Brevitalitrus Bousfield, 1971

Miyamoto, Hisashi & Morino, Hiroshi, 2012, Taxonomic Studies on the Talitridae (Crustacea: Amphipoda) of Taiwan. V. The Genus Brevitalitrus Bousfield, 1971, Species Diversity 17 (2), pp. 187-200 : 187-188

Genus Brevitalitrus Bousfield, 1971

Brevitalitrus Bousfield, 1971: 284 (type species: Talitrus hortulanus Calman, 1912 ).

Emended Diagnosis. Eyes small, rounded. Antenna 1 extending beyond middle of peduncular article 5 of antenna 2, peduncular article 3 elongate. Left mandible with 4-dentate lacinia mobilis. Maxilla 2 with several blunt spines on edges of outer and inner plates, with a few brushy sharp spines on ventral side of inner plate. Maxilliped palp with articles 2 and 3 narrow; article 2 lacking mediodistal lobe; article 3 longer than wide; palp article 4 conical. Gnathopod 1 not sexually dimorphic, simple; carpus swelling posteriorly; propodus slender, subequal in length to or shorter than carpus, narrowing distally, with bifid spines on posterior margin, and with sheathed spines on lateral and medial surface. Gnathopod 2 not sexually dimorphic, elongate; basis linear; ischium longer than merus; carpus with blister-shaped swelling on posterodistal corner; propodus subequal in length to or longer than carpus, mitten-shaped. Pereopods 3–7 cuspidactylate; distal spine on dactyl hinge reduced, occasionally lacking. Pereopods 5–7 heteropodous. Coxal gill of pereopod 2 large, leaf-shaped; gill of pereopod 6 convoluted, elongate. Pleopods 1–3 biramous. Pleopod 3 smallest, peduncle with plumose setae on outer margin. Uropod 1 with moderately developed prepeduncle; peduncle with long distolateral spine. Outer ramus of uropod 2 distinctly shorter than inner ramus. Uropod 3 with long lateral spine on peduncle. Telson incised apically, with 2 apical spines. Oostegites of pereopods 2–4 small, linear, with several simple-tipped setae.

Composition. Brevitalitrus dyaulanus , B. hortulanus (type species of the genus), B. kumanoi sp. nov., B. nesius , B. stephenseni , B. strinatii , B. toli , and B. wolffi .

Remarks. Bousfield (1982, 1984) divided the world talitrid species into four groups based on “systematic-ecological and behavioral” features: palustral talitrids, beach fleas, sand hoppers, and land hoppers. This grouping is not taxonomically based, though it has provided a practical framework for taxonomic research. The group “land hoppers”, which is characterized by fully terrestrial habitats and morphology specialized to terrestrial life, is further subdivided into two groups, viz., the simplidactylate and cuspidactylate groups. Simplidactylate species lack cusps on the dactyli of the pereopods ( Fig. 1A ) whereas cuspidactylate species bear paired cusps at “the outer base of the nail” ( Fig. 1C ). Brevitalitrus and some other genera had been considered to consist of simplidactylate species (see Bousfield 1984: Tables 4, 7), but Stock (1997), in his study of the talitrids of Mauritius, reexamined paratypes of Brevitalitrus hortulanus and found that they all had cuspidactylate pereopods. He also pointed out the cuspidactylate nature of B. toli based on illustrations in Barnard (1960: Fig. 2f, g, i ) and transferred Brevitalitrus from the simplidactylate to the cuspidactylate landhoppers. During our study, we found that the Taiwanese species of Brevitalitrus bear a single cusp ( Fig. 1B ) instead of paired cusps. Here we propose two subcategories of the cuspidactylate state, “uni-cuspidactylate” for species having a single cusp and “bi-cuspidactylate” for those with two cusps. This treatment may have merit from the phylogenetic viewpoint since the character of the dactyli armature is considered to reflect phylogenetic relationships among genera ( Bousfield, 1982); nevertheless, the exact number of cusps remains unknown for other congeneric species than B. hortulanus and B. kumanoi sp. nov.

Figures

Fig. 1. Diagrammatic figures of dactyli of pereopods of Talitridae, lateral view, showing patterns of armature (arrows). A, simplidactylate condition (Bousfield 1982); B, uni-cuspidactylate condition (present paper); C, bi-cuspidactylate condition (Bousfield 1982).

Fig. 2. Brevitalitrus hortulanus (Calman, 1912), female (NSMT-Cr 21457), 7mm, Green Island, Taiwan, habitus in lateral view.