Periclimenaeus ramili, Neves, 2022

Neves, Keider, 2022, Parascorpaena poseidon Chou and Liao 2022, Zoological Studies 61 (15), pp. 1-14 : 2-12

Family Palaemonidae Rafinesque, 1815 Genus Periclimenaeus Borradaile, 1915

Periclimenaeus ramili sp. nov. ( Figs. 1–5 ) urn:lsid:zoobank.org:act:58C11410-B0DC-49BA-BB7C-23D582CE2739

Material examined: Holotype. 1 male (pocl 4.2 mm, dissected), Cabo Verde Archipelago , São Vicente Island, Baía das Gatas (16°54'11.0"N 24°54'22.3"W), snorkelling, depth 1 m, in Spongia sp. growing under large rock, 12 Dec. 2020, leg. K. Neves ( RMNH. CRUS. D.57969) . Allotype. 1 ovigerous female (pocl 5.8 mm), same collection data as for holotype ( RMNH. CRUS. D.57970) . Paratypes. (I) 1 male (pocl 4.0 mm) and 1 ovigerous female (pocl 4.4 mm), same location as for holotype, snorkelling, depth 2–3 m, in Spongia sp. growing under large rock, 12 Dec. 2020, leg. K. Neves ( RMNH. CRUS.D.57971); ( II) 1 male (pocl 4.1 mm) and 1 ovigerous female (pocl 4.4 mm), same location as for holotype, snorkelling, depth 0.5 m, in Spongia sp. growing under large rock, 12 Dec. 2020, leg. K. Neves ( RMNH. CRUS.D.57972); ( III) 1 male (pocl 3.5 mm) and 1 ovigerous female (pocl 4.0 mm), same location as for holotype, snorkelling, depth 2–3 m, in Spongia sp. growing under large rock, 12 Dec. 2020, leg. K. Neves ( UCV 00346); ( IV) 1 male (pocl 3.0 mm) and 1 ovigerous female (pocl 4.0 mm), same location as for holotype, snorkelling, depth 2–3 m, in Spongia sp. growing under large rock, 12 Dec. 2020, leg. K. Neves ( UCV 00347); ( V) 1 male (pocl 4.1 mm) and 1 ovigerous female (pocl 4.6 mm), Cabo Verde Archipelago, São Vicente Island, Porto Grande Bay, Enseada de Corais da Matiota (16°53'47.6"N 24°59'33.6"W), snorkelling, depth 3 m, in Spongia sp. growing under large rock, 21 Sep. 2019, leg. K. Neves ( RMNH. CRUS.D.57973); ( VI) 1 male (pocl 3.2 mm) and 1 ovigerous female (pocl 4.3 mm), same location as previous specimens, snorkelling, depth 3 m, in Spongia sp. growing under large rock, 20 Jun. 2020, leg. K. Neves ( UCV 00348); ( VII) 1 male (pocl 3.2 mm) and 1 ovigerous female (pocl 4.4 mm), same location as previous specimens, snorkelling, depth 3 m, in Spongia sp. growing under large rock, 20 Jun. 2020, leg. K. Neves ( UCV 00349).

Other material examined

Male (not measured; mouthparts dissected for comparison) and ovigerous female (not measured; stomach dissected for analysis of content and mouthparts dissected for comparation), same location as for holotype, snorkelling, depth 4 m, in Spongia sp. growing under large rock, 12 Dec. 2020, leg. K. Neves (not deposited); 2 immature specimens (pocl 1.0, 1.2 mm) same location as for the previous specimens (not deposited).

Description of male holotype: Median sized palaemonid shrimp of subcylindrical body ( Fig. 5A ).

Rostrum ( Fig. 1A–C ) short, slender, compressed, 0.2 of post orbital carapace length, directed downwards, with tip failing to reach end of first segment of antennular peduncle; with 4 slender, acute dorsal teeth, all anterior to posterior orbital margin; tip short, acute; ventral margin nearly straight, unarmed.

Carapace ( Fig. 1B–C ) smooth, without epigastric, supraorbital, or hepatic spines; antennal spine present, well developed; inferior orbital angle not produced, with distinct angular process; pterygostomial angle broadly rounded.

