Peltogasterella aff. gracilis (Boschma, 1927)

Jung, Jibom, Yoshida, Ryuta & Kim, Won, 2019, Ophiacantha scissionis Lee & Stöhr & Bae & Shin 2019, sp. nov., Zoological Studies (Zool. Stud.) 58 (33), pp. 1-12 : 13-14

Peltogasterella aff. gracilis ( Fig. 5K )

Material examined: on Porcellanopagurus nihonkaiensis : 2 Inds., Jeju, 33°25'17.44"N 126° 9'38.96"E, Scuba, 24 Sep. 2011, Coll. Lee SK., MADBK 160730_002, host: males, SL 2.1, 2.3 mm.

Host: P. nihonkaiensis ( Paguridae ).

Distribution: Korea.

Remarks: This is the first report of peltogastrid species on Porcellanopagurus species host. The elongated and gregarious externae and absence of a chitinous shield on the present specimens reflect the characteristics of Peltogasterella gracilis . However, a mantle was not found and sequencing data could not be obtained from the present materials. Therefore, we tentatively identified these specimens as P. aff. gracilis . Additional data are necessary to confirm this identification.

One of the specimens attached on the Porcellanopagurus nihonkaiensis had only a single externa, which is not a characteristic of Peltogasterella gracilis morphology. However, Høeg and Lützen (1985) has shown that the majority of Peltogasterella sulcata specimens have gregarious externae, whereas some specimens have a single externa. Accordingly, the single externa of this specimen may be regarded as an individual variation.

Molecular Analysis

A total of 17 COI sequences (658-660 bp) and 15 sequences of 16S rRNA (372–432 bp) were obtained from the examined samples ( Table 2). The composition of these sequences was 22.21% of A, 42.59% of T, 20.96% of G, and 14.24% of C in COI; and 35.18% of A, 35.90% of T, 10.24% of G, and 18.69% of C in 16S rRNA. The COI and 16S rRNA alignment was 657 bp and 326 bp long, and had 303 and 142 variable sites (46.12% and 43.56%, respectively) and 266 and 120 parsimony informative sites (40.49% and 36.81%, respectively).

In the COI and 16S rRNA phylogenetic trees (Figs. 3, 4), the sequences of Korean peltogastrids are located near the sequences of the same species from NCBI, and they form a single clade. As mentioned above, the Peltogaster sp. 4 sequence formed a single clade, separate from those of other species.

The COI and 16S rRNA sequences of Korean peltogastrid species exhibited larger genetic gaps than the minimum interspecific variation of COI between Dipterosaccus indicus and D. shiinoi (7.80%, Fig. 3) or those of 16S rRNA between Briarosaccus auratum and B. regalis (2.71%, Fig. 4). Intraspecific variation in Korean peltogastrid species were very low ( Tables 4, 5).

Figures

Fig. 5. Korean peltogastrids. A, Peltogaster lineata on Pagurus brachiomastus and its mantle, MADBK 430101_001; B, Peltogaster postica on Pagurus filholi, MADBK 160707_009; C, mantle of B; D, Peltogaster aff. ovalis on Pagurus rathbuni, EVOSYS 260720#013; E, mantle of D; F, G, Peltogaster aff. reticulatus on Pagurus proximus and its mantle, MADBK 160718_040; H, Peltogaster sp. 2 on Areopaguristes nigroapiculus and its mantle, EVOSYS 260510#008; I, Peltogasterella gracilis on Pagurus pectinatus, MADBK 160715_016; J, mantle of I; K, Peltogasterella aff. gracilis on Porcellanopagurus nihonkaiensis, MADBK 160730_002.