Cymonomus cognatus, Ahyong & Ng, 2017

Ahyong, Shane T. & Ng, Peter K. L., 2017, Zavreliella undetermined, Zoological Studies (Zool. Stud.) 56 (24), pp. 1-20 : 4-7

Cymonomus cognatus sp. nov.

( Figs. 2 , 7B, C )

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Cymonomus quadratus andamanicus . - Sakai 1976: 37, pl. 8: fig. 1.

Cymonomus sp. 1 [ C. quadratus andamanicus Alcock, 1905 sensu Sakai 1976 ]. - Nagai 1994: 51, pl. 1, fig. 6.

Cymonomus sp. 2 . - Nagai 1994: 51, pl. 1, fig. 7.

Cymonomus andamanicus . - Ahyong et al. 2009: 179-180 (part), fig. 134.

Type material: HOLOTYPE: NTOU, male (cl 7.2 mm, pcl 6.4 mm, cw 7.0 mm), E of Su-Ao, Taiwan, 24°28.59'N, 122°12.66'E, 490-1027 m, TAIWAN 2003, stn CP214, RV Ocean Researcher 1, 27 August 2003.

Other material examined: JAPAN: WPMNH #45, 1 female (cl 6.8 mm, pcl 6.1 mm, cw 7.3 mm), Kumano Sea, trawl, 300 m, 1978.

SOUTH CHINA SEA, SE OF MACCLESFIELD BANK: ZRC, 1 spent female (cl 6.5 mm, pcl 5.9 mm, cw 6.4 mm), summit of V bis Seamount, 15° 04.3820 -05.1589 'N, 116° 31.1860 -32.4237 'E, 534-552 m, hard rocky bottom, NanHai 2014, stn DW4100, 1 January 2014; ZRC, 1 male (damaged, pcl 5.4 mm, cw 5.6 mm), 1 ovigerous female (cl 8.3 mm, pcl 7.5 mm, cw 7.9 mm), V bis seamount, 15° 04.5841 -03.3720 'N, 116° 31.5257 -31.2470 'E, 339-533 m, hard rocky bottom, NanHai 2014 stn DW4102, 2 January 2014; AM P100611, 1 ovigerous female (cl 10.1 mm, pcl 9.2 mm, cw 9.9 mm), NanHai 2014 stn DW4102.

Description of holotype: Carapace quadrate, almost square, lateral margins gently divergent posteriorly; regions weakly indicated; with 1-3 small anteriorly directed anterolateral spines in addition to other surface ornamentation; lower pterygostomian region swollen; surfaces sparsely setose; carapace slightly more inflated in females than males. Dorsal and lateral surfaces entirely covered with minute granules, with granules becoming larger and more elongate anterolaterally. Fronto-orbital margin (excluding rostrum and lateral projections) advanced slightly beyond anterolateral margins; exceeding half anterior carapace width (about 0.6); outer orbital processes, pointed, directed anteriorly, situated below plane of rostrum, laterally spinulate or granulate, reaching midlength of rostrum. Rostrum small, about half-length of eyestalks; 0.10-0.11 pcl; triangular, apex acute, margins concave, minutely granular laterally and dorsally. Eyestalks distinctly divergent, flattened, stout, width at midlength exceeding one-third length, fused to carapace below rostral base but demarcated from frontal margin; reaching anteriorly beyond midlength of antennular peduncle article 1; minutely granular; cornea apparently vestigial, not pigmented. Epistome with blunt tubercle mesial to base of antennules, small spine mesial to base of antenna, with pointed tubercle flanked by small granules at base of rostrum.

Antennular peduncle 0.98-1.00 pcl (male), 0.80-0.88 pcl (female); articles minutely granular. Basal antennal article fused to epistome; articles 2-4 irregularly granular or spinular; article 5 minutely granular.

Maxilliped 3 ischiobasis subquadrate, surface sparsely granular, spinular distally, with longitudinal sublateral groove; ischium and basis demarcated by faint groove. Merus shorter than ischiobasis, length twice width; tapering distally to rounded apex; surface sparsely granular or spinulate; margins spinulate. Dactylus, propodus and carpus spinulate or coarsely granulate. Exopod sparsely granular, reaching beyond carpo-meral articulation but not exceeding merus of endopod.

Chelipeds (pereopod 1) equal in size and ornamentation, sparsely setose. Merus finely granular, with occasional longer spinules. Carpus finely granular, dorsal margin with 3 or 4 spines, 1 distinctly longer. Palm surfaces with fine granules and few scattered acute granules, flexor and extensor margins irregularly spinulate. Dactylus longer than upper palm length; proximal dorsal two-thirds with spines and granules; with faint longitudinal carina on outer surface, occlusal surfaces of dactylus and pollex crenulate, without gape when fingers closed.

