Diogenes curvimanus, (CLEMENT, 1874)

Almón, Bruno, Cuesta, Jose A., Schubart, Christoph D., Armenia, Lisa & García-Raso, J. Enrique, 2022, Redescription of the hermit crab Diogenes pugilator (Decapoda: Anomura) reveals the existence of a species complex in the Atlanto-Mediterranean transition zone, resulting in the resurrection of D. curvimanus and the description of a new species, Zoological Journal of the Linnean Society 195, pp. 1116-1146 : 1132-1142

DIOGENES CURVIMANUS ( CLÉMENT, 1874)

( FIGS 5A–E , 6A–G , 7C, F, I, L )

Pagurus curvimanus Clément, 1874 : pl. III, fig. 1. Diogenes pugilator - Forest & Guinot, 1956: 32, fig. 3. Type material: Neotype: 1 ♂ 3.4 mm, Spain: Guadalquivir, Doñana National Park, Huelva, (MNHN-IU-2019-3214), 36°47 ′ 59.5 ′′ N, 6°23 ′ 27.3 ′′ W, sand, shallow sublitoral, 17 July 2018.

To p o t y p e s: 1 ♂, 1 ♀, s a m e d a t a a s n e o t y p e, ( IEOCD-BR/2581-2582 ) ; 5 ♂ ( IEOCD-BR/2585 ) .

Other studied material: Belgium: Nieuwpoort-bad, 5 ♂ and 5♀ ( IEOCD-BR/2611-2620 ), 51°09 ′ 08 ′′ N, 2°43 ′ 00 ′′ E, sand, intertidal, 29 September 2018 ; French Atlantic: Arcachon, 1 ♂ ( IEOCD-BR/2621 ), 44°40 ′ 0.04 ′′ N, 1°10 ′ 34.5 ′′ E, sand, shallow sublitoral, 02 October 2018 ; Spain: Ribeira, Galicia, 1 ♂, 1 ♀ ( ZSMA2019 0398-0399) ; 1 ♀ ( IEOCD-BR/2603 ), 42°33 ′ 46.36 ′′ N, 8°59 ′ 15.07 ′′ W, sand, 4–5 m depth, 07 October 2017 ; Doñana N.P., Huelva, 2 ♂ ( IEOCD-BR/2586 ), 36°48 ′ 13.6 ′′ N, 6°23 ′ 46.2 ′′ W, sand, intertidal, 09 September 2018 ; 2 ♂ ( IEOCD-BR/2589,2595 ), 37°12 ′ 06.5 ′′ N, 7°01 ′ 37.0 ′′ W, sand, intertidal, 01 October 2020 ; 1 ♂, 1 ♀ ( IEOCD-BR/2593-2594 ), 37°10 ′ 44.6 ′′ N, 7°20 ′ 37.3 ′′ W, sand, intertidal, 13 January 2020 ; 1 ♂ ( IEOCD-BR/2592 ), 36°58 ′ 02.6 ′′ N, 6°30 ′ 32.2 ′′ W, sand, intertidal, 14 January 2020 ; 4 ♂ ( IEOCD-BR/2587-88 , 2591-91 ), 36°48 ′ 11.6 ′′ N, 6°23 ′ 39.3 ′′ W, sand, intertidal, 11 February 2020 ; Isla Canela, Huelva, 2 ♂, 1 ♀ ( IEOCD-BR/2598-2600 ), 37°10 ′ 51.8 ′′ N, 7°20 ′ 15.3 ′′ W, sand, intertidal, 25 July 2014 ; Santibáñez, Cádiz, 3 ♂ ( IEOCD-BR/2609-2610 ), 36°27 ′ 52.3 ′′ N, 6°15 ′ 21.4 ′′ W, sand, intertidal, 5 October 2015 ; 2 ♂ ( IEOCD-BR/2605-2606 ), 15 October 2015 ; 2 ♂ ( IEOCD-BR/2607-2608 ), 30 May 2018 ; Fuengirola, Málaga, 15 ♂, 7 ♀ ( IEOCD-BR/2583-2584 ), 36°32 ′ 57.92 ′′ N, 4°36 ′ 30.89 ′′ W, sand, 4 m, 04 March 2014 ; La Carihuela beach, Torremolinos, Málaga, 3 ♂ ( IEOCD-BR/2601-2602 ), 36°36 ′ 28.2 ′′ N, 4°30 ′ 13.6 ′′ W, sand, 2–4 m, 11 December 2019 ; Guadarranque, Algeciras, 1 ♂, 1 ♀ ( IEOCD-BR/2696-2597 ), 36°10 ′ 49.7 ′′ N, 5°24 ′ 42.1 ′′ W, sand, 4m depth, 27 October 1995 ; San García, Algeciras, 1 ♂ ( IEOCD-BR/2604 ), 36°06 ′ 17.5 ′′ N, 5°25 ′ 56.7 ′′ W, sand, 4m depth, 25 July 1996 ; Cabo Pino, Marbella, 1 ♂ ( IEOCD-BR/2622 ), 36°29 ′ 05.6 ′′ N 4°45 ′ 00.4 ′′ W, intertidal, 28/04/2005 .

