Acartia lishaojingi Guo & Gong, 2025

Gong, Zhidi & Guo, Donghui, 2025, Acartia (Acanthacartia) lishaojingi sp. nov. (Copepoda, Calanoida) from Xiamen, southeastern China, Zootaxa 5646 (2), pp. 275-288 : 276-285

publication ID	https://doi.org/10.11646/zootaxa.5646.2.5
publication LSID	lsid:zoobank.org:pub:D0A04176-7406-4F26-AA99-E11BE309EFB6
DOI	https://doi.org/10.5281/zenodo.15849631
persistent identifier	https://treatment.plazi.org/id/897FEE71-D37F-E019-F2C6-3328BD8895B0
treatment provided by	Plazi
scientific name	Acartia lishaojingi Guo & Gong
status	sp. nov.

Treatment

Acartia lishaojingi Guo & Gong , sp. nov.

Figures 1–4 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4

Materials examined. Holotype: one adult ♀ (XOB-PC-AL 001) collected on June 22, 2022 from the Longzhou Pool , Xiamen, Fujian Province, China (24°33'58"N, 118°5'31"E), and specimen dissected on one slide GoogleMaps . Allotype: one adult ♂ (XOB-PC-AL 002) collected on same date and site, specimen dissected on one slide . Paratypes: 9 adult ♀♀ and 9 adult ♂♂ (XOB-PC-AL 003-020), all from same date and site, undissected and preserved in 5% neutralized formalin/seawater.

Descriptions. Female. Body ( Fig. 1A View FIGURE 1 ) length 0.83–0.92 mm (mean ± SD = 0.90 ± 0.03, n = 10). Anterior margin of cephalosome rounded in dorsal view. Rostral filaments present, curved and thin ( Figs. 1B View FIGURE 1 , 4A View FIGURE 4 ). Prosome 5-segmented, cephalosome completely separate from first pedigerous somite; fourth and fifth pedigerous somites fused. Posterior corners of fifth pedigerous somite rounded and typically naked, sometimes with 1–4 spinules on each side ( Figs. 1A, 1C View FIGURE 1 , 4B View FIGURE 4 ). Urosome 3-segmented; genital double-somite longer than width, bearing 0–8 (usually 4) spinules located at 4 loci on posterodorsal margin, each locus with 0–2 spinules; second urosomite armed with 2 spinules situated medially along posterodorsal margin, spinules obviously larger than those on genital double-somite ( Figs. 1C View FIGURE 1 , 4C View FIGURE 4 ), several specimens display minor variability in the lack of spinules. Caudal ramus about twice as long as wide.

Antennule ( Fig. 1D View FIGURE 1 ) 17-segmented, when reflexed reaching beyond posterior end of prosome, symmetrical, without rows of spinules on any segments, segmentation and setation patterns as follows (Roman numerals represent ancestral segments, ae: abbreviation for aesthetascs): (1) I = 1, (2) II–VIII = 6 + 2 ae, (3) IX–X = 2 (1 spiniform), (4) XI–XII = 2 + ae, (5) XIII = 0, (6) XIV–XV = 2 + ae, (7) XVI = 1 + ae, (8) XVII–XVIII = 2 + ae, (9) XIX = 1, (10) XX = 1, (11) XXI = 1 + ae, (12) XXII = 1, (13) XXIII = 1, (14) XXIV = 2, (15) XXV = 2 + ae, (16) XXVI = 2, (17) XXVII–XXVIII = 4 + ae.

Antenna ( Fig. 1E View FIGURE 1 ), coxa with medial seta; basis and first endopodal segment fused to form allobasis bearing 8 setae medially and 1 seta terminally along medial margin; second endopodal segment elongated, with 8 setae on distal half on medial margin; third endopodal segment with 6 setae; exopod 4-segmented, with 1, 2, 2, 3 setae.

Mandible ( Fig. 1F View FIGURE 1 ), coxa forming well developed gnathobase with cutting blade; basis with distal seta; exopod 4-segmented, setation formula as 1, 1, 2, 2; endopod 2-segmented, first endopodal segment with 2 setae, second segment with 7 setae.