Pleon smooth ( Fig. 1D ); first segment ( Fig. 1E ) with shallow, almost indistinct anteromedian dorsal lobe; pleura rounded, anteriorly rounded on third segment, posteriorly produced, rounded on fourth and fifth segments, sixth segment ( Fig. 1F ) 1.25 length of 5th segment, about 0.5 telson length, with posterolateral angle small, rounded, posteroventral angle produced, acutely rounded.

Telson ( Fig. 1F–G ) almost twice as long as maximal width; lateral margins convex, posteriorly convergent; dorsal surface with 2 pairs of spines, about 0.1 of telson length, situated at 0.1 and 0.55 of telson length, respectively; posterior margin convex, with 3 pairs of spiniform setae, outer pair short, intermediate pair long, slender, median pair slightly shorter than intermediate pair, setulose.

Eyes ( Fig. 1B–C ) well developed, cornea rounded, set obliquely on stalks, without accessory pigmented spot; stalk short, mesial length subequal to corneal diameter; distal margin of cornea reaching to about 0.8 length of first antennular segment.

Antennule ( Fig. 1H ) well developed; peduncle with basal article 2.7 times as long as central width, without ventromedial tooth; statocyst well developed, with statolith; stylocerite short, acute, broad, not reaching middle of segment; lateral margin of article forming a blunt angle at level of stylocerite tip, slightly tapering distally, distolateral tooth well developed, reaching middle of intermediate article; intermediate article about 0.3 of proximal article length, almost as long as wide; distal article slightly longer than preceding, length subequal to width; upper flagellum biramous, 7 proximal articles fused, short free ramus with three articles, about 10 groups of aesthetascs, longer free ramus slender, with about 9 subdivisions; lower flagellum similar, slender, broken off, with at least 12 subdivisions.

Antenna ( Fig. 1I ) with rounded boss proximomesially on coxa; stout, unarmed basicerite; ischiocerite and merocerite with few simple setae, otherwise without special features; carpocerite subcylindrical, with some small simple setae distally, longer than scaphocerite; scaphocerite short, about twice as long as broad, broadest at about 0.7 of length, rounded distally, reaching to about end of second article of antennular peduncle, lateral margin slightly convex, with distal tooth not overreaching lamella; flagellum moderately long.

Mouthparts from left side dissected.

Right mandible (left damaged during dissection) ( Fig. 2A ) without palp; incisor process strongly reduced, short, simple, tapering to single rather blunt distal tooth, mesial margin unarmed; molar process well developed, subcylindrical, truncate distally, with spine-like tuft of long setae proximally on dorsal margin, with dense brushes of short setae and single, blunt tooth distally; inferior margin with dense rows of setae.

Maxillula ( Fig. 2B ) with feebly bilobed palp, lower lobe slightly produced with simple terminal seta; upper lacinia short, moderately broad, dorsal margin convex, distal margin truncate, with about 7 stout marginal spines, and some slender setae; lower lacinia elongate, slender, distally rounded, with about 12 simple setae.

Maxilla ( Fig. 2C ) with non-setose tapering palp, distally rounded, about 3.3 times longer than basal width; basal endite with lobes fused, slender, tapering, rounded distally, with nine setae distally; coxal endite obsolete, non-setose; scaphognathite normal, broad, length about 3 times central width, anterior lobe 1.2 times longer than wide, mesial margin slightly convex, posterior lobe broadly rounded, 2 times longer than basal width; all margins bearing short plumose setae.

First maxilliped ( Fig. 2D ) with slender flattened palp, tapering, distally rounded, about 4 times longer than central width, with single seta on mesial margin; basal and coxal endites completely fused, distally rounded, mesial margin almost straight, with numerous slender setae; exopod with normal flagellum, with 11 plumose setae distally; caridean lobe large, 2.5 times longer than central width; epipod well developed, rounded, bilobed.

Second maxilliped ( Fig. 2E ) with normally developed endopod, dactylar segment narrow, about 3 times longer than maximal width, distomesial margin almost straight, with rows of long marginal setae; propodal segment with distomesial margin slightly produced, bearing 8 setae; carpus, merus and ischiobasis without special features; coxa mesially rounded; exopod normal, with 13 plumose setae distally; epipod small, elongate, rounded distally, without podobranch.

