Thalassina cangioensis Marin, Kolevatov & ễn, 2024, sp. nov.
Creators: name: Marin, Ivan N.
name: Kolevatov, Vasily M.
name: Nguy ễn, Tu ấn Anh
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Thalassinidae
Thalassina
Thalassina cangioensis

description: Thalassina cangioensis sp. nov.
(Figs 1–5)
Type material. Holotype: ♂, cl. 6.1 cm, tl. 15.3 cm, ZMMU Ma-6230, Vietnam, Ho Chi Minh District, Cần Giờ Mangrove Biosphere Reserve, deep forest of Sonneratia alba / Rhizopora apiculata and Nypa palm trees, 10°28’56.5”N 106°52’24.8”E, burrows in dry substratum (soil) located very close to uppermost boundary of highest tide level, digging with hand shovel, coll. N. Tuan Anh, I. Marin, P. Garibyan, 25.04.2023.
Paratype: ♀, cl. 7.0 cm, tl. 17.1 cm, ZMMU Ma-6231, Cần Giờ Mangrove Biosphere Reserve, deep forest of Sonneratia alba / Rhizopora apiculata and Nypa palm trees, 10°29’02.8”N 106°52’20.2”E, burrows in dry substratum located very close to uppermost boundary of highest tide level, digging with hand shovel, coll. Nguyen Tuan Anh, I. Marin, P. Garibyan, 25.04.2023.
Other material examined. 2♂♂ and 1♀, LEMMI —Cần Gi ờ Mangrove Biosphere Reserve, deep forest of Sonneratia alba / Rhizopora apiculata, 10°28’29.3”N 106°53’01.5”E, burrows in dry substratum located very close to uppermost boundary of highest tide level, digging with hand shovel, coll. N. Tuan Anh, I. Marin, V. Kolevatov, 20- 25.09.2022.
Etymology. The species is named after the type locality, the Cần Giờ Mangrove Biosphere Reserve, located in South Vietnam, and where it was first discovered.
Diagnosis. Rostrum with blunt tip; lateral margins each with well-marked blunt tubercles; median groove reaching posterior ends of rostral lateral carina. Carapace with smooth anterolateral carina; posterodorsal median process long and smooth; cervical groove bordered with numerous well-marked spines along entire its length; postcervical carapace covered with numerous well-marked spines. Pleurae of pleomeres III–V armed with triangular marginal tubercles. Sternites of pleomeres II–V each with 1 median tubercle only. Antennal scaphocerite small, feebly developed. Palm of pereopod I (cheliped) with dorsolateral carina feebly developed, extending along entire length of palm, with 39 or 40 tiny blunt tubercles; dorsomesial carina well defined, with 26 or 27 larger blunt tubercles, which become tooth-like in posterior part; numerous blunt granules present on intercarinal space between dorsolateral and dorsomesial carina. Merus of pereopod III with 6 conspicuous spines on dorsal margin over entire its length, and 4–5 smaller spines along ventral margin; dactylus with spiny tubercles on dorsal margin.
Description of holotype ♂. Rostrum (Fig. 3 b–d) short, reaching slightly beyond distal margin of basal segment of antennular peduncle; tip blunt; dorsal surface slightly depressed medially; lateral margins with 12 (left) and 13 (right) tubercles; lateral rostral carina diverging posteriorly, reaching to anterior 0.2 of distance between base of rostrum and cervical groove, with 2 obsolescent tubercles anteriorly; median groove shallow, reaching posterior ends of lateral rostral carinae.
