Cinetorhynchus gabonensis, Ďuriš & Šobáňová & Wirtz, 2019

Ďuriš, Zdeněk, Šobáňová, Anna & Wirtz, Peter, 2019, Cinetorhynchus gabonensis, a new species of hinge-beak shrimp (Crustacea: Decapoda: Rhynchocinetidae) from the eastern Atlantic, Zootaxa 4664 (2), pp. 191-205 : 193-203

Cinetorhynchus gabonensis sp. n.

( Figs. 1 – 6a, b )

Type material. Holotype male, PoCL 4.6 mm (MNHN-IU-2016-7701); off the coast of Gabon, 0º33.49ʹN, 9º17.75ʹE, 25 Nov. 2017, scuba at daytime, depth 10 m, below large rock, clove-oil spraying, coll. P. Wirtz. — Allotype ovigerous female, PoCL 5.2 mm (MNHN-IU-2016-7702); same data as holotype.— Paratype: 1 male PoCL 3.8 mm ( OUMNH ZC.2018-01-0071); same data as holotype .

Comparative material. See Tab. 1 .

Diagnosis. Small-sized rhynchocinetid shrimp with subcylindrical body. Ventral margin of rostrum with equi- distant teeth decreasing in size distally. Antennular peduncle with stylocerite overreaching distal margin of second peduncular segment. Podobranch on second maxilliped well developed. Pereiopods 1–3 with single arthrobranch, posterior legs without arthrobranch. Coxae of pereiopods 3 and 4 lacking spine or corneous projection; pereiopods 3 and 4 with meri laterally armed with 4–5 spines, fifth leg with 2–3 lateral meral spines, ischia with 2 spines; dactyli quadrispinose, with three corneous spines on flexor margin proximal to corneous unguis. In life, overall colouration by red spots densely set into irregular paths interspaced by narrow white oblique lines and dots.

Description of male holotype. Body covered with fine transverse tegumental striae ( Figs 1 , 2A ) arranged as series of dots formed by basal sutures of tegumental scales ( Fig. 2D, E ), latter lying tightly attached to covers, directed forwards on carapace and anterior pleomeres, or posteriorly on posterior pleomeres and telson.

Carapace ( Figs 1 , 2A, B ) with supraorbital tooth absent, orbit feebly developed, inferior orbital margin obsolete, antennal tooth slender acute, pterygostomial angle rounded. Dorsal median carina with 3 teeth, anteriormost tooth largest, situated closely behind rostral articulation and slightly in front of posterior orbital margin; intermediate and posterior teeth situated on anterior third of carapace, more closely placed than first and second tooth, more slender, with feeble basal suture. Rostrum ( Fig. 2A, B ) partially articulated with carapace, 1.5 times as long as PoCL, overreaching anterior margin of scaphocerite by distal third, nearly horizontal proximally, anterior half smoothly upturned, apex trispinose, i.e. formed by apical tooth and 2 smaller subapical dorsal teeth; dorsal margin with 2 large teeth widely spaced on proximal half; ventral margin unarmed basally, distal 3/4 armed with 8 almost equidistant teeth gradually decreasing in size distally, proximal 3 teeth placed more closely together and directed anteroventrad, distal teeth more widely spaced, lower, directed anteriad. Several tegumental scales present between larger dorsal and ventral teeth ( Fig. 2C ).

Ophthalmic segment with vertical median carina anteriorly, dorsally with short obtuse angle ( Fig. 2A ). Thoracic sternites ( Fig. 5A ) forming triangular platform on ventral cephalothorax, narrow on fourth segment, but strongly widening posteriorly to eighth segment; fifth sternite armed with pair of submedian hooked processes posteriorly of coxae; sixth and seventh sternites with pair of similar processes, smaller and situated more laterally.

Pleonal segments ( Fig. 1 ) with pleurae I–III broadly rounded; pleomeres VI and V with posterior lateral margin bearing posteriorly directed acute tooth, posteroventral margin rounded in outline, with small acute posteroventrally or posteriorly (respectively) directed tooth. Sixth segment dorsal length 0.7 of PoCL, depth 0.5 of dorsal length, posterolateral and posteroventral angles subtriangular, produced, posterior dorsal margin simple, not produced in midpoint; posterior ventral margin with strong slender preanal tooth ( Fig. 5B ).

