Lophogaster intermedius Hansen, 1910

Lophogaster intermedius Hansen, 1910 View in CoL

( Fig. 1 View Fig )

Lophogaster intermedius Hansen, 1910: 14 View in CoL , pl. 1, fig. 1; W.M. Tattersall, 1922: 448; Fage, 1942: 31, fig. 20; O. S. Tattersall, 1960: 534, fig. 2; Băcescu, 1985: 357, fig. 1; Casanova, 1996: 138, fig. 6a–d; — 1997: 96, fig. 2f; Fukuoka & Murano, 2002: 55; Yolanda et al., 2023a: 203 View Cited Treatment ; —, 2023b: 418.

Lophogaster hawaiensis View in CoL : Wang and Liu, 1994: 62; — 1997: 195; Liu and Wang, 2000: 59, fig. 1.

? Lophogaster typicus View in CoL : Ortmann, 1905: 967.

? Lophogaster hawaiensis Fage, 1940: 325 View in CoL : — 1942: 30, figs. 19, 24a, 25b; O. S. Tattersall, 1960: 537, fig. 4.

Not Lophogaster intermedius View in CoL : W. M. Tattersall, 1951: 20, fig. 1c (= L. japonicus W. M. Tattersall, 1951 View in CoL ).

Material examined. Central Pacific. 2 males (cl. 3.5, 3.6 mm), 1 juv. (cl 2.2 mm), 1 female (cl 8.8 mm), KH-74-2, St. 20, 28°07.3′N 178°25.0′W – 28°10.2′N 178°35.0′W, 10 June 1974, IKMT, ca. 1200–0 m, coll. M. Murano (NSMT-Cr 32872) GoogleMaps ; — 1 male (cl 4.5 mm), KH-74-2, St. 21-1, 28°15.0′N 178°38.8′W – 28°20.2′N 179°28.7′W, 11 June 1974, IKMT, ca. 1200–0 m, coll M. Murano (NSMT-Cr 32873). Sahul Shelf. 2 juvs (cl 1.3, 1.4 mm) (id tentative), KH-72-1, St. 30, 12°24.8′S 128°00.1′E – 12°24.8′S 128°00.2′E, June 25 1972, inner net of 3 m Beam Trawl, 115– 115 m, coll. M. Murano (NSMT-Cr 32874) GoogleMaps .

Diagnosis. Body integument somewhat weakly calcified.

Carapace ( Fig. 1a, b View Fig ) feebly granulated on dorsal and dorso-lateral surfaces; rostral plate developed, covering basal 2 segments of antennular peduncle and eye-stalk, anterior part slightly narrower than basal part, and anterior margin distinctly concave; antero-lateral tooth well developed, gently curving inwards; rostral process rather long, slightly curving upwards, apex falling just short of anterior tooth of antennal scale; post-ocular process absent; dorsal median carina on posterior part indistinct or bluntly ridged; postero-lateral tooth (= alar spine) moderately long, directed slightly upwards.

Abdomen ( Fig. 1c View Fig ) with ventral median tooth on first 5 somites, decreasing its height posteriorly; sixth somite sub-equal in length to fifth, with very short postero-lateral tooth; pleura on fourth and fifth somites ending in small spine but those on first 3 somites rounded, without tooth or spine.

Telson ( Fig. 1c, d View Fig ) about 2.5 times as long as sixth abdominal somite, with obtuse dorsal median tubercle in basal part, armed laterally with single, or rarely 2 setal-spines on either side, in addition to ordinary 2 distal pairs, penultimate pair of which close to terminal pair, less than half length of longest terminal pair; posterior plate weakly produced, bearing 4–6 short spinules and possible 1 pair of plumose setae.

Uropod ( Fig. 1c, d View Fig ) with both rami sub-equal in length, exopod ending laterally in distinct tooth.

Antennular lamina ( Fig. 1e View Fig ) with distal margin almost rounded or weakly advanced lobe, and disto-median part with short triangular process, with long seta arising from concaved part.

Antennal scale ( Fig. 1f View Fig ) sub-triangular, broadest in basal part, twice or slightly longer than broad, apical tooth rather long, directed straightly forward or very gently curving inwards, outer margin weakly convex, bearing 4 or 5 teeth increasing in length towards apex on its anterior half.

Remarks. This species was well-documented by Băcescu (1985) and Casanova (1996) (see also Hansen, 1910; O. S. Tattersall, 1960).

Casanova (1996) mentioned that L. hawaiensis Fage, 1940 could be a junior synonym of L. intermedius on the basis of the published data. To date, this might be a common taxonomic concept among the mysid researchers (e.g., WoRMS, accessed in March 2024), although O. S. Tattersall (1960) noted that these two species can be distinguished by several features such as tubercles on the carapace, the rostral length, as well as the shapes in the anterior margin of the antennular lamina.

So far documented, the form of the antennular lamina referred to L. intermedius appears to show some variations in its form, from well produced wide to short triangular or denticular or even undeveloped plain lobe ( Hansen, 1910; Băcescu, 1985; Casanova, 1996; this study). However, it deserves future studies in details to verify the taxonomic status for a little-known Hawaiian species based on further specimens by incorporating molecular data.

Distribution. This species is currently believed to be distributed in the western Pacific and its neighbouring regions, under a synonymy over L. hawaiensis , from Hawaii to New Caledonia, and eastern part of the Indian Ocean, through South-east Asian waters.