Carapace (Figs 2 c, 3 b) elongate oval in dorsal aspect, armed with numerous spines directed forward; linea thalassinica running over entire length of carapace, converging to posterodorsal median process posterior to cervical groove; anterolateral carina slightly diverging posteriorly in anterior part and then slightly incurved, reaching to anterior 0.3 of distance between rostral base and cervical groove, each with 5 faint tubercles; ocular spine acuminate, directed forward; antennal spine well marked, acute, directed laterally in dorsal aspect; cervical groove bordered posteriorly by a row of well-marked medium-sized tubercles, which are becoming stronger laterally; postcervical dorsum divided into three parts by transverse uncalcified sutures, first part armed with numerous strong tubercles in posteriorly, second part with several sharp tubercle anteriorly, and third part tapering posteriorly into long posterodorsal median process overhanging anterior section of pleomere I; branchiostegite with anterolateral margin armed with 2 strong spines, oblique hepatic carina bearing 14 spines or spiniform tubercles and row of long stiff setae, lateral surface armed with numerous strong spines, especially in anterodorsal part, with scattered smaller spines and blunt tubercles anteroventrally; anterior part with shallow sulcus extending to base of marginal spine, bordered ventrally by irregular row of tiny tubercles; strong, forwardly curved spine slightly anterolateral to base of posterodorsal median process.
Pleon (Fig. 3 f) moderately slender. Pleomere I (Fig. 3 e) subquadrate in dorsal aspect, slightly wider than long, with lateral margins concave, with deep depression on anterior two-thirds; pleuron triangular in general outline, lateral surface depressed, with thick keel overhanging dorsal to posterodorsal parts, ventral side continuous to sternite. Pleomere II with trapezoidal tergum, slightly widened posteriorly in dorsal aspect; tergal surface smooth, with scattered setose pits; pleuron with sinuous row of small triangular tubercles dorsally defining boundary between tergum and pleuron, submarginal carina along ventral margin sharply delimited, pleural margin bordered with row of spiniform tubercles (Fig. 3 g); sternite with 1 blunt median tubercle anteriorly (Fig. 3 k). Pleomere III rectangular, slightly longer than wide, tergal surface smooth, with scattered minute setal pits or punctate; pleuron slightly flared laterally, generally rounded ventral margin bordered with spiniform tubercles; sternite with 1 median blunt tubercle, otherwise unarmed (Fig. 3 f, g). Pleomeres IV and V similar in shape and ornamentation, tergal surface smooth; pleuron bordered with spiniform tubercles; sternites with 1 median tubercle, otherwise unarmed. Pleomere VI rectangular, about 1.4 times longer than wide; posterolateral angle weakly angular; ventral margin bordered with spiniform and blunt tubercles; sternite unarmed, with transverse groove adjacent to posterior margin.
Telson (Fig. 3 f) triangular, 1.2 times as long as wide; dorsal surface strongly convex transversely, with minute setal pits or punctate; posterolateral angles slightly defined, posterior margin rounded, with tiny median tubercle on ventral side of apex.
Eyestalk (Fig. 3 c, d) very short, strongly widened basally, unarmed ventromesially; corneal small, terminal, semispherical, darkly pigmented.
Antennular peduncle (Fig. 6 b) short; article I fused basally, slightly widening distally; article II slightly widened distally, shorter than article I; article III slender than previous articles, about 2 times as long as wide. Flagella subequal in lengths; outer flagellum slightly stouter than inner flagellum, articles all wider than long.
Antennal peduncle (Fig. 6 c) stout, with unarmed articles; article I with small tubercle distolaterally, distomesial part produced into bluntly produced process with gland opening terminally; scaphocerite small, subconical with blunt apex. Flagellum long.
Maxilliped III moderately slender, with long setae on articles; crista dentate well marked, with row of teeth of various sizes; exopod well developed; flagellum 2-articlated.
