Psalidichelia, Bird, 2020

Bird, Graham J., 2020, Additions to the Tanaidacea (Crustacea: Peracarida) of Rangitâhua, the Kermadec Islands, from the Southwest Pacific Expedition 2017, Zootaxa 4860 (2), pp. 151-178 : 162-163

Psalidichelia n. gen.

Diagnosis. Female. Cephalothorax as long as pereonites 1–2 combined, carapace plates not clearly delineated. Pereonite-1 shorter than pereonites 2–6. Pleonite epimera with two lateral setae. Antennule ‘four-articled’ (three peduncular articles, one discrete flagellar segment). Antenna article-2 with slender dorsodistal spine and inferodistal spine; article-3 dorsodistal spine, without ventrodistal seta or spine. Mandible molar weakly rugose not strongly ridged. Maxilliped bases with two setae; endites with three flat tubercles, mesial smallest. Cheliped merus with two inferodistal setae; carpus with two dorsal setae, at midlength and distal; propodus fixed finger with five distal setae. Pereopod-1 merus naked; carpus with four distal setae, superodistal longest; propodus with three superodistal/lateral setae; dactylus and unguis about equal in length. Pereopods 2–3 basis without superior simple seta; ischium with one seta; merus, carpus and propodus with inferodistal crotchet; propodus with two (P-2) or one (P-3) superodistal/ lateral setae. Pereopods 4–6 ischium with one seta; carpus with three crotchets and superodistal seta; propodus with three (P4–5) or five (P-6) superodistal simple spines. Pleopod peduncle with seta; endopod and exopod with about seven [except mesial] and nine pinnate setae, respectively. Uropod longer than pleotelson; peduncle naked; endopod five-segmented (mature individuals), exopod one-segmented, shorter than segment-1 of endopod.

Male. Most of above but eyes proportionately larger. Cephalothorax elongate, 1.5 times ltb. Rostrum shallow. Pereonites 1–3 combined longer than broad. Antennule about 1.4 times length of cephalothorax; peduncle threearticled, article-1 just longer than article-2; flagellum five-segmented (occasionally six-segmented), longer than peduncle article-1. Antenna article-4 more slender than in female. Cheliped about 1.5 times length of cephalothorax, gracile, setation as in female; merus shorter than ventral margin of carpus; carpus 2.4 times ltb; palm with weakly divergent dorsal and ventral margins, vertical mesial spine-comb; fixed finger incisive margin convex, without apophyses, finely crenulate; dactylus strongly arcuate, incisive margin finely crenulate. Pereopods generally similar to female but pereopods 4–6 propodus more slender. Uropod peduncle with distal seta.

Etymology. Contraction of Greek noun ψαλίδι ψαλίδια, psalídi psalídia, “pinking shears” with the suffix chelia; alluding to the crenulate incisive margins of the male cheliped fixed finger and dactylus.

Remarks. The taxonomy and classification of the Leptocheliidae is intensely complex, although Guţu (2016) made a creditable effort in trying to unravel this. Using his key to Leptocheliinae genera (ibid: 23–28) the taxon described above fails at couplet 8. The combination of characters such as the female’s very distinct antennular apical segment, two maxilliped basis setae, relatively sparse cheliped setation including that of the carpus, and small single inferodistal crotchets (spines) on the carpus and propodus of pereopods 2–3, is not easily compatible with any other genus in the family. The male’s cheliped does share two characters with other genera: the vertical alignment of the palm’s mesial comb (viz. Poorea Edgar, 2012 ) and the finely crenulate incisive margins of the fixed finger and dactylus (viz. Kalloleptochelia Guţu, 2016). Yet, the general shape is unlike either of these two genera, nor that of Cacoheterotanais Morales-Núñez & Heard, 2015 , Cocotanais Esquete, 2013 , Heterotanais Sars, 1882 , Makassaritanais Guţu, 2012 , Ogleus Morales-Núñez & Heard, 2013 , and Pseudonototanais Lang, 1973 that also have non-extended chelipeds but with the chela having a distinctly forcipate aspect (see Morales-Núñez & Heard 2015: 185). There is some similarity with two obscure Mediterranean species described by Smith (1906), Leptochelia mergellinae and L. mercantilis , particularly in the shape of the male cheliped.

I first identified this taxon as possibly belonging to the leptocheliid subfamily Catenariinae Bamber, 2013 , because of its antennule configuration and long superodistal seta on the carpus of pereopod-1. The original generic diagnosis (ibid) was modified by Bamber & Marshall (2015), partly leading to my decision, but the subfamily was not recognised by Guţu (2016).