Telson ( Fig. 2H, I ) length subequal to pleomere VI dorsal length, tapering posteriorly, with 3 regularly spaced pairs of dorsal spines on posterior half. Posterior margin with acuminate midpoint, with 3 pairs of marginal spines; lateral ones minute; intermediate pair longest, about 3 times longer than dorsal spines and about 0.12 of telson length; submedian subequal to dorsal spines, setulose on sides.

Antennular peduncle ( Fig. 2B, F ) reaching 0.4 of rostrum length. Proximal segment longer than distal two segments combined, dorsal surface moderately concave, with acute anterolateral tooth falling slightly short of distal margin of intermediate segment, ventromedial margin with small spiniform tooth; stylocerite well developed, with small hooked proximolateral tooth and strong elongate distolateral tooth, latter overreaching midlength of distal peduncular segment, statocyst small, rounded. Intermediate segment shorter than long, furnished with dense setae ventrolaterally. Distal segment subcylindrical, longer than broad, with dense row of ventral setae. Upper flagellum uniramous, distinctly swollen in about 30 basal segments, with dense brush of short aesthetascs along whole length of fused part, distal part slender. Lower flagellum distinctly more slender than upper flagellum.

Antenna ( Fig. 2B, G ) with stout basicerite armed laterally with acute tooth directed obliquely anteriad. Scaphocerite well developed, reaching level of distal third of rostrum, 3.0 times as long as maximum width, tapering on distal 2/3 to rounded distal margin, lateral margin almost straight, terminating in acute tooth subequal to distal margin of lamella, medial margin broadly convex. Carpocerite stout, reaching midlength of scaphocerite.

Eye ( Figs 1 , 2B ) with large globular cornea, maximum diameter greater than distal margin of stalk, about 0.3 of PoCL, dorsal accessory pigment spot large, about 0.2 of corneal diameter; stalk broad, shorter than cornea.

Paragnaths ( Fig. 3A ) with corpus deeply fissured in midline, with pair of carinae widely separated proximally, each one running obliquely towards obtusely produced distolateral angles; alae broad, transversely set, medially rounded, laterally acutely produced.

Mandible ( Fig. 3 B–D) robust; palp 3-segmented, distal segment oval, perpendicularly articulated and inward directed, with numerous stout spiniform setae distally, intermediate segment distolaterally with several long setae, obliquely articulated with proximal segment. Incisor process stout, outer margin rounded, inner margin obliquely truncate, oblique distal edge with 8 strong teeth (3 distal ones largest) and series of minute proximal serration; molar process with fine proximal serration continuing from incisor and ending with group of strong serrulate setae distally near molar field, molar process obliquely truncate distally, with brush-like structures of stout serrulate setae on molar surface.

Maxillula ( Fig. 3E ) with palp elongate, feebly bilobed distally, upper lobe broad, lower lobe distally with long stout seta; proximal endite subquadrate, with numerous stout setae medially; distal endite more elongate, with medial margin truncate, with dense series of stout spiniform or simple setae, midlength of anterior margin bearing 2 setae, posterior margin with row of long setae.

Maxilla ( Fig. 3F ) with palp tapering distally, apex feebly bilobed, with single apical seta; proximal endite broadened medially, medial margin broadly convex, densely furnished with long setae; distal endite broadened medially, bilobed, distal lobe ovate, larger than proximal, marginally densely setose, proximal lobe subquadrate, medial margin with dense setae; scaphognathite with anterior lobe much broader than posterior, marginally densely setose, medial margin furnished with short hooked setae, posterior lobe elongate, tapering, with posterior setae very long, up to scaphognathite length.

