Amphithyropsis shanti, Gasca & Suárez-Morales & Hendrickx, 2021

Gasca, Rebeca, Suárez-Morales, Eduardo & Hendrickx, Michel E., 2021, Hyperiids (Amphipoda, Hyperiidea) collected during the TALUD cruises in western Mexico. 5. Family Amphithyridae, with the description of a new species of Amphithyropsis Zeidler, Zootaxa 5039 (4), pp. 479-494 : 485-490

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Amphithyropsis shanti

sp. nov.

Amphithyropsis shanti   sp. nov.

( Figs. 4‒8 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 View FIGURE 8 )

Type material. Holotype, 1 male, TALUD III. St. 19B (25°18’24”N, 109°18’36”W), August 20, 1991, I-K from surface to 600 m (TD, 1890 m) (ECO-CH-Z-10545) GoogleMaps   . Allotype, 1 gravid female, TALUD IV, St. 25A2 (24°54’N, 108°59’W), August 26, 2000, BS from surface to ca. 800 m (ECO-CH-Z-10546) GoogleMaps   .

Type locality. Central Gulf of California , SW of Topolobampo, Sinaloa (25°18’24”N, 109°18’36”W) GoogleMaps   .

Distribution. Known only from two localities, in the central Gulf of California, Mexico ( Fig. 9 View FIGURE 9 ).

Etymology. The Sanskrit noun shanti   means peace. It is feminine as the genus gender, which ending on the suffix – opsis is to be treated as feminine ( Oren & Schink 2016). In this way, we manifest our wish for world peace.

Description of adult male.

Body. Body ( Fig. 4A View FIGURE 4 ) robust, weakly curved, total length, 2.66 mm. Surface of whole body sculptured with hexagonal and pentagonal polygons.

Head. Longer than high, hemispheric, representing 0.15 x of total body length (0.40 mm), not notoriously deeper than body. Eyes ( Fig. 4B View FIGURE 4 ) covering most of head surface except for triangular frontal space in front of head. Antenna 1 ( Fig. 4C View FIGURE 4 , 5A View FIGURE 5 ) prominent; peduncle 1-segmented, flagellum with large callynophore armed with transversally arranged rows of aesthetascs crossing the ventral zone, distal segment armed with spines and aesthetascs. Antenna 2 ( Fig. 5B, C View FIGURE 5 ) peduncle with dorsally flat and ventrally round first segment, as high as long; succeeding four segments zig-zagged, folded below eyes and thorax; segments with row of setae along anterior margins; terminal segment with setae extending to the tip, directed anteriorly. Segment 3 about 0.75 x length of segments 2, terminal article about 0.83 x the length of precedent.

Mandible ( Fig. 5D View FIGURE 5 ) about 0.75 x length of first mandibular palp. Mandibular palp ( Fig. 5E View FIGURE 5 ) 3-segmented, middle segment being longest (0.15‒0.20 x of segments 1 or 3 length).

Maxilliped ( Fig. 5F View FIGURE 5 ) fully sculptured, developed inner lobes completely fused, with two spines on the external apical margins ( Fig. 5G View FIGURE 5 ). Maxillae sculptured; maxilla 1 inner lobe wide and truncated, outer lobe triangular with long apical spines; maxilla 2 both lobes pyramidal, about 2 x as long as maxilla 1, with spines both along inner margin and apically ( Fig. 5H View FIGURE 5 ).

Pereon ( Fig. 4A View FIGURE 4 ) length about 2 x eyes diameter, all segments distinctly separate. Pereopods 1 and 2 ( Fig. 6A, B View FIGURE 6 ) bases longer than combined length of distal segments; carpus sub-rectangular, lacking anterodistal projection; propodus with rounded, thumb-like antero-distal projection. Pereopod 1 simple (ca. 0.41 mm), with long slender basis, straight anterior margin, and bulging posterior margin; isquium bent to the front, forming the internal part of an elbow (similar in pereopods 1–4); propodus 0.4 x narrower than carpus, thumb-like in posterodistal section; dactylus claw-shaped, ornamented with teeth-like processes and short spines. Pereopod 2 like pereopod 1, about 1.2 x its length, basis 1.3 x length of basis of pereopod 1; propodus narrower than carpus, with thumb-like process on postero-distal end. Pereopods 3 and 4 ( Fig. 6C, D View FIGURE 6 ) (0.7 mm) longer than 1 and 2 (ca. 0.50 mm). Pereopod 3 approximately 1.6 times as long as pereopod 1. Basis with weakly concave anterior margin and convex posterior margin; 70% wider than the widest portion of pereopod 1 basis. Pereopod 4 basis with straight anterior margin, posterior margin regularly convex, propodus almost 2 x as long as carpus, dactylus nearly half length of propus, bent backwards, with postero-proximal hump. Pereopod 5 ( Fig. 6E View FIGURE 6 ) being the longest leg (about 1 mm), 2 x as long as pereopod 2, basis 2 x as long as wide, with anterodistal lobe overlapping ischium, inserted terminally to basis, bent towards posterior end; carpus and propodus with short spines along anterior margin (seen at 400 magnification); propodus long, slender; dactylus short (0.1 x propodus length). Pereopod 6 ( Fig. 6F View FIGURE 6 ) basis longer than wide, with fissure but lacking telsonic groove; isquium inserted in ventral rounded socket of basis; merus dorsal margin approximately 0.5 length of anterior margin, with similar and regularly distributed spines along anterior margin; carpus about 0.5 x as long as merus width; propodus less than 0.5 carpus width; dactylus finger-shaped, 0.3 x propodus length. A strong structural union of isquium to basis appears like a separating segment. Pereopod 7 ( Fig. 6G View FIGURE 6 ) basis more than 3.5 x as long as wide, plus one additional crinkled segment, about 0.2 mm total length. All coxae, except seventh, separate from thorax, coxae 1‒5 rectangular, with rounded margins; coxa 6 posteriorly expanded, with groove and spines on posterior margin.

