Dardanus ctenodon, D'Acoz, 2025

Dardanus ctenodon sp. nov.

( Figs. 2–6 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 )

Pagurus striatus . — Miers 1881: 274 (in part, specimens from Gorée, Senegal only); Chevreux & Bouvier 1892: 119. Petrochirus arrosor pectinatus . — Rathbun 1900: 302 (in part: Senegal only). Pagurus arrosor var. pectinata . — Balss 1921: 43 (in part: Senegal only). Dardanus pectinatus View in CoL . — Schmitt 1926: 45, fig. 69C, 69F, 69I; Monod 1933: 480, 481 (discussion); Forest 1954: 1697, figs 1–3

(postlarval stages); 1955: 90 (key), 98 (ubi syn.), fig. 20; 1956: 356; 1958: 157 (new record); 1961: 229 (new records);

1966b: 149 (new records); Fize & Serène 1955: 223–224; Rossignol 1957: 99 (diagnosis and colour description), fig. 13;

Dechancé 1961: 529 (larvae); Forest & de Saint Laurent 1968: 93; Debelius 1999: 61, unnumbered colour photograph;

Wirtz & Debelius 2003: 138, unnumbered photograph. Dardanus arrosor pectinatus . — Zariquiey Álvarez 1952: 24.

non Pagurus striatus Latreille, 1803: 165 .

non Pagurus striatus var. pectinata Ortmann 1892a: 284 , pl. XII, fig. 10.

Type material. AFRICAN EASTERN ATLANTIC: ♂ holotype, RV Mercator, cruise 9, Senegal, Cap Rouge , 14°40'N, 16°08'W, 15 m, 14 Sep. 1935 ( RBINS, INV. 13673); 1 small paratype, RV GoogleMaps Mercator, cruise 9, Senegal, in front of Rufisque , 14°40'N, 16°15'W, 22 m, 14 Nov. 1935 ( RBINS, INV. 13668); 1 small paratype, RV Mercator, cruise 9, Senegal, in front of Rufisque , 14°40'N, 16°15'W, 22 m, 14 Nov. 1935 ( RBINS, INV. 13669); 1 small paratype, RV Mercator, cruise 9, Senegal, in front of Rufisque , 14°40'N, 16°15'W, 22 m, 14 Nov. 1935 ( RBINS, INV. 13670); 1 small paratype, RV GoogleMaps Mercator, cruise 9, Senegal, in front of Rufisque , 14°40'N, 16°15'W, 22 m, 14 Nov. 1935 ( RBINS, INV. 13671); 1 ♂ paratype, RV GoogleMaps Mercator, cruise 11, Republic of Guinea, between Tamara [ 9°29'N, 13°49'W] and Roume [ 9°28'N, 13°48'W] Islands , 8–10 m, 10 Dec. 1936 ( RBINS, INV. 13667); 1 small ♀ paratype, Angola, Luanda, Jun. 1949, coll. Dr. Dartevelle ( RMCA 36494 View Materials ); 1 paratype (sex indeterminate, not extracted from shell), in shell of Muricidae , D. R GoogleMaps . Congo, 8–14 km off Vista [currently Nsia-Fumu, 5°51'S, 12°18'E], 10 m, year 1959, coll. J. Meulenbergh ( RMCA 50743 View Materials ); 2 small ♂♂ paratypes, D. R GoogleMaps . Congo, 8–14 km off Vista [currently Nsia-Fumu, 5°51'S, 12°18'E], 10 m, year 1959, coll. J. Meulenbergh ( RMCA 50744 View Materials ); 1 small ♂ paratype, D. R GoogleMaps . Congo, 8–14 km off Vista [currently Nsia-Fumu, 5°51'S, 12°18'E], 10 m, year 1959, coll. J. Meulenbergh ( RMCA 50751 View Materials ); 2 ♂♂ (1 fairly large and 1 small) paratypes, between Banana (D. R. Congo) and Cabinda (exclave of Angola), 10–15 m, Oct. 1959 to Mar. 1960, coll. J. Meulenbergh ( RMCA 50808 View Materials ) GoogleMaps .

