On the identity of Hyastenus inermis (Rathbun, 1911), and description of a new species from Sulawesi, Indonesia (Crustacea: Decapoda: Majoidea: Epialtidae) Author Yan, Bee Author Lee Author Ng, Peter K. L. text Raffles Bulletin of Zoology 2019 2019-10-29 67 490 497 journal article 10.26107/RBZ-2019-0038 2345-7600 4577132 02C676DE-6038-4277-A68A-39214E7B7E51 Hyastenus tabolongi new species ( Figs. 2G, H , 3 , 4 ) Material examined. Holotype : male (10.7 × 6.6 mm ) ( MZB Cru 5010), North Sulawesi [= Sulawesi Utara ], Indonesia , coll. local divers, 2000s . Paratypes : 1 female (12.3 × 7.2 mm ) ( ZRC 2019.1324 ), Poh Poh , Tanahwanko village, North Sulawesi , Indonesia , 1°25.120’N 124°37.788’E , coll. local divers, 5 December 2014 ; 1 ovigerous female (10.6 × 6.6 mm ) ( ZRC 2019.1325 ), North Sulawesi [= Sulawesi Utara ], Indonesia , coll. local divers, 2000s ; 1 juvenile female (5.3 × 3.1 mm ) ( ZRC 2019.1326 ), North Sulawesi [= Sulawesi Utara ], Indonesia , coll. local divers, 2000s ; 1 male (9.8 × 5.7 mm ), 2 female (10.0 × 5.8 mm , 5.0 × 2.7 mm ) ( ZRC 2019.1327 ), North Sulawesi [= Sulawesi Utara ], Indonesia , coll. local divers, 2000s . Diagnosis. Carapace pyriform, regions defined. Pseudorostral spines straight, divergent. Supraorbital eave forming rectangular lobe; preorbital angle rounded, antorbital angle rounded, outer margin slightly constricted; orbital hiatus between supraorbital and postorbital lobes form narrow U-shape; postorbital lobe cup-like. Carapace lacking granules; gastric region prominently swollen; small tubercle on mesogastric region; epibranchial region swollen, slightly arched; cardiac region swollen; intestinal region swollen with 3 slightly swollen areas; 2 on metabranchial region and 1 medially on intestinal region ( Fig. 3A, D ). Antennal flagellum shorter than pseudorostral spine. Basal antennal article longer than broad, distolateral angle of article sharp, outer margin distinctly constricted medially. Pterygostomial region with single granule on outer margin ( Fig. 3B, E ). Cheliped slender; surface smooth ( Fig. 3A, D ). Ambulatory legs slender; P2 longest ( Fig. 3A, D ). Male thoracic sternum slightly concave anteriorly; sternites 3, 4 with lateral margin constricted. Male pleon slender, triangular, telson triangular ( Fig. 3B ). G1 slightly curved, distal tip sharp ( Fig. 2G, H ). Etymology. This species is named after Maxi Tabolong, a senior dive guide who first showed the crab to Andrew Podzorski, who was then able to photograph it over the years. Type locality. North Sulawesi , Indonesia . Remarks. Hyastenus tabolongi , new species , is most similar to H . inermis , with both species completely lacking the lateral branchial spines and possessing a swollen gastric region ( Figs. 1 , 3 ). The gastric region in H . tabolongi , new species , however, is prominently more swollen ( Fig. 3A, C, D, F ) (versus distinctly less swollen in H . inermis ; Fig. 1A, C ); the posterolateral region of the carapace is proportionately narrower ( Fig. 3A, D ) (versus the posterolateral region of carapace wider in H . inermis ; Fig. 1A ); the outer margin of the basal antennal article is more constricted ( Fig. 3B, E ) (versus the outer margin of the basal antennal article is relatively less constricted in H . inermis ; Fig. 1B ); the chelipeds are proportionately more slender and smooth ( Fig. 3A, D ) (versus the chelipeds propodus slightly swollen and granulate in H . inermis with; Fig. 1A ); and the G1 is slightly curved with the distal tip sharp ( Fig. 2G, H ) (versus G1 straight with ear-like lobe at distal tip in H . inermis ; Fig. 2 A–F). Ecology. Andrew Podzorski (pers. comm.) observed and photographed H . tabolongi , new species , from three sites in Indonesia , namely, the islands of Bunaken and Poh Poh, Tombariri in North Sulawesi , and Pulau Molana in Ambon . His many excellent photographs leave no doubt that his specimens are conspecific with the type material of H . tabolongi , new species . Amongst the three sites, the species is frequently observed on the island of Bunaken in North Sulawesi ( Fig. 4 ). Despite this, H . tabolongi , new species , is not commonly observed on the south side and only once on the north side of the Bunaken island. Hyastenus tabolongi , new species , has also been photographed from Poh Poh, Tombariri, North Sulawesi ( 1°25′6.00″N 124°37′48.95″E ). In Ambon , it has also been photographed at Pulau Molana ( 3°39′5.43″S 128°36′53.88″E ). Andrew Podzorski (pers. comm.) notes: “The habitat of this crab is very specialised and to date, absolutely consistent. It is found exclusively on a sparsely branched species of black Epizoanthus illoricatus Tischbierek, 1930 [Hexacorallia: Epizoanthidae ]. The crab places many polyps of Epizoanthus illoricatus all over its body, so much so it is almost impossible to distinguish the crab from the colony ( Fig. 4B ). The only suggestion that a crab is there, is a thickening of the branch. This species of Epizoanthus illoricatus is common across western Indonesia , growing up to 15 cm high, and generally occurs in areas that are influenced by strong currents. The zoanthid can also be found on flat rocky bottoms and on drop-offs. The only locations where the crab lives on the colonies, is on dropoffs, where the zoanthid grows in small hollows or caves on the face of the drop-offs. Here, the colonies are protected from direct currents. Hyastenus specimens have been found from depths of 11 to 30 m , but most often around 20 m . ” Distribution. Currently only known from its type locality, north Sulawesi , and Pulau Molana, Ambon , Indonesia .