Pereopods I (chelipeds) (Fig. 4) subchelate, strongly dissimilar in size and shape. Larger (right) pereopod I (Fig. 4 a, b) with coxa with minutely denticulate distal margin; basis short, ventrolaterally with narrow setal field flanked by minutely tuberculate outer ridge and inner row of small spiniform tubercles; ischium widened distally, with 6 strong spiniform tubercles on dorsal margin; ventral surface with narrow setal field flanked by outer row of small tubercles and inner row of strong spines increasing in size distally; merus widened distally, with carinate dorsal margin, armed with row of blunt spiniform tubercles increasing in size distally, subterminal spine strong, sharp; lateral surface slightly convex, with setal pits or punctate; ventral surface tricarinate, outer carina bordered with row of spiniform and blunt tubercles that becoming larger in proximal part, medial carina formed by row of strong sharp spines, inner carina minutely crenulate, space between outer and medial carina with row of long setae on medial side; mesial face slightly concave, with sparse setal pits or punctate; carpus with dorsal row of 15 spiniform tubercles increasing in size distally, with largest subterminal spine; lateral surface convex, almost smooth; mesial surface with minute granules centrally, with row of 10 blunt tubercles and large subterminal spine ventrally; propodus (palm) subrectangular, slightly widening distally, about 1.4 times as long as wide, compressed laterally; dorsal surface bicarinate, dorsolateral carina extending over entire length of palm, with 40 small blunt tubercles, dorsomesial carina with 27 larger tooth-like sharp tubercles (Fig. 4 h), space between two carina covered with numerous granules; lateral surface convex, entirely covered with minute granules, with feebly marked weak median carina; ventral margin bicarinate, lateral carina with row of small blunt tubercles increasing slightly in size distally, mesial carina armed with row of large triangular tubercles; mesial surface weakly convex, entirely covered with numerous granules; distodorsal margin faintly granulate; fixed finger shorter than dactylus, from 0.6 of its length, curved, terminating in corneous subacute tip, cutting inner margin with several large blunt teeth proximally; dactylus (Fig. 4 c, d) strong, tapering, 0.8 times as long as palm, with about 40° of rotation in dactylus-palm articulation; upper margin bicarinate, outer carina feebly developed and smooth, inner carina bordered with tubercles that becoming corneous proximally; outer surface divided in two parts by blunt longitudinal ridge accompanied by narrow longitudinal field of dense stiff setae, both upper and lower parts smooth; inner surface glabrous; opposable margin with distinct proximal and medial blunt teeth, with distal part smooth.
Smaller (left) pereopod I (Fig. 4 f) with coxa with minutely denticulate distal margin; basis short, ventrolaterally with narrow setal field flanked by minutely tuberculate outer ridge and inner row of small spiniform tubercles; ischium widened distally, with 6 strong spiniform tubercles on dorsal margin; ventral surface with narrow setal field flanked by outer row of small tubercles and inner row of strong spines increasing in size distally; merus widened distally, with carinate dorsal margin, armed with row of blunt spiniform tubercles increasing in size distally, subterminal spine strong, sharp; lateral surface slightly convex, with setal pits or punctate; ventral surface tricarinate, outer carina bordered with row of spiniform and blunt tubercles that becoming larger in proximal part, medial carina formed by row of strong sharp spines, inner carina minutely crenulate, space between outer and medial carinae with row of long setae on medial side; mesial face slightly concave, with sparse setal pits or punctate; carpus (Fig. 4 e) with dorsal row of 16 spiniform tubercles, with largest subterminal spine; lateral surface convex, almost smooth; mesial surface with minute granules centrally, with row of 9 blunt tubercles and large subterminal spine ventrally; propodus (palm) elongate oblong, about 2.5 times as long as wide, compressed laterally; dorsal surface bicarinate, dorsolateral carina extending over entire length of palm, with 40 small blunt tubercles, dorsomesial carina with 27 larger tooth-like sharp tubercles (Fig. 4 e), space between two carina covered with numerous granules; lateral surface convex, entirely covered with minute granules, with feebly marked weak median carina; ventral margin bicarinate, lateral carina with row of small blunt tubercles increasing slightly in size distally, mesial carina armed with row of large triangular tubercles; mesial surface weakly convex, entirely covered with numerous granules; distodorsal margin faintly granulate; fixed finger shorter than dactylus, from 0.5 of its length, curved, terminating in corneous subacute tip, cutting inner margin with several large blunt teeth proximally; dactylus (Fig. 4 g) slender, tapering, 0.8 times as long as palm, with about 40° of rotation in dactylus-palm articulation; upper margin with feebly developed and smooth both inner and outer carinae; outer surface divided in two parts by blunt longitudinal ridge accompanied by narrow longitudinal field of dense stiff setae, both upper and lower parts smooth; inner surface glabrous; opposable margin with distinct proximal tooth, proximal concavity and strongly denticulate convexity distal to proximal concavity, with distal part mostly smooth.