Redescription: Shield ( Figs 5A , 7F ) slightly broader than long; rostral lobe broadly rounded, exceeded by lateral projections that are triangular, acutely pointed, with single spine at apex; anterior margins of shield between rostral lobe and lateral projections slightly concave; anterolateral margins sloping, slightly concave, smooth; anterolateral angles rounded, with a small spine and usually another smaller below; lateral margin straight or slightly convex; posterior margin truncate; dorsal surface not vaulted, smooth, with groups of paired setae, and lateral margins with few faint transverse tuberculate ridges extending on to lateral surface of shield. Branchiostegites with dorsal margin bearing row of small spines (up to 12). Posterolateral plates not well calcified, unarmed.

Ocular peduncles (including corneas) about 0.6 times as long as shield, moderately stout, slightly inflated in distal half; corneas not dilated, corneal diameter about 0.3 peduncular length; row of short, plumose setae over inner surface of the peduncles. Ocular acicles ( Figs 5A, C ) broad, subtriangular, concealing basal part of ocular peduncles, with slightly concave mesial margin; anterior margin sloping outwards, bearing 14–16 acute spines, decreasing in size towards outer margin, covering the entire length of the anterior margin; innermost distal spine distinctly larger. Intercalary rostriform process simple, shorter than ocular acicles (including spines), tapering acutely.

Antennular peduncles ( Figs 5A, B ) overreaching distal corneal margin by about 0.4–0.6 length of ultimate segment, not reaching distal margin of antennal peduncle; third segment short, unarmed, broadened distally, maximum length slightly more than three times distal width, subequal in length to penultimate segment, with a tuft of setae on distodorsal margin; second segment unarmed, with tufts of plumose setae on dorsodistal and ventrodistal margins; basal segment moderately broadened distally, unarmed, except for tiny spinules on rounded ventrodistal border.

Antennal peduncles ( Fig. 5A ) overreaching distal corneal margin by almost the entire fifth segment length (0.8–0.9); fifth segment with row of moderately short, stiff setae on ventral surface, and tuft of short setae dorsodistally, unarmed; fourth segment unarmed, with tuft of long setae on distomesial margin; third segment unarmed; second segment with distolateral outer process stout and acute, with subdistal smaller spine and sparse, short setae on lateral outer margin; distomesial spine usually small and obtuse but evident with associated tuft of long setae; mesial margin bearing some sparse, short setae; first segment unarmed. Antennal acicle short and broad, subtriangular, slightly overreaching the proximal half of fourth peduncular segment, not reaching distal margin, bearing a simple strong terminal spine plus usually six to seven spines almost equal in size along mesial margin, and tufts of setae on both mesial and lateral margins. Antennal flagellum short and robust, noticeably setose, with rows of paired setae in dorsolateral (short), ventral (medium) and ventrolateral (long) surfaces.

Third maxilliped ( Fig. 5D ) basis unarmed; ischium with crista dentata bearing one prominent distal spine and two smaller on distal half, with additional one to two spinules on proximal half; ischium and merus with rows of scarce setae on lateral margins; carpus, propodus and dactylus with dense tufts of thick, long, simple and plumose setae at distolateral and distoventral margins, with less numerous long setae at distodorsal margin, concealing part of the segments; exopod peduncle reaching half carpal length of endopod.

Male left cheliped ( Figs 6A, B , 7C, F, I ) much larger than right ( Fig. 5E ); length and shape variable in males. Dactylus shorter than palm dorsal surface, slightly arched, ending in small but strong calcareous claw, crossing tip of fixed finger; upper, inner margins defined rows of small, obtuse tubercles, upper, outer by larger acute tubercles with associated sparse setae; dorsal surface between upper, outer and inner rows slightly concave; outer surface convex, not flattened, smooth; lower margin with tufts of stout, short setae; cutting edge almost straight, with row of teeth of similar sizes; inner surface with two rows of tubercles running parallel to upper margin on upper half, reaching distal part of dactylus; proximal surface with small subacute to obtuse tubercles.

