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 : 283-284

Thalestrella Monard, 1935a

Karllangia Noodt, 1964

Monard (1935a: 45) described Thalestrella ornatissima as the type species of his new genus Thalestrella , based on females dredged from sand near Roc’h Iliévec in the Roscoff area (Brittany). Lang (1944, 1948) rejected the validity of Thalestrella and transferred T. ornatissima to Parastenhelia , claiming a close relationship with P. anglica and P. hornelli . Gee (2006) recently assigned the species to Karllangia , repeatedly stating that the original description was based on only a single female but there is no evidence for that in Monard’s (1935a) paper.

Mielke (1994b: 152) recognized two evolutionary lineages within Karllangia , the more primitive branch comprising K. arenicola arenicola and K. tertia , and the more advanced one represented by K. psammophila , K. arenicola bengalensis and both Costa Rican species ( K. obscura , K. pulchra ). As pointed out by Gee (2006) the outstanding problem within the genus Karllangia is the fact that its type species, K. arenicola , apparently does not display the most important synapomorphy that supports the common ancestry of the remaining species (including the type species of Thalestrella ). This character state which distinguishes Karllangia from other members of the Parastenheliidae is the modification of the male antenna (allobasal seta much more plumose, exp-1 smaller and with only one strong, plumose seta, exp-2 broader with more strongly plumose setae than in ♀). The original description by Noodt (1964) of K. arenicola from coralline sands on the Egyptian coast of the Red Sea does not mention any sexual dimorphism in the male antenna which could be attributed to either an observational error or to genuine absence. This ambiguity surrounding the type species has now been removed by synonymizing Karllangia with its senior subjective synonym Thalestrella . The presence of antennary sexual dimorphism in its type species, T. ornatissima , has been demonstrated by Gee (2006) who confirmed a number of additional genus-level apomorphies in the species, including the compressed appearance of the distal antennulary segments in the female, the presence of only three setae on exp-2 of the antenna, two setae on the mandibular exopod, and one seta on the maxillipedal syncoxa; the absence of the inner seta on P2–P4 exp-1; and, a male P5 exopod with only four setae. Additional apomorphies which were not observed by Gee (2006) include (a) male antennule subchirocer, compound segment 5 (XIV–XX) swollen; (b) the male antennule with only three segments distal to the geniculation (XXI–XXIII, XXIV–XXV, XXVI–XXVIII); (c) ventral surface of segment 2 of male antennule with characteristic, backwardly directed, spiniform element, either displaying a serrate or flagellate tip ( Wells & Rao 1987: Fig. 110b; Mielke 1994b: Fig. 6A ); and (d) outer spine on P3 enp-3 reduced in size in ♂ ( Mielke 1994b: Fig. 6C ; Gee 2006: Fig. 5C ; Fig. 7 herein).

Diagnosis. Parastenheliidae . Sexual dimorphism in antennule, P3 enp-3 outer spine, P5–P6 and urosomal segmentation. Body subcylindrical; posterior margin of cephalothorax (typically) and all somites (except anal somite) typically with deeply divided, denticulodigitate or lobate, hyaline frills (plain in T. obscura comb. nov. and possibly T. arenicola comb. nov.). Rostrum defined at base, of moderate size, reaching at most to end of second segment of antennule; linguiform. Anal operculum semicircular, variously ornamented; usually bordered with fine spinules or denticles. Caudal ramus at most as wide as long, with dorsal spinular row; with seven setae, setae IV–V not basally inflated in ♀.

