figure 7. 

Pseudechinopsyllus andrei sp. nov. (syntype 1) A Mxl, coxa, and basis (marked with *) separated B Mx C Mxp. Scale bars: 50 µm.

Mx (Fig. 7B) syncoxa with two distinct endites, few long spinules along outer basal edge, and row of spinules along other distal margin.

Proximal endite stronger than distal one, with few spinules and two spines, the proximal one biplumose and fused to the endite, the distal one with one single ruffle; the distal endite apically with three small bare setae. Allobasis distinct, produced into strong claw that carries one strong spinulose ruffle; additionally, with two bare setae. Endopod small and knob-like, equipped with two bare setae.

Mxp (Fig. 7C) prehensile, syncoxa and basis densely covered with long spinules, syncoxa lacking seta. Enp produced into long bare claw, accompanied by slender seta at its base.

P1 (Fig. 8A, B) with transversely elongate basis and two-segmented exopod, both covered with long spinules; endopod absent.

Figure 8. 

Pseudechinopsyllus andrei sp. nov. (syntype 1), P1 A left leg, arrow indicating abnormal supernumerous seta on exp3 B Exp3 of right leg, showing the normal setation. Scale bar: 50 µm.

Basis with one bipinnate outer and one bare inner seta, the latter arising from protruding pedestal. Tube pore inserting proximally close to anterior margin. Exp1 ~ 1/2 as long as exp2, with one bipinnate outer seta; exp2 with one bipinnate outer spine and four (sub)apical geniculate setae, which present a very fine serration previous to the geniculation. Subapically on anterior surface with tube pore.

Pseudechinopsyllus andrei sp. nov. exhibits a remarkable intraspecific variability that is expressed in the abnormal development of supernumerary setae or even segments on some swimming legs in single individuals. For example, the left P1 exp2 on syntype 1 bears an inner seta (arrow in Fig. 8A), which is missing on the right exp2 (Fig. 8B). We interpret this additional seta as abnormal because it is not present in any other species of the Ceratonotus group. Further abnormal setal and segment formation was found on the P2 and the P5 (see below).

P2–P4 (Figs 9A, B, 10A, 11A, B) with laterally elongated, bow-like intercoxal sclerites as exemplified for P4 (Fig. 11B) and transversely elongate bases that are covered with several long spinules and carry one outer seta (bipinnate in P2, bare in P3 and P4) and one very long tube pore. Exopods three-segmented; exp1 with one bipinnate outer seta, exp2 with one bare inner seta and one bipinnate outer spine; in P2 additionally with long tube pore. In Syntype 1, however, like the left-hand P1 exp2 also the left-hand P2 exp2 bears an additional inner seta (arrow in Fig. 9B). Exp3 with two outer spines and two apical setae, the innermost of which narrower and shorter than the outermost one; P2 and P4 exp3 additionally with one inner, P3 exp3 with two inner setae. P3 laterally, P4 subapically at outer margin with tube pore. P2 (Fig. 9A) lacking enp. P3 and P4 (Figs 10A, 11A) each with small knob-like enp carrying one bare seta. Setal formula shown in Table 1.

Table 1.

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Pseudechinopsyllus andrei sp. nov., setation of swimming legs P2–P4. Roman numerals indicate outer setae/spines.

	Exp1	Exp2	Exp3	Enp1
P2	I;0	I;1	II;2;1	–
P3	I;0	I;1	II;2;2	1
P4	I;0	I;1	II;2;1	1

Figure 9. 

Pseudechinopsyllus andrei sp. nov. (syntype 1), P2 A right leg B Exp2 of left leg, arrow indicating abnormal supernumerous seta. Scale bar: 50 µm.

Figure 10. 

Pseudechinopsyllus andrei sp. nov. A female left P3 (syntype 1) B male P3 endopod, anterior (right-hand illustration) and posterior view (left-hand illustration) (syntype 10). Scale bar: 50 µm.

Figure 11. 

Pseudechinopsyllus andrei sp. nov. A female left P4 (syntype 1) B female P4 intercoxal sclerite (syntype 1), C. Male P4 right endopod (syntype 10). Scale bar: 50 µm.

P5 (Fig. 12A) Basoendopod and exopod not fused. Endopodal lobe of basoendopod with long spinules, one tiny bare and one long bipinnate seta, accompanied by three tube pores. Outer basoendopodal seta arising from extremely long setophore (see asterisk*), which is almost twice the length of the exopod and accompanied by one tube pore. Exp also equipped with long spinules, and with two outer, one subapical, one apical and one inner bipinnate setae, as well as with long slender tube pore distally.

