Parakonarus kajii, Kakui & Uyeno & Naruse, 2019

Kakui, Keiichi, Uyeno, Daisuke & Naruse, Tohru, 2019, First Molecularly Confirmed Conspecific Male and Female Pair in Konariinae (Crustacea: Tanaidacea), with the Description of a New Species, Species Diversity 24 (1), pp. 49-60 : 51-58

Parakonarus kajii sp. nov.

[New Japanese name: Haridashi-Kamakiri-tanaisu]

( Figs 2–7 )

Diagnosis. Male: outer ventral digitiform process on chelipedal carpus long, 1.50 times as long as wide, with one ventro-subproximal, one outer, and one inner simple setae in basal half of process; chelipedal dactylus with ventroproximal triangular process; dactylus and unguis of pereopods 4–6 fused to claw. Female: all pereonites wider than long; antennule 0.59 times as long as cephalothorax; chelipedal merus with six ventral simple setae; dactylus and unguis of pereopods 4–6 fused to claw; propodal palm of cheliped with two inner simple setae at insertion of dactylus.

Etymology. This species-group name is a noun in genitive and named for Tomonari Kaji, a researcher in the evolutionary and functional morphology of arthropods and a friend of the first author.

Material Examined. Holotype: male, NSMT-Cr 26209 (BL 1.88 mm, CW 0.32 mm), dissected, 6 slides and 1 vial; INSD accession number LC473040 ; off south coast of Sotopanari Island , Ryukyu Islands, southwestern Japan, 40 m depth, among cluster of sponges, 10.viii.2016, collected by D. Uyeno. Allotype: female without developing/developed oostegites, NSMT-Cr 26210 (BL 1.66 mm, CW 0.29 mm), dissected, 9 slides and 1 vial; INSD accession number LC473041 ; same collection data as for holotype .

Description of male. Based on holotype (NSMT-Cr 26209).

Body ( Figs 2 , 3A1–3, B, b1 ) slightly dorsoventrally flattened, 5.82 times as long as CW, translucent when alive ( Fig. 2 ). Cephalothorax 0.22 times as long as BL, 1.27 times as long as wide, pear-shaped in dorsal view, naked; eyes well developed, dark brown when alive ( Fig. 2 ). Pereonites 1–6, with length ratio of 1.00: 1.49: 1.89: 2.25: 2.33: 2.09; all wider than long, with posterior lateral expansion; pereonite 1 with pair of dorsal setae and pair of lateral setae in anterior region, and pair of lateral setae in posterior region; pereonites 2 and 3 each with pair of anterior dorsolateral setae and pair of posterior lateral setae; pereonites 4–6 naked. Pleon 0.32 times as long as BL. Pleonites as wide as pereonite 6; all wider than long, similar in shape, with ventral keel ( Fig. 3b 1 ); pleonite 4 with pair of lateral setae. Pleotelson 0.43 times as long as wide, narrower than pleonite 5, pentangular in dorsal view, with pair of lateral setae, pair of posterior lateral setae, two pairs of posterior setae, and pair of posterior lateral PSS.

Antennules ( Fig. 4A, a 1 , a 2 ) with 13 articles, 1.59 times as long as cephalothorax; articles 1–13 with length ratio of 1.00: 0.72: 0.15: 0.26: 0.28: 0.31: 0.27: 0.31: 0.33: 0.31: 0.35: 0.29: 0.08. Article 1 with one outer subdistal and one inner subdistal simple setae and three outer subdistal PSS. Article 2 with outer subdistal simple seta and three outer subdistal PSS. Article 3 with inner distal simple seta. Article 4 with three ventral rows of aesthetascs ( Fig. 4a 1 ). Articles 5–12 each with ventral row of aesthetascs. Article 13 with six simple setae, two PSS, and aesthetasc ( Fig. 4a 2 ). Antenna ( Fig. 4B ) with six articles, 0.39 times as long as antennule; articles 1–6 with length ratio of 1.00: 1.65: 1.00:2.99: 2.26:0.28. Article 1 naked. Article 2 with one dorsodistal and one ventrodistal simple setae. Article 3 with dorsodistal simple seta. Article 4 with three subdistal simple setae and several PSS. Article 5 with two distal simple setae. Article 6 with six distal simple setae (two longest setae slightly shorter than antenna length).

Maxillipeds ( Fig. 4C ) with basis bearing three ventrodistal simple setae. Palp with four articles, naked.

