Hyastenus tabolongi, Yan & Lee & Ng, 2019

Yan, Bee, Lee & Ng, Peter K. L., 2019, On the identity of Hyastenus inermis (Rathbun, 1911), and description of a new species from Sulawesi, Indonesia (Crustacea: Decapoda: Majoidea: Epialtidae), Raffles Bulletin of Zoology 67, pp. 490-497 : 495-496

publication ID	https://doi.org/ 10.26107/RBZ-2019-0038
publication LSID	lsid:zoobank.org:pub:02C676DE-6038-4277-A68A-39214E7B7E51
persistent identifier	https://treatment.plazi.org/id/792987CC-FFCB-FFD3-FEFC-04BFFD3CF9B2
treatment provided by	Carolina
scientific name	Hyastenus tabolongi
status	sp. nov.

Treatment

Hyastenus tabolongi View in CoL new species

( Figs. 2G, H View Fig , 3 View Fig , 4 View Fig )

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 View Materials ), 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 View Materials ), North Sulawesi [= Sulawesi Utara], Indonesia, coll. local divers, 2000s GoogleMaps ; 1 juvenile female (5.3 × 3.1 mm) ( ZRC 2019.1326 View Materials ), 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 View Materials ), 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 View Fig ). 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 View Fig ). Cheliped slender; surface smooth ( Fig. 3A, D View Fig ). Ambulatory legs slender; P2 longest ( Fig. 3A, D View Fig ). Male thoracic sternum slightly concave anteriorly; sternites 3, 4 with lateral margin constricted. Male pleon slender, triangular, telson triangular ( Fig. 3B View Fig ). G1 slightly curved, distal tip sharp ( Fig. 2G, H View Fig ).

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 View Fig , 3 View Fig ). The gastric region in H. tabolongi , new species, however, is prominently more swollen ( Fig. 3A, C, D, F View Fig ) (versus distinctly less swollen in H. inermis ; Fig. 1A, C View Fig ); the posterolateral region of the carapace is proportionately narrower ( Fig. 3A, D View Fig ) (versus the posterolateral region of carapace wider in H. inermis ; Fig. 1A View Fig ); the outer margin of the basal antennal article is more constricted ( Fig. 3B, E View Fig ) (versus the outer margin of the basal antennal article is relatively less constricted in H. inermis ; Fig. 1B View Fig ); the chelipeds are proportionately more slender and smooth ( Fig. 3A, D View Fig ) (versus the chelipeds propodus slightly swollen and granulate in H. inermis with; Fig. 1A View Fig ); and the G1 is slightly curved with the distal tip sharp ( Fig. 2G, H View Fig ) (versus G1 straight with ear-like lobe at distal tip in H. inermis ; Fig. 2 View Fig 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 View Fig ). 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 View Fig ). 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. ”