Meteusiroides keyensis Pirlot, 1934

Wang, Yan-Rong, Sha, Zhong-Li & Ren, Xian-Qiu, 2024, A new species of Eusirus Krøyer, 1845 (Amphipoda, Amphilochidea, Eusiridae) from the seamount of the Caroline Plate, with redescription of Meteusiroides keyensis Pirlot, 1934, Zoosystematics and Evolution 100 (2), pp. 645-662 : 645-662

Meteusiroides keyensis Pirlot, 1934

Figs 6 , 7 , 8 , 9

Meteusiroides keyensis Pirlot, 1934: 52–56, figs. 94–96.

Material examined.

Western Pacific • 1 female (ovigerous), 12.2 mm; seamount on Caroline Plate ; St. FX-Dive 218; 10 ° 07 ' N, 140 ° 14 ' E; depth 813–1242 m; 6 Jun. 2019; M 6090; MBM 286612 .

Description.

Body. Smooth; epimera 1 and 2 with posteroventral angle produced into small acute tooth; epimeron 3 with posteroventral angle broadly rounded. Head. Rostrum longer than anterior cephalic lobe, extending to 1 / 4 length of peduncular article 1 of antenna 1; anterior cephalic lobe rounded; eyes large, reniform. Antenna 1 with peduncular article 1 subequal in length to article 2, ventral margin produced distally; article 2 narrower than article 1, outer margin convex distally; inner margin bilobate distally; article 3 shortest, shorter than 1 / 2 length of flagellar article 1; primary flagellum 82 - articulate; accessory flagellum lacking. Antenna 2 much shorter than antenna 1, peduncular article 4 about twice as long as article 5; flagellum 61 - articulate.

Mouthparts. Upper lip margin smooth. Mandible with right incisor bearing 13 teeth, left incisor bearing 11 teeth; right lacinia mobilis with distal margin smooth, without tooth; left lacinia mobilis with 10 teeth; accessory setal row with 8 slender setae; molar strong, columnar; palp article 3 distinctly longer than article 2, with 7 apical long setae; inner margin with row of long simple setae. Lower lip with inner lobes distinctly smaller than outer lobes. Maxilla 1 inner plate subtriangular, with two long distal robust setae and one small setae; outer plate with 11 multicuspidated setae in two rows; palp 2 - articulate, with 6 apical robust setae and a row of subapical slender long setae. Maxilla 2 with inner plate shorter and broader than outer plate, bearing about 16 fine simple marginal setae; outer plate bearing row of slender long apical setae. Maxilliped with inner plate subrectangular, short; outer plate bearing about 6 plumose setae on distal margin and more than 10 slender setae on inner margin; palp article 3 expanded distally, bearing a row of setae on distal and inner margins; dactylus very slender, as long as article 3.

Coxae 1–4 subrectangular, gradually increasing posteriorly; coxa 1 anteroventral corner subacute; coxa 4 excavate posteriorly. Coxae 5 and 6 bilobate, posterior lobe deeper and larger than anterior lobe. Coxa 7 smallest, rounded. Coxal gills present on pereopods 2–7.

Gnathopods and pereopods. Gnathopods 1–2 similar in shape, but gnathopod 2 slightly longer. Gnathopod 1 basis with dense long simple setae on distal half of mesial surface; ischium posterior margin bearing group of setae distally; merus much shorter than carpus, posterior margin bearing groups of setae, distal margin with two acute mediodorsal pointed processes; carpus shorter than propodus, posterior margin bearing more than 10 groups of slender setae; propodus sub-ovate, propodus less than twice longer than wide, palmar margin obliquely convex, with a row of large robust setae and slender setae, posterior margin with 6 groups of slender setae, surfaces with 6 clusters of setae; dactylus 3 / 5 the length of propodus, curved. Gnathopod 2 basis not bearing dense setae on mesial surface, but margins setose; ischium to carpus similar to gnathopod 1; propodus about twice longer than wide, similar in shape to gnathopod 1; dactylus 1 / 2 the length of propodus, curved. Pereopods 3 and 4 slender, basis linear, margins setose; merus longer than carpus but shorter than propodus, margins bearing short robust setae; dactylus slender. Pereopods 5–7 slightly increasing in length; basis expanded, narrowing distally; posterodistal lobes shallow; postero-ventral corner rounded; merus to propodus with margins setose; merus longer than carpus but shorter than propodus; dactylus slender.