Figure 12. 

Pseudechinopsyllus andrei sp. nov. A female right P5; * showing the excessively long setophore (syntype 1) B female genital field with rudimentary P6 (syntype 7). Scale bars: 50 µm.

GF (Fig. 12B) P6 strongly reduced in size, each lobe bearing one tiny bare apical seta; margin on the inner side of the setae grown out into two small but distinctive spikes. Gonopore only indistinctly recognisable, ovoid in shape, and opening into two distal sclerotised formations.

Male. The male resembles the female in most characters, with the exception of the (sexually dimorphic) body size, development of the segments between thorax and abdomen, and in the likewise sexually dimorphic shapes of the A1, the P3 and P4 endopods, the P5, and the P6.

Habitus almost identical to that of the female but clearly (up to 1/3) smaller (mean 944.6 µm; range 908.8 µm–979.4 µm; n = 3) and lacking GDS (cf. Fig. 2B).

A1 (Figs 13A, 14) eight-segmented, haplocer. First segment longest, with several long spinules, and with one bipinnate distal seta (Fig. 14); second segment smaller than first one, with eight bare setae and several long spinules posteriorly (Fig. 14); third segment much smaller than preceding segments, with five bare setae (Fig. 14); fourth segment smallest, no setae discernible (Fig. 14). Fifth segment very slightly swollen, with rows of spinules, and bearing ten setae (all broken in Fig. 14) plus acrothek formed by two setae and one aes arising from long protrusion; sixth segment slender, with two setae (broken in Fig. 14); seventh segment small, with one seta (broken in Fig. 14); eighth segment enlarged, distally acute, with seven bare setae (1 broken in Fig. 14) and a subapical acrothek formed by aes and two additional setae. Segment apically spatulate (arrowed in Fig. 14). Setal formula: I-1; II-8; III-5; IV-0; V-12 + aes; VI-2; VII-1; VIII-9 + aes.

Figure 13. 

Pseudechinopsyllus andrei sp. nov., male A contour of the A1 (syntype 10) B P5, arrow pointing to the abnormally formed segment boundary (syntype 10) C P5 basoendopod, normal shape: endopodal lobe extended but 1-segmented. Scale bars: 50 µm.

Figure 14. 

Pseudechinopsyllus andrei sp. nov., male A1 (syntype 10) A first and second segments B third to fifth segments C sixth to eighth segments; single (*) and double asterisks (**) indicate the respective connections of the segments; length of the aes of the fifth segment indicated by dotted line; spatulate tip of eighth segment accentuated by arrow. Scale bar: 50 µm.

P3 exopod as in female; endopod (Fig. 10B) three-segmented, enp1 small, with some spinules at outer margin; enp2 longest segment, with a slender outwardly curved apophysis that is longer than the whole endopod; enp3 minute, with one long bare apical seta.

P4 exopod as in female; endopod (Fig. 11C) small, two-segmented, enp1 with few spinules on inner margin, enp2 with two bare apical setae.

P5 (Fig. 13B, C) of similar shape as that of female but without spinulose coverage. Endopod also fused to the basis (= basoendopod), exopod distinct. The outer basal setophore (Fig. 13B) is shorter than in the female, only reaching the length of the exopod. Endopodal lobe (Fig. 13C) of syntypes 4 and 5 apically with two short bare setae and two tube pores. In contrast, the endopodal lobe of syntype 10 is divided into two segments (Fig. 13B; arrow indicating boundary), armouring of second segment as in syntypes 4 and 5.

P6 not even rudimentarily recognisable, apparently completely reduced.

Etymology.

The epithet andrei is given in fondly and grateful memory of Prof. Dr André M. Esteves (Federal University of Pernambuco (UFPE), Brazil), who passed away on 30 April 2025.

The aim of the phylogenetic analysis was threefold:

• Justification of Pseudechinopsyllus as a monophylum and assignment of P. andrei sp. nov. to that genus;
• Characterisation of P. sindemarkae and P. andrei sp. nov. as independent species;
• Examination of a closer relationship between Pseudechinopsyllus and Echinopsyllus.