Fixed finger triangular, not proximally broadened and almost smooth, except for some sparse, small tubercles on outer surface and irregular row of low tubercles on lower margin; tufts of stout, short setae on upper margin; inner surface smooth, with tufts of short setae near cutting edge and lower, inner margin. Palm narrow, about 1.5 times as long as high (max. medial length – max. height); upper margin shorter than carpus; dorsal surface of palm slightly convex, covered with evenly spaced obtuse tubercles and rows of short setae; upper, inner margin not well defined; upper, outer delineated by obtuse tubercles; outer surface glabrous, with upper part slightly concave, medially strongly and evenly convex, with numerous small, obtuse tubercles arranged as discernible longitudinal rows; lower palmar margin slightly concave in distal half, defined by row of large obtuse tubercles, and tufts of short setae; inner surface covered with low, rounded tubercles and sparse, short setae.

Carpus of males long, about as long as merus and twice as long as high ( Fig. 6A, B ); usually longer and higher than palm; dorsal surface broadened, with upper, inner margin indistinctly delineated by row of tubercles; upper, outer well defined by curved row of subacute to obtuse tubercles, increasing in size distally, with associated medium-sized setae; outer surface with upper part slightly concave, medially strongly and evenly convex with small, obtuse evenly distributed tubercles, largest near distomesial margin; distal margin serrated; lower margin defined by row of small, obtuse tubercles; lower margin straight in distal part, short and slightly concave proximally, with tufts of short setae; inner surface covered with low, rounded tubercles and tufts of short simple setae.

Merus longer than high ( Fig. 6A, B, G ); subovate in dorsal view; distal margin spinose throughout, with short setae; dorsal surface with small subacute tubercles of similar sizes and tufts of long, simple and plumose setae; lateral surface with evenly distributed rows of rounded tubercles, except on distal lower area; small and shallow transversal furrow subdistally on lower half, with sparse, short setae; ventrolateral margin denticulate accompanied by sparse mediumsized simple and plumose setae, slightly concave in proximal half, with larger subacute tubercle on proximal margin; mesial face with weakly calcified, u-shaped patch; subdistal transversal furrow short and faint, with small tubercles and short setae ( Fig. 6G ); dorsodistal margin with spines of similar size; ventrodistal margin defined by slightly larger spines with associated plumose setae. Ischium with row of small tubercles on distal margin ( Fig. 6A ) and row of slightly bigger tubercles on ventromesial margin ( Fig. 6G ).

Variability. Propodus of male varies from form described to one where lower margin is strongly concave, giving a sinuous appearance. Carpus can also show on occasion a row of well-developed rounded tubercles at distomedial part. This is especially common in females and young males with short chelipeds (the reduction in size of the tubercles seems to be quicker because of the faster grow rate of male cheliped).

Female left cheliped differs from male in the following features ( Fig. 6C ). Dactyl higher and shorter in proportion, with upper margin delineated by row of acute to subacute tubercles. Palm short and broad, slightly longer than high; outer surface covered in small, acute tubercles, with two prominent, acute tubercles distodorsally. Carpus relatively much shorter; upper, outer margin with two to three strong spines distally; outer medial surface with large, rounded tubercles increasing in size distally. Merus dorsal margin with larger, acute tubercles; lower margin defined by row of acute tubercles; lateral surface with subdistal transversal furrow more evident; mesial face with acute tubercles on ventral area and subdistal transversal furrow well defined.

Right cheliped ( Fig. 5E ). Much shorter than left, robust (reaching one-third of carpus in neotype); dactylus and fixed finger with prominent hiatus, both terminating in small but strong calcareous claws. Dactylus (measured along mesial margins) about 2.5 times as long as palm upper margin, noticeably arched; upper, inner and outer margins defined by row of subacute tubercles with associated long setae; dorsal surface convex, broad and tuberculate; outer surface strongly convex with row of subacute tubercles parallel to the upper, outer margin; rest of outer surface with sparse, small tubercles and short, simple setae; inner surface with row of tubercles below upper, inner margin, and associated long, plumose setae; lower, inner margin with sparse setae.

Palm with dorsal surface broad, short and convex; upper, outer and inner margins defined by row of subacute tubercles; outer surface broad, convex medially, with evenly spaced, subacute tubercles grading distally to acute tubercles; lower palmar margin defined by flat, setosed tubercles with long setae; fixed finger proximally broadened, outer surface slightly concave, with flat, setosed tubercles grading to acute near cutting edge; lower margin defined by flat, setosed tubercles; inner surface with low, rounded tubercles and long setae especially dense on fixed finger inner surface.

Carpus dorsal surface narrow throughout; upper, outer margin defined by longitudinal row of spines and short setae; upper, inner margin defined by row of subacute tubercles with long, simple and plumose setae; additional row of small tubercles below the upper, outer margin, delimiting a shallow concave area; rest of outer surface slightly convex with low tubercles and numerous tufts of long setae; lower surface nearly smooth with sparse, short setae; inner surface weakly tuberculated, with sparse, long, plumose setae.

