Sternostylus investigatoris (Alcock & Anderson, 1899)

Osawa, Masayuki & Higashiji, Takuo, 2019, Two large squat lobsters of the superfamily Chirostyloidea (Crustacea: Decapoda: Anomura) from the Ryukyu Islands, southwestern Japan, with description of a new species of the genus Eumunida Smith, 1883, Zootaxa 4555 (3), pp. 319-330 : 320-321

Sternostylus investigatoris (Alcock & Anderson, 1899)

( Figs. 1 , 2 )

Ptychogaster investigatoris Alcock & Anderson, 1899a: 24 (type locality: Andaman Sea, 741 m).— Alcock & Anderson 1899b: pl. 45 fig. 1 (no record).— Alcock 1901: 281.— Alcock & McArdle 1902: pl. 58 fig. 4 (no record).— Kemp & Sewell 1912: 25.

Chirostylus investigatoris .— Doflein & Balss 1913: 132, figs 1, 2.— Tirmizi 1964: 386, figs 1, 2.

Gastroptychus investigatoris .— Zarenkov & Khodkina 1981: 86, fig. 3.— Baba 1988: 15, fig. 5.— Baba 2005: 213 (synonymies, key).— Baba et al. 2008: 22 (synonymies).— McCallum & Poore 2013: 10, figs 1, 11A.

Material examined. RUMF-ZC-5357, 1 male (pcl 23.5 mm), 2.3 km northeast of Kume Island, Ryukyu Islands, Japan, sluice gate of deep sea water, 612 m, Okinawa Prefectural Deep Sea Water Research Center (Maja, Kumejima, Okinawa), 4 October 2017.

Color ( Fig. 1A ). Body and P1–4 reddish orange in general. Carapace pale pink on anterior gastric and branchial regions and intestinal region. Abdomen pale pink on anterior parts of tergites. Ocular and antennular peduncles reddish orange; cornea black. Antennal peduncle pale red. P2–4 pinkish orange on carpi and propodi.

Distribution. Marcus-Necker Rise in the central Pacific, the Philippines (between Cebu and Leyte), Indonesia (west of Sumatra and Moluccas), Western Australia, Andaman Sea, southwest of India, and the Maldives; 390– 1500 m ( Baba et al. 2008; McCallum & Poore 2013). At present from Kume Island, Ryukyu Islands, southwestern Japan; 612 m.

Remarks. The genus Sternostylus Baba, Ahyong & Schnabel, 2018 includes 12 species worldwide, of which four species are recorded from the Indo-West Pacific ( Baba et al. 2018). In Japanese waters, only S. hendersoni (Alcock & Anderson, 1899) has been recorded from the Kyushu-Palau Ridge ( Baba 1986, as Gastroptychus Caullery, 1896 ).

The specimen examined agrees mostly with the recent description of S. investigatoris in the morphology and fresh coloration ( McCallum & Poore 2013, as Gastroptychus ). The diagnostic morphology of the species includes the following characters (cf. Baba 2005: 213; McCallum & Poore 2013: 150): carapace with prominent spines and interspersed smaller spines, gastric region with prominent spines in hexagonal arrangement with anteromedian spine ( Figs. 1C, D , 2A ); anterior margin of sternite 3 with median ridge anteriorly produced and sloping down in ventral view ( Fig. 2B ); sternite 4 with 2 anterior spines between first lateral spines ( Fig. 2B ); abdomen thickly covered with fine setae, tergites 3 and 4 without spines, pleura of somite 3 each with low, blunt process ( Fig. 1C, D ); and both Mxp 3 close to each other. In the present specimen, the Mxp 3 carpus has a small proximal spine in addition to a dorsodistal spine ( Fig. 2E ), although the proximal spine is not described nor illustrated by McCallum & Poore (2013: fig. 1F) for their material examined.

As reported by McCallum & Poore (2013: fig. 1C) for the north-western Australian material, the present specimen also has small scattered spines on the surface of thoracic sternite 4 ( Fig. 2B ), which are not illustrated by Baba (1988: fig. 5b). The antennal scale is present but rudimentary ( Fig. 2C, D ) as described by Baba (1988) and McCallum & Poore (2013) for the Philippine and north-western Australian specimens. The antennal article 5 is approximately two times longer than the article 4 and reaches to the midlength of the antennular penultimate article ( Fig. 2C, D ). The external appearance and armature of the P1–4 are generally similar to those of the previous illustrations ( Fig. 1B, E, F ; Alcock & Anderson 1899b: pl. 45, fig. 1; Alcock & McArdle 1902: pl. 58, fig. 4; McCallum & Poore 2013: fig. 1G, H).

Sternostylus investigatoris is distinguished from S. hendersoni , a morphologically close congener in the Indo- West Pacific, by the pleura of the abdominal segment 3 being unarmed instead of having spines (cf. Baba 2005; McCallum & Poore 2013).

There are no published records on the hosts of S. investigatoris and no host information of the present specimen. Nevertheless, many species of Chirostyloidea live in association primarily with anthozoans of Alcyonacea (Octocorallia) and Antipatharia (Hexacorallia) (cf. de Saint Laurent & Macpherson, 1990; Buhl- Mortensen & Mortensen 2004; Baba et al. 2009; Schnabel 2009; Guilloux et al. 2010; Hendrickx 2012). Sternostylus investigatoris and a new species of Eumunida described below probably have similar hosts and associations to those of the previous reports; such host colonies exist near the sluice gate of deep sea water as the present collection site.

A new Japanese name, Daidai-tsuno-waraebi (meaning orange-colored, horned straw lobster in Japanese), is given for G. investigatoris based on the present specimen.

Figures

FIGURE 1. Sternostylus investigatoris (Alcock & Anderson, 1899), male (pcl 23.5 mm), RUMF-ZC-5357. A, living animal in aquarium, dorsal view; B, entire preserved specimen, dorsal view; C, carapace, abdomen, and anterior appendages, dorsal view; D, carapace, abdomen, anterior appendages, and ambulatory legs, left lateral view; E, left P1 chela, dorsal view; F, left P2 propodus and dactylus, lateral view.

FIGURE 2. Sternostylus investigatoris (Alcock & Anderson, 1899), male (pcl 23.5 mm), RUMF-ZC-5357. A, anterior regions of carapace and eyes, dorsal view; B, anterior part of thoracic sternum, ventral view (setae omitted); C, left, anterior parts of carapace and pterygostomian flap and antennular and antennal peduncles, lateral view; D, left antennal peduncle, ventral view; E, merus and carpus of left Mxp3, lateral view (setae omitted). Scales = 5.0 mm.