Other material examined. AFRICAN EASTERN ATLANTIC: 1 ♂, Benin, Cotonou , eastern jetty of Cotonou harbour, outer side, 8–12 m depth, baited trap, 4 Oct 2022, coll. C. d'Udekem d'Acoz & Appolinaire Goussanou; collection University of Abomey Calavi, Bénin _2022_12, Xwlacodji .

Description of holotype. Cephalothorax and cephalic appendages ( Fig. 2A View FIGURE 2 ). Shield 0.65 as long as posterior region of carapace, as long as wide; frontal margin weakly convex and rounded (not forming a rostrum), not reaching level of strong, angular lateral projections (devoid of terminal denticle), with sparse tufts of short stiff setae; anterolateral margin anteriorly with a few denticles. Ocular peduncles with corneas slightly dilated, diameter 0.35 length, 0.61 as long as length of shield. Ocular acicles well separated, anterior margins obliquely rounded, with 8 denticles of increasing length towards tip. Antennular peduncles overreach corneas by approximately 0.15 length of last segment. Antennal peduncles nearly reaching tip of ocular peduncle. Antennal acicles elongate, denticulate, reaching proximal 0.6 of last peduncular segment.

Left cheliped ( Fig. 3A View FIGURE 3 ). Much stronger than right. Carpus with strong corneous-tiped conical spines on outer border, disposed in a continuous ridge on distal margin, on a ventral ridge just behind, not disposed in ridges elsewhere. Propodus proximally slightly dilated; outer surface ornamented with sinuous (many are uninterrupted), transverse ridges ornamented with strong corneous-tipped conical spines, becoming stronger on upper margin; a fringe of short setae occupies inter-ridge spaces. Dactylus with protruding squamiform processes disposed in incomplete oblique ridges, anteriorly bordered by medium-sized corneous conical spines; a fringe of short setae occupying inter-ridge spaces.

Right cheliped ( Fig. 3B View FIGURE 3 ). Carpus with corneous-tiped conical spines on outer border (strong on upper half, medium-sized on lower half), disposed in a continuous ridge on distal margin, on ventral ridge just behind, not disposed in ridges elsewhere. Propodus with outer surface ornamented with sinuous (many are uninterrupted), transverse ridges ornamented with medium-sized corneous-tipped sharp spines, becoming strong on upper margin; fringe of short setae occupies inter-ridge spaces. Dactylus with protruding squamiform processes not disposed in ridges, tipped with medium-sized corneous conical spines; fringes of short setae present in front of some squamiform processes.

Left pereiopod 2. Merus 2.3 × as long as wide, with outer surface smooth, with few minute transverse rows of setae but not forming fringes; posterior border lined with blunt but very distinct spines. Carpus 1.8 × as long as wide, with outer surface smooth, with few minute transverse rows of setae but not forming fringes; anterior margin with about 5 spines. Propodus 3.6 × as long as wide, without transverse ridges but with transverse fringes of setae, without longitudinal groove, without spines. Dactylus 4.8 × as long as wide; 0.9 × as long as propodus, without spines, with anterior and posterior tufts of stiff setae.

Right pereiopod 2. Similar to left pereiopod 2, except for presence of low non-dentate transverse ridges on propodus.

Left pereiopod 3 ( Fig. 2B View FIGURE 2 ). Merus 1.5 × as long as wide, with outer surface smooth, with few minute transverse fringes of setae; posterior margin with few blunt spines. Carpus 1.7 × as long as wide, with outer surface nearly smooth, with few small transverse fringes of setae, with about 5 spines on anterior margin. Propodus 2.1 × as long as wide; outer surface with strong transverse ridges on upper and lower half; narrow longitudinal irregular depression running between upper and lower ridges, ridges ornamented with corneous tipped spines, being small on anterior ridges and strong on posterior ridges; fringe of short setae in grooves separating ridges. Dactylus 3.6 × as long as wide; about 1.3 × as long as propodus; outer surface with strong transverse ridges on anterior and posterior half; narrow longitudinal irregular depression running between upper and lower ridges; ridges ornamented with corneous tipped spines, being strong both on anterior and posterior ridges; fringe of short setae in grooves separating ridges; irregularly disposed longer stiff setae irregularly disposed on different articles of pereiopod.