Merus distodorsal margin with spinules and long setae; dorsal margin defined by row of small, obtuse spines and tufts of long, plumose setae; lateral surface covered with low, rounded tubercles and sparse, short setae, giving an almost smooth appearance; shallow tuberculate furrow subdistally, bearing short setae; ventrolateral margin delimited by row of small spines decreasing in size proximally, and tufts of long, plumose setae; mesial face with small, weakly calcified, u-shaped patch proximally, smooth, with ventromesial margin defined by row of minute spines and long, plumose setae. Ischium crenulated on distolateral and ventromesial margins.

Second and third pereiopods slender ( Figs 6D , 7L ) subequal in length. Dactyl about 1.3 times as long as propodus, weakly curved; terminating in small corneous claw; upper and lower, outer margins unarmed, with rows of long thin setae, more numerous and longer on lower margin; outer surface with shallow, longitudinal sulcus medially, without setae in the proximal one-fifth, then continuing with sparse, short setae associated with sulcus; inner surface with two longitudinal rows of thin-spaced, long, stout setae adjacent to upper and lower margin, the proximal onethird with additional irregular rows of short, plumose setae placed over the sulcus.

Propodus slightly longer than merus in second and third pereiopods, with upper margin defined by row of small acute tubercles (second), or faintly dentate (third), covered with long, simple setae; two rows of small tubercles running parallel to upper and lower margins, with tufts of short setae associated with tubercles; lower margin smooth, with sparse, short setae.

Carpus upper margins defined by row of obtuse spines (second) or spinules (third), with dense, medium-sized, simple and plumose setae, ending in two (second) or one (third) conspicuous distal spines; rows of small, obtuse tubercles near outer upper, medial and lower surfaces with tufts of short setae in outer medial and lower surfaces; lower margin smooth with scarce short setae.

Meral length about three times the maximum width; upper margin defined by small tubercles (second and third), with sparse, long, plumose setae; lower margin defined by row of low, small, subacute tubercles (second and third), with poorly developed spinules on lower distal margin (second) or without distal spines (third), and dense rows of long, plumose setae. Ischium unarmed, with long, plumose setae on distal margin.

Fourth pereiopod ( Fig. 6E ). Dactyl with row of eight minute, spiniform setae on distal part of ventral margin. Propodus suboval, much longer than broad, with plumose, long setae along unarmed dorsal margin; propodal rasp consisting of five to six rows of corneous scales, covering distoventral part including fixed finger; rest of segments unarmed, with clumps of long, plumose setae.

Fifth pereiopods. Propodus slightly shorter than merus, and about 1.7 times longer than carpus; group of subacute corneous scales in distodorsal surface of propodus and smaller ones in dactylus and fixed finger; long clumps of strong simple setae.

Male unpaired left pleopods 2–5, uniramous, marginally setose. Female gonopores, paired; two to four unpaired pleopods well-developed, biramous; fifth pleopods without exopod, as in male.

Telson ( Fig. 6F ) with shallow, median cleft, slightly asymmetrical; left posterior lobe slightly larger than right, with small spines on lateral margin, becoming blunt tubercles anteriorly; oblique terminal margin with larger spines; right posterior lobe with row of spines on less oblique terminal margin, extending on to posterior half of lateral margin.

Coloration ( Fig. 7C, F, I, L ). Greyish white eye peduncles, with two diffuse bluish rings and a broader proximal brown triangular stain, projecting towards apex as a narrow line. Bluish ophthalmic scales. Whitish antennules, with triangular brown patch on second segment, orange in proximal two-thirds of third segment and flagellum. Antenna with greenish white or reddish peduncle, with scattered reddish brown streaks and conspicuous greenish blue spot on dorsal face of fourth segment. Carpus of the left cheliped with deep reddish orange background and an incomplete medial reddish brown ring. Orange coloured white hand with chestnut brown spot proximally, extending in two narrow lines towards middle outer surface; additional, more apparent, stain in proximal part of dactylus. Right cheliped with white background on merus and carpus, with some brown spots, and orange proximal carpal area; white palm with some brown spots in proximal upper area, which extends following central rows of tubercles. Second and third pereiopods with reddish white background colour; merus with reddish brown rings on middle (incomplete) and proximal areas. Carpus with an incomplete brown ring on medial area and small spot in the upper, proximal area. Propodus with large stain covering almost the entire proximal half, shorter in dorsal surface. Dactylus with a brown base that extends along the sulcus, sometimes faint and almost imperceptible.

Habitat: Sandy beaches, in tide pools and subtidal areas up to 15 m depth, with maximum abundances in the shallow subtidal, between 4– 6 m.

