Alloleptochelia falciformes, Tzeng & Wei & Ma & Li, 2023

Tzeng, You-Wei, Wei, Chih-Lin, Ma, Lin & Li, Xinzheng, 2023, Three new species of Paratanaoidea (Crustacea, Tanaidacea) from the South China Sea, Zootaxa 5375 (1), pp. 1-30 : 4-13

Alloleptochelia falciformes sp. nov.

Figs 2–6 , Table 1

Material examined. Holotype: non-ovigerous female ( NMNS8568-01 ), body length 1.8 mm, completely dissected and body parts preserved in 75% alcohol, Dongsha Atoll (20°43’31.6”N, 116°47’52.7”E), the South China Sea, from bottom sand of a patch of coral reef at a depth of 10 m, 16 September 2017.

Allotype: male ( NMNS8568-02 ), body length 1.7 mm, completely dissected and body parts preserved in 75% alcohol, Dongsha Atoll (20°42’29.9”N, 116°52’54.6”E), the South China Sea, from bottom sand of a patch of coral reef at a depth of 5 m, 16 September 2017.

Paratypes: non-ovigerous female ( NMNS8568-03 ), body length 1.3 mm, same collection data as allotype; postovigerous female ( NMNS8568-04 ), body length 1.0 mm, Dongsha Atoll (20°38’03.1”N, 116°49’30.5”E), the South China Sea, from bottom sand of a patch of coral reef at a depth of 5 m, 12 September 2017 .

Other material: male ( MBM287441 ), body length 1.8 mm, Linchang Reef (19°55’08.0”N, 109°27’26.9”E), Hainan, intertidal, washing from algae turf, 2 April 2019; non-ovigerous female ( MBM287442 ), body length 1.8 mm, same collection data as MBM287441; non-ovigerous female ( MBM287443 ), body length 2.0 mm, same collection data as MBM287441 .

Diagnosis. Female: Body about 5.3 times longer than wide. Carapace about 1.2 times longer than wide. Antennule four-articled with distinct distal cap-like segment, article-4 with one distal aesthetasc. Antenna article- 2 with one dorsodistal and one ventrodistal seta; article-3 with one thickened dorsodistal seta. Maxillule endite with eleven distal spiniform setae. Maxilliped endite with two larger and one smaller linguiform spiniform setae. Cheliped merus with two ventral setae; carpus without dorsal spinules. Pereopod-1 merus with one ventrodistal seta but without dorsodistal seta; carpus with four subdistal setae. Pereopods 2–3 basis dorsal margin with one especially long (longer than merus) seta on proximal half. Pereopod-6 propodus dorsal margin with a row of seven subdistal serrated setae. Male: Body about 4.3 times longer than wide. Carapace pear-shaped, about 1.2 times longer than wide; anterior margin flat, without conspicuous rostrum. Pereonites 1–3 short, combined shorter than carapace. Antennule shorter than body; flagellum six to seven-articled, each article with two distal aesthetascs except the last two articles. Antenna articles 2–3 both with one dorsodistal seta. Cheliped as long as body; merus with two ventral setae; carpus with five dorsal setae; propodus fixed finger without apophysis; dactylus incisive margin with five spinules. Pereopod-1 merus with one dorsodistal seta but without ventrodistal seta; carpus with four subdistal setae. Pereopods 4–6 dactylus and unguis without distinct demarcation, long falciform. Pereopod-6 propodus dorsal margin with a row of five subdistal serrated setae.

Description (some characters stated in genus or species diagnosis not included). Non-ovigerous female (holotype): Habitus ( Fig. 2A , 3A ) 1.8 mm long. Carapace 0.2 times as long as body; rostrum inconspicuous; lateral margin with one pair of anterior and one pair of middle setae. Eye lobe with visual elements. Pereon 0.6 times as long as body; pereonites 1–5 0.4, 0.5, 0.5, 0.7, 0.7 times as long as wide, respectively, each with two pairs of lateral setae; pereonite-6 0.5 times as long as wide, with one pair of lateral setae. Pleon 0.2 times as long as body; each pleonite with similar length, 0.2–0.3 times as long as wide, pleonite-1 with one pair of lateral setae, pleonite-2 with two pairs of lateral setae, pleonites 3–5 each with three pairs of lateral setae. Pleotelson semicircular, posterior margin with one pair of setae and one pair of broom setae.

