Thalestrella reducta ( Apostolov, 1975 ) 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 : 286

Thalestrella reducta ( Apostolov, 1975) comb. nov.

Parastenhelia reducta Apostolov, 1975

Original description. Apostolov (1975): 172–175; Fig. 3 .

Type locality. Bulgaria, Burgas Province; Tsarevo (formerly Michurin) and Lozenets ; sandy bottom, 5 m depth .

Notes. Gee (2006) transferred Parastenhelia reducta as species incertae sedis to Karllangia , based on the female antennule with distinctly compressed distal segments, the maxillipedal syncoxa with only one seta, and the reduced armature and absence of sexual dimorphism of P2–P4. The generic assignment of this species, known only from a single female and male from shallow sandy sediments along the Bulgarian Black Sea coast ( Apostolov 1975), was tentative since the male P5 exopod exhibits five setae (instead of four in the remaining Karllangia species ) and, according to the original text description the antenna lacks sexual dimorphism. Armature patterns on the fifth legs are known to vary in many harpacticoid genera and small differences in setal numbers are therefore likely to be of less significance in delimiting their diagnostic boundaries. We concur with Gee (2006) that the hirsute bulbous structure in Apostolov’s Figure 3h , partly concealed by the second segment of the male antennule, is conceivably the modified antennary exopod. Although a re-examination of Apostolov’s (1975) specimens would be desirable, there appears to be no reason to question its generic assignment. Parastenhelia reducta is here removed from the incertae sedis category of Karllangia and reinstated as a valid species of Thalestrella . Por’s (1964) specimens of T. ornatissima , the geographically closest record of the genus, agree with T. reducta comb. nov. in the length:width proportions of the female P5 exopod but conspecificity can be ruled out on the basis of differences in the anal operculum and caudal ramus length (as measured in dorsal aspect).

Thalestrella reducta comb. nov. can readily be distinguished from its congeners by the reduced armature on P3–P4 (P4 exp-3 with two inner setae vs three, P3–P4 enp-3 with one inner seta vs two) and the presence of six elements on the male P5 exopod. Apostolov (1975) did not figure the deeply incised hyaline frills on the body somites, however, his illustration ( Fig. 3a ) of the urosome showing the long pleural extensions (probably an optical section of the frills) indicates their presence. T. reducta is the only species in the genus that displays four setae on the mandibular exopod.

Figures

FIGURE 3. Johnwellsia bipartita gen. et sp. nov. (♀):A, mandible; B, mandibular coxa; C, maxillule; D, maxilla; E, maxilliped; F, P1, anterior (praecoxa omitted); G, P2, anterior (position of outer basal seta arrowed).