Distribution: Described from French Mediterranean, although according to the samples examined in this work, it is the dominant species in Atlantic European waters. Despite the limited geographic range of the samples studied (covering the Atlantic coast of the Iberian Peninsula, France and Belgium), the abundance of images posted online suggest that its distribution could be wider, probably including most part of the southern North Sea. Its presence in the Mediterranean, where there are at least two more species sharing part of its distribution, seems to be more reduced, currently with records in areas close to the strait of Gibraltar with strong influence of Atlantic waters (Málaga, Marbella, Algeciras) and Tunisia (see: Forest & Guinot, 1956: fig. 3; García Raso, pers. comm.).

Remarks: The specific name D. curvimanus is resurrected from Clément (1874), based on the striking consistency of his drawing with the here described species, including the characteristic shape of the left chela. Clément (1874) mentioned that this species occurs in the Gulf of Aigues-Mortes (French Mediterranean). However, all investigations carried out to locate the type of this species have been unsuccessful so far, bringing us to the conclusion that the type is most likely lost. Even if the mentioned locality raises some questions concerning the distribution range of the here described species, Clément’s short description, and especially the specimen shown on the accompanying plate, leave no doubt about the identity of his specimen with the above described morphotype. Following a series of synonymizations affecting most of the European species of Diogenes , in consequence of their presumed morphological variability and wide distributions ( Nöel, 2016), D. curvimanus became a junior synonym of Diogenes pugilator (Roux, 1829) . Despite the doubts of Clément (1876), the identity of his drawing and our morphotype brought us to the decision to restore the validity of this species within the genus Diogenes and to propose a neotype to replace the missing type.

Diogenes curvimanus ( Clément, 1874) can be easily differentiated from any other eastern Atlantic and western Mediterranean species of Diogenes by means of male left cheliped shape and size, which is slender and long, almost without pilosity and less spinose. The third antennular segment of the former is short and markedly broadened distally (shorter or equal than antennal peduncle), ocular scales serrated throughout and telson only slightly asymmetrical.

Female left chelipeds share some similarities with D. pugilator s.s., but are less globose in D. curvimanus , with the distal part narrowing towards the tip and the palm not inflated; spination is also less developed in the latter, usually with mesial evenly distributed tubercles increasing in size distally.

TAXONOMIC REMARKS

Seven other species of Diogenes occur in the East Atlantic Ocean. All of them can be easily differentiated from the three species described above by the following characters.

Diogenes mercatoris Forest, 1952 has a short and reduced intercalary rostriform process, long ocular peduncles and a shield bearing strong spines on the laterodorsal surfaces. Diogenes ortholepis Forest, 1961 and D. denticulatus Chevreux & Bouvier, 1981 have a well-developed intercalary rostriform process bearing denticles, while this piece is always smooth in the three species described above. Diogenes ovatus Miers, 1881 is characterized by a large depression on the upper face of the chelar carpus, which is not present in any of the three species of the D. pugilator complex. Diogenes brevirostris Stimpson, 1858 and D. extricatus Stebbing, 1910 have only two to three spines on the posterior branchiostegite, while our three species have continuously serrate branchiostegites. The left cheliped of D. costatus Henderson, 1893 has an obliquely longitudinal ridge on the outer surface and the carpi of the pereiopods bear some scarce spines, never being continuously serrated. A confusion is furthermore unlikely, as D. brevirostris , D. extricatus and D. costatus have been exclusively recorded from Atlantic South African waters.

The form described by Forest (1956) from Accra in Ghana as Diogenes sp. , although still not officially described (nor properly), is here included also for comparative purposes. This form has reduced corneas and ocular peduncles reaching behind the distal margin of antennal segment 4. There is also a conspicuous tooth on the disto-exterior upper margin of the left cheliped palm, which is not present in any of the three species described above.

Among the species recorded from the Indian Ocean coasts of South Africa, and that could possibly cross to the nearby Atlantic waters, only D. albimanus and D. custos seem to have currently valid records, while the presence of D. senex Heller, 1865 from Mozambican waters appears doubtful and still unconfirmed ( McLaughlin & Dworschak, 2001).

Diogenes albimanus has short antennal acicles, not reaching to mid-length of the fourth antennal peduncular segment; it also shows a different armature of the left cheliped, lack of spines on propodus and merus of pereiopods, and even different coloration ( Landschoff & Rahayu, 2018).

Diogenes custos has a spinose intercalary rostriform process ( McLaughlin & Holthuis, 2001), and the ocular peduncles are in D. senex are longer than the antennal peduncles; also, the shape and ornamentation of the left cheliped is different.