Antennule ( Fig. 3C ) article-1 0.6 times as long as antennule 2.9 times longer than wide, inner margin with one middle and one distal seta, outer margin with one middle and one distal long seta, and seven broom setae; article-2 0.3 times as long as article-1, distal margin with one inner and one outer seta; article-3 as long as article-2, naked; article-4 0.8 times as long as article-3, with two distal setae and one distal aesthetasc; distal segment very short, cap-like, with four distal setae and one distal broom seta.

Antenna ( Fig. 3E ) article-1 naked; article-2 1.2 times longer than wide, with one dorsodistal, one ventrodistal and one inner seta; article-3 0.6 times as long as article-2 0.8 times as long as wide, with one strong dorsodistal seta; article-4 3.1 times longer than article-3 3.5 times longer than wide, with three distal setae and four distal broom setae; article-5 0.6 times as long as article-4 3.5 times longer than wide, with one distal seta and one distal broom seta; article-6 very short, cap-like, with five distal setae.

Labrum ( Fig. 3G ) typical, covered with setules. Left mandible ( Fig. 3H ) lacinia mobilis with four anterior denticles; incisor with two anterior denticles; molar typical. Right mandible ( Fig. 3I ) incisor bifurcate; anterior margin crenulate; molar typical. Labium ( Fig. 4A ) typical, antero-outer corner covered with denser setules. Maxillule ( Fig. 4B ) endite distal half covered with denser setules, with eleven distal spiniform setae; palp not examined. Maxilliped ( Fig. 4C ) basis with four to five long inner distal setae; endite ( Fig. 4D ) distal margin with one seta, two larger and one smaller linguiform spiniform setae, inner margin with two long coupling hooks; palp article-1 naked, article-2 with four inner and one outer setae, article-3 with eight inner setae, article-4 with one outer seta, outer distal corner conspicuously concave, with two setae, distal margin with five setae.

Cheliped ( Fig. 4E ) coxal sclerite triangular, with one seta on posterior corner; basis 1.3 times longer than wide, with one outer seta; merus with two ventral setae; carpus 1.5 times longer than basis 1.9 times longer than wide, with one longer subdistal seta and three very short setae along dorsal margin, ventral margin with three setae on distal half; propodus palm 0.6 times as long as carpus 1.6 times longer than wide, inner setal row with three setae, outer surface with one distal seta between dactylus and fixed finger, fixed finger 0.6 times as long as palm twice as long as wide, with one ventral and one outer seta, incisive margin crenulate, with three setae; dactylus curved, 1.4 times longer than fixed finger 3.1 times longer than wide, inner surface with one dorsoproximal seta.

Pereopod-1 ( Fig. 4F ) coxa with one seta; basis 3.6 times longer than wide, dorsal margin with one simple seta and one broom seta on proximal half; ischium with one ventral seta; merus 0.4 times as long as basis 1.8 times longer than wide, ventral margin with one subdistal seta; carpus slightly longer than merus twice as long as wide, with two dorsal, one inner and one ventral subdistal setae; propodus 1.6 times longer than merus 3.8 times longer than wide, with two dorsal and one ventral subdistal seta; dactylus plus unguis slender and curved, 1.2 times longer than propodus.

Pereopod-2 ( Fig. 4G ) coxa with one seta; basis three times longer than wide, dorsal margin with one long seta (longer than merus) and two broom setae on proximal half; ischium with two ventral setae; merus 0.3 times as long as basis 1.4 times longer than wide, with one ventrodistal spiniform seta; carpus 1.2 times longer than merus 1.7 times longer than wide, with one dorsal and two inner subdistal setae, ventral margin with one subdistal spiniform seta; propodus 1.6 times longer than carpus 3.2 times longer than wide, dorsal margin with one subdistal seta, inner surface with one subdistal seta, ventral margin with one subdistal spiniform seta, dactylus plus unguis 0.4 times as long as propodus, with one middle transversal row of setules.