Third maxilliped ( Fig. 2F ) with slender endopod; coxa non-setose, lateral plate short, broadly rounded, arthrobranch absent; basis with ventral margin rounded; ischiomerus completely fused to basis, without suture, combined segment 3.3 times longer than basal width, tapering distally, with series of long and short setae mesially and short distolateral seta; penultimate segment slender, 4.15 times longer than wide, 0.7 of ischiomerus and basis length combined, with numerous long setae mesially and long distomesial setae, distolateral margin with four simple setae; terminal segment about 0.7 of penultimate segment length, slender, tapering distally, with dense tuff of setae medially, lateral margin with long and short setae; exopod well developed, reaching to distal half of penultimate segment, distal third with 6 and 5 plumose setae laterally and mesially, respectively, and 4 stouter and longer terminal plumose setae.

Thoracic sternites narrow, unarmed.

First pereiopod ( Fig. 3A–B ) moderately robust, overreaching scaphocerite by length of chela and carpus. Chela with palm subcylindrical, compressed, 1.3 times longer than deep; fingers about as long as palm, stout, subspatulate, cutting edges entire, tips with three terminal teeth, central tooth larger than adjacent teeth, bearing dense tufts of serrulate setae, dorsal margin of dactylus regularly sloping towards tip; carpus about 4 times longer than distal width, 1.3 times as long as chela, tapering proximally; merus 3.5 times longer than maximal width at about half length of segment and as long as carpus; ischium short, stout, about as broad as merus, 1.6 times longer than broad, about half as long as merus; basis and coxa without special features.

Second pereiopods well developed, robust, unequal in size, dissimilar in shape. Major second pereiopod ( Fig. 3C–E ) with chela about 1.8 of pocl; palm bearing minute granules mesially, outer surface smooth, 1.8 times longer than maximal depth, swollen proximally, oval in cross-section, tapering slightly distally; fingers 0.25 of palm length, distal parts strongly twisted mesially, sparsely setose; dactylus slightly exceeding fixed finger, high, compressed, about 1.6 times as long as central depth, dorsal margin strongly convex, with stout, sharp, hooked tip, cutting edge convex, entire, laminar, sharp, thickened proximally in a compressed, low and poorly demarcated small molar process, which is indistinct is lateral view; fixed finger tapering distally, with blunt tip, about 1.2 times as long as basal depth, with fossa proximally for reception of dactylar molar process, mesial margin with triangular process, distal part of cutting edge concave, sharp, entire; carpus short, about 0.3 of palm length, distally expanded, approximately as long as distal width, strongly tapering proximally, unarmed; merus 1.7 times as long as broad, 0.9 of carpus length and 0.3 of palm length, with 6 blunt tubercles ventrally; ischium about as long as merus, tapering proximally, 1.7 times longer than distal width, unarmed; basis and coxa robust, short, without special features.

Minor second pereiopod ( Fig. 3F–G ) smaller than major second pereiopod, with chela about 0.7 of pocl and 0.4 of major chela length; palm bearing small tubercles mesially, otherwise smooth, sub-rectangular in lateral view, 2.4 times as long as maximal height, tapering slightly distally; fingers about 0.3 of palm length; dactylus compressed, somewhat longer than fixed finger, about 1.6 times longer than maximal depth at midlength, dorsal margin strongly convex, with stout, sharp, strongly hooked tip, cutting edge slightly convex, entire, laminar, sharp; fixed finger tapering distally, with blunt tip, about 1.1 times as long as basal depth; carpus about 0.4 of palm length, distally expanded, about 1.4 times as long as high, smooth; merus stout, about as long as carpus, 1.8 times as long as central depth, unarmed; ischium slightly longer than merus, unarmed; basis and coxa short, without special features.