The species considered here as new share some characters with a group of Indo-Pacific species included in the informal ‘ edwardsii ’ group, defined by Asakura & Tachicawa (2010) by ‘having simple intercalary rostral process, antennal peduncles longer than ocular peduncles and antennal flagellum with paired long setae in each article’. Two of these species ( D. pallescens Whitelegge, 1897 and D. avarus Heller, 1865 ) have been recorded outside their original distribution area, reaching the Red Sea ( McLaughlin, 2002; Siddiqui et al., 2004; El-Wakeil et al., 2009), which opens the possibility for further expansion to the Mediterranean Sea. The species D. avarus is characterized by the presence of six (five to eight) minute spinules on the margins of the branchiostegites, a male left cheliped carpus 1.6–1.7 longer than palm (dorsally), the dorsal margin of the P3 carpus often with a single row of smaller spinules (occasionally only a dorsodistal spine), a P2 carpus with one or two rows of small spines (occasionally only a cluster of small spines distally) and a left cheliped without a longitudinal ridge on the outer surface. Moreover, D. pallescens has long ocular peduncles, equal in length to the antennular peduncle, a dorsal surface of left P2 carpus without a row of spines, but only with two spines (dorsodistal and dorsoproximal).

Diogenes tirmiziae Siddiqui & McLaughlin, 2003 , is currently known only from the Sindh coast of Pakistan and is easily recognizable by the short antennal peduncles, not reaching or slightly overreaching distal corneal margins and the subquadrate antennal acicles, reaching only to mid-length of fourth antennal segment, while in the species described above, acicles always overreach this length.

Like all other species of Diogenes , the three species included in this work show some morphological variation, especially of the left cheliped. This feature is more accentuated in D. curvimanus , where both the length and width of the male left cheliped can be markedly variable, probably produced by a markedly ontogenic allometry, although always conserving the unique morphological characters of the species, thus distinguishing it from the rest of the congeners.

PHYLOGENETIC ANALYSES

We analysed the phylogenetic relationships among five species of Diogenes in order to test whether they constitute genetically separate evolutionary units. Maximum likelihood analyses of the combined ( Fig. 8A ) and individual genes datasets (Supporting Information, Figs S1–S 3 ) all yielded similar results, recovering the three putative species as monophyletic units, with relatively long branches and strong nodal supports ( Fig. 8A ). These three species are clustered together as a species complex, here referred to as the D. pugilator species complex, with strong support. Therefore, the DNA evidence agrees with separations based on morphological characters and live colour patterns and confirms the taxonomic delimitation of the species.

The partitions defined by the ABGD method ( Puillandre et al., 2012) are also congruent with the species delimitation obtained from the other methods. The groups recovered by the ABGD method (COI) were equivalent to those obtained from the concatenated dataset and have been included in the concatenated tree for illustrative purposes ( Fig. 8A ). For this species complex, the barcode gap seems to be between 0.05 and 0.12% divergence ( Fig. 8B ).

Results from individual gene analyses allowed us to obtain a general overview of the taxonomic status of the species complex, based on the sequences obtained from NCBI/BOLD databases (Supporting Information, Figs S1–S 3 ). For the 16S gene, only nine sequences were available and none of them corresponds to species within the study area, while for the nuclear 28S gene, no sequence was available for species of this genus. However, the greater number and representatives of species among the sequences of the COI gene allowed us to draw some conclusions that agree with the preliminary geographical distribution of the different species arising from the examination of the samples included in this work. The specimens sequenced by Lobo et al. (2013) originating from the Portuguese coast, correspond without doubt to D. armatus , while the rest of the species collected from Atlantic European waters and labelled as D. pugilator correspond to the species described here as D. curvimanus , and should, therefore, be reviewed and renamed in the light of new information. None of the available sequences on the online databases matched those of Diogenes pugilator s.s..

KEY TO THE PRESENTLY KNOWN ATLANTIC SPECIES OF DIOGENES DANA, 1851

Most studies of taxonomic significance dealing with the genus Diogenes in eastern Atlantic waters were published in the late-19 th and mid-20 th centuries, being frequently devoted to limited areas, as a result of surveys or specific collecting campaigns (Roux, 1829; Rossignol, 1962; Clément, 1874; Chevreux & Bouvier, 1892; Forest, 1955, 1956, 1961). Despite the fact that identification keys were included in some of these monographs ( Barnard, 1950; Forest, 1956; Ingle, 1993), an effort to summarize current information, including the maximum number of species in the genus, appears useful in order to compare all the species and account for the changes implemented in the last decades. Hence, we present below an updated identification key, including all the species recorded so far from the eastern Atlantic.