Pereopod-3 ( Fig. 4H ) very similar to pereopod-2 but basis with one less broom seta, propodus with one less subdistal seta.

Pereopod-4 ( Fig. 5A ) basis 2.5 times longer than wide, naked; ischium with two ventral setae; merus 0.4 times as long as basis 1.8 times longer than wide, with two ventrodistal spiniform setae; carpus as long as merus 1.6 times longer than wide, distal margin with one dorsal seta, one inner and two outer bifurcated spiniform setae; propodus 1.2 times longer than carpus three times longer than wide, dorsal margin with one subdistal spinule and three distal serrated setae, ventral margin with two subdistal spiniform setae; dactylus and unguis not fused, together 0.7 times as long as propodus.

Pereopod-5 ( Fig. 5B ) very similar to pereopod-4 but basis with one ventral broom seta.

Pereopod-6 ( Fig. 5C ) similar to pereopod-5 but basis ventral margin with one more subdistal seta, propodus dorsal margin with seven distal serrated setae.

Pleopod-1 ( Fig. 5D ; all setae circumplumose, setules omitted in figure) peduncle with one inner circumplumose seta; exopod with 20 outer circumplumose setae; endopod with twelve outer circumplumose setae, inner margin with one middle circumplumose seta.

Uropod ( Fig. 5E ) peduncle naked; exopod two-articled, article-1 with one distal seta, article-2 with two long distal setae; endopod six-articled, articles 1–2 both with two subdistal setae, article-3 and 5 both with one distal seta, article-4 with one distal seta and two distal broom setae, article-6 with four distal setae and two distal broom setae.

Variations. The maxilliped of the holotype female (NMNS8568-01) has four long distal setae on the left part of the basis and five on the right.

Male (allotype): Habitus ( Fig. 2B , 3B ) dorsoventrally flattened, 1.7 mm long, 4.3 times longer than wide. Carapace 0.2 times as long as body; lateral margin with one pair of middle setae. Pereon half as long as body; pereonites 1–3 short, 0.3 times as long as wide, each with one pair of anterolateral setae and one pair of posterolateral setae; pereonites 4–6 0.5, 0.5, 0.4 times as long as wide, respectively, each with one pair of middle setae on lateral margin. Pleon 0.3 times as long as body; each pleonite 0.2–0.3 times as long as wide, with three pairs of lateral setae. Pleotelson 0.4 times as long as wide, posterior margin with two pairs of setae and one pair of broom seta.

Antennule ( Fig. 3D ) 0.7 times as long as body; peduncle article-1 0.4 times as long as antennule, 1.2 times longer than carapace, inner margin with one distal seta, outer margin with one subproximal seta, two distal setae and two distal broom setae, article-2 0.3 times as long as article-1, inner margin with one subdistal seta, outer margin with one distal seta and two distal broom setae, article-3 0.7 times as long as article-2, distal margin with one inner and one outer seta; flagellum about 0.8 times as long as peduncle article-1, last article very short, cap-like, with three distal setae and one distal broom seta, next-to-last article with one distal seta and one distal aesthetasc on inner margin, the remaining articles each with two distal aesthetascs on inner margin.

Antenna ( Fig. 3F ) six-articled; article-1 naked; article-2 1.2 times longer than wide, distal margin with one dorsal broom seta, one dorsal and one inner seta, outer surface with one seta; article-3 0.6 times as long as article-2 0.8 times as long as wide, with one dorsodistal seta; article-4 3.5 times longer than article-3 3.2 times longer than wide, with two subdistal setae and four subdistal broom setae, dorsal margin with one middle broom seta; article-5 0.8 times as long as article-4 4.7 times longer than wide, with one distal seta and one distal broom seta; article-6 very short, cap-like, with five distal setae.

