Gnathostenetroides Amar 1957

Genus Gnathostenetroides Amar, 1957

Gnathostenetroides Amar, 1957: 1; Hooker, 1985: 276.

Maresia Fresi, 1973: 302 [preoccupied name].

Maresiella Fresi and Scipione, 1980: 313; Müller 1992: 205; Kensley and Schotte 2002: 1422 (new synonymy).

Type species. Gnathostenetroides laodicense Amar, 1957, by monotypy.

Included species (in addition to the new species here described): Gnathostenetroides aldabrana (Kensley and Schotte, 2002), comb. nov., Aldabra Atoll, Seychelles; Gnathostenetroides barringtoniana (Fresi, 1973), comb. nov., East Pacific, Galapagos Islands; Gnathostenetroides brevicornis (Carvacho 1983), comb. nov., East Pacific, Gulf of California, Mexico; Gnathostenetroides indica (Müller, 1992), comb. nov., Indian Ocean, Reunion Island; Gnathostenetroides laodicense Amar, 1957 (type species), Mediterranean Sea, Syria; Gnathostenetroides polynesica (Müller, 1992), comb. nov., Society Islands, French Polynesia; Gnathostenetroides pugio Hooker, 1985, North Atlantic, Florida Middlegrounds; Gnathostenetroides samariensis (Müller, 1992), comb. nov., Caribbean Colombia, Santa Marta (Table 1, Fig.1)

Diagnosis: Body elongate, length 4.0–5.5 width. Cephalon subequal in width and length to pleotelson, rostrum strong, slightly concave anteriorly. Eyes dorsolateral, with 3 to 8 ommatidia. Antennula about 0.2 of body length, with 4–5 articles, straight, directed anteriorly, gradually narrowing distally. Antenna more than half body length, article 3 scale slender, as long as lateral margin of article 4; flagellum subequal in length to article 6. Mandible molar process subcylindrical, distally serrated, palp article 1 with 2 long distal setae. Pereopod 1 about twice longer and more robust than pereopods 2–7 which similar in length to each other. Pereopod 1 propodus with band of elongate mesial setae, ventral margin strongly setose, anterior margin nearly straight, bearing robust distoventral seta and row of oblique pectinate setae, which different in males and females; dactylus subequal in length to anterior width of propodus. Pereopods 2–7 decreasing slightly in length from pereopod 2 to pereopod 4 (shortest) and then slightly increasing in length to pereopod 7. Pereopods 1–4 coxae not visible in dorsal view. Pereopods 5– 7 coxae visible in dorsal view as small rings behind posterolateral extensions of pereonites 5–7. Penes arising from medial part of coxa of pereopod 7, long, tubular. Pleopod 3 endopod about twice wider than exopod, distomedial seta separated from two distolateral setae closely located to each other, exopod of two articles. Pleopod 4 exopod of one article, half length of endopod. Uropod shorter than pleotelson, endopod longer than protopod and exopod.

Remarks. Gnathostenetroides Amar, 1957 was established for the new species Gnathostenetroides laodicense Amar, 1957. Amar (1957) simultaneously placed this new genus in the family Parastenetriidae Amar, 1957 and the superfamily Parastenetrioidea, later shown to be invalid (Kussakin, 1967). The pleopod structure was considered intermediate between the Stenetrioidea Hansen, 1905 and Paraselloidae Hansen, 1905 (= Janiroidea G.O. Sars 1897) and Gnathostenetroides was further distinguished by the apparently anomalous mandibles with a prominent elongate anteriorly directed process (“horn”) in males. The genus included only two species to date, G. laodicense from the Mediterranean Sea and G. pugio Hooker, 1985 from the Florida Middlegrounds in the northeastern Gulf of Mexico.

Maresia Fresi, 1973 was established for M. barringtoniana Fresi, 1973 from the Galapagos Islands. The name Maresia was preoccupied and was later changed to Maresiella Fresi and Scipione, 1980. Six described species of Maresiella differ from Gnathostenetroides by the lack of the mandibular projections and having a median slit on the female pleopod 2. Comparison of the two species of Gnathostenetroides to all other species of Maresiella shows that the shape of body, size, ratios and shape of the body parts, the morphology of antennula and antenna, pereopods, and the mouthparts of the two genera are different only at species level (Figs 30 – 35). The morphology of the most delimiting character, the male pleopod 2, especially of the stylet, is highly similar in all species of Gnathostenetroides and Maresiella, differing only in details of the distal armament. Effectively, pleopod 2 does not show any character to distinguish the two genera (Fig. 34). The slit on the female pleopod 2 described for G. laodicense and G. pugio also occurs in Gnathostenetroides renbourni sp. nov. and two species of Maresiella, M. samariensis, M. brevicornis. As such this slit is not a distinguishing generic character as length of the pleopod 2 slit, when present, varies and integrades between the different species (Fig. 35).

The size of Gnathostenetroides specimens with mandibular horns is relatively large: males of G. laodicense are 2.2 mm and 2.4 mm in length and G. pugio is 3.2 mm. All specimens of Maresiella are smaller than are specimens of Gnathostenetroides: 1.1 – 1.9 mm. It is very likely that males with mandibular horns are at a terminal developmental stage and rare in the population. Considering the apparent lack of critical character difference and the absence other evident synapomorphies distinguishing these two genera we here regard Maresiella Fresi and Scipione, 1980 as a junior synonym of Gnathostenetroides Amar, 1957.

Distribution: Marine tropical shallow water, sediments in coral reefs (Table 1, Fig. 1). Distribution of the new species in the Great Barrier Reef is given in Fig. 2.