Stylodactylus gracilis Cleva, 2008, new species
Creators: name: Cleva, Régis
Publisher: name: Zenodo
Year: 2008
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Stylodactylidae
Stylodactylus
Stylodactylus gracilis

description: Stylodactylus gracilis new species
(Figs. 1, 3A)
Type material. Philippines, Panglao I., stn. CP2386, 8°49.3’N – 123°1.9’E, 2149–2217 m, sandy substrate, 29 May 2005: 1 female 15.5 mm, holotype.
Description. Body slender, integument of cephalothorax and abdomen glabrous, noticeably thin. Distal part of rostrum missing. Rostrum long, curved dorsally; RL/CL ratio estimated close to 2.0 (preserved portion of rostrum measuring 1.78 times carapace length); preserved portion of rostrum with 42 mobile spines along dorsal margin (4 on the carapace proper) and 43 mobile spines along ventral margin (posteriormost ventral spine situated just anterior to distal margin of first segment of antennular peduncle).
Carapace with only reduced ornamentation: no supraorbital spine, antennal spine slender, short, branchiostegal spine short.
First to fourth abdominal pleura rounded, that of fifth ending in sharp postero-ventral tooth; posterior margin of third abdominal segment with 2 sharp dorsal parasagital teeth. Sixth somite about 1.8 times longer than fifth somite (when measured along dorsal margin). Telson with 2 rows of eight (?) dorsal spines, 1.6 times longer than sixth somite.
Eye well developed, without ocellus; cornea wider than ocular peduncle, well pigmented (black). Stylocerite extending to end of first article of antennular peduncle. Antennular peduncle particularly long, measuring 0.8 times carapace length; second article 0.45 times carapace length, 1.8 times longer than first (when measured along external margin), and 6.0 times longer than third article. Scaphocerite about 0.7 times CL, reaching end of antennular peduncle, 5.5 times longer than wide, with parallel margins; distolateral spine not overreaching distal margin of blade.
Mandibular palp with 2 segments.
Second maxilliped with disto-ventral article much longer than disto-dorsal article.
Third maxilliped exceeding tip of scaphocerite by length of ultimate article plus about 1/4 of penultimate. First pereopod exceeding tip of scaphocerite by length of chela plus about distal third of carpus; second pereopod exceeding tip of scaphocerite by almost fingers length; third pereopod exceeding tip of scaphocerite by length of dactyl plus propodus, carpus and distal fourth of merus; fourth pereopod exceeding tip of scaphocerite by length of dactyl plus propodus and almost carpus length; fifth pereopod exceeding tip of scaphocerite by length of dactyl plus propodus and end of carpus.
Ischio-meri of P3 with 12, 15 external-ventral spines, merus of P4 and P5 with respectively 11 and eight similar spines. Ischium and merus of P4 and P5 not fused, separated by a distinct suture line. Ischio-merus/ carpus, propodus/carpus and propodus/dactylus ratios of P3 to P5 equal to: P3: 8.6; 4.0; 10.6; P4: 6.0; 5.1; 12.0; P5: 3.4; 3.5; 15(?).
Colouration. General colour of body and appendages more or less deep orange; anterior region of cephalothorax deep orange, rest of body pale orange; distal part of second maxillipeds reddish; legs pale orangewhitish.
Etymology. From the Latin gracilis for the thin, slender and fragile aspect of the new species.
Affinities with other species. Hanamura & Takeda established a new genus Bathystylodactylus for species with the following characters: 1) stylocerite extending nearly to mid-length of first segment of antennular peduncle; 2) posterior three pereopods unusually longer than anterior pereopods; 3) carapace with distinct supraorbital ridge; 4) third to fifth abdominal somites weakly carinated dorsally (Hanamura & Takeda 1996: 930). Three species of Bathystylodactylus are currently recognized: B. bathyalis (Cleva, 1994) (N.E. Australia, Coral Sea, 3502–3515 m), B. inflatus Hanamura & Takeda, 1996, (east coast of Taiwan, 3436–3452 m) and B. echinus Wicksten & Martin, 2004, (Baja California, Mexico, and California, U.S.A., 3427–3689 m). In this last species, described after the establishment of Bathystylodactylus, only the third abdominal somite is consistently weakly carinated (Wicksten & Martin 2004: 381). Other characters in common in these three species are: 1) the eyes are very reduced in size with cornea unpigmented; 2) the antennular peduncle is elongated, clearly overreaching the antennal scale, the lengthened first and second articles being of about the same size; 3) all last three pairs of pereopods are outstandingly long and slender, their ischio-meral segment overreaching the antennal scale as well as the antennular peduncle (particularly P3 and P4).
The new species clearly can not be assigned to the genus Bathystylodactylus but should be instead assigned to Stylodactylus:
1. The eyes are of normal shape, with the cornea wider than the ocular peduncle. Eyes are well pigmented. 2. The stylocerite of the elongated antennular peduncle is of usual Stylodactylus shape, reaching the end of
the first article, and the second article is much longer (1.8 times longer) than the first.
3. The scaphocerite is proportionally longer (0.7 CL versus about 0.45 CL in Bathystylodactylus species)
and reaches the end of antennular peduncle.
4. No trace of a dorsal carina on third to fifth abdominal somites.
5. Third to fifth pereopods are very long and slender, with the lengthening of the merus and propodus as in
Bathystylodactylus, but noticeably not as long: ischio-meral segment of P3 overreaching by far the end of the scaphocerite or antennular peduncle, but that of P4 and P5 not extending so much.
Among the 15 described species in the genus Stylodactylus, four members are remarkable in having an elongated antennular peduncle, the elongated second segment being at least as long as the first, versus more shorter usually: Stylodactylus macropus Chace, 1983, (Philippines, New Caledonia, Chesterfield Is, Vanuatu, 700–925 m), S. major Hayashi & Miyake, 1968, (East China Sea, 122–124 m (?) and Taiwan, 880–1211 m), S. brucei Cleva, 1994, (Australia, 900–1000 m, Wallis I., 820–840 m) and S. profundus Cleva, 1990 a, (New Caledonia, 1395–1740 m, Florida Strait and Bahamas, 1020–1399 m). But none of these four species displays such as long second article of the antennular peduncle associated with very long P3 to P5 as in the new species.
Distribution. Philippines, 2149–2217 m. Stylodactylus gracilis is found deeper than any species in the genus.
description: Published as part of Cleva, Régis, 2008, Stylodactylidae and Bathypalaemonellidae (Crustacea: Decapoda: Caridea) from the PANGLAO 2004 and 2005 expeditions to the Philippines, with description of a new species of Stylodactylus A. Milne - Edwards, 1881, pp. 29-41 in Zootaxa 1813 on pages 32-34, DOI: 10.5281/zenodo.182835