IDENTIFICATION KEY FOR THE SPECIES OF DIOGENES FROM THE EAST ATLANTIC OCEAN 1. Intercalary rostriform process between ocular acicles reduced. Shield with oblique rows of strong spines (see Forest, 1952: figs 1–5; Forest, 1955: fig. 14, pl. II, 8)........................... Diogenes mercatoris Forest, 1952

1’ Intercalary rostriform process between ocular acicles not reduced. Spines on shield not as above .............2

2. Intercalary rostriform between ocular acicles process spinose.......................................................................3

2’ Intercalary rostriform process between ocular acicles smooth .......................................................................4

3. Ocular peduncles not overreaching base of fifth segment of antennal peduncles. Inner border of antennal acicle concave (see Forest, 1955: fig. 13, pl. II, fig. 7)........ Diogenes denticulatus Chevreux & Bouvier, 1892

3’ Ocular peduncles long, overreaching base of fifth segment of antennal peduncle. Inner border of antennal acicle straight (see Forest, 1961: figs 1–4) ................................................... Diogenes ortholepis Forest, 1961

4. Branchiostegites partially serrated..................................................................................................................5

4’ Branchiostegites serrated throughout .............................................................................................................6

5. Upper surface of carpus of left chela convex, with irregularly arranged conical tubercles; no red spot on left chela. Wide ocular acicles (see Barnard 1950: figs 81a, c, d).............. Diogenes brevirostris Stimpson, 1858 *

5’ Upper surface of carpus of left chela flat, with two conspicuous rows of tubercles; one red spot on outer surface at propodus base of left chela. Narrow ocular acicles (see Barnard, 1950: fig. 81h)........................... .................................................................................................................. Diogenes extricatus Stebbing, 1910 *

6. Palm of left cheliped oval, depressed; outer surface with depression at lower region. Carpus short, with deep depression on upper face (see Forest 1955: figs 15, 16; pl. II, 9) ............... Diogenes ovatus Miers, 1881

6’ Palm of left cheliped not oval. Carpus without depression on upper face ......................................................7

7. Palm of male left cheliped clearly longer than wide, carpus frequently higher than palm; outer surface of palm finely granulate or smooth. Lower margin of carpus of left cheliped long and straight distally, slightly concave proximally. Antennular peduncle shorter than antennal peduncle, widened distally ( Forest & Guinot, 1956: fig. 3; Figs 5 , 6 , 7C ).......................................................... Diogenes curvimanus Clément, 1874

7’ Palm of male left cheliped not clearly longer than wide, carpus about the same height as palm; outer surface of palm with tubercles or spines, not smooth. Lower margin of carpus of left cheliped convex at distal half, forming a prominent sinus proximally. Antennular peduncle subequal or longer than antennal, not markedly widened distally .........................................................................................................................8

8. Antennular and antennal peduncles subequal in length. Ocular acicles subtriangular, with three to five distal spines (innermost larger), rest of anterolateral outer margin with small tubercles of similar size. Outer surface of left cheliped palm medially inflated, covered with small spinose tubercles; lower, inner surface of palm defined by a sinuous crest-like row of large, rounded tubercles ( Figs 1 , 2 , 7A, D )................ .......................................................................................................................... Diogenes pugilator Roux, 1829

8’ Antennular peduncles longer than antennal ones. Ocular acicles with spines on the whole length of anterolateral margin, or few spines on distal half, without tubercles. Outer surface of left cheliped palm not medially inflated, with at least some larger tubercles or spines defining ridges; lower, inner surface of palm not defined by a sinuous crest-like row of large, rounded tubercles .....................................................9

9. Ocular acicles subtriangular with 11–12 acute spines decreasing in size, innermost larger, covering entire length of anterolateral margin. Outer surface of male left cheliped palm spinose, with largest spines forming longitudinal rows. Left cheliped hirsute ( Figs 3 , 4 , 7B, E )....................... Diogenes armatus sp. nov.

9’ Ocular acicles with minor dentition restricted to distal half of anterolateral margin. Outer surface of left cheliped palm almost smooth, with short, but prominent oblique granulated proximal ridge. Left cheliped glabrous (see Barnard, 1950: fig. 81e, f; Henderson 1893: pl. 39: 7, 8; Lewinsohn 1969: fig. 6) ...................... ................................................................................................................. Diogenes costatus Henderson, 1893 * *Species with Atlantic records restricted to South African waters only. The form Diogenes sp. mentioned in Forest (1956) is not included here, as it has not yet been formally described as a new species. Nevertheless, this form can be easily separated from the rest of the Atlantic species by the reduced corneas and ocular peduncles reaching behind distal margin of antennal segment 4. Forest also points out the presence of a conspicuous tooth on the disto-outer upper margin of the left cheliped palm.