Ambulatory pereiopods of usual shape for genus, similar, with third pereiopod strongest. Third pereiopod ( Fig. 4A–B ) with dactylus biunguiculate, short, 0.2 of propodus length, compressed, with apex recurved; unguis distinctly demarcated from corpus, curved, 2.6 times longer than basal width and 0.3 of dorsal corpus length, simple; corpus about as long as deep, dorsal border convex, ventral margin concave, armed with large, acute, recurved distal accessory tooth slightly shorter and stouter than unguis; ventral margin posterior to accessory tooth smooth; propodus 6.3 times as long as distal width and about 4.9 times longer than dactylus, with pair of stout distoventral spiniform setae and 3 irregularly spaced spiniform setae along ventral margin decreasing in size posteriorly, with setae distally on dorsal, lateral and mesial margins; carpus about as stout as propodus, slightly tapering proximally, 0.9 of propodus length, 3.5 times as long as distal width, unarmed; merus very stout, about 3 times as long as broad, 1.25 of propodus length and 1.4 times as long as carpus, unarmed; ischium about twice as long as distal deep, 0.6 times length of merus, tapering proximally, unarmed; basis and coxa short, without special features.

Fourth pereiopod ( Fig. 4C–D ) similar and subequal in length to third pereiopod, slenderer; dactylus biunguiculate, short, 0.27 of propodus length, recurved and compressed; unguis distinctly demarcated from corpus, curved, simple; corpus about as long as deep, dorsal border convex, ventral margin concave, simple, with large, acute distal accessory tooth, strongly curved, subequal to unguis; propodus 7 times as long as distal width and 3.75 times longer than dactylus, with pair of stout distoventral spiniform setae and two spiniform setae along ventral margin, with setae distally on dorsal, lateral and mesial margins; carpus 0.87 times of length of propodus, 3.7 times as long as distal width, unarmed; merus stout, about 3.3 times as long as broad and 1.4 times length of carpus, unarmed; ischium 2.7 times as long as distal width, 0.7 of length of merus, unarmed; basis and coxa short, without special features.

Fifth pereiopod ( Fig. 4E–F ) slenderer than third and fourth pereiopods, subequal in length; dactylus biunguiculate, short, 0.15 of propodus length, recurved and compressed; unguis distinctly demarcated from corpus, curved, simple; corpus slightly longer than depth, dorsal border convex, ventral margin concave, simple, with large, acute distal accessory tooth strongly curved, subequal to unguis; propodus 8.3 times as long as wide and 6.4 times longer than dactylus, with distoventral tufts of setulose setae and with setae distally on dorsal, lateral and mesial margins; carpus 0.8 of length of propodus, 4.3 times as long as distal width, unarmed; merus about 4.2 as long as mesial width and 1.4 times length of carpus, unarmed; ischium about half as long as merus and twice as long as wide, unarmed; basis and coxa short, without special features.

First male pleopod ( Fig. 1J ) with basipodite bearing two simple setae distally, one on lateral and other on mesial margin; exopod 4.5 times longer than wide, bearing plumose setae on both margins; endopod 0.45 of exopod length, about 3.8 times longer than central width, distally rounded, mesial margin with 15 simple short and long setae, and distomesial long simple seta; apex with pair of long simple seta, lateral margin with five simple setae.

Second male pleopod ( Fig. 1K ) with non-setose basipodite; endopod 0.9 length of exopod, about 4.5 times longer than central width, with numerous marginal plumose setae; appendices ( Fig. 1L ) inserted at 0.4 of mesial margin of endopod length, appendix masculina subcylindrical, 3.5 times longer than wide, about 0.09 times length of endopod, with two apical and four lateral serrate setae increasing in length distally, apical seta longest, about 1.5 times length of appendix masculina; appendix interna far exceeding appendix masculina, with few distomesial cincinnuli.

Uropods ( Fig. 1F ) with protopodite posterolaterally unarmed; rami subequal to telson length; exopod broadly ovate, about two times longer than central width, lateral margin slightly convex, bearing few small, thin setae, entire, distolateral angle with acute tooth and larger movable spine mesially; diaeresis distinct; endopod elongate, oval, slightly longer than exopod, 1.8 times longer than maximal width.

