Naxioides sahulensis, Manikandan & Megalaa & Valliappan & Nandini & Rani & Dakshinamurthi & Nagappan, 2022

Manikandan, K, Megalaa, N, Valliappan, Subramanian, Nandini, K, Rani, Lourdu V, Dakshinamurthi, Senthil & Nagappan, Nagappan, 2022, Crabs (Crustacea, Decapoda) from the Seas of East and Southeast Asia Collected by the RV Hakuhō Maru (KH- 72 - 1 Cruise) 3. Sahul Shelf, Bulletin of the National Museum of Nature and Science. Series A, Zoology 48 (2), pp. 35-83 : 49-52

Naxioides sahulensis sp. nov.

( Fig. 7)

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Material examined. RV Hakuhō Maru KH-72-1 cruise, sta. 32, 1 $(holotype), ( CB 10.6 mm excluding lateral spines× PCL 13.8 mm excluding intestinal spine), NSMT-Cr 30722.

Comparative material examined. Naxioides tenuirostris (Haswell, 1880) . Queensland, Australia: N end Albany Passage, Cape York, dredged, August–September 1928, 3 ƏƏ (8.5× 11.8 mm – 14.7× 20.5 mm), 3 juv. $$ (9.0× 13.6 mm – 12.0× 17.7 mm), 1 spent $ (12.1× 18.4 mm), 1 ovig. $ (14.1× 19.6 mm), AM P13491 ; lRamaz trawl sta. 1541, 10 November 1964, SE Gulf of Carpentaria, 16°45′40″S, 140°13′35″E, 29 m, 1Ə (13.0× 19.5 mm), 1 juv. $ (14.7 × 21.7 mm), AM P18589 ; FNQ 79-49, 3 miles E of Turtle Head , Island, Cape York, 10°55′S, 142°41′E, 18 m, 15 February 1979, AM P64814 , 1 juv. $ (5.9× 8.9 mm); FNQ 79-50, Cape York, 10°39′S, 142°30′E, 20 m, 15 February 1979, carapace only (10.3× 15.2 mm), AM P64816 .

Description of holotype. Carapace ( Fig. 7A–B) pyriform, surface closely tomentose; gastric, cardiac, branchial, intestinal regions well-demarcated, moderately elevated. Gastric region low, bearing 4 long spines, 11 tubercles; anterior end with 2 acute tubercles just behind basis of pseudorostrum; anterior slope medially with slender spine, low spine on both sides; protogastric spines short, directed anterolaterally; mesogastric spine longest, upright, slightly curving anteriorly, with low acute tubercle on both sides, broad U-shaped row of 3 distinct tubercles anteriorly. Cardiac region conical, dorsally elongated into long slender spine, as high as mesogastric spine. Hepatic region inflated, dorso-subproximal sur- face bearing minute tubercles, lateral surface bearing 2 spines, upper spine longer than lower spine, weakly curved dorsally. Branchial region not markedly inflated, longitudinally with 2 long, slender mesobranchial spines of similar size, small spine anterior to anterior spine, anteromesially with large protuberance mounted with small tubercles; lateral subsurface with 3 short spines of similar size; metabranchial region with small medial spine just anterior to posterolateral carapace margin. Intestinal region elongated posteriorly into large, conical projection, length one-third of PCL. Posterior carapace margin moderately convex, unarmed, not visible in dorsal view.

