Glyphocrangon obtusis Komai & Chang & Chan 2022, n. sp.
Creators: name: Komai, Tomoyuki
name: Chang, Su-Ching
name: Chan, Tin-Yam
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Glyphocrangonidae
Glyphocrangon
Glyphocrangon obtusis

description: Glyphocrangon obtusis n. sp.
(Figs. 1–4)
Glyphocrangon robusta. — Han & Li 2007: 550, fig. 5. [not Glyphocrangon robusta Komai, 2004]
Material examined. Holotype: NTOU M02458, male (cl 11.3 mm), off Pratas Island, South China Sea, about 300 m, 18 February 2021, commercial trawler.
Paratypes: NTOU M02459, 3 males (cl 11.2–12.3 mm), 1 female (cl 8.0 mm), same data as holotype; CBM-ZC 17086, 1 male (cl 9.7 mm), same data as holotype.
Description. Body (Figs. 1, 2) robust. Integument of carapace and pleon firm, glabrous.
Rostrum (Fig. 2A, B) moderately narrow in posterior part, deepest at about midlength, 0.75–0.80 times of carapace length, directed slightly downward in proximal part, gently upturned in distal half; outline of dorsal margin distal to anterior pair of rostral teeth gently sinuous in lateral view; dorsolateral ridges generally low, blunt, with 1 pair of small tubercles proximal to midlength and 1 pair of obtuse convexity at rostral base; proximal part of dorsolateral ridge between 2 lateral prominences low, devoid of longitudinal groove; middorsal carina confined to distal 0.2 of rostrum; dorsal surface lacking or at most with trace of transverse septa; ventral surface with shallow median groove flanked by bluntly edged ventrolateral carinae; midventral carina absent.
Carapace (Figs. 1, 2, 3A, B, D–F) 1.1–1.2 times longer than greatest width across 0.7 length; major carinae and prominences all generally low, more elevated in females than in males, divisions of major carinae protuberance-like, eroded with minute pits on surfaces; intercarinal spaces devoid of conspicuous tubercles or granules. Anterior first (submedian) carina composed of 4 greatly unequal lobes separated by shallow notch; posterior first carina bi-lobed by constriction only visible in dorsal view (in lateral view, dorsal outline varying from entire or faintly concave medially to clearly two-lobed), its posterior end not overhanging posterodorsal margin of carapace. Anterior second carina composed of 3 blunt protuberances; posterior second carina weakly divided into 3 unequal elevations. Anterior third (antennal) carina absent; posterior third carina rather obsolescent, entire, terminating obtusely at anterior end. Anterior fourth (lateral) carina divided into 2 discontinuous, aligned lobes, each anterior end obtuse; posterior fourth carina broad, weakly divided into 4 lobes, posteriormost fourth lobe smallest (Fig. 3F). Fifth (sublateral) and sixth (submarginal) carinae obsolescent. Seventh (marginal) carina sharply delimited. Submarginal posteroventral ridge not delimited. Postorbital region unarmed. Median part of gastric region with distinct anteromedian tubercle. Posterior dorsolateral region anteriorly with small elevation. Hepatic region upper part with 2 or 3 small, low protuberances. Antennal spine short, blunt or subacute, weakly ascending in lateral view. Branchiostegal spine strong with blunt tip, directed forward in both lateral and dorsal views, extending to midlength of antennal scaphocerite; lateral face with 3 longitudinal carinae (faint in holotype, distinct in paratypes). Marginal posterolateral corner rounded. Anterior, lateral, and cervical grooves shallow.