Variation: The relatively abundant material available for examination allowed to appreciate the variation exhibited by the new species. Two small immature specimens are morphologically identical to the largest specimens examined, exhibiting most diagnostic features of the new species, and can be distinguished from the closely related species using the same features. The females, although generally similar to males, are larger in size, with a more robust and clumsy body and with relatively smaller and less inflated major second chela. The pleon in the ovigerous females ( Fig. 5A ) is greatly expanded enclosing a very large number of eggs. In terms of the rostral formula, all examined specimens possess four dorsal teeth, except one ovigerous female which possesses only three. In most specimens, the rostrum does not overreach the cornea as it does in the male holotype, being more downwards curved in some ovigerous females and not reaching as far forward. The upper antennular flagellum has 7 proximal articles fused in the male holotype, while in most specimens only 4 proximal articles are fused. In some specimens, the telson possesses a minute acute median process, while in others, including the holotype, it does not. The distal cutting edges of fingers of the major second cheliped in the male holotype are not so sharp as is most paratypes, and the tip of the dactylus is somewhat blunt, but this is due to abrasion and few damages caused while handling it. Also, the merus of the major second cheliped of the holotype possesses some blunt tubercles in its ventral border, that are absent in most specimens.

Colouration: Semi-transparent whitish, with inconspicuous red chromatophores scattered over the carapace, pleon, second pair of pereiopods chelae, eye stalks and antennular peduncles; second pair of pereiopods with the distal portion of the palm, and dorsal and ventral margins of dactylus and pollex whitish, with cutting edges amber yellow; walking legs and tail fan transparent. Females with light creamcolored ovary and eggs ( Figs. 5–6 ).

Etymology: It is a great pleasure for the author to dedicate this new species to Professor Dr Francisco Ramil, University of Vigo, Spain, who has been a friend and mentor for several years, and for his numerous contributions in the study of marine invertebrates, especially cnidarians.

Distribution: Presently only known with certainty from the type locality (Baía das Gatas) and Enseada de Corais da Matiota, Porto Grande Bay, both in São Vicente Island, Cabo Verde. However, its presence in the Canary Islands is suspected based on a colour photograph of a specimen from Lanzarote Island (see DISCUSSION below; Fig. 6 ).

Biology: Periclimenaeus ramili sp. nov. is, as all other species in the genus, an ecologically highly cryptic species, living inside the demosponge Spongia sp. (Porifera: Demospongiae: Spongiidae ), in heterosexual pairs. The sponges inhabited by the shrimps ( Fig. 5 ) are typically massive in shape; varying in colour from yellowish to dark grey, depending on exposition to solar light, invariably yellowish internally; with few and very narrow dermal pores (up to 5 mm in diameter) and internal aquiferous channels of about the same diameter as the dermal pores; of firmly compressible consistency, resistant to tearing. When harbouring specimens of the new species, the sponges possess a relatively large internal burrow ( Fig. 5 , see DISCUSSION) which normally is not opened to the exterior, but in a few cases, it was found to have an aperture at the base of the sponge, of about the same diameter as the gallery (designation used for the burrows excavated by the shrimps). This shrimp species is probably host-specific since all examined specimens were always found in the same host species despite several sponge species were inspected in its type-locality searching for symbiotic shrimps.

When disturbed, specimens of P. ramili sp. nov. produces a snapping sound by rapidly closing the dactylus of the major chela.

Taxonomic remarks: Periclimenaeus ramili sp. nov. is morphologically closest to P. aurae , P. pearsei and P. hancocki , all sharing: (1) the short ventrally unarmed rostrum with similar dorsal dentition; (2) the absence of supraorbital spines or tubercles; (3) the strongly reduced incisor process of the mandible; (4) the feeble distolateral tooth of the scaphocerite not overreaching the lamina; (5) the general shape of the second pair of chelipeds and ambulatory pereiopods; and (6) the shape and armament of the telson ( Holthuis 1951; Ríos 1986; dos Santos et al. 2008). These species also share the presence of numerous plumose setae in the distal part of all maxilliped exopods, excepting for P. hancocki where this feature has not been described (but seemingly absent at least in the third maxilliped: cf. Holthuis, 1951, plate 29: Fig. E). Another feature shared by these three species, i.e., P. aurae , P. pearsei , and P. ramili sp. nov., is the slender distal articles of the third maxilliped endopod. Some of the above-mentioned features can be commonly found in species belonging to the genus Periclimenaeus whilst others, such as the strongly reduced incisor process of the mandibles, is an unusual feature described in only three others nonrelated congeners, viz the eastern Pacific P. pacificus Holthuis, 1951 , the western Atlantic P. pectinidactylus Ďuriš, Horká and Sandford, 2009 , and the east African P. trispinosus Bruce, 1969 ( Bruce 2001; Ďuriš et al. 2009; Holthuis 1951).