Chelipeds ( Fig. 4D, d 1 ) subchelate, with triangular articulation with cephalothorax via sclerite; sclerite with simple seta ( Fig. 3B ). Basis longer than wide, with free posterior portion and outer dorsal simple seta; inner side with oval plate-like structure ( Fig. 4D : †) and elongate platelike structure ( Fig. 4D : ‡). Merus with six ventral simple setae. Carpus with one dorsoproximal and one dorsodistal simple setae and outer ventral digitiform process; digitiform process 1.50 times as long as wide, with one ventrosubproximal, one outer, and one inner simple setae in basal half of process. Propodus more than twice as long as wide. Propodal palm with simple seta at insertion of dactylus, and inner comb-row of 16 setae; comb-row almost perpendicular to dorsal margin of propodal palm. Fixed finger short, with two ventral and three dorsal simple setae, and coneshaped claw. Dactylus-unguis far longer than fixed finger, and almost as long as propodal palm; dactylus with inner proximal simple seta, five ventral spiniform setae, and ventroproximal triangular process; unguis conic, 0.22 times as long as dactylus.

Pereopods 1–6 cylindrical, with length ratio of 1.00: 0.73: 0: 65: 0.80: 0.85: 0.82. Pereopod 1 ( Fig. 5A, a 1 ) 0.43 times as long as BL, with length ratio of basis, ischium, merus, carpus, propodus, and dactylus-unguis 1.00:0.05: 0.35: 0.51: 0.68: 0.58. Coxa with simple seta. Basis cylindrical, narrow, 4.80 times as long as wide, with dorsoproximal simple seta. Ischium wider than long, with two ventral simple setae. Merus 2.20 times as long as wide, with inner, ventrodistal tiny spiniform seta ( Fig. 5a 1 ). Carpus 3.82 times as long as wide, with four subdistal simple setae and inner subdistal spiniform seta. Propodus 5.70 times as long as wide, serrate dorsally, with two dorsosubdistal simple setae and ventrosubdistal spiniform seta. Dactylus setulate proximally, with proximal simple seta. Unguis 1.43 times as long as dactylus, naked. Pereopod 2 ( Fig. 5B, b 1 ) with length ratio of articles from basis to dactylus-unguis 1.00: 0.09:0.37: 0.41: 0.60: 0.28; similar to pereopod 1, except carpus with inner distal simple seta and one dorsodistal, one inner distal, and one ventrodistal spiniform setae (dorsodistal one broken distally); propodus with ventral serrations; and unguis subequal length to dactylus. Pereopod 3 ( Fig. 5C, c 1 ) with length ratio of articles from basis to dactylus-unguis 1.00: 0.08: 0.33: 0.38: 0.64: 0.30; similar to pereopod 2, except ischium with ventral seta. Pereopod 4 ( Fig. 5D, d 1 , d 2 ) without coxa. Length ratio of articles from basis to dactylus-unguis 1.00: 0.10: 0.41: 0.41: 0.67: 0.37. Basis cylindrical, 2.65 times as long as wide, with two midventral PSS. Ischium wider than long, with two ventral simple setae. Merus 2.11 times as long as wide, with two ventrodistal spiniform setae. Carpus 2.55 times as long as wide, serrate ventrally, with dorsodistal simple seta and one longer and three shorter distal spiniform setae. Propodus 6.33 times as long as wide, serrate dorsally and ventrally, with two longer and one shorter dorsodistal simple setae, and two ventrosubdistal spiniform setae. Dactylus and unguis fused to claw; claw nearly straight, with dorsosubproximal simple seta and ventral serrations ( Fig. 5d 2 ). Pereopod 5 ( Fig. 5E ) with length ratio of articles from basis to dactylus-unguis 1.00: 0.10: 0.39: 0.35: 0.60: 0.32; similar to pereopod 4, except basis with two dorsal PSS but lacking ventral PSS. Pereopod 6 ( Fig. 5F ) with length ratio of articles from basis to dactylus-unguis 1.00: 0.09: 0.33: 0.39: 0.56: 0.32; similar to pereopod 4, except basis with dorsal PSS but lacking ventral PSS; and propodus with two inner distal simple setae.

Pleopods ( Fig. 5G, g 1 ) five pairs, all similar. Setal numbers/conditions summarized in Table 1 .