Pleon (Figs. 1, 2) with well developed interlocking mechanism on pleomeres 4–6 and telson as in other congeneric species (Rice 1981); major carinae low, protuberance-like, more elevated in females than in males, as in carapace. Pleomere 1 tergum with low median elevation, its anterior margin slightly produced anteriorly, dorsal midline not carinate; transverse groove absent; dorsolateral carinae reduced to low protuberances; lateral carina showing also as obsolescent elevation; pair of obsolescent protuberances on posterior half of tergum; pleuron anterior margin with small tubercle, anteroventral angle produced anteriorly in blunt or subacute point, posterior margin smooth. Pleomeres 2 and 3 terga devoid of median carina or with trace of it; transverse grooves very shallow or faint; dorsolateral and lateral carinae strongly reduced, only trace of anterior parts of dorsolateral carinae discernible; pleural elevations obsolescent; pleuron 2 with sinuous anterior margin, anteroventral margin forming obtuse angle; ventral margin with anterior tooth reduced to obtuse lobe and blunt posterior tooth, posterior margin sinuous; pleuron 3 with concave anterior margin, anteroventral angle produced to blunt tooth, posteroventral angle with small subacute tooth, posterior margin sinuous. Pleomere 4 with low, poorly defined median carina, bearing median groove in posterior half; posterodorsal margin moderately produced; dorsolateral carinae absent; transverse grooves shallow, posterior transverse groove not reaching dorsal midline; lateral carinae reduced into low, broad elevations; pleural elevations also low, obsolescent; pleuron 4 anterior margin sinuous, anteroventral angle produced into broadly triangular lobe, posteroventral angle with small blunt tooth, posterior margin slightly sinuous. Pleomere 5 with anterior median carina reduced to low, rounded tubercle; posterior submedian carinae rather clearly delimited, weakly diverging posteriorly, each with narrow median groove; posterodorsal margin weakly produced; lateral carinae reduced into low protuberances; pleuron 5 anterior margin faintly sinuous, anteroventral angle rounded, posteroventral angle slightly produced into small subacute tooth, posterior margin nearly straight inferior to interlocking projection. Pleomere 6 with distinct, moderately elevated median carina, strongly produced posteriorly into blunt projection; tergum with 2 or 3 small protuberances on both sides of median carina; lateral carina blunt, divided into 3 unequal lobes; pleuron 6 with 2 widely separated protuberances, posteroventral angle produced into stout tooth somewhat diverging in dorsal view and not reaching interlocking projection. Telson (Fig. 3F, G) 0.7 x as long as carapace, gradually tapering to subacute tip; dorsal surface shallowly sulcate, with blunt, tubercle-like anterior projection; dorsolateral carinae unarmed; ventrolateral carinae faintly tuberculate in anterior third.
Cornea (Figs. 1, 2) relatively small (maximal width 0.15 x as long as carapace length), subspherical. Eyestalk short, with small papilla-like tubercle on anteromesial surface (not illustrated).
Antennular peduncle (Figs. 1, 2, 3H) overreaching anterior margin of antennal scale by half length of article 3. Article 1 with stylocerite showing as low convexity. Article 2 widened anteriorly, 1.6 x as long as wide. Article 3 distinctly shorter than article 2. Outer flagellum aesthetasc bearing portion thicker in males than in females, 0.4 x as long as carapace.
Antenna with scaphocerite (Figs. 1, 2, 3I) oval, slightly less than 0.4 x as long as carapace, 2.2 x as long as wide, armed with small lateral tooth located slightly proximal to midlength. Carpocerite (article 5 of antennal peduncle) reaching distal margin of scaphocerite.
Maxilliped 3 (Figs. 4A, 5A) moderately stout for genus, slightly overreaching distal margin of scaphocerite. Ultimate and penultimate articles compressed, former slightly longer than latter, tapering to acute, basally demarcated unguis, armed with several strong spiniform setae on margins and mesial face. Penultimate article (= carpus) with 2 extensor, 3 flexor, and 1 distomesial spiniform setae, mesial face with dense stiff setae adjacent to extensor margin. Antepenultimate article (merus-ischium-basis fused article) with keel-like carina extending from lateral surface to dorsolateral margin; distomesial face somewhat inflated; ventral surface rounded, with scattered setae. Exopodal flagellum slightly overreaching midlength of endopodal antepenultimate article.