Right pereiopod 3. Merus and carpus similar to left pereiopod 3. Propodus outer surface with non-dentate transverse ridges, with fringe of short setae in grooves separating ridges, without longitudinal depression; dactylus missing in holotype; in a paratype, narrower than in left pereiopod 3, outer surface with transverse fringes of setae on upper and lower border (but without ridges and spines), with weak longitudinal depression.

Telson . Lobes unequal, regularly rounded, bordered by short spiniform setae.

Size ( holotype). Carapace length 40 mm; shield length 16 mm.

Colour pattern (specimen from Cotonou, Benin) ( Figs 4 View FIGURE 4 , 5 View FIGURE 5 ). Cephalothorax pale purple with complex, low-contrast pattern and scattered white dots. Abdomen pale pink with traces of whitish mottling. Telson pink, with complex, low-contrast pattern. Eye peduncles with greenish cornea, pink peduncle with red transverse stripe proximally, medially and distally.Antennules and antennae orange. Chelipeds with chela dorsally wine-red with few white dots at top of some spines, ventrally mottled white on red background (white colour more intense on granules and spines); carpus dorsally wine-red with few white dots at top of some spines, except proximal part being pale purple; merus largely pale purple, with some red markings and white granules. Pereiopods 2–3 largely wine-red with white dots, but proximal part of propodus slightly paler, and proximal part of carpus pale purple; merus with red pattern on pale purplish background and with white dots. Pereiopods 4–5 with red pattern on pale purplish background and white dots.

Distribution. Mauritania to Angola, Cape Verde Islands, Islands of the Gulf of Guinea, 4–50 m ( Forest 1955, 1956, 1958, 1961, 1966b, all as Dardanus pectinatus ).

Etymology. From the Greek, κτείς (kteís), genitive κτενός (ktenós): comb; and όδούς (odoús), genitive όδόντος (odóntos): tooth. Ctenodon is a noun in apposition. The name refers to the spinular crests of the chelipeds, which can be compared to toothed combs.

Remarks. As already indicated by Schmitt (1926) under the name Dardanus pectinatus , Dardanus ctenodon sp. nov. can be easily separated from D. arrosor , a similar sympatric species, by the more prominent ridges on the propodus and carpus of the chelipeds, and on the propodus and dactylus of pereiopods 2–3, and by the presence of strong spines on these ridges (at least anteriorly) instead of microscopic spines or the absence of spines. The differences are less obvious in juveniles and subadults than in fully grown specimens (compare the figures of the large holotype (fig. 3) with those of the smaller specimen from Cotonou, Benin (fig. 5)). Dardanus ctenodon sp. nov. is wine-red with white spots and pale purple patches on the merus and carpus of pereiopods 1–3, and pale purplish pink on the cephalothorax. This is quite different from the almost uniform orange-red colour of Dardanus arrosor as illustrated in various manuals and nature guides.

The African Atlantic species discussed here had been known for over a century (since the publication of Rathbun 1900)) as Dardanus pectinatus (Ortmann, 1892) , but Ortmann's (1892a) description was almost certainly not based on that species. The holotype of Pagurus striatus var. pectinata Ortmann, 1892 was labelled as coming from Brazil and Ortmann's (1892a) account of its locality runs as follows (translated from German): "The Strasbourg Museum's locality information for undetermined specimens is consistently quite reliable. Only in the case of specimens whose species has been determined is the locality often given according to textbooks (from Milne-Edwards crustaceans). This specimen was only identified as ' Pagurus sp. ', and the locality 'Brazil' is probably only to be doubted because the gastropod forming its habitation is a common Mediterranean form. The specimen is located within a Dolium galea ". Rephrased in a more understandable way, Ortmann (1892a) stated that the locality indications of formerly unidentified specimens in the Strasbourg Museum are generally correct, but that he was nevertheless somewhat skeptical about the origin of his specimen because he was inside a shell of Dolium galea (currently Tonna galea (Linnaeus, 1758)) , which he believed to be a gastropod endemic to the Mediterranean.