Mouthparts reduced; rudimentary maxilliped and epignath not examined.

Cheliped ( Fig. 6A ) long and slender; coxal sclerite triangular, with one seta on posterior corner; basis 1.5 times longer than wide, naked; merus triangular, 0.7 times as long as basis 1.6 times longer than wide, with two ventral setae; carpus slightly longer than antennule peduncle 3.8 times longer than basis 7.2 times longer than wide, with five dorsal and two ventral setae; propodus palm 3.1 times longer than wide, inner setal row with 13 setae, outer surface with one distal seta between dactylus and fixed finger, fixed finger 1.3 times longer than palm, with two ventral setae on distal half, incisive margin with three setae on distal half; dactylus 1.2 times longer than fixed finger, with five spinules along incisive margin.

Pereopod-1 ( Fig. 6B ) coxa with one seta; basis long and thin, 5.4 times longer than wide, dorsal margin with one seta and one broom seta on proximal half; ischium with one ventral seta; merus 0.4 times as long as basis 2.6 times longer than wide, dorsal margin with one subdistal seta; carpus slightly longer than merus three times longer than wide, dorsal margin with two subdistal setae, ventral margin with two subdistal setae; propodus long, 1.7 times longer than carpus 5.5 times longer than wide, ventral margin with one subdistal spiniform seta; dactylus plus unguis slender and curved, 0.9 times as long as propodus, unguis half as long as dactylus.

Pereopod-2 ( Fig. 6C ) very similar to that of female in setal and spinal pattern but basis relatively longer and with shorter seta; carpus, propodus and dactylus also relatively longer.

Pereopod-3 ( Fig. 6D ) very similar to that of female in setal and spinal pattern but basis relatively longer and with shorter seta; carpus, propodus and dactylus also relatively longer.

Pereopod-4 ( Fig. 6E ) 3.7 times longer than wide, dorsal margin with three middle broom setae, ventral margin with two middle broom setae; ischium with two ventral setae; merus 0.4 times as long as basis 2.2 times longer than wide, with one dorsodistal seta, ventral margin with two subdistal spiniform setae; carpus slightly shorter than merus, 2.8 times longer than wide, distal margin with two dorsal setae, two outer and two inner spiniform setae; propodus 1.5 times longer than carpus 4.8 times longer than wide, dorsal margin with spinules and three subdistal serrated setae, ventral margin with two long and slender subdistal spiniform setae; dactylus and unguis combined 0.7 times as long as propodus.

Pereopod-5 ( Fig. 6F ) very similar to pereopod-4 but basis naked.

Pereopod-6 ( Fig. 6G ) very similar to pereopod-5 but basis dorsal margin with one middle broom seta, ventral margin with one middle broom seta and one subdistal seta, propodus with five serrated setae.

Pleopods (not figured) similar to those of female.

Uropod (5H) most setae very long; peduncle with six distal setae; exopod two-articled, article-1 with one distal seta, article-2 with two distal setae; endopod six-articled, articles 1, 2, 3, 5 and 6 with eight, four, two, one and four distal setae, respectively, article-4 with three distal setae and two distal broom setae.

Variations. The allotype male ( NMNS8568-02 ) possesses a seven-articled flagellum on its left antennule and six on its right .

Etymology. The name is from the Latin falciformis referring to the long falciform dactylus on male pereopods 4–6.

Type locality. Dongsha Atoll, the South China Sea.

Distribution. It is only known from the South China Sea and Hainan.

