Thalestrella Monard, 1935a

Huys, Rony & Mu, Fanghong, 2021, Johnwellsia, a new intertidal genus of Parastenheliidae (Copepoda, Harpacticoida) from the Taiwan Strait, China, including a review of the family and key to genera, Zootaxa 5051 (1), pp. 236-318 : 287-288

Key to species of Thalestrella Monard, 1935a

A dichotomous key to the six valid species of Thalestrella was provided by Gee (2006) which is updated below to include T. reducta comb. nov. and to rectify a mistake in his couplet 3 ( T. obscura comb. nov. has only five setae on P5 exopod ♀). Additional unidentified species have been recorded from Papua New Guinea ( Willen 2000), the Galápagos Archipelago ( Mielke 2003), Zanzibar ( Gheerardyn 2007; Gheerardyn et al. 2008; Callens et al. 2012) and possibly Heron Island ( Iwasaki 1994), indicating a circum(sub)tropical distribution of the genus.

1. P3 exp-3 with two inner setae...........................................................................2.

– P3 exp-3 with three inner species.........................................................................4.

2. P4 exp-3 with two inner setae; P3–P4 enp-3 with one inner seta; P5 exopod ♂ with five setae............................................................................................. T. reducta ( Apostolov, 1975) comb. nov.

– P4 exp-3 with three inner setae; P3–P4 enp-3 with two inner setae; P5 exopod ♂ with four setae.......................3.

3. P1 exp-2 without inner seta; P5 exopod ♀ about three times as long as maximum width; P5 exopod ♂ semicircular; anal operculum without spinous projections but fringed by small setules/spinules........ T. arenicola ( Noodt, 1964) comb. nov.

– P1 exp-2 with inner seta; P5 exopod ♀ about five times as long as maximum width; P5 exopod ♂ about twice as long as wide; anal operculum with 6–8 conspicuous spinous projections............................. T. ornatissima Monard, 1935a .

4. Antennule ♀ 8-segmented; P3 enp-3 without sexual dimorphism; P5 exopod ♀ with five setae; anal operculum with about 40 setules..............................................................................................5.

– Antennule ♀ 9-segmented; outer spine of P3 enp-3 very reduced in ♂; P5 exopod ♀ with six setae; anal operculum with about 12–25 spinules.......................................................................................6.

5. Outer corner of proximal antennulary segment attenuated; second outer seta of P5 exopod ♀ distinctly longer than proximalmost; proximal outer seta of P5 exopod ♂ distinctly shorter than segment............ T. psammophila ( Wells, 1967) comb. nov. 1

– Outer corner of proximal antennulary segment normal; second outer seta of P5 exopod ♀ very short, distinctly shorter than proximalmost; proximal outer seta of P5 exopod ♂ distinctly longer than segment................................................................................................. T. bengalensis ( Wells & Rao, 1987) comb. nov.

6. Hyaline frills of abdominal somites plain; P1 exp-2 without inner seta; P5 exopod ♀ with five setae.......................................................................................... T. obscura ( Mielke, 1994b) comb. nov.

– Hyaline frills of abdominal somites lobate; P1 exp-2 with inner seta; P5 exopod ♀ with six setae............................................................................................ T. pulchra ( Mielke, 1994b) comb. nov.

1 According to Wells (1967: Text-fig. 52M) P2 exp-3 has three inner setae which is a unique condition within the genus. The extreme distal position of the third inner seta, originating from the inner distal corner suggests that Wells observed an aberrant specimen with a supernumerary element on the P3 exopod. Gee (2006) re-examined the type material from Inhaca Island and made some corrections to the original description but did not comment on this character state. Although he stated that there are “…significant differences in the setation of the swimming legs … to warrant specific status for both these forms” he refrained from using them in his key. Wells & Rao (1987: 218, Table 7) used it as a character to differentiate both subspecies but Wells (2007: 596) pointed out that his original observation was probably wrong, an opinion that is adopted here.