Antennule ♀ compact, 8- or indistinctly 9-segmented; segment 1 not elongate, distal four or five segments small with combined length only slightly longer than segment 4; with aesthetascs on segments 4 and 8 (or 9). Antennule ♂ subchirocer, 7-, 8- or indistinctly 9-segmented; ventral surface of segment 2 with characteristic, backwardly directed, spiniform element; with geniculation between segments 5 and 6 (or 6 and 7 when indistinctly 9-segmented) and 2–3 segments distal to geniculation; compound segment 5 ( XIV – XX) swollen, occasionally subdivided dorsally by transverse surface suture; with aesthetasc on segments 5 and 7 or 8; segmental homologies of 8-segmented antennule: I, II– VIII, IX – XII, XIII, XIV – XX, XXI – XXIII, XXIV – XXV, XXVI – XXVIII. Antenna sexually dimorphic. Female antenna with proximal endopodal segment largely fused to basis forming allobasis, with short pinnate seta on abexopodal margin; exopod 2-segmented (or segments partially fused), proximal segment with 1–2 setae, distal segment with one lateral and two apical elements (surrounded at base by serrate hyaline frill); distal endopodal segment without penicillate elements. Male antenna with enlarged, highly plumose seta on allobasis; exopodal segments of different size, with only one seta on proximal segment and all lateral setae enlarged and highly plumose. Mandible with three elements on basis; endopod with eight setae; exopod 1-segmented, with 2–4 setae. Maxillulary coxal epipodite represented by one seta. Maxilla with three endites on syncoxa; endopod discrete, with 4–5 setae. Maxilliped with one seta on syncoxa; basis with 0–2 setae on palmar margin; endopod represented by pinnate claw, accompanied by one accessory seta .

P1 exopod 3-segmented; segments subequal; exp-2 with or without inner seta; exp-3 with two pinnate spines and one geniculate spine and one (non-)geniculate seta. P1 endopod 2-segmented; enp-1 elongate, about twice as long as exopod, with well developed, pinnate inner seta originating from proximal half in a region of reduced chitinization of segment wall; enp-2 very small, with one naked minute seta and two unipinnate claws, longest of which geniculate. P2–P4 rami 3-segmented; outer spine of P3 enp- 3 ♂ reduced in size. Armature formula of P2–P4 as follows:

P 5 ♀ endopodal lobe triangular, with five setae; inner margin without transverse striae; exopod elongate (2–5 times longer than wide), with 5–6 elements. P 5 ♂ endopodal lobe with two elements; exopod 1-segmented, with 4–5 elements. Vestigial P 6 ♀ represented by 2–3 short setae. P 6 ♂ with three setae/spines.

Type species. Thalestrella ornatissima Monard, 1935a (by monotypy).

Other species. Karllangia arenicola Noodt, 1964 = T. arenicola ( Noodt, 1964) comb. nov.; K. psammophila Wells, 1967 = T. psammophila ( Wells, 1967) comb. nov.; Parastenhelia reducta Apostolov, 1975 = T. reducta ( Apostolov, 1975) comb. nov.; K. arenicola bengalensis Wells & Rao, 1987 = T. bengalensis ( Wells & Rao, 1987) comb. nov.; K. obscura Mielke, 1994b = T. obscura ( Mielke, 1994b) comb. nov.; K. pulchra Mielke, 1994b = T. pulchra ( Mielke, 1994b) comb. nov.

Species inquirenda. Parastenhelia ornatissima ( Norman & Scott, 1905) sensu Por (1964) .

Figures

FIGURE 5. Johnwellsia bipartita gen. et sp. nov. (♂): A, antennule, ventral (armature omitted); B, antennule, ventral (disarticulated, showing armature); C, P2 endopod, anterior; D, P3 endopod, anterior; E, P4 endopod, anterior; F, P5, anterior; G, P6; H, maxilliped.

FIGURE 6. Sexual dimorphism of P2 (A–E) and P4 (F–G) endopodal segmentation and armature within the Parastenheliidae. A, Foweya tertia (Kunz, 1975); B, Microthalestris costata (Pallares, 1982) comb. nov., M. variabilis sp. nov., Parastenhelia similis Thompson & Scott, 1903, P. willemvervoorti sp. nov., Porirualia pyriformis (Song, Kim & Chang, 2003) comb. nov.; C, Johnwellsia bipartita sp. nov.; D, Parastenhelia hornelli Thompson & Scott, 1903 sensu Apostolov (1973); E, Parastenhelia oligochaeta Wells & Rao, 1987; F, Microthalestris bulbosa (Gee, 2006) comb. nov., Parastenhelia willemvervoorti sp. nov.; G, Microthalestris minuta (Pallares, 1982) comb. nov., Penicillicaris penicillata sp. nov.