Figures

Figure 1. Diogenes pugilator s.s. ♂ 3.0 mm, Frontignan, France, neotype, (MNHN-IU-2019-3215): A, anterior part of body; B, ophtalmic scales; E, right cheliped, outer aspect; F, telson, dorsal aspect. Diogenes pugilator s.s. ♂ 2.7 mm, Frontignan, France, topotype (ZSMA2019 0400): C, right antennular, inner view; D, left maxiliped 3, (inset: detail of the spines, ventral aspect). (Scales: A, C, E = 1 mm, B, D, F = 0.5 mm).

Figure 2. Diogenes pugilator s.s. ♂ 3.0 mm, Frontignan, France, neotype, (MNHN-IU-2019-3215): A, left cheliped, outer aspect (arrow indicating bispinose protuberance); B, left cheliped, dorsal aspect (inset: detail of the row of tubercles on the lower, inner surface). Diogenes pugilator s.s. ♀ 2.5 mm, La Carihuela, Málaga, Spain, topotype, (IEOCD-BR/2660-2661): C, left cheliped, outer aspect. Diogenes pugilator s.s. ♂ 2.7 mm Frontignan, France, topotype, (ZSMA2019 0400): D, left pereiopod 2 (insets: variations in P3 carpus; dactylus inner aspect); E, pereiopod 4; F, merus, mesial view (setae omitted). (Scales: A–C, F = 2 mm, D = 1 mm, E = 0.5 mm).

Figure 3. Diogenes armatus sp. nov. ♂ 3.4 mm, Torregorda, Cádiz, Spain, holotype, (MNHN-IU-2019-3213): A, anterior part of body; B, right antennule, inner aspect; C, ophtalmic scales; D, left maxiliped 3 (inset: detail of the spines, ventral aspect); E, right cheliped, dorsal aspect; F, left pereiopod 2 (insets: variations in P3 carpus; dactylus inner aspect); G, telson, dorsal view. (Scales: A, E–G = 1 mm, B–D = 0.5 mm).

Figure 4. Diogenes armatus sp. nov. ♂ 3.4 mm, Torregorda, Cádiz, Spain, holotype, (MNHN-IU-2019-3213): A, male left cheliped, outer aspect (arrow indicating bispinose protuberance); B, left cheliped, dorsal aspect; C, left cheliped inner surface; D, left cheliped dactylus, dorsal aspect; F, left pereiopod 4, outer aspect; G, left cheliped merus, mesial view (setae omitted). Diogenes armatus sp. nov. ♀ 3.8 mm, Isla Canela, Huelva, Spain, allotype, (MNHN-IU-2014-5736): E, female left cheliped, outer aspect. (Scales: A, C, G = 2 mm; B, D, E = 1 mm; F = 0.5 mm).

Figure 5. Diogenes curvimanus. ♂ 2.6 mm, Guadalquivir N.P., Huelva, Spain, neotype, (MNHN-IU-2019-3214): A, anterior part of body; B, right antennular, inner aspect; C, ophtalmic scales; D, maxiliped 3 (inset: detail of the spines, ventral aspect); E, right cheliped, outer aspect. (Scales: A = 1 mm, B = 0.2 mm, C–E = 0.5 mm).

Figure 6. Diogenes curvimanus. ♂ 2.6 mm, Guadalquivir N.P., Huelva, Spain, neotype, (MNHN-IU-2019-3214): A, left cheliped, outer aspect; B, left cheliped, dorsal aspect; D, left pereiopod 2 (insets: variations in P3 carpus; dactylus inner aspect); E, left pereiopod 4, outer aspect; F, telson, dorsal aspect; G, merus, mesial view (setae omitted).Diogenes curvimanus. ♀ 2.9 mm, Ría de Arousa, Galicia, Spain (ZSMA2019 0399): C, Left cheliped, outer aspect (arrow indicating bispinose protuberance). (Scales: A–B, G = 1 mm; C, E–F = 0.5 mm; D = 2.0 mm).

Figure 7. Live coloration of the three species of Diogenes: A–C, left cheliped, outer aspect; D–F, cephalothorax and cephalic appendages; G–I, detailed photographs of the inner face of palms, showing the shape of the row of tubercles; J–L, left pereiopod 2. A, D, G, J, Diogenes pugilator; B, E, H, K, Diogenes armatus sp. nov. C, F, I, L, Diogenes curvimanus.

Figure 8. A, maximum likelihood phylogenetic tree based on the concatenated mitochondrial data (COI + 16S) using 1000 nonparametric bootstrap replicates. Numbers on the branches represent ML bootstrap values; only bootstrap values> 70 (ML) are included. The species Dardanus arrosor and Paguristes eremita are included as outgroups. Groups recovered from the ABGD analysis (G.1–G.9) are also included. B, histogram of genetic distances (JC69 Jukes–Cantor) showing the barcoding gap for the COI gene.