Maxillule ( Fig. 1G View FIGURE 1 ), precoxa and coxa incompletely fused, precoxal arthrite with 9 spiniform setae, proximal one of them bearing strong spinules, and with round process armed with small protrusions; coxal endite with 3 setae; coxal epipodite with 9 setae; basal endite with 1 seta; basal exite with 1 seta; exopod 1-segmented with 2 setae laterally and 5 setae terminally; endopod absent.

Maxilla ( Fig. 1H View FIGURE 1 ), precoxa and coxa incompletely fused, setation formula of endites 4, 2, 2, 3; basis with 1 seta; endopod 3-segmented, with setation formula 2, 1, 2.

Maxilliped ( Fig. 1I View FIGURE 1 ) 4-segmented; syncoxa with 5 setae; basis proximally with spiniform seta; endopod 2- segmented, with 3, 2 spiniform setae fused to segment.

Legs 1–4 ( Figs. 2A–D View FIGURE 2 ) biramous, each with 3-segmented exopod and 2-segmented endopod. Seta and spine formula as follows:

Leg 5 ( Figs. 2E, 2F View FIGURE 2 , 4D View FIGURE 4 ) basis longer than wide, with lateral seta shorter than exopod; exopod with knob-like basal swelling producing posteriorly; blade-like distal portion of exopod slightly broader at about 1/3 length, with spinule row on both distal 2/3 margins.

Male. Body ( Fig. 3A View FIGURE 3 ) length 0.77–0.80 mm (mean ± SD = 0.78 ± 0.01, n = 10). Rostral filaments thin and curved ( Fig. 4E View FIGURE 4 ). Posterior corners of fifth pedigerous somite rounded, naked or furnished with spinule (seldom with 2) dorsally on each side ( Figs. 3A, 3C View FIGURE 3 , 4F View FIGURE 4 ). Urosome 5-segments; second urosomite with 0–8 (commonly 4) spinules on posterodorsal margin, longitudinally-located 3–4 hair-like spines on each ventrolateral side, along with several spinules along posteroventral margin ( Fig. 3D View FIGURE 3 ); third urosomite unarmed along posterodorsal margin, except for few specimens bearing 2 spinules; fourth urosmite ornamented with 0–8 (usually 2) spinules on posterodorsal margin, and size of spinules subequal to those on second urosomite ( Figs. 3C View FIGURE 3 , 4G View FIGURE 4 ). Caudal ramus about 1.3 times longer than wide.

Right antennule ( Fig. 3B View FIGURE 3 ) 17-segmented with geniculation between 13th and 14th segments; segmentation and setation patterns as follows: (1) I = 1, (2) II– VI = 4 + ae, (3) VII–VIII = 2, (4) IX–XI = 2 (1 spiniform) + ae, (5) XII = 0, (6) XIII = 0, (7) XIV = 3 (1 spiniform), (8) XV = 2 (1 spiniform), (9) XVI = 1 + ae, (10) XVII = 1, (11) XVIII = 1, (12) XIX = 2 (1 spiniform), (13) XX = 1, (14) XXI–XXIII = 4 (3 spiniform), (15) XXIV–XXV = 4, (16) XXVI = 2, (17) XXVII–XXVIII = 4 + ae.

Leg 5 ( Figs. 3E View FIGURE 3 , 4H View FIGURE 4 ), left leg basis with thumb-like projection directed laterally and narrow at distal part, lateral seta on posterior surface, and without acute projection on medial margin; exopod 2-segmented, first segment unarmed; second segment with process and hairs on proximal region, medially with terminally-hooked long spine, with row of teeth along medial margin and basal accessory process; this segment terminates in acute spine. Right leg 5 basis with lateral seta; exopod 3-segmented, first segment with medial seta at about 2/3 length on posterior surface; second segment with medial lobe grooved at about 2/3 on posterior surface, lobe bearing spine on distal border; third segment with short medial spine and curved terminal spine.

Etymology. The new species is named in honour of Prof. Li Shaojing of Xiamen University (1931–2023) for his significant contributions to marine biology in China. The suggested Chinese name for this species is “ṪKä DZAEā”.

Type locality. The Longzhou Pool GoogleMaps , Xiamen, Fujian Province, China (24°33'58"N, 118°5'31"E). The surface temperatures of the pool on June 22, 2022 and June 15, 2023 were both 30.5°C, and the salinities were 20 and 30, respectively.