Ortmann's (1892a) description of Pagurus striatus var. pectinata follows an enumeration of the classic (real) Pagurus striatus (currently Dardanus arrosor ) and reads as follows (translated from German): "A single specimen in my possession shows such a peculiar sculpture on the surface of the chela that I was in doubt for a long time whether I should not recognise it as a special species. However, as all the other characteristics correspond to those of P. striatus , I am listing it here as a variety. Whereas in young specimens of striatus typ. the transverse lines of the chela are quite entire, and only in specimens of considerable size do slender, irregularly and scattered and differently sized spines become noticeable on them, the above-mentioned specimen of medium body size shows the transverse lines covered with black-tipped spines. These spines are extremely regularly arranged, of equal length and only near the inner margin do they become somewhat larger (as in typ.)". The only illustration given by Ortmann (1892a) is a schematic figure of the propodus and dactylus of the left cheliped. In this figure, the propodus is shown with spines of the same size arranged in long transverse lines, and the dactyl with irregularly arranged spines. These poor diagnosis and figure can apply equally well to the West Atlantic species Dardanus insignis ( de Saussure, 1857) and to the tropical East Atlantic species described here as Dardanus ctenodon sp. nov. At the same time, Ortmann (1892a) erroneously considered Dardanus insignis to be a junior synonym of Dardanus venosus (H. Milne Edwards, 1848) , whereas the two species are in fact valid and very different. A few years later, Rathbun (1900) identified specimens from Dakar, West Africa, as Petrochirus arrosor pectinatus (Ortmann, 1892) , also mentioning Ortmann's (1892a) type locality: Brazil, without questioning it. In other words, Rathbun (1900) treated her Petrochirus arrosor pectinatus as amphi-Atlantic. She also added that the taxon ' pectinatus ' could be a species in its own right and not a variety. Two and a half decades later, W.J. Schmitt, who began his career as an assistant to M.J. Rathbun ( McCain 1972), resumed the study of the taxon. Schmitt (1926) recognized the existence of three Atlantic species of Dardanus with long transverse ridges on the palm of the left cheliped and gave good comparative descriptions and figures of these species. He correctly applied the names D. arrosor to the species widely distributed in the eastern Atlantic, Mediterranean and beyond, D. insignis to the western Atlantic species, and surprisingly the name D. pectinatus to the tropical eastern Atlantic species with strong spinose ridges on the left cheliped. This is very puzzling because, as we saw above, the type locality of D. pectinatus is Brazil. What is even more perplexing is that Schmitt (1926) gave no justification for his action.

Based on Ortmann's (1892a) poorly formulated account, Monod (1933) asserted that the type locality ( Brazil) of D. pectinatus was not certain and added that it may be a West African species — without giving any argument to justify his hypothesis, which falls within the realm of speculation. Forest (1955) stated that "The specimen described by A. Ortmann as ' Pagurus striatus var. pectinata ' is said to come from Brazil, but the author himself considers this locality doubtful". He followed Schmitt (1926) in applying the name Dardanus pectinatus to the West African species. In more recent literature, the name Dardanus pectinatus has been applied to the West African species with strong spinose ridges on the chelipeds and a vinous coloration, as proposed by Schmitt (1926) and Forest (1955) without further discussion of the question of the true identity and origin of Ortmann's (1892a) type specimen.