Pereopod II(Fig.5 a) subchelate;coxa fairly inflated posteroventrally,with several minute granules at ventromesial distal angle; basis incompletely fused with ischium, ventral margin with 3 spiniform tubercles; ischium widened distally, ventral margin slightly sinuous with 5 spiniform tubercles; merus subcylindrical, thicken in the middle part, ventral margin gently convex and unarmed, covered with long stiff setae, dorsal margin straight with 2 small spines; carpus widened distally, cup-like, lateral surface convex, ventral surface covered with stiff setae; propodus strongly compressed laterally, suboval, dorsal and ventral margins smooth, covered with numerous long stiff setae, ventrodistal angle produced as triangular tooth forming fixed finger, terminating in sharp triangular tip, opposable margin well denticulate with blunt corneous teeth (Fig. 6 d); dactylus subequal in length to propodus, strongly compressed, dorsal margin covered with long stiff setae; lateral surface with narrow median setal field extending almost over entire length, ventral margin slightly convex, bordered by corneous or corneous-tipped teeth.
Pereopod III (Fig. 5 b) coxa with 3 or 4 minute sharp tubercles; basis incompletely fused with ischium, ventral margin unarmed; ischium widening distally, ventral margin slightly sinuous, unarmed; merus subcylindrical, thicken in the middle part, ventral margin gently convex, armed with 8 sharp tubercles, dorsal margin almost straight, armed with 7 sharp spines increasing distally, distal spines curved, proximal most spine smaller than terminal spine; carpus (Fig. 5 c) widened distally, dorsal margin armed with 3 spines, with largest distal spine, ventral margin unarmed; propodus strongly compressed laterally, with dorsal margin convex, with 5 sharp corneous tubercles, ventral margin with rather sparse stiff setae; dactylus (Fig. 6 e) subequal in length to propodus, twisted, sinuous, terminating in blunt corneous tip, dorsal surface laterally with row of 9 corneous tubercles and tufts of stiff setae, ventral margin unarmed, with row of minute spinules.
Pereopod IV (Fig. 5 d) generally similar to pereopod III; coxa with 4 minute sharp tubercles; ischium with 4 minute sharp tubercles along ventral margin; merus with 10 sharp tubercles along ventral margin, dorsal margin unarmed; carpus with 1 distodorsal spine; propodus with 6 corneous tubercles on dorsal margin; dactylus with dorsal margin armed with 9 corneous tubercles.
Pereopod V with coxa armed with 3 minute sharp tubercles; merus with 4 minute tubercles along ventral margin; carpus and propodus unarmed, latter with prominent tufts of stiff setae on outer surface and dense stiff setae along inner distal margin; dactylus subconical, slightly twisted, becoming corneous distally; outer surface with corneous ridge extending from midlength to tip adjacent to flexor margin.
Pleopod I uniramous (Fig. 6 g, h) relatively stout, outer proximal end modified to intromittent organ, armed with 1 strong spine, distal part wide, suboval, about 1/4 of entire length and about twice wider than proximal part of peduncle, subterminal keel bluntly pointed, with setae present only on inner surface, “neck” behind keel broad, inner distal setal row modified in disc-like structure, slightly producing forward. Pleopods II–V biramous, mostly equal size, without appendix interna.
Uropod (Fig. 3 f) with incompletely basally fused protopod; rami slender, styliform, endopod slightly longer than exopod tapered to blunt apices, slightly directed inward in dorsal aspect, sparsely setose on lateral margin and ventral surface, almost glabrous on dorsal surface.
Colouration in life. The carapace, pleon, telson and appendages are generally whitish-orange-brown in color; the lateral surface of the carapace, pleura and the basal part of all pereopods are whitish; the dorsal surface of the pereopods I (chelipeds) are bright orange-red, and the lateral surfaces are whitish; cornea of eye are blackish in color (Figs 2, 8).