Remarks. The new species should be classified into subgenus Acanthacartia based on the following morphological characteristics: 1) rostral filaments present; 2) rounded posterior corners of fifth pedigerous somite; 3) the stout spine on terminal segment of male left leg 5 is not a simple spine and has one accessory process arising from its base ( Steuer 1923; Bradford-Grieve 1999). Ueda and Hiromi (1987) divided three species of Acanthacartia to form the A. plumosa species group, namely, A. plumosa Scott T., 1894 , A. sinjiensis Mori, 1940 , and A. tropica Ueda & Hiromi, 1987 . According to them, the A. plumosa group is defined as follows: in the female, the terminal segment of leg 5 with a basal swelling, projecting noticeably backward; in the male, left leg 5 with a thumb-like projection on the basis, a long terminal segment which is as long as the basis and a short terminal spine. Given that in the female, exopod of leg 5 has a basal knob-like swelling producing posteriorly; in the male, left leg 5 has a thumb-like projection on the basis, a long terminal segment and a short terminal spine, Acartia lishaojingi sp. nov. clearly belongs to A. plumosa species group. Among the five species hitherto documented in A. plumosa group ( Ueda & Hiromi 1987; Sakaguchi & Ueda 2020), A. lishaojingi sp. nov. mostly resembles A. sinjiensis and can be distinguished from other species by curved rostral filaments of both sexes, broader intermediate portion on exopod of female leg 5, as well as distally-narrowed thumb-like projection on basis of male left leg 5 ( Table 1 View TABLE 1 ).

In the original description of Acartia sinjiensis , it displays the following three diagnostic characteristics: posterior corners of female fifth pedigerous somite naked, exopod of female leg 5 filamentous, and second to fourth urosomites in male has four spinules respectively ( Mori 1940). Tanaka (1965) perceived that A. sinjiensis and A. plumosa were conspecific. Ueda & Hiromi (1987) reexamined specimens from both the Atlantic and Indo-West Pacific, who proposed that A. sinjiensis and A. plumosa were different species, while A. iseana Ito, 1956 and A. baylyi Greenwood, 1972 were both synonyms of A. sinjiensis . Such changes may be primarily due to lack of genetic data. A. sinjiensis depicted by different authors display some differences in the ornamentation of posterior corners of fifth pedigerous somite, spinulation patterns of urosomite and structure of leg 5 ( Table 2 View TABLE 2 ). It is noteworthy that the relative size of posterodorsal spinules on genital double-somite and second urosomite in female A. sinjiensis was also utilized as one of the diagnostic features ( Sakaguchi & Ueda 2020).

Acartia lishaojingi sp. nov. closely resembles A. sinjiensis but differs in the following morphological characteristics: 1) posterior corners of fifth pedigerous somite are typically naked in female ( A. sinjiensis has one row of spinules on each side); 2) second urosomite of female has only two spinules on posterodorsal margin ( A. sinjiensis has two to eight spinules); 3) posterodorsal spinules on genital double-somite are smaller than those on second urosomite in female (spinules on these two urosomites are the same size in A. sinjiensis ); 4) third urosomite of male is unarmed on posterodorsal margin ( A. sinjiensis possesses two to eight spinules); 5) distally-narrowed thumb-like projection and absence of the acute medial projection on basis of male left leg 5 (the thumb-like projection is rounded and the acute medial projection is present in A. sinjiensis ) ( Table 2 View TABLE 2 ).

Molecular analyses. A 569-bp partial region of mtCOI was obtained from six individuals of Acartia lishaojingi sp. nov. (GenBank accession numbers PQ366008–PQ366013). The intra-specific mtCOI genetic differences within A. lishaojingi sp. nov. were 0–0.9% and 0 within A. sinjiensis . Besides, the inter-specific mtCOI genetic differences between A. lishaojingi sp. nov. and A. sinjiensis ranged from 20.9–21.3%. The mtCOI genetic differences of these species from A. hongi used as the outgroup species were 20.0–24.6% ( Table 3 View TABLE 3 ). The NJ phylogenetic tree showed that A. lishaojingi sp. nov. was clearly distinct from A. sinjiensis ( Fig. 5 View FIGURE 5 ).