Uropod ( Fig. 5H ) with basal article bearing five inner distal simple setae. Endopod with four articles; articles 1 and 2 each with three distal simple setae and distal PSS; article 3 with two distal simple setae and two distal PSS; article 4 with one middle and four distal simple setae and two distal PSS. Exopod uniarticulate (pseudoarticulation present), longer than endopodal article 1, with one middle and two distal simple setae.

Description of female. Based on allotype (NSMT-Cr 26210).

Body ( Fig. 3C1–5 , D) slightly dorsoventrally flattened, 5.71 times as long as CW. Cephalothorax 0.20 times as long as BL, 1.19 times as long as wide, almost rectangular in dorsal view, with one or two pairs of lateral simple setae posterior to eye, and pair of mid-lateral simple setae; dorsal demarcation of second thoracomere present; eye with colored ommatidia. Pereonites 1–6 with length ratio of 1.00: 1.09: 1.08: 1.80: 1.83: 1.29; all wider than long, rectangular; pereonite 1 with pair of dorsal setae and pair of lateral setae in anterior region; pereonites 2 and 3 each with pair of anterior dorsolateral setae; pereonites 4–6 with two pairs of anterior dorsolateral setae and pair of lateral setae. Pleon 0.27 times as long as BL. Pleonites as wide as pereonite 6; all wider than long, similar in shape, with pair of dorsolateral simple setae and pair of lateral simple setae. Pleotelson 0.58 times as long as wide, narrower than pleonite 5, trapezoid in dorsal view, with rounded posterior expansion; setation similar to male.

Antennules ( Fig. 6A ) with four articles (article 4 caplike), stout, 2.82 times as long as wide, 0.59 times as long as cephalothorax; articles 1–4 with length ratio of 1.00: 0.24: 0.41: 0.03. Article 1 with one mid-outer, one midventral, one mid-inner, and one outer distal simple setae, four outer distal PSS, and several ventroproximal fine setae. Article 2 with one outer distal and one inner distal simple setae, and inner distal PSS. Article 3 with two simple setae, PSS, and aesthetasc in distal region. Article 4 with two distal simple setae (one subequal length to article 1) and distal PSS. Antenna ( Fig. 6B ) with six articles, 0.80 times as long as antennule; articles 1–6 with length ratio of 1.00: 1.00: 0.76: 2.13: 1.08: 0.21. Articles 1–4 similar to those of male (dorsodistal seta on article 3 partly broken). Article 5 with distal PSS. Article 6 with five distal simple setae (two longest setae longer than or as long as combined length of articles 3–6).

Labrum ( Fig. 6C ) not projecting anteriorly, setulate. Mandibles ( Fig. 6D, E ) with molar well developed; masticatory region broad. Incisor of left mandible ( Fig. 6D ) with slightly bifurcate tip; lacinia mobilis with four small and one large teeth. Incisor of right mandible ( Fig. 6E ) bifurcate distally, with anterior subdistal crenulation. Labium ( Fig. 6F ) bilobed; inner and outer lobes setulate. Maxillulae ( Fig. 6G, g 1 ) with setulate endite bearing nine (left) or 10 (right) distal spines; palp biarticulate, with one subdistal and one distal simple setae. Maxilla lost during dissection. Maxillipeds ( Fig. 6H, h 1 ) with bases not fused medially, each bearing four (left) or three (right) simple setae at insertion of palp. Endites not fused medially, reaching distal margin of palp article 1, each with long incurving simple seta in outer distal region, three distal spiniform setae (two outer ones spatulate; other one rounded, with serrate tip), and one long and one short spiniform setae in inner dorsal region; outer distal margin setulate. Palp article 1 naked; article 2 with one midouter and one outer distal simple setae, and three inner distal spiniform setae; article 3 with seven inner simple setae; article 4 with one outer and six distal simple setae and distal bipinnate seta. Epignath ( Fig. 6I ) elongate, slender, setulate.

Chelipeds ( Fig. 6J, j 1 ) chelate, with triangular articulation with cephalothorax via sclerite; sclerite with two simple setae ( Fig. 3D ). Basis longer than wide, with free posterior portion and outer dorsal simple seta; inner side with oval plate-like structure ( Fig. 6J : †). Merus with six ventral simple setae. Carpus 1.86 times as long as wide, slightly longer than basis, with one dorsodistal and three ventral simple setae, and several inner dorsal tiny spiniform setae ( Fig. 6j 1 ); outer ventrodistal margin extending as cuff over proximal region of propodus. Propodal palm with one outer and two inner simple setae at insertion of dactylus. Fixed finger with two ventral and three dorsal simple setae, and coneshaped claw. Dactylus-unguis as long as fixed finger; dactylus with inner proximal simple seta ( Fig. 6j 1 ); unguis as long as claw on fixed finger, bifurcate at tip.