Pereopod 1 (Figs. 4B, 5B) not reaching midlength of antennal scale. Dactylus curved, reaching midlength of palm when flexed; palm glabrous on lateral face, with several tufts of stiff setae on mesial surface. Carpus short, cup-like. Merus lateral surface without longitudinal ridge; ventral margin bluntly ridged, with row of stiff setae arising. Ventral lamina of ischium prominent, acutely pointed distally; ventral margin with row of stiff setae increasing in length distally.
Pereopods 2 slightly unequal and dissimilar, right longer and more slender than left. Left pereopod 2 (Figs. 4C, 5C) overreaching antennal scale by length of chela and 0.3 of carpus. Chela substantially flattened, subequal in length to distal 2 segments of carpus, with strongly oblique occlusal margin of palm; dactylus slightly curved, 0.6 x as long as palm. Carpus distinctly longer than merus and ischium combined, divided into 22–24 segments. Merus distinctly shorter than ischium. Ischium with distinct convexity in proximal half of ventral margin, accommodating distal part of carpus when flexed.
Right pereopod 2 (Figs. 4D, 5D) overreaching distal margin of scaphocerite by slightly more than 0.3 length of carpus. Chela small, subequal in length to distalmost carpal segment; occlusal margin of fixed finger nearly transverse, distinctly concave; dactylus strongly curved, about 0.6 x as long as palm. Carpus distinctly longer than merus and ischium combined, divided into 26–28 segments. Merus and ischium similar to those of left pereopod 2.
Pereopod 3 (Fig. 4E) moderately slender, reaching or slightly overreaching distal margin of scaphocerite by tip of dactylus. Dactylus compressed laterally, nearly straight, tapering to acute tip, 0.4 x as long as propodus. Propodus linear. Carpus half-length of propodus. Merus subequal in length to distal 3 articles combined; merus-ischium linear.
Pereopod 4 (Figs. 4F, 5E) moderately slender, reaching distal margin of scaphocerite. Dactylus 0.8 x as long as propodus, subspatulate, slender, terminating in acute tip; extensor surface shallowly grooved with sharply edged, elevated margins. Propodus with tuft of stiff setae on dorsodistal margin, partially obscuring basal part of dactylus. Carpus 0.4 x as long as propodus. Merus-ischium combined slightly longer than distal 3 articles combined.
Pereopod 5 (Figs. 4G, 5F) similar to pereopod 4, reaching mid-length of scaphocerite. Dactylus 0.7 x as long as propodus, subspatulate, slender, terminating in acute tip; extensor surface shallowly grooved with sharply edged, elevated margins. Propodus with tuft of stiff setae on dorsodistal margin, partially obscuring basal part of dactylus. Carpus 0.5 x as long as propodus. Merus-ischium combined slightly longer than distal 3 articles combined.
In males, pleopod 1 endopod (Fig. 5G) subovate with slightly sinuous mesial margin; appendix interna arising at about midlength of endopod, distinctly overreaching distal margin of endopod. Pleopod 2 (Fig. 5H) appendix masculina rod-like, falling slightly short of appendix interna, bearing numerous long, relatively thin setae, particularly on terminus and lateral face; appendix interna more slender than appendix masculina.
Pleopods 3–5 and uropod without distinguishing features.
Etymology. From the Latin obtusis (= obtuse), in reference to the low, obtuse major carinae on the carapace. Used as a noun in apposition.
Colouration in fresh. Generally pinkish orange with lateral carapace, tip of rostrum, antennular and antennal flagella, pereopods, pleopods, posteroventral tooth of pleuron 6 and telson whitish, pleura of pleomeres somewhat more pinkish; cornea dark brown with golden reflection (Fig. 1).
Distribution. Presently known only from the South China Sea around Pratas and Hainan islands; at depth of about 300m.