Based on these characteristics, P. aurae , P. pearsei , P. hancocki and P. ramili sp. nov. form a morphologically homogeneous and well-defined group within the genus Periclimenaeus , distributed throughout the Atlantic and Eastern Pacific, which is established here as the P. pearsei species group.

Periclimenaeus ramili sp. nov. can be easily distinguished from the only other known eastern Atlantic congener, P. aurae , by: (1) the antennular peduncle basal segment ( Fig. 1H ) with a welldeveloped distolateral tooth reaching to the middle of the second segment (versus distinct but small tooth; dos Santos et al. 2008: Fig. 2B ); (2) the incisor process of the mandible ( Fig. 2A ) lacking a tooth in its mesial margin in P. ramili sp. nov. (versus incisor process of the mandible bearing one tooth in its mesial margin; dos Santos et al. 2008: Fig. 2D ); (3) the scaphognathite posterior lobe ( Fig. 2C ) broad in P. ramili sp. nov. (versus posterior lobe of scaphognathite very slender; dos Santos et al. 2008: Fig. 2F ); (4) the third maxilliped ( Fig. 2F ) with penultimate article slenderer (versus somewhat broader; dos Santos et al. 2008: Fig. 3B ); (5) the first cheliped fingers ( Fig. 3A–B ) as long as the palm and the dactylus with the upper margin regularly sloping towards the tip in P. ramili sp. nov. (versus the fingers 0.8 length of palm and dactylus with upper margin convex; dos Santos et al. 2008: Fig. 3C ); and (5) the minor second cheliped dactylus ( Fig. 3F–G ) with the upper margin strongly convex, being almost semi-circular in P. ramili sp. nov. (versus convex distally but not semi-circular; dos Santos et al. 2008: Fig. 3E–F ).

Periclimenaeus ramili sp. nov. can be distinguished from P. pearsei by: (1) the slender rostrum ( Fig. 1A–C ) reaching beyond middle of the first segment of the antennular peduncle (versus rostrum triangular shaped in lateral view in the latter, reaching to about middle of the first segment of the antennular peduncle; Holthuis 1951, pl. 28: fig. R; dos Santos et al. 2008: figs. 5A–B, D); (2) the incisor process of the mandible lacking a tooth in its mesial margin in P. ramili sp. nov. (versus incisor process bearing one or two teeth); (3) the first cheliped fingers ( Fig. 3A–B ) as long as the palm and the dactylus with the upper margin regularly sloping towards the tip in P. ramili sp. nov. (versus fingers slightly shorter than palm and dactylus with upper margin strongly convex; Holthuis 1951, pl. 28: Fig. J) and (4) by the less clumsy body.

Periclimenaeus ramili sp. nov. is morphologically even closer to the eastern Pacific P. hancocki , with the differences between these two species being rather subtle, and besides the above-mentioned features, the new species also resembles P. hancocki in the strong distolateral tooth on the first antennular segment (also shared with P. pearsei ), the absence of tooth on the mesial margin of the incisor process of mandible and the general shape and proportions of the first cheliped dactylus and palm. Nevertheless, the new species can be distinguished from P. hancocki by: (1) the relatively shorter rostrum ( Fig. 1A–C ) not reaching distal margin of the first segment of the antennular peduncle in P. ramili sp. nov. (versus longer rostrum, reaching to or slightly overreaching the end of the first segment of the antennular peduncle in P. hancocki ; Ríos 1986: Fig. 2B ); (2) the dorsal margin of the rostrum ( Fig. 1A–B ) armed with four teeth (rarely three) in the new species (versus dorsal margin of the rostrum armed with five teeth in the former; Holthuis 1951, pl. 28: fig. A); (3) more reduced incisor process of the mandible ( Fig. 2A ) in the new species (versus more developed; Holthuis 1951, pl. 29: fig. D); (4) the scaphocerite ( Fig. 1B–C ) reaching to the distal margin of second segment of the antennular peduncle in P. ramili sp. nov. (versus reaching beyond middle of the third segment; Ríos 1986: Fig. 2B ); (4) very slender two distal articles of the third maxilliped ( Fig. 2F ) in P. ramili sp. nov. (versus two distal articles broad; Holthuis 1951, pl. 29: fig. D); (5) the sinuous cutting edge of the major second cheliped dactylus ( Fig. 3C–E ) in P. ramili sp. nov. (versus straight; Holthuis 1951, pl. 29: fig. I); and (7) the relatively shorter dorsal telson spines ( Fig. 1F ) (versus longer and slenderer; Ríos 1986: fig. 2H). These two species also seem to differ in number of plumose setae in the third maxilliped exopod. While P. ramili sp. nov. possesses 15 plumose setae in the distal third of the flagellum ( Fig. 2F ), P. hancocki apparently has only the typical four plumose setae ( Holthuis, 1951, pl. 29: fig. E).

