Trachysalambria Burkenroad, 1934

Chan, Tin-Yam, Cleva, Régis & Chu, Ka Hou, 2016, On the genus Trachysalambria Burkenroad, 1934 (Crustacea, Decapoda, Penaeidae), with descriptions of three new species, Zootaxa 4150 (3), pp. 201-254 : 204-206

Genus Trachysalambria Burkenroad, 1934

Trachypeneus .— Alcock, 1905: 522 (in part); Burkenroad, 1934b: 94 (in part); 1959: 285 (in part); 1983: 281 (in part). Trachypeneus (Trachysalambria) Burkenroad, 1934a: 49 [type species: Penaeus curvirostris Stimpson, 1860 ]. Trachypenaeus .— Kubo, 1949: 391 (in part); Dall, 1957:202 (in part); Motoh & Buri, 1984: 80 (in part); Liu & Zhong, 1988:

184 (in part); Dall & Rothlisberg, 1990: 102 (in part); Hayashi, 1992: 137 (in part); Chan, 1998: 903 (in part). Trachyslambria.— Pérez-Farfante & Kensley, 1997: 146; De Grave & Fransen, 2011: 228.

Trachypenaeus (Trachysalambria) .— Davie, 2002: 152.

Diagnosis. Body robust, size small to moderate. Integument thick, generally densely pubescent. Rostrum relatively short, extending to second or third segment of antennular peduncle; armed only with dorsal teeth; epigastric tooth well separated from first rostral tooth. Carapace with orbital, antennal and hepatic spines; pterygostomian angle blunt to sharp; postocular sulcus absent; orbito-antennal sulcus shallow; cervical sulcus from moderately long to short or absent; hepatic sulcus marked or indistinct; branchiocardiac carina rudimentary or absent; longitudinal suture short, weak, sometimes even indistinct, terminating anterior to hepatic spine; transverse suture short, rudimentary to well developed. Antennule without parapenaeid spine; antennular flagella shorter than carapace. Basial spine absent on maxilliped III but well developed on pereiopods I and II. Small ischial spine present or absent on pereiopod I. All pereiopods bearing exopods. Epipod present on pereiopods I to III, or on II and III, or on III only. Pereiopods IV and V with dactyl neither elongate nor subdivided. Petasma symmetrical and “T”-shaped; with distolateral projections extensively produced laterally and horizontally, almost straight, sometimes curving slightly backwards. Thelycum closed; anterior and posterior plates both well developed and clearly separated; anterior plate not produced caudally onto posterior plate; anterior margin of posterior plate slightly cleft (mostly) or anterior produced medially. Seminal receptacles consisting of paired bilobed sacs. Abdominal somite VI lacking cicatrix. Telson with 3 or 4 pairs of movable lateral spines; distal and subapical pair always present and largest, another pair abutting subapical spines, if present, often minute.

Distribution. Indo-Pacific, shallow water to 271 m deep but mostly less than 100 m deep.

Remarks. Most characters previously used to separate the species of Trachysalambria (e.g., Starobogatov 1972; Motoh & Buri 1984; Liu & Zhong 1988; Dall & Rothlisberg 1990; Chitiamvong & Supongpan 1992; Chan 1998; Sakaji & Hayashi 2003) were found to be quite variable and sometimes related to size and sex. Unlike most penaeoids, the shape of the genitalia is not especially useful for distinguishing the species in this genus. Sakaji & Hayashi (2003) also commented that the shape of the petasma cannot be used to separate the species of the “ T. curvirostris ” group. Only the petasma of T. malaiana and T. brevisuturae significantly differs from that of the other species of the genus. The thelycum is also very similar in most species of the genus and useless for species separation, except for T. malaiana , T. brevisuturae , T. crosnieri sp. nov. and T. palaestinensis . For the latter two species, only the thelycum of large females are different but the thelycum of small females may not be very different from the general shape (i.e., anterior plate semi-triangular) of the genus. The length of pereiopod V was often treated as diagnostic in Trachysalambria (e.g., Alcock 1905, 1906; Dall 1957; Racek & Dall 1965). Although it is true that the pereiopod V tends to be shorter or longer in some species, its length can be rather variable in the same species and often relatively longer in smaller specimens. Thus, this character may be misleading if used alone for distinguishing species. While the length of postrostral carina is rather constant in most of the species, in T. malaiana , T. longipes , T. aspera and T. nansei , the posterior part of the carina behind the epigastric tooth can vary from very distinct to nearly absent. The ischial spine of pereiopod I is often (but not always) distinct in T. curvirostri s but absent in T. longipes , T. dentata sp. nov. and T. brevisuturae . This spine, however, can be small, minute or completely absent in the other eight species of the genus. Sexual dimorphism is often marked in the shape of the rostrum in this genus. Nevertheless, it was found that the rostrum shape is quite diagnostic even though the rostrum is usually more strongly curved upwards in mature females but straighter in males and small females. The number of rostral teeth varies significantly within a species when large series were examined, though there is a trend towards more or fewer rostral teeth in certain species. The same applies for the armature at the tip of the rostrum, which is related to the total number of teeth on the rostrum. Furthermore, the length of the rostrum and the height of the abdominal carinae may vary with size; with smaller individuals generally having a shorter rostrum and lower abdominal carinae. All these variations resulted in juveniles of this genus being sometimes very difficult to identify. On the other hand, large females generally fully exhibit the characteristics of the species. The number of lateral spines on the telson had been described differently for various species. Actually, all species of this genus normally bear 3 or 4 lateral spines on the telson. The subapical pair is always distinct. The other lateral spines are quite small and sometimes rather minute, particularly the pair immediately adjacent to the subapical lateral spines (when present, Fig. 16 H; also see De Man 1907; Sakaji & Hayashi 2003). Nevertheless, the lateral telson spines, except the subapical pair are often very minute in T. malaiana (see Motoh & Buri 1984; Dall 1957) but relatively larger in T. brevisuturae (see Hendrickx 1996). Since the lateral spines on the telson are movable, they are sometimes detached, making it very difficult to determine if these minute lateral spines were originally present or absent on the telson.