Pereopods 1–6 cylindrical, with length ratio of 1.00: 0.65: 0.57: 0.57: 0.60: 0.60. Pereopod 1 ( Fig. 7A ) 0.33 times as long as BL, with length ratio of articles from basis to dactylus-unguis 1.00: 0.08: 0.36: 0.63: 0.72: 0.94. Coxa naked. Basis slightly arched, 3.72 times as long as wide, with dorsoproximal simple seta and dorsoproximal PSS. Ischium wider than long, with ventral simple seta. Merus 1.60 times as long as wide, with ventrodistal short (0.28 times as long as merus width) simple seta. Carpus 2.54 times as long as wide, with four distal simple setae. Propodus 3.30 times as long as wide, serrate dorsally, with three dorsosubdistal and one ventrosubdistal simple setae. Dactylus with proximal simple seta. Unguis 1.35 times as long as dactylus, naked. Pereopod 2 ( Fig. 7B ) with length ratio of articles from basis to dactylus-unguis 1.00: 0.06: 0.33: 0.34: 0.48: 0.36. Coxa with simple seta. Basis cylindrical, 2.95 times as long as wide, with mid-dorsal simple seta and two mid-dorsal PSS. Ischium wider than long, with two ventral simple setae. Merus 1.38 times as long as wide, naked. Carpus 1.20 times as long as wide, with one dorsodistal and one ventrodistal simple setae. Propodus 2.40 times as long as wide, serrate dorsally, with one dorsosubdistal and one inner subdistal simple setae, and ventrodistal spiniform seta. Dactylus with middle simple seta. Unguis 0.94 times as long as dactylus, naked. Pereopod 3 ( Fig. 7C ) with length ratio of articles from basis to dactylus-unguis 1.00: 0.05: 0.30: 0.34: 0.52: 0.42; similar to pereopod 2, except ischium with ventral seta. Pereopod 4 ( Fig. 7D, d 1 , d 2 ) without coxa. Length ratio of articles from basis to dactylus-unguis 1.00: 0.09: 0.37: 0.35: 0.39: 0.38. Basis thick, 1.43 times as long as wide, with three dorsal and one ventral PSS. Ischium wider than long, with ventral simple seta. Merus 1.44 times as long as wide, with two ventrodistal tubercle-mounted setae ( Fig. 7d 1 ). Carpus 1.30 times as long as wide, with two distal spiniform setae. Propodus 1.80 times as long as wide, with two dorsodistal simple setae, two ventrodistal spiniform setae, and dorsodistal serrated spiniform seta ( Fig. 7d 2 ). Dactylus and unguis fused to claw; claw nearly straight, with dorsosubproximal simple seta and serrations. Pereopod 5 ( Fig. 7E ) with length ratio of articles from basis to dactylus-unguis 1.00: 0.06: 0.37: 0.32: 0.45: 0.36; similar to pereopod 4, except basis with one dorsal PSS. Pereopod 6 ( Fig. 7F ) with length ratio of articles from basis to dactylus-unguis 1.00: 0.07: 0.32: 0.35: 0.42:0.29; similar to pereopod 4, except basis naked, carpus with dorsodistal simple seta, and propodus with two serrated spiniform setae.

Pleopods ( Fig. 7G, g 1 ) five pairs, all similar. Setal numbers/conditions summarized in Table 1 .

Uropod ( Fig. 7H ) with basal article naked. Endopod with four articles (articulation between articles 1 and 2 very slight); article 1 with PSS; article 2 with two distal simple setae and distal PSS; article 3 with distal simple seta and two distal PSS; article 4 with one subdistal and four distal simple setae and distal PSS. Exopod uniarticulate, longer than endopodal article 1, with one middle and two distal simple setae.

Distribution. So far known only from the type locality.