First maxilliped ( Fig. 3G ) with palp slightly overreaching anterior margin of caridean lobe, setose medially, simple, not subdivided; proximal endite small, swollen, well separated from distal endite, distomedial margin with group of slender setae; distal endite with medial margin slightly concave, with dense marginal and submarginal setae; exopod with well-developed flagellum, distally and distomedially with long plumose setae, with shorter plumose setae along whole lateral margin of flagellum and longer plumose setae on distolateral margin of caridean lobe; caridean lobe broadly convex, broadening distally; epipod large, deeply bilobed.

Second maxilliped ( Fig. 3H ) with dactylus narrow, with medial margin nearly straight, densely furnished with long serrulate setae; propodus elongate, stout, with anterior margin broadly rounded, with dense long distomedial setae; carpus and merus subquadrate, ischium setose along distal outer margin; basis short, broad with several distomedial setae; exopod with well-developed flagellum far overreaching endopod, setose along distal margins; coxa produced medially, angular, epipod ovate, podobranch well developed, large, with about 10 lamellae.

Third maxilliped ( Fig. 3I ) large, about 1.2 times as long as PoCL, with endopod reaching midlength of scapho- cerite; ultimate segment furnished with transverse rows of dense setae medially, ventrolaterally with numerous setae, apex corneous, bispinose, dorsally with additional 7 subdistal corneous spines; penultimate segment about 0.7 of ultimate segment, fringed sparsely with short setae, with several long setae distally; antepenultimate segment (ischiomerus) subequal to ultimate segment, stout, distal margin armed with strong spiniform tooth on dorsal and lateral side, and with single stout sinuate distoventral spine, ischium short, feebly separated from meral part of combined segment, setose medially; basis fused to coxa, angularly projecting and setose medially; exopod overreaching distal margin of merus, setose along distal margins; coxa short, stout, lateral plate forming proximally directed hooked process; praecoxa with 2 small but well developed arthrobranchs.

First pereiopod ( Fig. 4A, B ) stout, slightly compressed, short, subequal to PoCL, falling short to reach half length of scaphocerite. Chela 1.3 times as long as carpus; palm distinctly longer than fingers, twice longer than deep, ventral surface with numerous transverse rows of short brush setae; fingers about 0.5 of palm length, short, stout, gaping in midlength, terminating in set of corneous finger-like ungues; dactylus with long setae distodorsally and ventrally; fixed finger with row of long proximal setae directed into cavity between fingers. Carpus subequal to palm length and depth, distal end slightly swollen with several long brush setae distoventrally. Merus slightly longer than carpus, obliquely articulated with ischium. Ischium as long as merus; basis short, unarmed; coxa with strap-like epipod proximally expanded into small transverse lobe.

Second pereiopod ( Fig. 4C, D ) slender, slightly compressed, slightly overreaching midlength of scaphocerite; length about 1.4 times PoCL. Chela with palm slightly tapering distally, length about 3.5 times greater than proxi- mal depth, and 3 times as long as fingers; fingers gaping; dactylus slightly arched, terminating in set of corneous ungues, with long subapical sensory setae; fixed finger terminating in set of long corneous ungues, longest ungues much longer than corpus; long proximal setae on sides of finger base or directed into cavity between fingers. Carpus 1.6 times as long as chela, and about 7 times longer than deep distally, unarmed. Merus about 0.6 of carpus length, obliquely articulated with ischium. Ischium and basis short, unarmed; coxa bearing strap-like epipod similar to that of preceding leg.

Third pereiopod ( Fig. 4E, F ) overreaching apex of scaphocerite by distal half of propodus and dactylus (left leg lost after examination). Dactylus ( Fig. 4F ) with corneous unguis, flexor margin armed with 3 accessory corneous spines, diminishing proximally, distal spine about half length of unguis, and twice as long as last proximal spine. Propodus about 6 times as long as carpus, ventral surface armed with two groups of 2 small spines, proximal and distal, in addition to pair of small distoventral spines near articulation with dactylus, dorsal surface sparsely furnished with long setae. Carpus about 0.7 of propodus length, armed with 2 lateral spines, with dorsodistal angle produced anteriorly. Merus 1.9 times as long as carpus, armed with 4 (left leg) or 5 (right) lateral spines (2 distal and 2 or 3 near midlength) and 2 ventral spines. Ischium short, armed with 1 lateral and 1 ventral spine; basis short, unarmed; coxa bearing strap-like epipod similar to those of preceding legs.