Pseudechinopsyllus and Echinopsyllus undoubtedly belong to the Ceratonotus group (George 2020, 2021), which is why no corresponding further phylogenetic justification is provided. It is also not the intention of the present study to provide a comprehensive phylogeny of the Ceratonotus group itself. The selection of characters for the analysis conducted here is therefore limited to 41 potential aut- and synapomorphies in the direct comparison of Pseudechinopsyllus and Echinopsyllus. The characters are listed in Table 2.

The comparison of P. sindemarkae and P. andrei sp. nov. yielded six derived characters (Table 2, characters 1–6), all except one exclusively shared by these two species, which could be proven by means of a comparison with the remaining taxa of the Ceratonotus group. They are postulated to be synapomorphies of P. sindemarkae and P. andrei sp. nov. Based on these, the monophyly of Pseudechinopsyllus can be satisfactorily and unequivocally substantiated.

Both P. sindemarkae and P. andrei sp. nov. can be characterised as independent species by a number of exclusive derived characters. For P. sindemarkae, six putative autapomorphies are listed in Table 2 (characters 7–12). Five of them are neither detectable in P. andrei sp. nov. nor in any other representative of the Ceratonotus group and thus characterise P. sindemarkae as an independent species.

In addition to the absence of characters 7–12, P. andrei sp. nov. can also be justified as a separate species by seven exclusive characters (Table 2: characters 13–19). None of them converges with P. sindemarkae. The apomorphic state of characters 13 and 14 are considered here as a further development, namely as a secondary reduction of the FLH and the CLDP instead of their primary absence, as assumed for Paratouphapleura and Touphapleura (for Dorsiceratus the judgement is still unclear, but does not play a role in the present context). Why we assumed a secondary reduction of these processes in P. andrei sp. nov. is explained in detail in the following discussion.

Conroy-Dalton (2003a), in the frame of a detailed re-description of Echinopsyllus normani Sars, 1909, assumed that this species holds an isolated position within the then Ancorabolinae. George (2006a) supposed that Echinopsyllus and Pseudechinopsyllus may be closely related on the basis of character similarities that, however, he had not examined in detail. Wandeness et al. (2009) carried out a comprehensive phylogenetic analysis, by means of which they attempted to substantiate the close relationship of the two genera on the basis of nine synapomorphies. Six of these were included in our analysis and are listed in Table 2 (characters 32–34, 36–38). However, one character mentioned by Wandeness et al. (2009: 74, character 32: “Rostrum elongate in its proximal half”) is not included because we cannot beyond doubt confirm an elongation of the proximal half of the rostrum for Echinopsyllus. In the case of Pseudechinopsyllus andrei sp. nov., however, it is clear that the rostrum was not extended; only P. sindemarkae shows a clear elongation of the proximal half (Table 2, character 7). Two further characters of Wandeness et al. (2009) were not considered because they are widespread in the Ceratonotus group, so that their assessment as synapomorphies is currently not possible.

In addition to the six synapomorphies mentioned by Wandeness et al. (2009), we found five more (Table 2, characters 31, 35, 39–41). The synapomorphies found are treated in detail in the discussion. They justify the close relationship of Echinopsyllus and Pseudechinopsyllus clearly and beyond doubt. Moreover, Echinopsyllus can also be clearly established as a monophylum by including the eight autapomorphies listed by Wandeness et al. (2009) and three additional putative autapomorphies (Table 2, characters 20–30).

Pseudechinopsyllus sindemarkae and P. andrei sp. nov. could be grouped into a monophylum based on six synapomorphies (Table 2, characters 1–6):

P. sindemarkae can be characterised as an independent species by means of six autapomorphies (Table 2, characters 7–12). All of them – the clearly elongated anterior rostral part (character 7), the FR studded with many spinules on their proximal section (character 8) the extremely elongated lateral tube pores on the cphth (character 9), the paired small cusps on the second abdominal somite (character 10), as well as the female P5 presenting an excessively long tube pore close to the setophore (Character 11) and subapically on the exopodal lobe (character 12) – occur exclusively in P. sindemarkae, substantiating its establishment as distinct species.