Remarks. Parakonarus kajii sp. nov. is the ninth species described in this genus (cf. Anderson 2016). Among its eight congeners, both sexes have been described in six species: P. fairgo ( Bamber, 2005) , P.juliae ( Morales-Núñez et al., 2013) , P. kopure Bird, 2011 , P. provincialis ( Dollfus, 1898) , P. robertsoni Edgar, 2012 , and P. sozo Bamber, 2013 . Parakonarus corrigendum Bamber, 2013 lacks information from females, and P.oregmus Bamber, 2013 lacks information from males. Parakonarus kajii is the seventh member with male and female information, and the first case where the male and female pair was confirmed by molecular data.

Male P. kajii has a well-developed digitiform process on the ventral margin of the chelipedal carpus ( Fig. 4D, d 1 ). This feature is also found in male P. juliae ( Morales-Núñez et al. 2013) ; however, the positions of the three simple setae on the process are different between the two species. In P. kajii , one ventro-subproximal, one outer, and one inner setae are distributed in the basal half of the process. In contrast, in P.juliae , one seta is placed at the tip of process, and the other two are located near the base of the process and distal to the process ( Morales-Núñez et al. 2013: fig. 8B, C); this pattern is also found in P. corrigendum , P. fairgo , and P. sozo ( Błażewicz-Paszkowycz and Bamber 2012; Morales-Núñez et al. 2013). These differences indicate that, even though the shape of the process is similar, the region of origin of the process is not identical: the process in P.kajii must form as an expansion of the exoskeleton originating more distally on the carpus than in P.juliae .

In terms of the setal positions, male P. kajii closely resembles male P.kopure ( Bird 2011) , but can be distinguished from the latter by having the ventral process on the chelipedal carpus longer than wide (wider than long in P. kopure ); the inner comb-row on the chelipedal propodus comprising 16 setae (about nine in P. kopure ); and the dactylus and unguis of pereopods 4–6 fused (separate in P.kopure ).

Parakonarus robertsoni has more than 10 ventral simple setae on the chelipedal merus in both sexes, and males have four ventral simple setae on the chelipedal carpus (based on figs 13 CH and 17 CH in Edgar 2012), which distinguish this species from P.kajii .

Very limited morphological information is available for P. provincialis , but it differs from P. kajii in that the ventral process on the chelipedal carpus is wider than long (longer than wide in P. kajii ), the chelipedal dactylus lacks a ventroproximal triangular process (present in P. kajii ), and the uropodal endopod has five articles (four in P. kajii ) ( Dollfus 1898).

Among the eight species with information on females, the females of P. kajii , P. kopure , P. robertsoni , and P. sozo have a short body, with pereonite 4 shorter than wide. Female P. kajii differs from female P. kopure in that the ventrodistal seta on the pereopod-1 merus is short, or 0.28 times as long as the merus width (long, or 1.20 times as long as the merus width in P. kopure ); the pereopod-1 unguis is 1.35 times as long as the dactylus (1.77 times as long as the dactylus in P. kopure ); the carpi of pereopods 2 and 3 lack the ventrodistal spiniform seta (present in P. kopure ); the propodal palm of the cheliped has two inner simple setae at the insertion of the dactylus (five in P. kopure ); and article 2 of the maxillipedal palp has one mid-outer and one outer distal simple setae (one mid-outer seta only in P. kopure ) ( Bird 2011). Female P. kajii differs from female P. robertsoni in having the chelipedal merus and carpus respectively bearing six and three ventral simple setae (more than 10 [merus] and five or six [carpus] in P. robertsoni ) ( Edgar 2012). Female P.kajii differs from female P. sozo in having six ventral simple setae on the chelipedal merus (four in P. sozo ), and the dactylusunguis fused in pereopods 4–6 (not fused in P. sozo ) ( Bamber 2013).

Female P. kajii differs from P. oregmus , a congener for which only information on females is available, in having all pereonites wider than long (pereonites 4 and 5 longer than wide in P. oregmus ); the chelipedal merus with six ventral simple setae (nine in P. oregmus ); the pereopod 1 dactylusunguis 1.3 times as long as that of the pereopod-1 propodus (1.7 times as long in P. oregmus ); and the dactylus and unguis of pereopods 4–6 fused (not fused in P.oregmus ) ( Bamber 2013). Information on the morphology of P. provincialis females is very limited, but this species has the antennule being longer than the cephalothorax length ( Dollfus 1898: fig. 4b) whereas it is shorter in P.kajii .

