Synidotea laticauda Benedict, 1897

Liu, Wenliang, Liang, Xiaoli & Zhu, Xiaojing, 2017, A new record and mitochondrial identification of Synidotea laticauda Benedict, 1897 (Crustacea: Isopoda: Valvifera: Idoteidae) from the Yangtze Estuary, China, Zootaxa 4294 (3), pp. 371-380 : 372-376

Synidotea laticauda Benedict, 1897

Figs 1–4

Synidotea laticauda Benedict, 1897: 393 –394, fig. 4.— Menzies & Miller 1972: 13–16, figs 4–5.— Poore 1996: 385–389, figs 1b, e, h, l, 2b.— Poore 2012: 329.

Synidotea laevidorsalis— Shen 1955: 81–82, plate?13–16.— Huang et al. 1981: 531–537 (list).— Chapman & Carlton 1991: 386–400.—Mees & Fockedey 1993: 61–63.—Chapman & Carlton 1994: 700–714, fig. 2b–c, e–f.— Liu & He 2007: 99, plate 99.— Cuesta et al. 1996: 43.— Buschek & Boyd 2006: 697–702.

Material examined. 31♀♀ (8.8–16.7 mm) and 21 ♂♂ (9.9–18.9 mm) specimens collected from the Yangtze Estuary during June 2011 were examined, 1.8–6 m depth, soft mud and sand bottom.

Diagnosis. Body about 2.7 times as long as wide in male, 2.5 times in female; depressed and smooth, lateral margin smooth. Cephalon frontal margin almost straight, without median excavation. Eyes bulge outward, forming part of lateral cephalic margin ( Figs 1 A, B, 2A, D). Dorsum of each pereonite smooth, margin slightly arched; distolateral angle of pereonites 1–4 rounded, those of pereonites 5–7 subrectangular. Pleotelson about 1.1 times as long as greatest width; posterior margin broad and concave, about 0.4 of the greatest width. Antenna 1 flagellum uniarticulate, with 10 pairs of jointed aesthetascs ( Fig. 2 B). Antenna 2 0.6 body length, flagellum with 18–22 articles. The lower surfaces of all the pereopods in male are covered with an extremely dense mat of long setae ( Fig. 4 A–G). Females have longer setae splayed at right angles to the axis of the pereopods ( Fig. 3 A–G). Penial plate fused along entire length, 1.3 times as long as wide, swollen distally, with notched lateral margins ( Fig. 4 I). Pleopod 2 with appendix masculina 1.1 times as long as endopod, apex bluntly pointed, distal quarter slightly curving medially ( Fig. 4 H). Uropod 4.1 times as long as distal peduncle width, distolateral angle with 3 plumose setae; endopod about 0.21 length of peduncle, distal margin truncate, lateral margin curved into distal margins ( Fig. 2 C).

Distribution. San Francisco Bay ( Benedict 1897) and Delaware Bay, USA ( Buschek & Boyd 2006); Gironde Estuary, France (Mees & Fockedey 1993); Guadalquiver Estuary, Spain ( Cuesta et al. 1996); Yangtze Estuary, China; Korea.

Habitat. The species prefers the warmer parts of San Francisco Bay, where salinity is reduced ( Menzies & Miller 1972). In the Yangtze Estuary it is found in 1.8–6 m depth, soft mud and sand bottom, salinity 8.3–28.8 ‰, and the optimum salinity is about 20 ‰.

Molecular results. A total of about 605 bp were reconstructed through direct sequencing of amplified DNA. The tree topology was in agreement with the one of the Maximum Composite Likelihood (MEGA7) which is shown in Fig. 5 and bootstrap values exceeding 50 %. According to this phylogeny both specimens of S. laticauda , and the individual identified as S. laevidorsalis from Korea ( JX502963 ) shared the same COI sequence, and formed a monophyletic clade. Specimens of Synidotea nipponensis ( KR095340 ) from Korea formed a sister clade with high confidence value.

Remarks. S. laticauda was described from a single specimen in San Francisco Bay ( Benedict 1897). Chapman & Carlton (1991, 1994) treated it as a synonym of S. laevidorsalis . Poore (1996) differentiated the two species on body size; the shapes of the pleotelson, the head and the pereonite margins, and on fused penial plates, and uropodal exopod; and setal pattern of the pereopods, and on ecological preference. He also argued that the record of S. laevidorsalis from the Yangtze Estuary, China ( Huang et al. 1981) was a misidentification because S. laevidorsalis is marine species of high salinity, and not in estuarine situations. All specimens of Synidotea from the Yangtze Estuary can safely be identified as S. laticauda based on Poore’s (1996) criteria. Molecular comparison using the mitochondrial sequence COI shows that S. laticauda from the Yangtze Estuary is identical to a NCBI sequence of S. laevidorsalis from Korea, probably misidentified. The COI sequence was taken from NCBI (Genbank # JX502963 ). It had been lodged in 2012 by Kim, Kim & Koo as part of their project “DNA Barcoding of Marine Intertidal Invertebrates in Korea ”. Unfortuately, no voucher material of the Korean specimen identified as S. laevidorsalis is available and its morphology could not be verified.

There is no suggestion that the species is similarly widespread. Transportation by shipping seems more probable, because the ability of these species to raft cannot be used to suggest that this is how S. laticauda became distributed between estuaries in San Francisco Bay, Delaware, France and Spain (Mees & Fockedey 1993; Cuesta et al. 1996; Buschek & Boyd 2006). Poore (1996) suggested that the species originated in San Francisco Bay, from where the species was first described in 1897. But Chapman & Carlton (1991) and Mees & Fockedey (1993) thought the record of S. laticauda from the San Francisco Bay and Gironde Estuary were likely introduced from China, because it was discovered these two places no later than 1896 and 1975, respectively. The molecular results showed that S. laticauda probably also occurs in Korea. Several species were also found in the Yangtze Estuary and Korean estuaries, such as Chongxidotea annandalei ( Tattersall, 1921) ( Kwon 1986, Liu et al. 2010), Cleantioides emarginata Kwon & Kim, 1992 ( Liu & Poore 2013) and Gnorimosphaeroma chinense ( Tattersall, 1921) ( Kim & Kwon 1985). Ponder et al. (1991) have suggested that a possible explanation for the fragmentation of suitable habitat is that lower sea levels during the Pleistocene, combined with the great aridity during this period, much reduced the habitats available for estuarine animals, and some marine animals might go into estuaries of rivers fed by melting snow and ice probably persisted for seeking refuge.

Figures

FIGURE 1. Synidotea laticauda Benedict, 1897. A, female (total length, 9.7 mm); B, adult male (total length, 13.4 mm), habitus in dorsal view. Scale = 1 mm.

FIGURE 2. Synidotea laticauda Benedict, 1897. A – C, female (total length, 9.7 mm); D, adult male (total length, 13.4 mm). A and D, habitus in dorsal view; B, Antenna 1 flagellum; C and E, uropod. Scale = 1 mm.

FIGURE 3. Synidotea laticauda Benedict, 1897. Female (total length, 9.7 mm). A – G, pereopods 1 – 7. Scale = 1 mm.

FIGURE 4. Synidotea laticauda Benedict, 1897. Adult male (total length, 13.4 mm). A – G, pereopods 1 – 7; H, pleopod 2 and appendix masculina; I, penial plate. Scale = 1 mm.

FIGURE 5. Phylogram showing relationships among selected species of the family Idoteidae, inferred from ML analysis of COI sequences. Numbers below branches are bootstrap values (950 replicates); only values higher than 50 % are shown.