Rhopalophthalmus egregius Hansen, 1910

Yolanda, Rofiza, Ambarwati, Reni, Rahayu, Dwi Anggorowati, Budijastuti, Widowati, Fitrihidajati, Herlina, Kuntjoro, Sunu, Rachmadiarti, Fida & Purnomo, Tarzan, 2023, An annotated checklist of the species of Lopogastrida and Mysida (Crustacea Peracarida) from Thailand and its adjacent waters, Zootaxa 5244 (3), pp. 201-232 : 218

Rhopalophthalmus egregius Hansen, 1910

= Rhopalophthalmus phyllodus Murano, 1988

Type locality. Bawean Island , Indonesia ( Hansen 1910) .

Record from Thailand. Songkhla Lagoon System (W.M. Tattersall 1921), Surat Thani water ( Murano 1988; Hanamura et al. 2011), Chonburi and Phuket Island ( Hanamura et al. 2011).

Habitat and depth range. Brackish water of the Songkhla Lagoon System, most abundant in the mouth area rather than the middle to upper reaches of this estuarine river. Depth: 4.5 m ( Hanamura et al. 2011).

Distribution. This species has a wide distribution from Indonesia ( Hansen 1910; Hanamura et al. 2011), Japan ( Nakazawa 1910), India (W.M. Tattersall 1915; 1922; Panikkar & Aiyar 1937; Pillai 1957; Hanamura et al. 2011), New Caledonia and New Zealand ( Colosi 1920), Australia and New South Wales (W.M. Tattersall 1936; 1940), Krusadai Island ( Chacko 1950), South Africa (O.S. Tattersall 1952), Sierra Leone (O.S. Tattersall 1957), Singapore (O.S. Tattersall 1960; Hanamura et al. 2011), Malaysia ( Hanamura et al. 2011; Ramarn et al. 2012a) and Thailand ( Murano 1988; Hanamura et al. 2011).

Remarks. Among the species of the genus Rhopalophthalmus , this species can be easily distinguished by the antennal sympod bearing 3 prominent graduated spines flanked by 2 small lateral spines ( Hanamura et al. 2011).

The occurrence of Rhopalophthalmus egregius in the Songkhla Lagoon System is of special interest. This species first report in Thailand was based on specimens collected by W.M. Tattersall (1921). Earlier studies of mysids by the first author in the Songkhla Lagoon System concluded that there was no R. egregius in this lagoon, but was actually R. hastatus ( Yolanda et al 2022b). We hyphothesized that there is a possibility for R. egregius to occur in this lagoon, since Hanamura et al. (2011) reported this species also present in the Surat Thani Province (upper part of the Songkhla Province), Gulf of Thailand. During the dry season, large amounts of seawater from the Gulf of Thailand always enter the Songkhla Lagoon System due to the water circulation (Yolanda & Lheknim 2020) and this circulation may transfer the R. egregius into this lagoon.