Fourth and fifth pereiopods ( Fig. 4G, H ) similar to third pereiopod in length and segments proportion, with propodi only slightly slenderer and meri slightly shorter, and in shape and armament of dactylus, carpus, ischium and basis. Fourth pereiopod ( Fig. 4G ) propodus bearing 7 (+ 2 distoventral) ventral spinules; and merus armed with 4 or 5 lateral, and 3 or 2 ventral spines (on left or right leg, respectively). Fifth pereiopod ( Fig. 4H ) propodus only distoventrally spinulose with 3 (+ 2) spinules; merus armed with 3 or 4 lateral spines (1 distal and 2 or 3 more posterior) (on left or right leg, respectively), and 2 ventral spines. Fourth pereiopod coxa bearing strap-like epipod similar to those of preceding legs, fifth pereiopod coxa without epipod.

Endopod of first male pleopod ( Fig. 5C ) large, greatly overreaching distal end of exopod, generally oval, with lateral margin sparsely setose, distal margin entire, non-setose; appendix interna well developed, tapering distally, apex bent anteriad, with few terminal cincinnuli; proximomedial margin of endopod and margin of appendix masculina with multiple short setae running distally up to bent portion of appendix. Endopod of second male pleopod ( Fig. 5D ) with appendices masculina and interna ( Fig. 5D, E ) arising from midlength of medial margin; appendix interna stout, short, about 3 times longer than broad, with about 15 cincinnuli terminally; appendix masculina slightly shorter than appendix interna, with series of 9 slightly curved terminal and distolateral setae, longest seta distolateral, little longer than appendix masculina.

Uropod ( Fig. 2H ) with protopodite posterolaterally obtusely produced, with 2 posteroventral acute teeth, me- dial one larger ( Fig. 5B ). Both exopod and endopod overreaching level of tip of telson; exopod with lateral margin straight terminating in acute tooth, medially with movable spine longer than distolateral tooth; endopod slender, tapering distally.

Branchial formula:

Ovigerous female allotype. The rostrum of the allotype is broken in front of the second proximal ventral tooth, the distal part is lost, distal halves of the upper antennular flagella, and the left uropod, are equally lost; the propodus of the fourth pereiopods is only partly developed, short; the specimen is otherwise in good condition. The specimen shows no significant morphological differences from the male holotype, except possessing broader pleonal pleurae as typical for females. The carapacial dorsal teeth and the first pereiopod are as in the holotype, the second pereiopod carpus is about 1.3 times as long as chela (vs 1.6 times in holotype). The ambulatory legs have their spination similar in number and position to that of the holotype, except the unarmed ischia of the fifth pereiopod: all carpi have 2 lateral spines, all fourth and fifth pereiopods ischia have 1 lateral and 1 ventral spine, the third and fourth pereiopods have their meri with 5 (except right fourth leg with 4) lateral and 2 ventral spines, while the fifth pereiopods have their meri with 3 (left) or 2 (right) lateral spines (i.e. 1 anterior, others about midlength), and 2 ventral spines. The dorsal telson spines are asymmetrical in their numbers, with 2 and 3 spines on the left and right side, respectively. The female bears eggs with early eyespots.

Male paratype. The male paratype is partly damaged, with distal 2 segments of the left maxilliped, the right first pereiopod, the left second pereiopod, and most part of the third right pereiopod, detached or broken, lost; the left first pereiopod is detached, but present in the tube. The specimen shows no significant morphological differenc- es from the holotype. Minor differences are as follows: the rostral formula is the same as in the holotype, with only 2 proximal ventral teeth (vs 3 in holotype) being elongate, anteroventrally directed, while the third one is moderately lower, anteriad, intermediate between proximal and distal teeth; the first pereiopod has the chela as in the holotype, while the carpus to ischium segments are shorter, stouter; the second pereiopod carpus is about 1.2 times as long as chela (vs 1.6 times). The available ambulatory legs have their spination within the range shown for the holotype: all carpi have 2 lateral spines, all ischia have 1 lateral and 1 ventral spine, the third and fourth pereiopods have their meri with 5 lateral and 2 ventral spines, while the fifth pereiopods have their meri with 3 (left) or 2 (right) lateral spines (i.e. 1 anterior, others about midlength), and 3 (left) or 2 (right) ventral spines. The dorsal telson spines are asymmetrical in their numbers, with 2 and 4 spines on the left and right side, respectively.