While George (2006a) thought to recognise the elongated anterior rostral region (character 7) in P. sindemarkae as a special generic feature, Wandeness et al. (2009: character 32) even assumed it to be a synapomorphy of Pseudechinopsyllus and Echinopsyllus. Obviously, both were wrong because P. andrei sp. nov. has a small, almost square rostrum (cf. Fig. 5A), which is more similar to those of the genus Dorsiceratus (Drzycimski 1967; Coull 1973; George 2006a; George and Plum 2009; George et al. 2025). And as noted above in relation to Echinopsyllus, we could confirm a clear elongation of the anterior rostral region for the species of this genus, as claimed by Wandeness et al. (2009). Therefore, such rostral elongation cannot be maintained neither as a generic autapomorphy for Pseudechinopsyllus nor a synapomorphy for that genus and Echinopsyllus. It must therefore be assumed that the long rostrum of P. sindemarkae is an exclusive new formation of this species.

On the other hand, it should not be concealed that, in addition to P. sindemarkae, with Pseudopolyascophorus monoceratus (George, Wandeness & Santos, 2013) another representative of the Ceratonotus group bears a clearly elongated anterior rostral region (George et al. 2013: fig. 3A). However, both species differ so drastically from each other morphologically that an inheritance of the elongated rostrum from an ancestor common only to them seems unfounded. Apart from the matching elongation, the rostra themselves are also different in their shape. We therefore assumed a convergent development here.

Pseudechinopsyllus andrei sp. nov. for its part is characterised by seven autapomorphies (Table 2, characters 13–19). Except for characters 13 and 14, all derived states occur exclusively in this species; they include the formation of particularly long spinules on segments 3 and 4 of the A1 (characters 15, 16), the formation of a strongly protruding attachment of the inner seta at the P1 basis (character 17) and the extreme elongation of the female P5 exopod (character 18) and of the setophore on the same swimming leg (character 19). All these characters are not found in any other taxon of the Ceratonotus group and undoubtedly represent autapomorphies of P. andrei sp. nov. However, some uncertainties exist with regard to characters 13 and 14, i.e., the here-presumed secondary loss of the frontolateral horns (FLH) and the cephalothoracic dorsolateral processes (CLDP). This assumption requires a detailed elaboration, which is limited here to the CLDP as an example, but can also be applied to the FLH: despite occasional attempts to homologise the cuticular processes in the Ancorabolidae as well as the Ceratonotus group (e.g., Conroy-Dalton and Huys 2000; Conroy-Dalton 2001; George 2020), no satisfactory analysis is available to date. With the standardised naming of the appendages, however, Lee and Huys (2019) have created a very important prerequisite for attempts of homology, which was further refined by George (2021). However, George’s (2020) statement that homology of the appendages requires comprehensive comparative studies still applies. Nevertheless, these could not be carried out within the scope of the present work but require their own detailed analysis. Yet, because George (2006a) postulated the lack of spinules on the cephalothoracic laterodorsal processes (CLDP) and the dorsal processes 1–4 (DP1–DP4) as an autapomorphy of Pseudechinopsyllus, an attempt was made here to subject the appendages in question to an intergeneric comparison. CLDP and DP, which are structurally almost identical and bear a sensillum at their tip, may be divided into five groups according to their size, shape and armouring: (i) small, conical, more or less rigid and naked (Fig. 15A), (ii) medium-sized, conical, more or less rigid and naked (Fig. 15B), (iii) medium- to large-sized, conical, more or less rigid and covered with many small spinules (Fig. 15C), (iv) large, conical, flexible and knobbed (Fig. 15D, (v) large, flexible, knobbed and dendroid (Fig. 15E). However, despite the similarity of the CLDP and DP, it was necessary to at least partially break up what in fact was a character complex, which is due to the fact that the CLDP are missing in Pseudechinopsyllus andrei sp. nov. We have therefore treated the CLDP and the DP1–DP4 complex separately.

Figure 15. 

Semi-schematic illustrations of the thoracal dorsal processes 1 (DP1) of different representatives of the Ceratonotus group, which can be divided into five groups according to their length, structure, and armouring A group (i) B group (ii) C group (iii) D group (iv) E group (v), drawn to approximately the same scale. Further explanations in the text.