Pereopods 2 and 3 sparsely setose; all articles finely granular; propodus, carpus and merus with serrated granules and scattered spinules on extensor margins. Pereopod 3 longest; merus 1.01-1.11 pcl (male), 0.89-0.98 pcl (female). Dactyli broadly curved, finely granular, with longitudinal rib, though slightly less distinct proximally; sparsely setose. Pereopod 3 dactylus about as long as combined length of propodus and carpus.

P e r e o p o d s 4 a n d 5 m i n u t e l y g r a n u l a r, sparsely setose; longer than merus of pereopod 3; dactyli markedly shorter than propodi, falcate, with corneous apex and 4 or 5 obliquely inclined, corneous spines on flexor margin. Pereopod 5 merus, when folded against carapace, reaching anterior one-third of carapace.

Thoracic sternite 3 pentagonal, about 1.6 × wider than long; lateral margins divergent posteriorly, surface granulate. Margins of sternites 4 and 5 granulate.

Abdomen with margins and surface finely granular or minutely spinulate; telson immovably fused to abdominal somite 6 forming pleotelson; demarcation indicated by notch in lateral margins and shallow, complete or near complete transverse groove in males, by distinct, complete transverse groove in females; telson proportions similar in both sexes, width twice length, apex broadly rounded.

Gonopod 1 distal article cannulate, forming copulatory tube, with long distal setae. Gonopod 2 with articles fused, L-shaped; distomesial margin slightly hollowed, apex acute.

Etymology: The specific name, cognatus, Latin , meaning related or kindred, alludes to the strong similarities between the new species and its regional congeners C. diogenes and C. delli .

Remarks: Ahyong et al. (2009) reported Cymonomus cognatus sp. nov. from Taiwan, provisionally as C. andamanicus Alcock, 1905 . Cymonomus cognatus belongs to the C. delli group, an assemblage of species within the genus characterised by: a small, triangular rostrum that is distinctly shorter than the eyestalks; short, stout, relatively broad, ventrally flattened eyestalks; a relatively swollen carapace with a finely granular surface and margins, rounded anterolateral and slightly divergent lateral margins; and a pleotelson with a partial to full demarcation between abdominal somite 6 and the telson (yet to be confirmed in C. andamanicus ). This group includes C. andamanicus Alcock, 1905 (Andaman Sea), C. cubensis Chace, 1940 (Caribbean Sea), C. delli Griffin and Brown, 1976 (southern Australia), and C. diogenes Ahyong and Ng, 2009 (southern Philippines). It should be noted that C. cubensis and C. delli were previously placed in Cymonomoides Tavares, 1993a , together with C. guinotae Tavares, 1991 (type species; Brazil) and Cymonomoides fitoi Lemaitre and Bermúdez, 2000 (Caribbean Sea) on the basis of the 7-segmented abdomen. Members of the C. delli group, however, do not appear to be closely related to the type species of Cymonomoides , differing in rostral (well-developed versus obsolete) and eye form (short, broad and stout versus slender, elongate). The clear demarcation of the telson from somite 6 in Cymonomoides and some members of the C. delli group is most parsimoniously interpreted as plesiomorphic. Moreover, the demarcation between the telson and abdominal somite 6 in species of the C. delli group varies from mere notches in the lateral margins to a distinct groove across the pleotelson making the taxonomic effectiveness of this feature questionable ( Ahyong and Ng 2009). Pending further study, Cymonomoides is restricted to the American C. guinotae and C. fitoi .

Cymonomus cognatus appears to be morphologically closest to C. delli from southern Australia and C. diogenes from the Philippines. Cymonomus cognatus resembles C. delli in having similar walking leg morphometrics, but is distinguished by proportionally more elongate antennular peduncles (1.0 pcl in males, 0.8-0.9 pcl in females versus 0.9 pcl in males, 0.7-0.8 pcl in females), a narrower thoracic sternite 3 (width 1.6 × length versus 1.8 × length; Fig. 2E ), and in the slightly greater fronto-orbital width (0.6 × anterior carapace width or greater versus about half; Fig. 1A ). Cymonomus cognatus resembles C. diogenes in fronto-orbital proportions (0.6 carapace width or greater) ( Fig. 2A ) and length of the maxilliped 3 exopod (reaching distally beyond the mero-carpal articulation; Fig. 2D ), but differs in the shorter pereopod 3 merus (1.0-1.1 pcl versus 1.4 pcl in males; 0.9-1.0 pcl versus 1.1-1.2 in females) and the presence of a longitudinal rib on the pereopod 2 and 3 dactyli (rib absent in C. diogenes ). The new species resembles C. andamanicus in the similar fronto-orbital width and thoracic sternite 3 proportions, but differs in having a longer maxilliped 3 exopod, reaching distally beyond the mero-carpal articulation ( Fig. 2D ) versus reaching almost to level of mero-carpal articulation ( Alcock et al. 1907: pl. 79 fig 2a). Additionally, C. cognatus possesses anterolateral spines (which C. andamanicus apparently lacks).