Pleon. Pleon ( Fig. 4A View FIGURE 4 ) 1.3 x combined length of pereon segments; epimeral plates rounded, with slightly elongated distal margin, directed backwards (illustrated for female in Fig. 8G View FIGURE 8 ); pleonic segments with height similar to thoracic segments, projected downward. Third epimeron with median dorsal and lateral teeth. Pereon and urosome subequal in length (0.70 mm). Urosome first segment about as long as fused segments 2 and 3 (0.19 mm), shorter than telson (0.23 mm). Uropods maximum length about 1.35 x telson length; margins of uropod endopods and exopods serrate; endopod of uropod 3 fused with basis; uropod 1 ca. 0.50 mm long, exopod and basis sub equally long, with serrate margins, exopod 1.25 times as long as endopod, with both margins serrate; uropod 2 about 0.60 mm long, exopod 0.6 x uropod 2 total length, endopod about 0.5 x as long as exopod, with serrate margins specially on endopod; uropod 3 about 0.55 x uropod 1 length, endopod length 2/3 of total uropod 3 length (ca. 0.28 mm), inner and outer rami serrate along inner margins, especially apically. Telson not fused to urosome.

Description of allotype female (gravid)

Body ( Fig. 4D View FIGURE 4 ) smaller than male (2.4 mm).

Head. Higher than long (vs. longer than high in male), the longest part in the dorsal portion and not in the middle, head not as rounded as in male. Antenna 1 ( Fig. 7A, B View FIGURE 7 ) 2-articulated, directed backwards; callinophore resembling a truncate cone, with several transverse tight rows of aesthetascs; terminal segment about 0.35 x preceding one, with distinctive thumb-like projection forming an incomplete “U”, armed with setae. Antenna 2 absent.

Pereon. Pereopods ( Fig. 8 View FIGURE 8 ) similar to those of male, but with some variations: carpus of pereopod 1 wider proximally in female ( Fig 8A View FIGURE 8 ); propodus of female pereopod 5 equally wide along segment ( Fig 8E View FIGURE 8 ).

Urosome and uropods ( Fig. 7A View FIGURE 7 ) as illustrated.

Remarks. Hitherto, the genus Amphithyropsis   contained a single species, A. pulchellus   , described from a male found off New Zealand, but it was not described in detail. Barnard (1930) pointed out some of its specific characteristics, like the reticulate cuticular sculpturing, and described and illustrated the 4th segment of pereopod 6, specifying that its structure “… seems to be quite distinctive”. Amphithyropsis pulchellus   had so far been found in the southwestern Pacific, including waters around New Zealand and Australia and, as stated by Zeidler (2016), it also occurs along the southeast coast of Africa, where specimens show the same attributes as those from the Pacific.

The specimens collected in the Gulf of California have the main distinctive generic features of Amphithyropsis   but cannot be assigned to A. pulchellus   because these specimens possess: 1) different segment proportions in the male antenna 2; 2) a shallower head; 3) pereopods lacking spines; 4) the basis of pereopods 1 and 2 longer than the combined length of distal segments; 5) the middle segment of the male mandibular palp longer than the others; and 6) a female first antenna with a thumb-like projection. All these characters allowed us to distinguish our material from A. pulchellus   and propose a new species.

Amphithyropsis shanti   sp. nov. most closely resembles A. sculpturatus   mainly in the body sculpturation, urosome and uropods shape, and in the general structure of pleonite VI. Amphithyropsis shanti   sp. nov., however, is easily distinguished from this species by having segments 4‒6 of pereopods 1 and 2 more rectangular, segment 5 without anterodistal projection, and segment 2 longer than the combined length of distal segments. Amphithyropsis shanti   sp. nov. also has the uropod 2 endopod about 0.5 x the length of the exopod, which is longer than basis, and the pleonite VII lacks segments 3‒5. The shape of the female antennae 1 is also a conspicuous distinctive characteristic between the two species.