As mentioned above, the only reason Ortmann (1892a) had any doubts about the specimen's origin was the gastropod shell occupied by the hermit crab, which he believed to be a Mediterranean form. However, Tonna galea occurs not only in the Mediterranean but also on both sides of the Atlantic ( Nicklès 1950), and Alf et al. (2020) even consider its distribution to be "worldwide in tropical and subtropical seas". The identity of the hermit crab's shell cannot therefore be used as an argument to question its Brazilian origin. As we have also seen, the meagre diagnosis and poor illustration of Pagurus arrosor var. pectinata by Ortmann (1892a) applies equally to the West Atlantic Dardanus insignis and to the East Atlantic species, whose chelipeds have strong spinose ridges and a vinous coloration. Although it cannot be definitively ruled out that Ortmann's (1892a) holotype originated in West Africa, there is no positive evidence for this. None of the previous authors who studied the arrosor / insignis / pectinatus complex ( Rathbun 1900; Schmitt 1926; Forest 1955; Forest & de Saint Laurent 1968) examined the holotype of D. pectinatus . However, the holotype of ' Pagurus striatus var. pectinatu s' is no longer present in the Strasbourg Museum collections, and only a small proportion of the ' Pagurus striatus ' listed by Ortmann (1892a) is registered there (Marie-Dominique Wandhammer, Strasbourg Museum, pers. com.). The holotype of ' Pagurus striatus var. pectinatus ' must therefore be considered lost.

A perusal of Ortmann's various articles in the series 'Die Decapoden-Krebse des Strassburger Museums' ( Ortmann 1890, 1891a, b, 1892a, b, 1893a, b, 1894) revealed that the collections of the Strasbourg museum included 21 crustacean species labelled as coming from Brazil, 14 of which included specimens simply labelled as " Brasilien " and one as "Brasilische Küste", the rest bearing more precise locality data. Eight of them, namely Aegla laevis (Latreille, 1818) , Hepatus angustatus (Fabricius, 1798) [= Calappa angustata Fabricius, 1798 , accepted as Hepatus pudibundus (Herbst, 1785) ], Libidoclea brasiliensis Heller, 1865 [accepted as Libinia spinosa Guérin, 1832 )], Mithrax verrucosus H. Milne-Edwards, 1832 [accepted as Amphithrax verrucosus (H. Milne Edwards, 1832) ], Mithrax hispidus (Herbst, 1790) , Neptunus ( Achelous) spinimanus (Latreille, 1819) [accepted as Achelous spinimanus (Latreille, 1819) ], Eriphia gonagra (Fabricius, 1781) , Dilocerus panoplus (von Martens, 1869)) [accepted as Trichodactylus panoplus (von Martens, 1869) ] have no close relative in West Africa, and therefore certainly originated from the American Atlantic or mainland. The remaining species were either amphi-Atlantic: Senex argus (Latreille, 1804) [accepted as Palunirus argus (Latreille 1804) ] (rare in the eastern Atlantic), Cronius ruber ( Lamarck, 1818) , or from the western Atlantic (or American mainland) with some possibility of confusion (at the time of Ortmann) with species from the tropical eastern Atlantic and African mainland: Palaemon acanthurus Wiegmann, 1836 [accepted as Macrobrachium acanthurus (Wiegmann, 1836) ], Palaemon jamaicensis (Herbst, 1792) [accepted as Macrobrachium carcinus (Linnaeus, 1758) ], Palaemon olfersii Wiegmann, 1836 [accepted as Macrobrachium olfersii (Wiegmann, 1836) ], Petrolisthes danae (Gibbes, 1854) [= Porcellana danae Gibbes, 1854 , accepted as Petrolisthes galathinus ( Bosc, 1801) ], Pachycheles laevidactylus Ortmann, 1892 , Pagurus striatus var. pectinata Ortmann, 1892 [accepted as Dardanus insignis ( de Saussure, 1857) ], Pagurus venosus H. Milne-Edwards, 1848 [accepted as Dardanus venosus (H. Milne Edwards, 1848) ], Petrochirus granulatus (Olivier, 1812) [accepted as Petrochirus diogenes (Linnaeus, 1758) ], Clibanarius speciosus Miers, 1878 [accepted as Clibanarius symmetricus (Randall, 1840) ], Coenobita diogenes (Linnaeus, 1758) [accepted as Petrochirus diogenes (Linnaeus, 1758) ], Neptunus ( Callinectes) diacanthus (Latreille, 1825) [accepted as Callinectes sapidus Rathbun, 1896 ]. Ortmann's papers also recorded 13 species from West Africa, of which 10 were specifically labelled as 'Senegambian -Linnaea (vend. 1885)': Sicyonia sculpta H. Milne-Edwards, 1830 [accepted as Sicyonia carinata (Brünnich, 1768) ], Pagurus granulimanus Miers, 1881 [accepted as Pseudopagurus granulimanus ( Miers, 1881) ], Diogenes varians (O.G. Costa, 1838) [accepted as Diogenes pugilator (Roux, 1829) ], Ilia spinosa Miers, 1881 , Ebalia tuberculata Miers, 1881 [accepted as Merocryptus tuberculata ( Miers, 1881) ], Ebalia affinis Miers, 1881 , Pisa carinimana Miers, 1879 [accepted as Afropisa carinimana (Miers, 1879) ], Heterocrypta maltzami Miers, 1881 [accepted as Distolambrus maltzami ( Miers, 1881) ], Xantho pilipes A. Milne-Edwards, 1867, Xantho melanodactylus (A. Milne-Edwards, 1867) [accepted as Nanocassiope melanodactylus (A. Milne-Edwards, 1867)], one as coming from Lagos, Nigeria: Palaemon vollenhovenii Herklots, 1857 [accepted as Macrobrachium vollenhovenii (Herklots, 1857) ] and two are simply labelled as African: Atya sculptata Ortmann, 1890 [accepted as Atya gabonensis Giebel, 1875 ] and Neptunus ( Neptunus) sayi (Gibbes, 1850) [accepted as Portunus sayi (Gibbes, 1850) ]. Without being a definitive argument, these data on the crustacean collections examined by Ortmann do not plead in favour of widespread errors of labelling in the Strasbourg Museum and confirms that the museum possessed quite a lot of material of unmistakably Brazilian origin in Ortmann's time.