The specimens of C. cognatus from the South China Sea comprise females and one damaged male. The male corresponds well to the holotype, though the transverse groove demarcating the telson from abdominal somite 6 is more distinct than in the holotype. In the holotype, the groove separating the telson from somite 6 is shallow and indistinct, especially medially. In the South China Sea male, the groove is also shallow, though defined throughout its length. In females, the pleotoelson groove is well-defined.

Nagai (1994) reported female C. cognatus from southeastern Japan, from the Kumano Sea (~ 300 m depth) as “ Cymonomus sp. 1 ”, and males off Shionomisaki (~ 400 m depth) under the name “ Cymonomus sp. 2 ”. The dry female specimen from the Kumano Sea is damaged, lacking chelipeds, pereopods 3-4 and the abdomen, but what remains agrees well with C. cognatus . The specimen figured and reported by Sakai (1976: pl. 8 fig. 1) as C. andamanicus from Mimase, Tosa Bay, at 250 m depth, corresponds in all respects to C. cognatus

Distribution: Southern Japan and Taiwan to Macclesfield Bank, South China Sea; 250 to 490- 1027 m.

Figures

Fig. 2. Cymonomus cognatus sp. nov. A-I: male holotype, cl 7.2 mm, pcl 6.4 mm, cw 7.0 mm, E of Su-Ao, Taiwan, stn CP214 (ZRC 2014.0159); J: male, pcl 5.4 mm, cw 5.6 mm, SE of Macclesfield Bank, stn DW4102 (ZRC); K: ovigerous female, cl 10.1 mm, pcl 9.2 mm, cw 9.9 mm, SE of Macclesfield Bank, stn DW4102 (AM P100611). A, dorsal habitus; B, fronto-orbital region; C, right basal antennal spine; D, right maxilliped 3; E, thoracic sternite 3; F, abdominal somites 4-5 and pleotelson. G, right gonopod 1, abdominal view; H, right gonopod 2, abdominal view; I-K, pleotelson. Scale bars: A, F, K = 2.0 mm; B = 1.3 mm; C = 0.5 mm; D, E, G, H-J = 1.0 mm.

Fig. 7. A, Cymonomus chani sp. nov., female holotype, pcl 7.9 mm, SW of Kaohsiung, Taiwan, NTOU; B, Cymonomus cognatus sp. nov., male holotype, pcl 6.4 mm, E of Su-Ao, Taiwan, NTOU; C, Cymonomus cognatus sp. nov., spent female, pcl 9.2 mm, SE of Macclesfield Bank, stn DW4102, AM P100611; D, Cymonomus curvirostris Sakai, 1965, ovigerous female, pcl 3.3 mm, off Miura, Sagami Bay, Japan, CBM (specimen not examined); E, Cymonomus deforgesi Ahyong and Ng, 2009, male, pcl 5.5 mm, SW of Dongsha, stn CP4132, ZRC. Photos: A, B, C, E (T.Y. Chan), D (T. Komai).

Fig. 1. Cymonomus chani sp. nov. A-F: female holotype, cl 8.7 mm, pcl 7.9 mm, cw 9.0 mm, SW of Kaohsiung, Taiwan, CP362 (NTOU); G: female paratype, cl 9.1 mm, pcl 8.3 mm, cw 9.5 mm, NE of Su-Ao, Taiwan, stn CP61 (ZRC 2004.0761); H: female, cl 8.1 mm, pcl 7.5 mm, cw 8.3 mm, Japan (NSMT Cr16341). A, dorsal habitus; B, fronto-orbital region; C, right basal antennal lobe; D, right maxilliped 3; E, thoracic sternite 3; F, abdomen, posterior; G, H, telson. Scale bars: A, F-H = 2.0 mm; B = 1.3 mm; C = 0.6 mm; D, E = 1.0 mm.