Microthalestris forficuloides ( Scott & Scott, 1894 ) Huys, Rony & Mu, Fanghong, 2021

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 : 272-273

Microthalestris forficuloides ( Scott & Scott, 1894) comb. nov.

Thalestris forficuloides Scott & Scott, 1894

Scott & Scott (1894: 143) compared T.forficuloides with T. forficula and stated that both species are closely related but differed in the segmentation of the female antennule (9- vs 8-segmented), the proportional lengths of the antennulary segments, and the relative size of the rami of P1. However, their claim (see also Scott 1894b: 256) that the two species also differed in the proportional length of the other swimming legs is unfounded since Claus (1863) neither described nor illustrated P2–P4. Sewell’s (1940: 189) statement that the P4 has an additional seta on exp-3 and enp- 3 in T. forficuloides is also incorrect. Comparison shows that the proportional length (relative to exp-1) of P1 enp-1 is virtually identical in both species but that the size of exp-2 is dissimilar (enp-1:exp-2 1.5 in T. forficula vs 2.2 in T. forficuloides ). Differences can also be observed in the male antennule which is uncharacteristically elongate and slender in T. forficula ( Claus 1863: Plate XVII, Fig. 9). Both species are similar in the morphology of caudal ramus seta V which displays a slight basal swelling posterior to the fracture plane. Based on the differences listed above, T. forficuloides is reinstated here as a valid species under the new combination Microthalestris forficuloides comb. nov.

Original description. Scott & Scott (1894): 142–144, 149; Plate IX, figs 4–9.

Additional description. Scott (1894b): 255–256; Plate X, figs 13–25.

Type locality. Scotland, Firth of Forth ; mud near low-water mark at Seafield, in the vicinity of Leith .

Differential diagnosis. Microthalestris . Body length 730 μm in ♀, smaller in ♂. Antenna with 2-segmented exopod bearing one seta on exp-1 and two lateral and three apical elements on exp-2. P1 exopod about two-thirds length of endopod; exp-2 elongate, about twice as long as exp-1, and about 45% length of enp-1; insertion point of inner seta of enp-1 at 25% of inner margin length; exp-3 with two unipinnate spines and two geniculate setae; enp-2 with one minute seta, one geniculate seta and one geniculate claw. Armature pattern of ♀ P2–P4:

P3 endopod ♂ 3-segmented, with apophysis on enp-3, armature pattern [1.1.02 + apo]. P 5 ♀ with elongate exopod (about 2.4 times as long as maximum width), inner margin and proximal half of outer margin straight, with eight elements, proximal outer one long, outer apical one short; endopodal lobe with five elements, innermost one short. P 5 ♂ exopod 1-segmented, with seven elements; endopodal lobe with two elements, outer one shortest. Armature of P 6 ♂ unconfirmed. Caudal ramus seta V with slightly swollen proximal part .

Notes. Unconfirmed records of M. forficuloides include Inveraray and near Largabruach in Loch Fyne, Scotland by Scott (1897), Holy Island in Northumberland, England by Brady (1904) and Norman & Brady (1909 – as M. forficula ) and the Isle of Man by Herdman (1897 – as Thalestris forficuloides ).

Scott (1899) recorded T. forficula (= probably Microthalestris polaris sp. nov.; see below) dredged at 55 m depth off Cape Gertrude in Franz Josef Land and added, with a slight inclination, that T. forficuloides is probably to be regarded as merely a local form of the latter. This view was reiterated in a later paper reporting on the presence of the species (as “ T. forficulus ”) in Fairlie and Hunterston in the Firth of Clyde ( Scott 1900). Scott (1906), accepting Sars’s (1905) synonymy, reported the species (as M. forficula ) from pools near low-water between Leith and Portobello in the Firth of Forth but it is likely that his record referred to T. forficuloides . Norman & Scott (1906) recorded M. forficula from rock-pools at and above the high-water mark in Plymouth, Devon, listing T. forficuloides as a synonym, but the identity of this record remains indeterminable.