Variability. The most pronounced morphological variation observed among all studied individuals is in the size and shape of the pereopods I (chelipeds), which differ between ♂♂ and ♀♀. Pereopods I (chelipeds) in ♂♂ (Figs 2, 8 a) differ markedly in shape and size, the larger claw (propodus+fingers) is much stouter and wider than the smaller one, as well as the shape of the dactylus is very different, on which (the larger) the median teeth are well developed (Fig. 4). In contrast, pereopods I (chelipeds) in ♀♀ are of approximately the same size and generally of the same shape, the larger claw is somewhat stouter and wider than smaller one (Figs 7 d–k, 8 b, c). Pleopod I in ♀♀ uniramous, 2-articulated and elongated, distal part not modified.
GenBank (NCBI) accession number. PP796476 (holotype ♂), PP796477 (paratype ♀), PP796388– PP796390.
Distribution. Presently, the species is known only from the type locality in the mangrove swamps of the Cần Giờ Mangrove Reserve of South Vietnam.
Remarks. The armature of carapace and pereopods I (chelipeds) (see Ngoc-Ho & de Saint Laurent 2009; Lin et al. 2016), as well as the shape of the pleopod I in males (see Sakai & Türkay 2012; Moh & Chong 2009), represent the main morphological features that differentiate species within the genus. The genus is generally divided into two groups based on the shape of the rostrum: 1) species with blunt rostral tip (T. krempfi, T. anomala, T. spinosa, T. pratas, T. kelanang, T. squamifera); and 2) species with acute or subacute rostral tip (T. spinirostris, T. gracilis, T. saetichelis, T. australiensis) (Ngoc-Ho & de Saint Laurent 2009; Lin et al. 2016). The new species belongs to the first group of species because of the blunt rostral tip (Fig. 3 c, d), and appears most similar to T. anomala, T. spinosa and T. pratas.
The new species is morphologically mostly similar to T. anomala, which is considered as a sister species (Fig. 9). Both species are similar in a blunt tip of the rostrum, with lateral margins armed with blunt tubercles; smooth and well-defined anterolateral carina; the presence of posterodorsal median process on posterior margin of carapace; the presence of a single median tubercle on pleonal sternites II–V. However, the strong spinulation of the posterior dorsal and branchiostegal parts of the carapace, the armature of pereopod I (chelipeds), and the presence of spines on the proximal part of pleopod I in males are mostly similar to T. spinosa. The general shape of the pleopod I in males, especially its modified distal part, of the new species is closest to that of T. squamifera, distinguishing by bulging downward median part of tip (modified disc-like structure).
The new species can be separated from T. anomala (after Sakai & Türkay 2012; Moh & Chong 2009) by: 1) the shape of the distal part of pleopod I in males, which is 1.4 times as long as wide with a downwardly bulging median part (see Fig. 6 g, h) (vs. distal part about two times as long as wide, without downwardly bulging median part)); 2) cervical groove of carapace bordered by at least several well-developed lateral spines (similar to T. pratas) (see Fig. 2 c) (vs. unarmed or bordered with few blunt tubercles; 3) stronger spinulation of posterior dorsal and branchiostegal parts of the carapace (vs. mostly smooth).
From T. pratas, presently represented only by the holotype ♀ (Lin et al., 2016), the new species can be separated by: 1) propodus of pereopod I (chelipeds) is about two times as long as wide (see Fig. 4) (vs. almost 3 times as long as wide; 2) fixed finger of about 0.5 length of dactylus in larger cheliped, and about 0.4 in smaller cheliped (vs. fixed finger less than 0.2 times as long as dactylus with a crease-like structure at the base (see Fig. 4); 3) dorsolateral carina of propodus (palm) of pereopod I (chelipeds) feebly developed with 40 tiny tubercles (see Fig. 4) (vs. well-marked with 23–25 tubercles); 4) tubercles in ventral lateral carina of propodus (palm) of pereopod I (chelipeds) larger than in ventral median carina (see Figs 4, 7) (vs. ventral lateral and median carina consist of well-developed tubercles of the same size; 5) propodus of pereopod II almost suboval (see Fig. 5 a) (vs. distinctly longer then wide); 6) merus of pereopod III covered with spines over entire length of dorsal edge (see Fig. 5 b, c) (vs. covered with spines only in distal part of dorsal margin).