Measurements [mm]. Holotype male: PoCL 4.6, RL 6.8, TL 25; RF 3 + 2/2 + 3. Allotype ovigerous female: PoCL 5.2, RL 7.0, TL 26.5, eggs 0.54 x 0.40; RF 3 + 2/2 + 3. Paratype male: PoCL 3.8, RL 5.6, TL 22; RF 3 + 2/2 + 3.

Colouration. In life, overall colouration is dark red spots densely set into irregular paths interspaced by narrow white oblique lines and dots. Two small white spots with a red ring around each of them are on the highest point of the third pleomere ( Fig. 6A, B ).

Etymology. Derived from the name of the Gabonese Republic, a country on the west coast of Central Africa in which marine waters the new species was collected.

Molecular analysis. As is plainly evident from the present molecular analysis of a series of specimens of Atlantic Cinetorhynchus species ( Fig. 7 ), there are four basally well-supported genetic lineages separated within the examined samples. Besides an independent position of the pair of examined C. gabonensis sp. n. specimens, there is a clade formed by three specimens of C. rigens from different eastern Atlantic localities ( Table 1 ), and two remaining clades of different species of Cinetorhynchus from the Western Atlantic in our samples—one with C. manningi represented by three specimens from Mexico, and one with four specimens of an another Atlantic species, from Mexico and St. Martin, here called ‘ Cinetorhynchus sp.’.

Cinetorhynchus gabonensis sp. n. is in a sister position with C. manningi in the current analysis (with genetic divergences 9.6 % on 16S marker, and 13.7 % on CO1; Tab. 2 ), while C. rigens and Cinetorhynchus sp. are genetically more distant.

Remarks. Cinetorhynchus gabonensis sp. n. is the 12 th species of the genus, and the third known Atlantic representative. The new species shares its geographic distribution to the eastern part of the ocean only with the amphi- Atlantic C. rigens ( Fig. 6C ) which, besides its distinctly larger body size, differs from C. gabonensis sp. n. also by the rounded posteroventral angle of pleomere IV (vs acutely produced in the new species), trispinose ambulatory dactyli (vs quadrispinose), the carpi and meri of ambulatory pereiopods usually armed with 1 and 5 lateral spines, respectively (vs 2 and 4 spines), with vestigial podobranch on the second maxilliped (vs well developed, multilamellate), and colour pattern ( Gordon 1936; Okuno 1997; present report). As in the present new species, the tegumental scales were previously reported by De Grave & Wood (2011) for C. rigens as well as for the other Atlantic species, C. manningi from the tropical western Atlantic, and some other rhynchocinetids.

Cinetorhynchus manningi ( Fig. 6D ) shares with the new species three accessory teeth on the ventral margin of the ambulatory dactyli, a small posteroventral tooth on the fourth pleonal pleura and the acute projection near posterior articulations of the pleomeres IV and V, and a well-developed podobranch on the second maxilliped. Cinetorhynchus manningi differs from the new species by the distinct interval between the proximal and distal groups of the ventral rostral teeth (vs almost equidistant teeth). The former species, as well as the Indo-West Pacific (IWP) C. brucei Okuno, 2009 , are unique amongst all congeners by the lack of arthrobranchs on pereiopods II and III, whereas all other species (including C. gabonensis sp. n. and C. rigens ) have an arthrobranch on each of the first three pereiopods ( Okuno 1996, 1997, 2009; Okuno & Tachikawa 1997).