Uropods and telson. Uropod 1 with peduncle slightly longer than inner ramus, margins setose; rami lanceolate, lacking apical setae, margins setose; outer ramus shorter than inner one. Uropod 2 with peduncle shorter than outer ramus, margins setose, with ventromedial spur; rami lanceolate, lacking apical setae, margins setose; outer ramus much shorter than inner one. Uropod 3 with peduncle shorter than rami, outer margin lacking setae; rami subequal in length; both rami outer and inner margins setose; inner ramus with inner margin bearing long plumose setae. Telson linguiform; cleft about 70 % of its length; posterior margin of each lobe concave; bearing three pairs of stout setae; keeled ventroproximally; margins bearing several stout setae on each side laterally.

Coloration.

The body is transparent, pale red in color, with red gnathopods 1–2, and antennae 1–2, and deep red eyes.

Distribution.

A seamount of the Caroline Plate at a depth of 813–1242 meters; Indonesia (5 ° 48 ' S, 132 ° 13 ' E) at a depth of 304 meters ( Pirlot 1934; Barnard and Karaman 1991).

Remarks.

Meteusiroides keyensis Pirlot, 1934 , was originally described from Indonesia, with the description based on a female holotype found at a depth of 304 meters. The current ovigerous female specimen was collected from a depth of at least 813 meters, significantly deeper than the depth originally recorded. Morphologically, the present specimen only slightly differs from the original description of M. keyensis by the rami of Uropod 3 subequal in length, while the outer ramus is somewhat shorter than the inner ramus in the original illustration ( Pirlot 1934, fig. 96). Nonetheless, the present specimen should be identified as M. keyensis .

Molecular data analysis

The phylogenetic trees produced by BI and ML analyses were congruent and generally well supported (Fig. 10 ).

The monophyly of the genera Eusirus and Rhachotropis S. I. Smith, 1883 , was recovered in both ML and BI trees (BP = 54 % and PP = 0.96). The genus Meteusiroides and Dorotea Corbari, Frutos & Sorbe, 2019 clustered together and were separated from Cleonardo Stebbing, 1888 (BP = 51 % and PP = 0.87) The genus Eusirus was separated into two relatively moderately supported clades (BP = 50 % and PP = 0.94). The new species, E. carolinus sp. nov., was separated from E. hirayamai with strong support (BP = 97 % and PP = 0.83), with E. pontomedon Verheye & d’Udekem d’Acoz, 2020 , and E. perdentatus Chevreux, 1912 , as sister groups (BP = 85 % and PP = 0.98). The species delimitation based on both ABGD and bPTP methods has validated the new species (Fig. 11 ).

Figures

Figure 6. Meteusiroides keyensis Pirlot, 1934. Photographed immediately after collection by Shao-qing Wang.

Figure 7. Meteusiroides keyensis Pirlot, 1934. G 1 R. Right gnathopod 1; G 2 R. Right gnathopod 2.

Figure 8. Meteusiroides keyensis Pirlot, 1934. UL. Upper lip; LL. Lower lip; Md L. Left mandible (not showing molar and palp); Md R. Right mandible; Mx 1. Maxilla 1; Mx 2. Maxilla 2; Mxp. Maxillipeds.

Figure 9. Meteusiroides keyensis Pirlot, 1934. P 3 R. Right pereopod 3; P 4 R. Right pereopod 4; P 5 R. Right pereopod 5; P 6 R. Right pereopod 6; P 7 R. Right pereopod 7; E 1–3. Epimeral plates 1–3; U 1 R. Right uropod 1; U 2 R. Right uropod 2; U 3 R. Right uropod 3; T. Telson; H. Head, with antenna 1 and antenna 2.

Figure 10. Maximum likelihood (ML) and Bayesian inference (BI) trees of Tropiometroidea using combined sequences of COI and 16 S. The numbers at each node represent bootstrap values (BP) (left) and posterior probabilities (PP) (right). Eusirus carolinus sp. nov. is highlighted in bold.

Figure 11. Bayesian Inference (BI) phylogenic tree based on COI showing the phylogenetic relationship between Eusirus carolinus sp. nov. and related eusirids, with bootstrap replications (BS) labeled (> 50). Putative species identified by DNA-based species delimitation methods [Automated Barcode Gap Discovery (ABGD) and Bayesian implementation of the Poisson Tree Processes (bPTP)] applied to the COI tree / distance matrices are indicated by bars on the concatenated tree. Color codes indicate the support of each putative species.