Another feature that seems to be important to separate these four species is the number and position of setae on the appendix masculina. In male specimens of P. ramili sp. nov. (three males checked), the appendix masculina possesses two apical and four lateral serrate setae, whereas the appendix masculina of P. aurae possesses one apical and three lateral setae, P. hancocki has two apical and two lateral setae, and P. pearsei bears there two apical and seven lateral setae ( Ríos 1986; dos Santos et al. 2008).

Among the Indo-West Pacific congeners, only three species, Periclimenaeus marini Bruce, 2013 , Periclimenaeus quadridentatus (Rathbun, 1906) and Periclimenaeus stylirostris Bruce, 1969 , showed some affinity to the herein established species group. However, they do not appear to belong to this grouping, and can be easily distinguished from all four currently included species using important morphological features, especially the shape of the rostrum and the peculiar shape of the minor second chela fingers ( Bruce 1969 1972 2012b 2013b; Marin et al. 2004).

Figures

Fig. 1. Periclimenaeus ramili sp. nov., male holotype (RMNH.CRUS.D.57969): A, rostrum, lateral; B, frontal region of carapace and appendages, dorsal view; C, same, lateral view; D, pleon, lateral view; E, posterior carapace and first pleonite, dorsal view; F, sixth pleonite, telson and uropod, dorsal view; G, posterior margin of telson, dorsal; H, antennule, dorsal view; I, antenna, ventral view; J, first pleopod; K, second pleopod; L, same, appendices masculina and interna. Scale bar: B–F, H–K = 1 mm; A, G, L = 0.5 mm.

Fig. 2. Periclimenaeus ramili sp. nov., male holotype (RMNH.CRUS.D.57969): A, right mandible; B, left maxillula; C, left maxilla; D, left first maxilliped; E, left second maxilliped; F, left third maxilliped. Scale bar: A–C = 0.5 mm; D–E = 1 mm.

Fig. 3. Periclimenaeus ramili sp. nov., male holotype (RMNH.CRUS.D.57969): A, first pereiopod, lateral; B, same, lateral; C, major second pereiopod, lateral; D, same, fingers, lateral; E, same, fingers, mesial; F, minor second pereiopod, lateral; G, same, fingers, mesial. Scale bar: A–G = 1 mm.

Fig. 4. Periclimenaeus ramili sp. nov., male holotype (RMNH.CRUS.D.57969): A, third pereiopod, mesial; B, same, dactylus and distal propodus, mesial; C, fourth pereiopod, lateral; D, same, dactylus and distal propodus, mesial; E, fifth pereiopod, lateral; F, same, dactylus and distal propodus, lateral. Scale bar: A, C, E = 1 mm; B, D, F = 0.5 mm.

Fig. 5. Periclimenaeus ramili sp. nov and host sponge Spongia sp. A, male holotype (RMNH.CRUS.D.57969) and female allotype [(RMNH.CRUS. D.57970); B, sponge host: Spongia sp.; C, spongin fibers obtained from stomach content of Periclimenaeus ramili sp. nov. Scale bar = unscaled.

Fig. 6. Periclimenaeus cf. ramili sp. nov. from Lanzarote, Canary Islands. Photographic Credits: Leopoldo Moro.