Pseudorostrum ( Fig. 7A–C) distinctly divergent (ca. 30°), straight in lateral view. Pseudorostral spine slender, length 0.3 of PCL, dorsal surface weakly ridged toward frontal region, bearing short, subdistal spine dorsomesially, tips tapered laterally. Supraorbital eave ( Fig. 7A–B) strongly expanded laterally; anterior angle pro- duced into long, sharp preorbital spine projecting anterodorsally, almost parallel to anterior gastric spine, gently incurved, with pointed apex; antor- bital angle produced into small, acute triangular tooth, directed laterally. Dorsal orbital hiatus rounded. Postocular cup apically bifid; upper postorbital margin generally concave (in dorsal view), proximally with distinct finger-shaped intercalated lobe; lateral wall consisting of 2 triangular lobes divergent anteriorly, upper lobe medially ridged, with tooth; lower postorbital margin sinuous, distally with broad, rounded lobe; distinct tubercle right behind ventral orbital hiatus. Pterygostomian region moderately inflated, armed with 3 strong spines directed ven- trally, second spine largest.

Basal antennal article ( Fig. 7C) narrow, distolateral angle produced anterolaterally into elongated sharp spine, visible in dorsal view; lateral margin generally straight; strong triangular tooth near mid-length, directed anterolaterally, as long as distolateral spine. Antennal articles slender, penultimate article two-thirds of ultimate article in length; flagellum reaching tip of pseudo- rostrum.

Thoracic sternites 1, 2 unarmed, sternite 3 with small spine mesially, sternite 4 occupied with largest spine, sternite 5 with second largest spine mesially, small spine laterally, sternites 6 with 2 tubercles, mesial one larger than lateral one, sternite 7 with low tubercle. Sterno-pleonal cavity not sharply defined.

Pleon ( Fig. 7C) somites demarcated, but functionally fused in somites 3–6, telson; somites 1–6 each armed with large medial spine; somites 3–6 narrowly ridged medially, somites 1–5 laterally armed with 1–5 spines, somite 5 with hard microscopic setae.

Ambulatory legs (P2–5) ( Fig. 7A) slender, much longer than PCL, length decreasing posteriorly. Merus cylindrical, extensor surface termi- nated with strong spine projecting laterally. Carpus slightly compressed laterally, extensor surface depressed. Propodus cylindrical, 1.2, 1.0, and 0.8 as long as merus in P2, P3, P4–5, respectively. Dactylus slightly curved distally, 1.1, 0.9. 0.8 as long as propodus in P2, P3, P4–5, respectively.

Etymology. Named after the Sahul Shelf.

Remarks. Among nine congeneric species of the genus Naxioides , the new species described herein, N. sahulensis , is morphologicially closest to N. tenuirostris (Haswell, 1880) (type locality: Darnley Island, Torres Strait), with which Naxia cerastes Ortmann, 1894 (type locality: Thursday Island, Torres Strait) was synonymized by Griffin and Tranter (1986), known from western to northeastern Australia including the Arafura Sea. Although the holotype female of N. sahulensis is not fully mature, with the left P2, right P4 and both chelipeds missing, two species can be distinguished by the following characteristics that are stable in juveniles through adults of both sexes of N. tenuirostris determined from the specimens examined here (and the detailed account and figures of Griffin (1966a: figs. 2–9) and Griffrin and Tranter (1986): 1) the preorbital spine projects anterodorsally and is subparallel only to the anteriorly inclined anterior gastric spine (versus projecting vertically or inclined posteriorly and subparallel to the upright gastric and cardiac spines in N. tenuirostris ); 2) the protogastric and hepatic spines of both sides are directed anterolaterally (usually directed laterally in N. tenuirostris ); 3) the protogastric spines are similar to the hepatic spines (distinctly longer than the hepatic spines in N. tenuirostris ); 4) the intestinal spine is long and distinct from the posterior carapace margin (versus proximally fused with additional short projection on the posterior carapace margin in N. tenuirostris , although the intestinal spine itself may also be long and slen- der); and 5) the P2 dactylus is as long as its propodus and much longer than its merus (shorter than both propodus and merus in N. tenuirostris ). Also, it is remarkable that the pleon is armed with many strong spines in N. sahuelsns , compared to the smooth or nodular surface in N. tenuirostris .

Distribution. Known only from the Sahul Shelf, the type locality in the Timor Sea, E of Ashmore Reef, 74–78 m depth.