Dardanus Paul'son, 1875

D'Acoz, Cédric D'Udekem, 2025, Designation of a Brazilian topotypic neotype for Dardanus pectinatus (Ortmann, 1892) and establishment of D. ctenodon sp. nov. for the East Atlantic hermit crab previously misidentified with it (Crustacea, Decapoda, Anomura, Diogenidae), Zootaxa 5701 (3), pp. 292-314 : 292-314

Genus Dardanus Paul'son, 1875

Seven species of Dardanus are found in the Atlantic Ocean and its adjacent seas. The three species with large transverse ridges on the left cheliped palm ( D. arrosor (Herbst, 1796) , D. ctenodon sp. nov., and D. insignis ( de Saussure, 1857)) are discussed in detail below. Brief details are given here of species with tuberculated or scaled left cheliped palms. Among these, Dardanus calidus is easy to identify. In contrast, D. fucosus , D. imperator and D. venosus can be difficult to distinguish from each other and require careful examination of the best published illustrations. A brief guide to the literature is given below, together with the type locality of the species.

Dardanus calidus ( Risso, 1827) . Type locality: implicitly Nice, Mediterranean ( Risso 1827). Identification of this species is not problematic but only Ingle (1993) has given an extensive description with detailed drawings. Although it is very old, the engraving given by Roux (1828) is of good quality. Neves (1977) gave a fairly good taxonomic photograph of the species. Technical illustrations of the colour pattern are given by Almón et al. (2023). Colour field photographs have been provided in a number of manuals such as González Pérez (1995), Debelius (1999), and Kuiter & Debelius (2009).

Dardanus fucosus Biffar & Provenzano, 1972 . Type locality: French Guiana, 5°29'N, 51°37'W, 64 m depth ( Biffar & Provenzano 1972). Identification references: Biffar & Provenzano (1972), Takeda (1983: colour photographs), Williams (1984), Abele & Kim (1986), Schmidt de Melo (1999), Nucci & Schmidt de Melo (2015); Poupin (2018) and Lima et al. (2019).

Dardanus imperator ( Miers, 1881) . Type locality: St. Helena ( Miers 1881). Taxonomic and iconographical references: Biffar & Provenzano (1972), Manning & Chace (1990), Lima et al. (2019, with several colour photographs) and Brown (2014: colour photographs).

Dardanus venosus (H. Milne Edwards, 1848) . Type locality: Guadeloupe (H. Milne Edwards 1848). Taxonomic and iconographical references: Biffar & Provenzano (1972), Abele & Kim (1986), Manning & Chace (1990), Schmidt de Melo (1999), Debelius (1999: colour photograph), Kuiter & Debelius (2009: colour photograph), Nucci & Schmidt de Melo (2015); Charteris (2017: colour photograph), Poupin (2018: cover page and fig. 157); Lima et al. (2019, with several colour photographs) and Mantelatto et al. (2021: colour photograph).

Key to Atlantic and Mediterranean species of Dardanu s

1. Upper surface of palm of left cheliped with strong isolated conical spines/tubercles, or conical spines/tubercles in short transverse scaly groups................................................................................. 2

– Upper surface of palm of left cheliped with long transverse ridges bearing small or strong conical spines/granules......... 5

2. Upper surface of the palm of left cheliped with isolated conical spines/tubercles. Left pereiopod 3 propodus without longitudinal depression on lateral surface. Overall almost uniformly intense scarlet red. Northeastern Atlantic (southwards to Cape Verde Islands) and Mediterranean..................................................... Dardanus calidus ( Risso, 1827)

– Upper surface of palm of left cheliped with conical spines/tubercles forming short, scaly transverse groups. Left pereiopod 3 propodus with longitudinal depression flanked on each side by granular transverse ridges on its lateral surface. Colour pattern not uniformly scarlet red, Western and Central Atlantic....................................................... 3

3. Dactylus of left pereiopod 3 with ventral (posterior) margin forming rounded ridge................................. 4

– Dactylus of left pereiopod 3 with ventral (posterior) margin incised by longitudinal groove. Western Atlantic............................................................................. Dardanus fucosus Biffar & Provenzano, 1972

4. Carpus of left cheliped with continuous fringe of setae along distal margin on lateral surface, overlapping articulation with propodus; lateral surface of palm with numerous scales, each with one or more tubercles/spines; tubercles/spines well developed, set back from anterior edge of scales, directed laterally and distally. Cephalothoracic shield of variable colouration but never magenta purple. Western Atlantic...................................... Dardanus venosus (H. Milne Edwards, 1848)

– Carpus of left cheliped with scattered tufts of setae forming discontinuous fringe on distal margin of lateral surface; lateral surface of palm with numerous scales, each scale with strong central tubercle/spine, some with up to three smaller tubercles laterally; tubercles very well developed, usually on center of scale, directed laterally. Cephalothoracic shield magenta purple. Saint Helena and Ascension Islands............................................ Dardanus imperator ( Miers, 1881)

5. Palm of left cheliped with ridges bearing very strong granulations or with very granulated crests...................... 6

– Palm of left cheliped with ridges bearing tiny granulations. [Left pereiopod 3 propodus with regularly convex outer surface (no longitudinal depression)]. Body and pereiopods uniform orange-red. Temperate and tropical eastern Atlantic (in tropical waters below 100 m depth), Mediterranean............................................. Dardanus arrosor (Herbst, 1796)

6. Palm of left cheliped with ridges bearing very strong granulations, at least anteriorly (spreading on a larger surface in large specimens). Left pereiopod 3 propodus with longitudinal depression on outer surface. Pereiopods 1–3 intense wine-red with white dots and patches of pale purple; cephalothorax pale purple. Tropical eastern Atlantic, in shallow-water........................................................................................... Dardanus ctenodon sp. nov.

– Palm of left cheliped with very strongly granulated crests. Left pereiopod 3 propodus with regularly convex outer surface (no longitudinal depression). General colour pale orange, with the tips of the crests of the pereiopods whitish. Western Atlantic....................................................................... Dardanus insignis ( de Saussure, 1857)