Orchestia Leach, 1814

Wildish, David J., 2014, New genus and two new species of driftwood hoppers (Crustacea, Amphipoda, Talitridae) from northeast Atlantic and Mediterranean coastal regions, Zoosystematics and Evolution 90 (2), pp. 133-146 : 136-137

Taxon classification Animalia Amphipoda Talitridae

Orchestia Leach, 1814

Orchestia : Leach 1814: 402; Bousfield 1982: 22; Lowry and Fanini 2013: 205.

Type species.

Orchestia gammarellus (Pallas, 1766).

Component species.

Since the erection of Orchestia Leach, 1814 the genus has been uncritically used to include many new species from around the World. In more recent times genera have been split off from Orchestia including: Platorchestia by Bousfield (1982), Palmorchestia by Stock and Martin (1988) and Macarorchestia by Stock (1989). Bousfield (1982) re-defined the range of Orchestia , limiting species to those found in the Atlantic/ Mediterranean region. I have further limited the geographic range of this taxon to the northeast Atlantic, the Mediterranean and Black Seas, but excluding the western Atlantic coastline of North America. The northeast Atlantic islands including: Canary, Madeira and Azore archipelagos are also included in the region. The northerly limit is arbitrarily set at the Arctic Circle (thus including Iceland) and the southern one at the Tropic of Cancer. Circumstantial evidence ( Henzler and Ingolffson 2008) supports the presence of Orchestia gammarellus on northwest Atlantic coastlines (as far south as Maine), as a result of recent, post glacial, synanthropic, dispersal from the northeastern shores of the Atlantic.

Taking only Orchestia species which occur within this newly defined geographic range and excluding those outside it, synonyms, and where the taxonomic or ecological status is unclear (inclusive of Orchestia kosswigi Ruffo, 1949-which is figured and described in Ruffo (1993) but its ecological status remains unclear); Orchestia guerni Chevreux, 1889 and Orchestia gambierensis Chevreux, 1908), leaving a total of 13 species (Table 1). The placement of these 13 species in five clearly separate habitats is consistent with a polyphyletic origin for them and that we can expect further generic splitting of Orchestia . In fact Lowry and Fanini (2013) have recently proposed a revision of the genus Orchestia in which all the species belonging to freshwater and terrestrial rain forest leaf litter of the northeast Atlantic islands (columns 3 and 4 in Table 1) were removed to a newly created genus Cryptorchestia. O. kosswigi is also transferred to the new genus and these authors describe a new species referable to Orchestia : Orchestia xylino Lowry & Fanini from the Mediterranean Sea. Recent molecular evidence ( Pavesi et al. 2014) does not support the close genetic relationship required by Lowry and Fanini’s proposal between cavimana and the Atlantic islands endemic " Orchestia " listed in column 4 of Table 1. One of these taxa, Orchestia guancha , was shown to be close genetically to Orchestia gammarellus , confirming earlier work by Villacorta et al. (2008). Pavesi et al. (2014)also show that Orchestia montagui and Orchestia stephenseni are not closely linked genetically to the other species of Orchestia inclusive of the type species Orchestia gammarellus , plus Orchestia mediterranea , Orchestia aestuarensis and Orchestia guancha . With the transfer of Orchestia microphtalma to Macarorchestia herein, this reduces the habitats occupied by " Orchestia " to 4. The genetic findings of Pavesi et al. (2014) suggest the polyphyletic status of Orchestia and a generic level re-alignment like that shown in Table 2. Further genetic and taxonomic work is needed to include all the species listed in Tables 1 and 2.

Diagnosis.

An interim diagnosis is provided based on the type species, Orchestia gammarellus from the Medway estuary, U.K., as listed in Table 2. This is because of the demonstration of polyphyly ( Pavesi et al. 2014) within the older view of the genus Orchestia and because of the resultant taxonomic uncertainty regarding which of the taxa in Table 1 should be included within Orchestia . A diagnosis of the 5 genera listed by letter in Table 2 is delayed because the current COI phylogeny ( Pavesi et al. 2014) does not include 6 species of " Orchestia " (indicated by brackets in Table 2). This omission might change the final phylogentic tree obtained with all species listed in Table 2 included.

Adult total body length up to 22 mm; dorsal pigment patterns present; eyes medium in size, approximately one quarter of head length; antenna 1 flagellum just reaching antenna 2 peduncle of article 4; antenna 2 sexually dimorphic, peduncle slightly incrassate in adult males and without ventral fig on peduncle article 3; upper lip without robust setae; mandible left lacinia mobilis 4 dentate; maxilliped palp 3 articulate, article 2 with well developed medial lobe; gnathopod 1 of male subchelate with palm equal to dactyl, carpus and propodus free and with rounded lobes covered with palmate setae; gnathopod 1 of female parachelate, without lobes on carpus and propodus; gnathopod 2 of male strongly subchelate, merus and carpus free, dactylus with blunted tip and is half the length of the enlarged propodus; gnathopod 2 of female, ovigerous oostegite long and wide with many, long, simple, marginal setae, basis expanded anteriorly; peraeopods 3-7 cuspidactylate; peraeopods 5-7 lack slender setae lining the anterior margin of the dactyl; peraeopod 7 sexually dimorphic, adult males with merus and carpus enlarged; distinctive tufts of long simple setae on propodus of peraeopod 7 absent in both sexes; pleon segments 1-3 lacking vertical slits; pleopod rami slightly, or not, reduced; uropods without apical, spade-like robust setae, uropod 1 not sexually dimorphic, peduncle lacking well developed dorsolateral robust setae distally, outer ramus with marginal robust setae, uropod 2 rami equal in length, uropod 3 ramus shorter than peduncle; telson apically notched with 6-8 robust setae per lobe and shorter than uropod 3.