The 9 other species of the genus Cinetorhynchus are distributed in the IWP biogeographic area. From those, C. gabonensis sp. n. seems to be most closely related to three species possessing arthrobranchs on pereiopods I-III, three accessory ventral teeth on the ambulatory dactyli, equidistant ventral rostral teeth, and a single ventromedial tooth on the basal antennular segment. Cinetorhynchus hendersoni ( Kemp, 1925) differs from the new species by the presence of corneous coxal projections on the pereiopods I and III, and by pleomere IV unarmed posteriorly on the somite articulation and on the posteroventral pleural angle, while both C. reticulatus Okuno, 1997 and C. hawaiiensis Okuno & Hoover, 1998 usually have 3 spines on carpi of the ambulatory legs (vs 2 carpal spines) ( Kemp 1925; Okuno 1997; Okuno & Hoover 1998; Okuno & Tachikawa 1997). Both latter species possess similar lateral projections posteriorly near the articulation of pleomeres IV and V, as in the new species, but both the fourth and fifth pleura are posteriorly acute in C. hawaiinesis , while the fifth one being unarmed in C. reticulatus . The first chelipeds are sexually dimorphic in C. hawaiiensis and C. reticulatus , while no differences have been observed on the pereiopods between sexes of C. gabonensis sp. n. and a dominant ‘robustus’ male morphotype (sensu Baeza et al. 2014) was not noted.

The present molecular analysis reveals, in addition to C. gabonensis sp. n., a presence of at least one other undescribed Atlantic species of the genus Cinetorhynchus . A possibly new western Atlantic species from Guadeloupe was already mentioned, and colour photograph provided, by Poupin (2018: Fig. 85); its colour pattern and geographic affiliation differ from the latter species. The western Atlantic ‘ Cinetorhynchus sp.’ will be described as a new species in a subsequent study based on a closer morphological and molecular revision of the Atlantic species of the genus.

Figures

FIGURE 1. Cinetorhynchus gabonensis sp. n., holotype male, habitus, lateral view.

FIGURE 2. Cinetorhynchus gabonensis sp. n., holotype male. A, anterior carapace and rostrum, lateral view. B, anterior cephalothorax with left eye and appendages, dorsal. C, part of dorsal margin of rostrum with tegumental scales, lateral. D, detail of tegumental scales laterally on carapace. E, tegumental scale. F, left antennule, lateral. G, left antenna, ventral. H, sixth pleomere, telson, and left uropod, dorsal. I, distal end of telson, dorsal.

FIGURE 3. Cinetorhynchus gabonensis sp. n., holotype male, mouthparts (right side dissected). A, paragnaths, posteroventral view. B, mandible. C, same, incisor and molar processes, outer view. D, same, with palp, inner view. E, maxillula. F, maxilla. G, first maxilliped. H, second maxilliped. I, third maxilliped. A, unscaled.

FIGURE 4. Cinetorhynchus gabonensis sp. n., holotype male. A, left first pereiopod, lateral view. B, same, chela and distal carpus. C, left second pereiopod, lateral view. D, same, chela and distal carpus. E, third pereiopod, lateral. F, same, dactylus and distal propodus. G, fourth pereiopod. H, fifth pereiopod.

FIGURE 5. Cinetorhynchus gabonensis sp. n., holotype male.A, fifth to eight thoracic sterna and bases on pereiopods 2–5. B, posterior end on sixth pleomere, and proximal parts of uropods, ventral view. C, first male pleopod, anterior aspect. D, second male pleopod, posterior aspect. E, same, appendices interna and masculina.

FIGURE 6. Colour pattern in life of three Atlantic species of the genus Cinetorhynchus. A–B, C. gabonensis sp. n., oviger- ous female allotype. C, C. rigens (Gordon, 1936), UO-Mdr.2018.06.08, Madeira. D, C. manningi Okuno, 1996, Brazil. Photos: A, Thomas Menut; B, C, Peter Wirtz; D, Carlos Eduardo Ferreira.

FIGURE 7. Phylogenetic position of Cinetorhynchus gabonensis sp. n. among Atlantic congeners resolved by Maximum Likelihood (ML) method based on the combined 16S and COI gene sequences (with a stenopodid species as outgroup). Maximum Likelihood bootstrap support and Bayesian posterior probabilities (ML/BI) expressed as percentages are indicated in nodes.