Remarks. The new species, A. falciformes sp. nov., exhibits the most stout body among the congeners. The female and male bodies are approximately 5.3 times and 4.3 times longer than wide, respectively, which is significantly less than the range provided in the generic diagnosis by Guţu (2016: 100). Additionally, several other characteristics of the new species do not align with the original generic diagnosis (ibid: 100–101): 1) having a pear-shaped carapace with a flat anterior margin and an inconspicuous rostrum in males, resembling those of the Leptochelia species ( Guţu 2016: 30); 2) having only two setae on the cheliped merus in both sexes (three or more setae in the diagnosis); 3) having only ventrodistal seta on the pereopod-1 merus in the female, and only dorsodistal seta the in male (both ventrodistal and dorsodistal seta present in both sexes in the diagnosis; Figs 2B , 3B , 4E, F , 6A, B ). However, such discrepancies are not exclusive to the Alloleptochelia species. For instance, A. evansi also exhibits only two setae on the cheliped merus and only dorsodistal seta on the pereopod-1 merus of the male ( Edgar 2012: 12, figs 6, 7; Table 1 ). Similarly, A. helenae has a naked pereopod-1 merus in females, and A. multiarticulata also possesses only a dorsodistal seta on the pereopod-1 merus in males ( Guţu 2011: 46, fig 2; Bamber 2006: 15, fig 6; Table 1 ). Apart from those few inconsistencies, the features of A. falciformes largely conform to the generic diagnosis.

A. falciformes is geographically closest to A. longimana ( Shiino, 1963) and also shares some morphological similarities. The males of the two species both possesses a pear-shaped carapace, a similar number of antennule flagellum articles, and long falciform dactylus on pereopods 4–6. Nevertheless, the new species can be readily distinguished from A. longimana by the following male features: 1) shorter antennules compared to the body (versus antennules longer than the body in A. longimana ), 2) chelipeds as long as the body (versus twice as long as the body in A. longimana ), and 3) smooth fixed finger without apophysis or denticles (versus proximal denticles present in A. longimana ; Shiino 1963: figs 24A, E, 25A, B, H, I; Figs 2B , 3B, D , 6A, E–G ; Table 1 ).

Among Alloleptochelia species, A. falciformes shares most morphological features with the more distant Australian A. evansi .As mentioned above, both of them have only two setae on the cheliped merus and one dorsodistal seta (without a ventrodistal seta) on the pereopod-1 merus in males. Moreover, both species bear a smooth cheliped fixed finger and the pereopods 4–6 dactylus is partially fused with unguis in males. However, the stout body of the males distinguishes the new species from A. evansi , whose males have the most slender body (ten times longer than wide) in the genus. Other differences include fewer articles on the antennule flagellum and relatively longer pereopods 4–6 dactylus (combined with unguis) in the males of the new species compared to the males of A. evansi ( Edgar 2012: figs 6, 7; Figs 2B , 3B, D , 6A, B, E–G ; Table 1 ).

Regarding the female characters, A. falciformes exhibits two distinct features that are unique among its congeners: 1) having only a ventrodistal seta on the pereopod-1 merus; 2) possessing a conspicuously long seta (longer than the merus) on the proximal half of the dorsal margin of pereopods 2 and 3 ( Figs 4F–H ; Table 1 ).

Figures

FIGURE 2. Alloleptochelia falciformes sp. nov. specimens (ethanol-preserved), photo by You-Wei Tzeng: A, holotype female (NMNS8568-01), dorsal view; B, allotype male (NMNS8568-02), dorsal view.

FIGURE 3. Alloleptochelia falciformes sp. nov. Holotype (NMNS8568-01), female: A, body dorsal view; C, right antennule; E, right antenna (outer view); G, labrum; H, left mandible; I, right mandible. Allotype (NMNS8568-02), male: B, body dorsal view; D, right antennule; F, right antenna (outer view).

FIGURE 4. Alloleptochelia falciformes sp. nov. Holotype (NMNS8568-01), female:A, labium; B, maxillule; C, maxilliped; D, maxilliped endite; E, left cheliped; F–H, right pereopods 1–3.

FIGURE 5. Alloleptochelia falciformes sp. nov. Holotype (NMNS8568-01), female: A–C, right pereopods 4–6; D, right pleopod-1 (all setae circumplumose, setules omitted); E, right uropod.

FIGURE 6. Alloleptochelia falciformes sp. nov. Allotype (NMNS8568-02), male: A, left cheliped; B–C, right pereopods 1–2; D, left pereopod-3; E–G, right pereopods 4–6; H, left uropod.