Semibalanus sp.

Vu, Binh Thuy Dang Sang Quang Tran Oanh Thi Truong Oanh Thi Kieu Le Quyen Dang Ha, 2022, Species diversity and molecular taxonomy of symbiotic crustaceans on Portunus pelagicus (Linnaeus, 1758) in Vietnam, with remarks on host records and morphological variation, Nauplius (e 2022027) 30, pp. 1-18 : 5-6

Semibalanus sp.

Host and Location. Portunus pelagicus , at Khanh Hoa, Vietnam, new record for the genus to both host and location.

Material examined and measured. All specimens (n = 4) from a female crab (141 mm CW, 17 Mar 2016, locality Nha Trang Bay, collector L. T. K. Oanh) .

Morphological description ( Fig. 3A, B ). The shell is ovoid, diameter of 3.35 ± 1.04 (2 – 4.5) mm (n = 4), with 6 plates (1 carina, 1 rostrum, 2 carinolateral and 2 lateral) truncated pyramidal, grey-white, thin, fragile, and rather smooth surface. Parietes tubiferous with a single row of major tubes. Carina trapezoidal-shaped; lateral borders overlap and do not close up with the carinolateral plates. Rostrum wide, curved trapezoidal-shaped, borders overlap the border of the laterals. Carinolateral narrow with border overlapped by carina and laterals. Orifice wide, diamond-shaped; operculum cover, diamond-shape; scutum wide, triangular with horizontal striations parallel with the basal edge and inconspicuous adductor ridge; tergum narrow and beaked with a narrow and long spur ( Fig. 3A ). The basis is membranous and very closely cemented to the crab carapace. The tissue inside is white ( Fig. 3B ).

Infestation status. Semibalanu s sp. occurred with low prevalence (0.21 %), and was only found on the carapace of one individual host crab.

Remarks. Semibalanus Pilsbry, 1916 is the genus of acorn barnacle most abundant on tropical intertidal zones. Four species are currently recorded for this genus.The two common ones ( Semibalanus balanoides ( Linnaeus, 1767) , and Semibalanus cariosus ( Pallas, 1788)) are found mostly attached to rock(Takeda e t al., 1998; Brousseau and Goldberg, 2007; Gyory, 2011), and rarely on crabs ( McDermott, 2007); Semibalanus madrasensis ( Daniel, 1958) was found on a fishing craft ( Daniel, 1958), and Semibalanus sinnurensis ( Daniel, 1962) on a mollusc shell ( Daniel, 1962). This Semibalanus specimen shared some similar characters with S. balanoides (parallel grooves on the opening surface), and S. sinnurensis (parietes provided with minute calcareous projections), however, the observed external morphological characters (of only two individuals), and the DNA sequences are not enough for species identification. Moreover, the occurrence of Semibalanus sp. on Portunus pelagicus is assumed to be incidental.

Figures

Figure 3. Line drawing (A) and photo image (B) of Semibalanus sp. individuals (arrows) attached to the carapace of Portunus pelagicus. Note:two unidentified gastropod snails in image.1: Carina; 2: Carinolateral; 3: Lateral; 4: Rostrum, 5: Scutum;6:Tergum. Scale bar = 1mm for A, and 0.5 mm for B.