Remarks. Glyphocrangon obtusis n. sp. is morphologically close to G. hakuhoae, known from the Philippines and Indonesia, and G. robusta, known with certainty from the Philippines. Shared characters include: body integument glabrous; rostrum with two pairs of blunt or subacute dorsolateral teeth; anterior third carina on carapace absent; anterior fourth carina on carapace not expanded, but divided into two divisions, each terminating anteriorly in blunt tip; and branchiostegal spine on carapace more than twice as long as antennal spine; dactyli of pereopods 4 and 5 0.6 or more length of propodi. The new species is distinguished from the latter two species as outlined below. The dorsal surface of the rostrum at most has only traces of transverse septa in G. obtusis n. sp. (Fig. 3B), whereas it has distinct transverse septa in the anterior part in G. hakuhoae (cf. Komai 2004: fig. 67) and G. robusta (cf. Komai 2004: fig. 69). The dorsolateral margin of the rostrum is gently sinuous anterior to the anterior pair of lateral teeth in G. obtusis n. sp. (Fig. 3A) and G. robusta (cf. Komai 2004: fig. 70A), whereas it is noticeably sinuous with a prominent convexity on the proximal side in G. hakuhoae (cf. Komai 2004: fig. 68A). The two divisions of the anterior fourth carina on the carapace are only slightly unaligned in G. obtusis n. sp. (Fig. 1, 2, 3E) and G. hakuhoae (cf. Komai 2004: fig. 67), rather than strongly unaligned in G. robusta (cf. Komai 2004: fig. 69). The posterior fourth carina of the carapace are subdivided into four lobes in G. obtusis n. sp. (Figs. 1, 2, 3F), but uninterrupted (mainly in males) to subdivided into three lobes in G. robusta (cf. Komai 2004: fig. 69) and G. hakuhoae (cf. Komai 2004: fig. 67). The posteriormost fourth lobe, though smallest, is always distinct in G. obtusis n. sp. Only in a few ovigerous females of G. robusta there is a trace of this posteriormost fourth lobe on one side of the posterior fourth carina. The middorsal carinae on the pleomeres 2–5 are less elevated in G. obtusis n. sp. (Figs. 1, 2) and G. robusta (cf. Komai 2004: fig. 69) than in G. hakuhoae (cf. Komai 2004: fig. 67; Komai et al. 2020: fig. 1A). All the three distinguishing characters (rostrum lacking transverse septa, anterior fourth carina with two division slightly unaligned, posterior fourth carina subdivided into four lobes) mentioned by Han & Li (2007) for the material from Hainan Island reported as “ G. robusta ” fit well with the characteristics of G. obtusis n. sp. Hainan Island is also in north of the South China Sea not far from Pratas, and the illustrations provided by Han & Li (2007: fig. 5) clearly showed that their “ G. robusta ” material belongs to the present new species.
Genetic divergence of the barcoding segments of the mitochondrial COI gene (657bp) is 3.0% between the new species (holotype NTOU M02458, paratype NTOU M02459, GenBank nos. ON351604, ON351601, respectively) and G. hakuhoae (ZRC 2020.0295, GenBank no. MT571448), and 4.9–6.1% between the new species and G. robusta (NTOU M02307, NTOU M02457, GenBank nos. ON351605, ON351603, respectively). The genetic divergence between G. obtusis n. sp. and G. hakuhoae is rather low, being close to the thresholds considered for interspecific divergences in decapods (Lefébure et al. 2006). However, as discussed above, the morphological differences between G. obtusis n. sp. and G. hakuhoae are substantial.
description: Published as part of Komai, Tomoyuki, Chang, Su-Ching & Chan, Tin-Yam, 2022, A new species of the deep-sea shrimp genus Glyphocrangon A. Milne-Edwards, 1880 (Decapoda: Caridea: Glyphocrangonidae) from the South China Sea off Pratas Island, pp. 140-150 in Zootaxa 5141 (2) on pages 141-148, DOI: 10.11646/zootaxa.5141.2.2, http://zenodo.org/record/6581554