Siriella gibbosa ( Ledoyer, 1970 ), 2018

Daneliya, Mikhail, Price, W. Wayne & Heard, Richard W., 2018, Revision of the Siriella brevicaudata species group (Crustacea: Mysida: Mysidae) from the West Indo-Pacific, European Journal of Taxonomy 426, pp. 1-80 : 25-26

Siriella gibbosa ( Ledoyer, 1970) stat. rev.

Siriellerythrops gibbosa Ledoyer, 1970: 223 , figs 1–2.

Siriella brevicaudata – Băcescu 1973 b: 645, partim. — Murano & Fukuoka 2008: 33, partim.

Diagnosis

Carapace with anterodorsal margin angular, apically acute; sides concave. Subrostral process seemingly covered entirely by carapace. Carapace with dorsal cephalic tubercle and slight postcervical elevation. Eye cornea narrower than eye stalk. Telson considerably narrowed posteriorly, anterior width 2.3 times posterior width, apically truncated, 1.3 times as long as wide anteriorly. Lateral margins of telson with three anterior and four posterior spiniform setae; among posterior spiniform setae, anterior three pairs short and one terminal pair long, 0.31 times as long as telson and 3.1 times as long as subterminal pair of spiniform setae; subterminal 1.2–1.8 times as long as preceding posterolateral spiniform setae. Telson apically without emargination, with three minute, but clearly visible spinules, about 0.09 times as long as posterolateral terminal spiniform setae. Labrum seemingly without anterior spine. Maxilla 1: outer ramus robust setae smooth. Segment 2 of maxilla 2 endopod with two lateral setae. Endopod of pereopods 1–3, merus 3.2 times as long as wide. Uropodal exopod 2.9 times as long as wide, with four or five distolateral spiniform setae; exopod of segment 1 is 2.7 times as long as segment 2. Uropodal endopod with three spiniform setae in both sexes, broadly set, along proximal half of inner margin. Body length of male 6 mm, female 5.5 mm ( Ledoyer 1970).

Type material

Ledoyer (1970) did not designate any types from his large amount of material, consisting of 81 specimens. It is not known whether the original specimens still exist in any museum collection, but they are absent in the National Museum of Natural History, Paris ( MNHN), Endoume Marine Station, Marseille, where Michel Ledoyer worked, and the Verona Museum of Natural History, where he deposited many amphipod types. However, Ledoyer described in detail and figured well-recognisably a 5.5 mm long adult female from “station 24” ( Ledoyer 1970: 223–225, figs 1–2), and a 6 mm long male, providing a figure of its antennular peduncle ( Ledoyer 1970: 225, fig. 1d’). No further material on the species is known so far.

Type locality

Madagascar, Toliara.

Comparison

Siriella gibbosa is distinguishable from other species of the brevicaudata group by having (1) the carapace with an apically acute anterodorsal margin, (2) the telson being narrow apically (less than twice as wide anteriorly as posteriorly in other members of the group), (3) the telson with the longest terminal pair of spiniform setae in relation to the subterminal ones (more than three times as long as the subterminal setae compared to less than 1.6 in other members of the group), (4) the uropodal endopod with three medial spiniform setae (other members of the group with 10 or more setae) and (5) the labrum lacking a spine, a unique feature among Siriella species. Notwithstanding, this last character requires confirmation using additional specimens, because this small spine is sometimes broken in other species. The terminal spiniform setae of the telson, which are about ¼ of its length, are the second longest compared to telson length after those of S. brevicaudata .

Siriella gibbosa appears to be most closely related to S. brevicaudata . Apart from the previously mentioned characters unique to S. gibbosa , it differs from S. brevicaudata by having (1) the cornea of the eye narrow (wider than the eye stalk in S. brevicaudata ), (2) endopod of maxilla 2 with two lateral setae (five in S. brevicaudata ) and (3) the telson with a pair of long apical spiniform setae (two or three pairs in S. brevicaudata ), well-developed apical spinules, and lacking a posterior emargination.

Distribution

South-West Madagascar, Toliara ( Ledoyer 1970) ( Fig. 1 ).

Habitat

Seagrass ( Ledoyer 1970).

Remarks

Synonymising Siriellerythrops gibbosa soon after its original description, Băcescu (1973 b) did not provide any comments about his comparisons and decision. The original description ( Ledoyer 1970) and illustrations of this species were detailed; comparing them with S. brevicaudata , one can easily find multiple differences between the two species, particularly in the shape of the anterodorsal margin of the carapace, shape and armature of the telson, setation of maxilla 2, armature of uropodal endopods and eye shape. Supporting the opinion of Murano & Fukuoka (2008) about significant difference of S. gibbosa from S. brevicaudata , we re-establish the species here. At the same time, we synonymise the genus name Siriellerythrops Ledoyer, 1970 with Siriella Dana, 1850 and include S. gibbosa in the brevicaudata group.

Figures

Fig. 1. Distribution of species in the Siriella brevicaudata species group. Question mark (?) indicates published record requires verification.