Taking all of this into account, the most parsimonious hypothesis concerning the origin and identity of Ortmann's (1892a) lost holotype of Pagurus striatus var. pectinata is that it did indeed come from Brazil, as its author asserts, and that it belonged to a species present in this country, which presents characters compatible with its description and figures. Such a species does exist, namely, Dardanus insignis ( de Saussure, 1857) , which Ortmann (1892a) wrongly regarded as a synonym of D. venosus . The photograph of D. insignis given by Forest & de Saint Laurent (1968) clearly shows that the propodus ridges of the chelipeds are adorned with strong spines, as in the rather schematic drawing by Ortmann (1892a). This is confirmed by my direct observation of the specimen illustrated by Forest & de Saint Laurent (1968).

This indicates the need for nomenclatural action. There are two possibilities: either to validate Schmitt's (1926) very probably erroneous interpretation by designating an African Atlantic neotype for Dardanus pectinatus , or to correct his probable error by designating a Brazilian neotype for D. pectinatus and describing the African Atlantic taxon as a new species. Considering that the number of records of the African species in the literature is not high and that it has no commercial importance, it seemed preferable to correct Schmitt's (1926) presumed error rather than take the intellectually questionable step of validating his probable misinterpretation (i.e., to consider that an error repeated a sufficient number of times becomes a truth).

Therefore, on the basis of available information, I treat Pagurus striatus var. pectinatus Ortmann, 1892 as a junior synonym of Pagurus insignis de Saussure, 1857 . A Brazilian neotype (the specimen already illustrated by Forest & de Saint Laurent 1968: RV Calypso , cruise Amérique du Sud 1961–1962, stn 52, Brazil, 31°24’S, 50°36’W, MNHN-IU-2025-168) is designated below for Pagurus striatus var. pectinatus Ortmann, 1892 , in order to stabilize the nomenclature once and for all. By this action, the West African species is unencumbered by any previously available name and is now described as a new species: Dardanus ctenodon sp. nov.