Lepidocharon Galassi & Bruce

Galassi, Diana M. P., Bruce, Niel L., Fiasca, Barbara & Dole-Olivier, Marie-Jose, 2016, A new family Lepidocharontidae with description of Lepidocharon gen. n., from the Great Barrier Reef, Australia, and redefinition of the Microparasellidae (Isopoda, Asellota), ZooKeys 594, pp. 11-50 : 15-17

Taxon classification Animalia Isopoda Lepidocharontidae

Lepidocharon Galassi & Bruce gen. n.

Type species.

Lepidocharon priapus Galassi & Bruce, sp. n.; here designated.

Other species.

Lepidocharon lizardensis Galassi & Bruce, sp. n.

Diagnosis.

Male. Body slender, 8.5-9.7 as long as wide. Free pleonite narrower than pereionites and pleotelson, visible in dorsal view. Cephalon medio-frontal margin not produced, anterior margin straight, rostrum absent. Pereionites 1-3 anteriorly widest, with distinct anterolateral angle, pereionite 4 sub-rectangular, pereionites 5-7 posteriorly widest, lateral margin with distinct posterolateral angle. Pereionites dorsally ornamented by paired setae. Cuticle with small semicircular thickening present or absent both dorsally and ventrally. Antennula 6-segmented; long aesthetascs on articles 5 and 6, long brush seta on article 2 extending to tip of article 6. Antenna with 6 podomeres; article 3 with long blade-like or candle flame-like scale, reaching article 5; lateral margin with 2 setae; flagellum with 8-12 articles.

Mandible palp article 1 unarmed, article 2 with 2 stiff spinulose setae, article 3 with 5 stiff spinulose setae. Right mandible: incisor with 6 to 9 cusps; lacinia mobilis absent; molar process conical, with 3 setae. Left mandible: incisor with 2 to 3 cusps; lacinia mobilis present and produced in 2 cusps; molar process conical, with 3 setae. Maxillula: mesial lobe slender and tapering at distal part, bearing 1 short apical seta accompanied by subapical shorter setae and lateral thin and short setae. Lateral lobe sub-rectangular in shape. Apical setation composed by a variable number of setae. Maxilla: mesial ramus with 8-9 setae; 1 apical comb-like seta, strong, unipinnate and ornamented with fine regularly-spaced setules parallel to one another. Lateral rami close-set, each bearing 4 slender and simple setae, respectively. Maxilliped palp wider than endite, mesial margin of articles 2 and 3 expanded. Pereiopods all subequal in length, all subsimilar in size and general morphology; all with 2 dactylar claws; pereiopod 1 dactylar claws subequal; pereiopods 2-7 superior claw slender (3.8 –4.3× basal width), inferior claw robust (2.3 –2.6× basal width). Coxae rudimentary reduced to small sclerites, not discernible in dorsal view, coalescent to body wall of the sternites, located on the anterior margin of the concavity which houses the propodus, and apparently not articulated to the sternites.

Pleotelson 1.3-1.7 as long as wide, 1.7-1.9 as long as pereionite 7. Penial papillae opening on postero-medial margin of sternite 7. Pleopod 1 rami proximally fused; proximolateral margins with cuticular imbricate scales on posterior side; distolateral margins convex; stylet-guiding groove represented by a folded hyaline lamella running sub-parallel to free lateral margin of rami; pleopod 1 transverse stylet-guiding grooves absent, unlike Janinella . Pleopod 2 stylet long and slender, of variable length. Pleopod 3 endopod bearing 3 distal plumose setae; exopod elongate, lateral margin with thin setae, article 2 with 1 subapical seta; pleopod 4 rudimentary, ovoid, uniramous. Uropodal protopod as long as the pleotelson, slender (length/width ratio: 4.3), not sexually dimorphic, with long and slender exopod and endopod.

Female. As for the male, except for sexual characters. Operculum (pleopod 2) longer than broad, with surface smooth or with semicircular thickening, with distal margin faintly incised, and 4 apical setae.

Etymology.

The generic name is derived from the ancient Greek name λεπις, λεπιδος meaning “scale”, which refers to the unique rim of scale-like elements bordering the proximal part of the first male pleopod on the posterior side, combined with the mythological name Charon, Charontis referring to the Ferryman of Hades. Gender: masculine.

Remarks.

Lepidocharon gen. n. is most similar to the genus Microcharon , the two genera sharing the following characters: well-developed uropods with slender endopod and exopod; pereiopodal coxal plates not discernible in dorsal view, small, incorporated to the sternite body wall; male pleopod 1 with similar general organization, the distal lateral lobe with a folded hyaline lamella (stylet-guiding groove) running almost parallel to the lateral margins of the pleopod (this orientation and structure of the stylet-guiding groove appears different from that of Janinella , where a transversal and oblique groove hosts the stylet of the male pleopod 2 which seems not to be enveloped by a hyaline lamella); pleopod 2 identical in the development of both exopod and endopod, the latter ending with a stylet of different length depending on the species; penial papillae small and located at the posteromesial margin of sternite 7; female operculum as long as the pleotelson, faintly incised, bearing 4 apical setae (a condition shared by some predominantly marine, and rarely freshwater, Microcharon species).

Lepidocharon gen. n. shares with Janinella the morphology of the tergites, the first three pereionites with antero-lateral protrusions, the fourth sub-rectangular in shape, and the last three postero-laterally protruded, together with the lateral insertion of pereiopods 1-7 oriented outwards (vs. ventrally in Janinella , see Albuquerque et al. 2014); pereiopodal coxal plates small in Janinella , very reduced and incorporated to body wall in Lepidocharon gen. n. The female operculum of Lepidocharon is more than twice as long as wide, as long as the pleotelson, only faintly incised and bearing 4 apical setae, the mesial pair being close-set. These apical setae resemble that of Janinella species, where only the two close-set setae are present.

Lepidocharon gen. n. differs from all the other lepidocharontid genera by the combination of the following morphological characters: (1) the unique presence of scale-like elements bordering the postero-lateral margins of the proximal part of the male pleopod 1; (2) pereionites with coxal plates hardly discernible, small, and incorporated into the sternite body wall, not visible in dorsal and lateral views; (3) the long and slender pereiopods that are inserted laterally and directed outwards; (4) pereionites that are not cylindrical, except pereionite 4 (vs. cylindrical in Microcharon ); (5) the presence of elongate antennal scale (vs. rudimentary in Janinella , and generally reduced in Microcharon ); (6) the mandible incisor with up to 9 cusps (lower number of cusps in Microcharon and Janinella ).

Microcharon galapagoensis Coineau & Schmidt, 1979 is closer to Lepidocharon gen. n., especially in the general body morphology, pereionite shape, slender pereiopods directed outwards, a long antennal scale, and slender and elongate uropods; however the unique scale-like elements of the male pleopod 1 of Lepidocharon are not present in this species. These scales are not easily detected under optical microscopy (if not at 100 × magnification), nor were they seen using SEM because located on the posterior side of the pleopod.

The mid-section of the male pleopod 1 shows lateral margins expanded in both species of Lepidocharon gen. n. In contrast to the new genus, Microcharon galapagoensis shows a 5-segmented antennula. Coineau and Schmidt (1979) had informally proposed the creation of an intermediate group between the genus Microcharon and Janinella (formerly Paracharon Coineau, 1970) for Microcharon galapagoensis Coineau & Schmidt, 1979 (from marine interstitial habitats in the Galapagos), Microcharon salvati Coineau, 1970 (from coral sands in New Caledonia) and Microcharon herrerai Stock, 1977 (from brackish groundwater in the Netherlands Antilles) ( Stock 1977).