The coloration of this genus is not particular striking. The single Eastern Pacific species T. brevisuturae seems to have a very different coloration of a semi-transparent body scattered with red and white dots. The Indo-West Pacific species are either greyish or pinkish with reddish brown or whitish antennal flagella and whitish or yellowish margined uropods. Some species have very similar coloration and can sometimes be rather variable within the same species (e.g., from grey to pink in T. curvirostris and with or without a red saddle on the abdominal somite II in T. aspera ). Therefore, coloration cannot be used alone for positive identification, though, together with morphological characters, coloration can greatly assist species separation. For example, T. dentata sp. nov. and T. aspera are most colorful in the genus with the white markings on the body very prominent. However, their coloration is almost identical ( Figs. 19 C, 20B) and can only be separated by T. dentata sp. nov. with two dorsal carinae on the abdominal somite II and the dorsal carinae of the abdominal somites IV and V bearing posterior spines (vs. one dorsal carina on abdominal somite II and dorsal carinae of abdominal somites IV and V without posterior spine in T. aspera ).

Although Trachysalambria species are morphologically very similar, the genetic data well support the separation of the 12 species in this study. The lowest sequence divergences amongst the species in the 12S and 16S rRNA genes are 4.1% and 2.3% respectively, with intraspecific divergences being 2.6% and 0.5%, respectively ( Tables 2, 3). The molecular phylogenetic tree produced suggests that Trachysalambria may be polyphyletic ( Fig. 21). The eastern Pacific T. brevisuturae and Australian T. crosnieri sp. nov. are very different from other Trachysalambria as well as Trachypenaeus s.l. Trachysalambria malaiana , which lacks epipods on the pereiopods I and II, appears to be closer to Trachypenaeus s.s. and Megokris Pérez-Farfante & Kensley, 1997 . On the other hand, T. longipes , which lacks an epipod on the pereiopod I, is nested within the “ T. curvirostris ” group. The relationships amongst the species of the “ T. curvirostris ” group shown in the genetic tree, however, do not generally align with the apparent morphological similarities as observed in the key provided below. Comprehensive molecular analysis with more genetic markers and taxonomic sampling across Trachypeanaeus s.l. is needed to elucidate the evolutionary relationships amongst these shrimps.

Figures

FIGURE 16. Trachysalambria albicoma (Hayashi & Toriyama, 1980), Kochi Prefecture, Japan: A, C, G, H, female cl 24.6 mm (MNHN IU- 2014 - 7040); B, D – F, male cl 14.6 mm (MNHN IU- 2014 - 7039). A, cephalothorax, lateral view; B, rostrum, lateral view; C, dorsal part of abdominal somites II to VI, lateral view; D – F, petasma, ventral, dorsal and upper views, respectively; G, thelycum, ventral view; H, telson, dorsal view.

FIGURE 19. A, B,? Trachysalambria brevisuturae (Burkenroad, 1934 a), Panama, Pacific coast, Urraca cruise, specimens details unknown, dorsal and lateral views, respectively (photographed by A. Anker); C, T. dentata sp. nov., the Philippines, AURORA, stn CP 2747, female cl 19.1 mm (NTOU M 01983); D, T. parvispina sp. nov., Vanuatu, SANTO, stn AT 42, female cl 21.2 mm (MNHN IU- 2014 - 6941); E, T. palaestinensis (Steinitz, 1932), Israel, Mediterranean coast, specimens details unknown (photographed by B. S. Galil); F, T. nansei Sakaji & Hayashi, 2003, Dasi fishing port, Yilan County, Taiwan, female cl 20.4 mm (NTOU M 01995).