Salmoneus erasimorum Dworschak, Anker & Abed Navandi 2000

Salmoneus erasimorum Dworschak, Anker & Abed Navandi, 2000

(Figs. 2–3)

Salmoneus erasimorum Dworschak, Anker & Abed Navandi, 2000: 313, figs. 42–56.

Salmoneus erasimorum. — Anker 2010: 192; Anker 2011: 73; De Grave & Fransen 2011: 402; Anker et al. 2014: 491; Anker & Ashrafi 2019: 68, 71; Anker 2020: 360, 362, 365.

Material examined. 1 non-ovigerous specimen (cl 5.6 mm, tl ca. 14 mm, right cheliped missing), MNHN-IU-2018- 5654, France, northern Brittany, municipality of Plougrescant, Beg ar Vilin, near mouth of Jaudy river, 48.84628°N, 3.2063°W, muddy shore, slightly below mid-tide level, suction (yabby) pump, in burrow of unknown host, leg. F. Gully & M. Cochu, 16 February 2021.

Diagnosis. Body not setose. Rostrum about 1.4 times as long as broad, triangular, with margins scarcely concave, reaching beyond middle of second article of antennular peduncle. Orbital teeth short, about 0.2 length of rostrum. Telson trapezoidal, about 1.9 times as long as wide; dorsal surface with 2 pairs of spiniform setae at about 0.4 and 0.8 of telson length, respectively; posterior margin almost straight, except for very shallow median sinus, with two pairs of stout spiniform setae, lateral longer than median. Eyes visible in dorsal view, but only in deep notch between rostrum and orbital teeth. Antennule stout, with stylocerite reaching tip of second article of antennular peduncle; second article slightly longer than broad. Blade of antennal scaphocerite broad, slightly overreaching distolateral tooth. Third maxilliped slender; lateral plate on coxa rounded; arthrobranch well developed. Major cheliped relatively slender, elongate; ischium armed with 2 spiniform setae; carpus vase-shaped, subtriangular in cross-section, about 1.7 times as long as wide, without ventromesial tooth; chela elongate, palm slender, slightly broader than fingers, latter noticeably longer than palm, strongly crossing distally; finger cutting edges with 3 or 4 small, widely spaced teeth distally and short area of continuous serration proximally. Minor cheliped missing in the specimen from Brittany [in holotype more robust than major cheliped, with all articles shorter; carpus cup-shaped, without ventromesial tooth; chela stout, almost twice as long as fingers; dactylus strongly curved and reaching well beyond pollex; finger cutting edges armed with 3 large, blunt teeth]. Second pereiopod with ischium armed with small spiniform seta; carpus subdivided into 5 subarticles, first slightly longer than total length of others.Ambulatory pereiopods slender; ischium armed with small spiniform seta(e) or unarmed; dactylus conical, moderately slender, 0.3–0.4 times as long as propodus. Second pleopod with appendix masculina not elongate, slightly shorter than appendix interna.

Colour pattern. Largely translucent; body pale yellowish; cheliped hyaline white; yellow mass (ovaries) in visceral cavity visible through body translucence; eyes dark brown; antennae, pereiopods and tail-fan largely colourless (Fig. 2).

Distribution. North-East Atlantic. Presently known from two distant localities: Kvarner, Opatja, on the Croatian coast of the Adriatic Sea (Dworschak et al. 2000), and Beg ar Vilin, Plougrescant, on the coast of northern Brittany, France (present study).

Ecology. Salmoneus erasimorum is clearly an infaunal shrimp, living symbiotically in burrows of larger hosts. Indeed, the holotype of S. erasimorum was collected from the burrow of the callianassid ghost-shrimp Gilvossius tyrrhenus (Petagna, 1792), together with the host, in about 1.5 m water depth (Dworschak et al. 2000). Gilvossius tyrrhenus (Petagna, 1792) is largely known in literature as Pestarella tyrrhena (Petagna, 1792) and Callianassa tyrrhena (Petagna, 1792) but was transferred to the genus Gilvossius Manning & Felder, 1992 by Sakai (2011). The present specimen was collected at low tide, on an intertidal mudflat with some sandier areas, large rocks and clusters of algae (Fig. 1A), and was extracted with a suction pump from a burrow similar to those depicted in Fig. 1B, however, without host. The presence of lugworms (Arenicola sp.) was noted by the collectors (FG and MC) in the immediate vicinity of the collection site, although they were most likely not the hosts of S. erasimorum. On the other hand, the presence of G. tyrrhenus as a possible host of S. erasimorum in Brittany cannot be discounted, as it is a common ghost-shrimp species throughout Brittany (d’Udekem d’Acoz 1999; Ngoc-Ho 2003).

Discussion. Salmoneus erasimorum appears to be present both in the Adriatic Sea and in the temperate North-East Atlantic, but so far has been collected only twice (Dworschak et al. 2000; present study). It is likely to be present in many places situated in between, but this needs confirmation. Its apparent rarity is probably largely due to the species’ highly cryptic lifestyle, i.e. dwelling deep in burrows of larger hosts (e.g., Gilvossius tyrrhenus in the Adriatic Sea). Specific collecting techniques such as use of suction pumps or use shovel and sieves, would be necessary to collect S. erasimorum. However, it is also possible that populations of S. erasimorum generally have a low density. After the capture of the first specimen, two of the authors (FG and MC) repeatedly returned to the collection locality to obtain additional specimens and their hosts, but were unsuccessful. Therefore, the host of S. erasimorum in Brittany (which might be close to the northern end of its distributional range) remains unknown. Several other species of Salmoneus are known to be associated with the burrows of larger decapods, including some that are morphologically similar to S. erasimorum (Dworschak et al. 2000; Komai 2009; Anker 2019b; Anker & Ashrafi 2019).

Although the present specimen of S. erasimorum lost its minor (left) cheliped, probably during the collection, it agrees very well with the holotype from the Adriatic Sea, except for a few minor details. The rostrum is a little longer and a little narrower than in the holotype, with the margins very slightly concave instead of straight. Dworschak et al. (2000) stated that in the holotype, the eyes were “completely covered by carapace in dorsal view, but visible from anterior and side views”. However, in their figure 43, a very small portion of the eyes remains visible in dorsal view, in the deep notch formed by the mesial base of each orbital tooth and the proximolateral portion of the rostrum, just like in the specimen reported here (Fig. 3).