Our specimens showed an unusual feature on the inner surface of the chelipeds: an oval plate-like structure present in both sexes ( Figs 4D †, 6J†) and an elongate plate-like structure present in males ( Fig. 4D ‡). The elongate platelike structure may be a reduced ischium. In Tanaidacea , the ischium has been noted to occur on the chelipeds in only three taxa in two superfamilies (Neotanaoidea and Tanaidoidea) to date: Neotanaidae (cf. Larsen et al. 2015: fig. 59.19B), and the two tanaidoid genera Arctotanais (cf. Kakui et al. 2012: fig. 5) and Tanais (cf. Lauterbach 1970: fig. 25) (Kakui et al. 2012). In these taxa, the ischia comprise a narrow, incomplete ring or arc, and are sometimes overlooked by researchers (e.g., Sieg 1980). The structure we found in P. kajii resembles the ischium in Arctotanais and Tanais . Morales-Núñez et al. (2013: fig. 7A) illustrated a similar structure in male P. juliae . There have been no reports of a chelipedal ischium in the superfamily Paratanaoidea , which includes Parakonarus , although this article may be present but has just been overlooked in some paratanaoid species. Instead of the ischium-like structure, it is uncertain about what the oval plate-like structure is.

Figures

Fig. 2. Living male Parakonarus kajii sp. nov. (holotype), dorsal (A) and left (B) views.Insert shows outer view of distal half of left cheliped.

Fig. 3. Parakonarus kajii sp. nov. A, B, holotype, male; C, D, allotype, female. A1–3, body, dorsal views from different angles (at the front of carapace, pereonite 4, and pleotelson, respectively); B, body, right view; b1, ventral keel on pleon, right view; C1–5, body, dorsal views from different angles (at the front of carapace, pereonites 4, 5, 6, and pleotelson, respectively); D, body, left view. Solid lines link same segment.

Fig. 4. Parakonarus kajii sp. nov., holotype, male. A, right antennule, dorsal view; a1, same, article 2 (distal portion) and articles 3–5, ventral view; a2, same, article 12 (distal portion) and article 13, dorsal view; B, right antenna, outer view; C, maxillipeds, ventral view; D, right cheliped, inner view; d1, same, outer view. †, inner oval plate-like structure; ‡, inner elongate plate-like structure.

Fig. 5. Parakonarus kajii sp. nov., holotype, male. A–F, right pereopods 1–6, outer view; a1, b1, c1, inner, ventrodistal tiny spiniform seta on merus of pereopods 1–3, respectively; d1, inner spiniform seta in ventrodistal region of pereopod-4 propodus, outer view, outer spiniform seta omitted; d2, pereopod-4 dactylus-unguis, outer view; G, right pleopod 1, posterior view, most setal ornamentation omitted; g1, same, endopod, posterior view, most setal ornamentation omitted; H, right uropod, dorsal view.

Fig. 6. Parakonarus kajii sp. nov., allotype, female. A, left antennule, ventral view; B, left antenna, inner ventral view; C, labrum, anterior view; D, E, left and right mandibles, respectively; F, left labium; G, right maxillule; g1, same, distal portion of endite; H, maxillipeds, ventral view, left palp and right palpal articles 3 (distal half) and 4 omitted (palp artificially bent 180 degrees at arrowed point); h1, same, right palpal articles 3 and 4, dorsal view; I, right epignath; J, left cheliped, outer view; j1, same, distal half, inner view.†, inner oval plate-like structure.

Fig. 7. Parakonarus kajii sp. nov., allotype, female. A–F, left pereopods 1–6, outer view; d1, tubercle-mounted seta; d2, serrated spiniform seta; G, left pleopod 1, anterior view, most setae on endopod and most setal ornamentation omitted; g1, same, endopod, anterior view, most setal ornamentation omitted; H, left uropod, ventral view.

Fig. 1. Map showing the global distribution of Konariinae. Arrowhead, Sotopanari Island. Based on data from G. O. Sars (1882), Dollfus (1898), Stebbing (1905), Smith (1906), Lang (1973), Băcescu (1977), Riggio (1996), Bamber (2005, 2006, 2008, 2013), Bird (2011), Araújo- Silva and Larsen (2012), Błażewicz-Paszkowycz and Bamber (2012), Edgar (2012), Morales-Núñez et al. (2013), Bamber and Marshall (2015), Guţu (2016), and this study. The map and plots (except the insert) were generated with GMT5 software (Wessel et al. 2013). The raw data for the plots are available in the figshare repository (Kakui 2018).