CLDP: these processes are missing in Dimorphipodia, Paratouphapleura, Polyascophorus, Poropsyllus, and Touphapleura (cf. George 2021: fig. 15). The question of whether the CLDP developed as the last pair of dorsal processes – which would be suggested by the fact that ancestral representatives such as Paratouphapleura and Touphapleura lack them –, whether they were reduced secondarily – which could be the case in Dimorphipodia, Polyascophorus and Poropsyllus –, or whether both developmental pathways can be found in the Ceratonotus group, cannot be answered at this point. The spinule-less CLDP in Pseudechinopsyllus sindemarkae, which were hypothesised here as homologous to those of the other CLDP-bearing taxa, correspond to the above-listed group (ii) and were considered a plesiomorphic state (compared to groups iii–v), whereas their absence in P. andrei sp. nov. was hypothesised as a secondary reduction (Table 2, character 14). Pseudechinopsyllus may be regarded as a rather derived taxon in the Ceratonotus group, which seems to be evident from the autapomorphies of the genus (Table 2, characters 1–6). P. sindemarkae shares the possession of CLDP with several other derived representatives of the Ceratonotus group, which, underpinned by their identical position on the cphth, suggests that these processes represent homologous structures, which were certainly inherited as synapomorphies from a last ancestor common only to their bearers. In contrast, there are presumably older taxa (Touphapleura, Paratouphapleura) in which the absence of the CLDP is probably a primary condition. This could be inferred from the fact that these more primitive taxa also exhibit a comparably primitive state with regard to other characteristics (e.g., the formation and size of DP1–DP3). If Pseudechinopsyllus were also assigned to these primitive representatives, then the lack of CLDP in P. andrei sp. nov. would have to be interpreted as primary, like in Touphapleura and Paratouphapleura. However, this would then mean that P. sindemarkae must have developed the processes convergent to the other CLDP-bearing taxa; its CLDP would not be homologous, but analogous to those of the other representatives and convergent as well as merely coincidentally developed at exactly the same attachment point on the cphth. This assumption, the primary absence of the CLDP in P. andrei sp. nov., and their convergent formation in P. sindemarkae seemed less plausible to us than their secondary regression in P. andrei sp. nov.

The same reasoning also applies to the FLH (character 13). Regarding the latter, however, it remains unclear at present how its absence in Dorsiceratus, a relatively derived genus, is to be interpreted.

In the present analysis, we assumed that a secondary reduction of the CLDP and FLH in P. andrei sp. nov. offers the most parsimonious explanation. Thus, characters 13 and 14 are also to be considered as autapomorphies of the new species.

Basing on the discussed autapomorphic characters 13–19, P. andrei sp. nov. can be justified as a distinct species.

The phylogenetic analysis conducted by Wandeness et al. (2009), in which a sister-group relationship between Echinopsyllus and Pseudechinopsyllus was postulated, is not particularly robust in the opinion of Lee and Huys (2019). They based their doubts essentially on the assumption of Wandeness et al. (2009) that the anterior and posterior lateral processes on the Cphth (LII and LIII in Wandeness et al. (2009), CLVPa and CLVPp in Lee and Huys (2019) and here) should be interpreted as synapomorphies for Echinopsyllus and Pseudechinopsyllus. Lee and Huys (2019) correctly argued, however, that these processes are also formed in other representatives of the Ceratonotus group (indeed in Ceratonotus, Dendropsyllus, Tauroceratus). Though, Wandeness et al. (2009) had already admitted this and made their assumption subject to further studies. If, like Lee and Huys (2019), limiting oneself to the presumed homologous position of the processes on the cphth, one must agree with them, as Wandeness et al. (2009) had also only cited the presence/absence of the CLVPa respectively CLVPp as character states. We therefore took a closer look at the structure of the processes (Fig. 15A–E) and were able to include them in the analysis by modifying the character description of Wandeness et al. (2009) accordingly.

In comparison with the remaining representatives of the Ceratonotus group, we were able to identify five further potential synapomorphies of both genera in addition to six out of nine characters proposed by Wandeness et al. (2009) (Table 2, characters 31–41). Whether they will continue to be considered synapomorphies of Echinopsyllus and Pseudechinopsyllus in the future or must be assigned to a larger group of taxa of the Ceratonotus group will only be known after a comprehensive comparison of all representatives of the Ceratonotus group.

The authors have declared that no competing interests exist.

No ethical statement was reported.

No funding was reported.

Conceptualization: KHG. Formal analysis: APW, KHG, PJPS. Funding acquisition: PJPS. Investigation: KHG, APW, PJPS. Methodology: APW, KHG. Project administration: PJPS. Writing - original draft: KHG. Writing - review and editing: KHG, PJPS, APW.

Kai Horst George https://orcid.org/0000-0001-6464-0099

Adriane P. Wandeness https://orcid.org/0000-0003-3193-5784

Paulo J. P. Santos https://orcid.org/0000-0003-4826-362X

All of the data that support the findings of this study are available in the main text.