Petrolisthes aegyptiacus, Werding, Bernd & Hiller, Alexandra, 2007

Werding, Bernd & Hiller, Alexandra, 2007, The Porcellanidae (Crustacea: Decapoda: Anomura) of the Red Sea with description of a new species of Petrolisthes, Zootaxa 1460, pp. 1-24 : 5-7

4. Petrolisthes aegyptiacus n.sp.

( Fig. 4 )

Material examined. Holotype: Ψ (ov) ( SMNS from ZIa 3365), Egypt, Red Sea, Koseir, leg. Klunzinger, 1883. Paratypes: 1 ɗ, 1 Ψ (ov) ( SMNS from ZIa 3365), same data as holotype; 6 ɗ, 4 Ψ (ov) ( SMNS from ZIa 3375), Egypt, Red Sea, Koseir, leg. Klunzinger; 1 ov Ψ ( SMNS from ZIa 3375), Egypt, Red Sea, Koseir, leg. Klunzinger; 1 ɗ ( SMNS from ZIa 3374), Egypt, Red Sea, Koseir, leg. Klunzinger, 1884; 1 ɗ (from SMNS ZIa 3370) (one cheliped missing), Egypt, Red Sea, Koseir, leg. Klunzinger. Other material. 1 ɗ ( SMF 25678) (without walking legs), Red Sea, Sudan, Sanganeb, S-Jetty, SAN 119, from living Acropora , leg. Hamza, 30 Sep.1992; 1 ɗ ( SMF 16926), Indo-Pacific.

Measurements. Largest ɗ 4.2 x 3.8 mm; largest Ψ 4.3 x 4.3 mm.

Diagnosis. Carapace slightly longer than broad, with a few transverse ridges on anterior region. Front trilobate. One supraocular spine, one epibranchial spine and two mesobranchial spines present. Chelipeds with transverse ridges on surface; anterior margin of carpus with four serrate-edged teeth. Manus with a conspicuous longitudinal ridge.

Description. Carapace slightly longer than broad, widest on mesobranchial region. Front broad, slightly produced beyond the eyes and noticeably trilobate, median lobe produced beyond the right-angled lateral lobes. Supraorbital spine present, infraorbital angles rounded. One epibranchial spine, two additional spines on mesobranchial margin, the first one usually prominent, the second one occasionally inconspicuous. Posterior region of front with continuing transverse ridges; additional transverse ridges upon gastric region and lateral parts of metabranchial regions. A deep horizontal groove limits frontal and gastric regions. First movable segment of antenna with a narrow, anteriorly-directed tooth.

Chelipeds slender, merus armed with 1 or 2 forwardly-directed spines on anterior margin, an additional one on dorsal surface; the inner edge produced into a spine-tipped tooth; ventral side with 2 or 3 marginal spines. Carpus with 4, spine-tipped, serrated teeth on anterior margin, the foremost distal edge forming an additional blunt tooth. Posterior margin with a row of scale-like granules, the distal ones produced forming a row of 4 or 5 spines (seldom 3 or 6), the posterodistal spine bifid. Dorsal surface of carpus with a longitudinal ridge, formed by a row of oblique, scale-like elevations. Manus subequal, outer margin serrated, with 4–7 curved spines, and with a fringe of feathered setae reaching the base of pollex. Dorsal surface of manus densely covered with minute scale-like granules and scattered cone-tipped granules, and a longitudinal ridge of scales, similar to that of carpus, extending to the dactylus. Gape of fingers without setation.

Walking legs slender, covered with irregular transverse ridges; merus with scattered feathered setae, and with spines on anterior margin, distributed as follows: L1 3–5, L2 3 or 4, L3 2 or 3. Merus of L1 and L2 with posterodistal spine; carpus with scattered long setae, dorsodistal edge produced into a spine in L1. Propodus with similar setation, ventrally with a triplet of movable distal spinules, L1 with 2 and L2 and L3 with 1 additional spine. Dactylus with 4 movable spines on inner margin.

Remarks. Petrolisthes aegyptiacus is closely related to the West-Pacific P. heterochrous Kropp. Characters shared by the two species include the form of the body, particularly the trilobate front, the sculpturing of the carapace’s surface consisting of transverse ridges, and the presence of spines on the supraorbital, epibranchial, and mesobranchial regions. The cheliped’s spination and sculpturing, and the walking legs’ spination are, to a great extent, identical in the two species. In general, P. aegyptiacus has fewer spines on the extremities than P. heterochrous . The two species are clearly distinguishable by the presence of only one epibranchial spine in P. aegyptiacus versus two in P. heterochrous . An additional distinguishing feature seems to be the spination of the propodi of the walking legs. The propodus in P. aegyptiacus bears two spines on L1, and one on L2 and L 3 in addition to the three terminal spines, whereas the compared paratypes of P. h e t e ro c h ro u s show two such spines on L1 and on L2, and L3 is only armed with one additional spine. Altogether, the body form of P. aegyptiacus appears more compact than that of P. heterochrous , because of a narrower front and more slender walking legs.

Other closely related species are P. militaris (Heller) and P. scabriculus (Dana) , distinguished from the new species by a triangular front lacking laterally produced lobes, and two epibranchial spines. The character combination consisting of one epibranchial spine and further additional mesobranchial spines is not found in the genus in any other Indo-West Pacific species, but is observed in P. amoenus (Guérin) from the western Atlantic, as well as in P. sanfelipensis Glassell from the eastern Pacific. These species are not closely related to each other (see Hiller et al. 2006) or to the new species.

It is remarkable that P. aegyptiacus , which is well represented in the material of the Stuttgart museum, was not found in other collections. Previously, only one additional specimen of unknown origin was found in the collections of the Senckenberg Museum. Another specimen was found in a living Acropora colony on the coasts of Sudan as part of a study on fauna associated with corals (see above, leg. Hamza). The material collected by Klunzinger has no specific collection data.

Distribution. The species was found only in the northern and central Red Sea, what suggests that it is endemic to this region. Nevertheless, the specimen found in the collection of the Senckenberg Museum (SMF 16926) had the locality specification “Indo-West Pacific”.

Etymology. The name of the species is derived from Egypt, the country where the type locality of P. aegyptiacus is situated.

Figures

FIGURE 4. Petrolisthes aegyptiacus n. sp., female, holotype, Red Sea, Koseir. (a) Dorsal view. (b) Right first walking leg, ventral view. (c) Ischium and merus of left cheliped, ventral view. (d) Basal segment of antennule. (e) First movable segments of antenna.