From T. spinosa (after Sakai & Türkay 2012; Ngoc-Ho & de Saint Laurent 2009), the new species can be separated by 1) only lateral spines of cervical groove are well-marked (see Fig. 2 c) (vs. cervical groove bordered by a row of strong spine-like tubercles entire it length; 2) lateral carina of anterior part of carapace smooth or with 1 or 2 blunt tubercles (see Fig. 3 a, b) (vs. with 9 or 10 tubercles; 3) meri of pereopods I–III are less spinose (vs. covered with numerous well-developed spines; 4) distal part of pleopod I in males with downwardly bulging median part (see Fig. 6 g, h) (vs. without bulging downward median part).
The new species can be separated from T. squamifera (after Ngoc-Ho & de Saint Laurent 2009; Sakai & Türkay 2012) by 1) one median tubercle on the sternites of pleomeres II–V (see Figs 3 k, 6) (vs. several lateral tubercles; 2) lateral dorsal carina of pereopod I (chelipeds) extending to the full length of the propodus (see Fig. 4) (vs. extending to half or 2/3 length of the propodus); 3) weekly differentiated scaphocerite of the antenna (see Fig. 6 b) (vs. welldifferentiated (Moh & Chong 2009: Fig. 4C)); 4) mesial blunt tooth located on the middle of inner margin of the dactylus of larger pereopod I (chelipeds) (see Fig. 4) (vs. mesial blunt tooth located on the proximal half inner margin of the dactylus, near the proximal blunt tooth); 5) long spiny posterodorsal median process of carapace (see Figs 3 e, 7 c) (vs. short posterodorsal median process); and 6) different shape of pleopod I in males, distinguished by a downwardly bulging median part at the tip (see Fig. 6 g, h vs. Fig. 6 i, j).
From T. kelanang (after Moh & Chong 2009), the new species can be separated by: 1) one median tubercle on sternites of pleomeres II–V (see Fig. 3 k, 6) (vs. several lateral tubercles); and 2) long spiny posterodorsal median process of carapace (see Figs 3 e, 7 c) (vs. short posterodorsal median process).
From T. krempfi (after Ngoc-Ho & de Saint Laurent 2009; Sakai & Turkey 2012), the new species can be separated by 1) lateral margins of rostrum with 10–12 evident tubercles (see Figs 3 d, 6 a, 7 b) (vs. lateral margins unarmed or with a few obscure tubercles); and 2) lateral rostral carina and anterolateral carina of carapace armed with tubercles (see Figs 3 d, 6 a, 7 b) (vs. lateral rostral carina and anterolateral carina unarmed).
DNA analysis. The interspecific genetic divergence between the new species and other species of the genus Thalassina, whose sequences are available in the GenBank (NCBI) database, exceeds 15%. The lowest genetic divergence is observed for possible sister species, T. anomala, with 0.1514±0.0147 substitutions per 100 nucleotides (about 15%) (see Table 1; Fig. 9). Genetic divergence exceeds 18% from other studied species, such as T. squamifera, T. kelanang and T. gracilis, and about 26% to T. krempfi, which is considered as the most basal to other species (see Table 1).
description: Published as part of Marin, Ivan N., Kolevatov, Vasily M. & Nguy ễn, Tu ấn Anh, 2024, A new mud lobster of the genus Thalassina Latreille, 1806 (Crustacea: Decapoda: Gebiidea: Thalassinidae) from the mangrove forest of the C ần Gi ờ Mangrove Reserve, South Vietnam, pp. 533-549 in Zootaxa 5474 (5) on pages 535-547, DOI: 10.11646/zootaxa.5474.5.5, http://zenodo.org/record/12730866