Periclimenaeus denticulodigitus Bruce, 2014, sp. nov.

Periclimenaeus denticulodigitus sp. nov.

(Figs 1 –4)

Material examined. 1 ovig. ♀, holotype, Heron Island, Queensland, coll. N.L. Bruce, from reef slope, 7.0 m, 8 December 1979, QM W29199

Diagnosis. ♀, rostrum slender, dentition 6/0, carapace without supraorbital spines or tubercles: first abdominal tergite without antero-dorsal lobe; scaphocerite with tooth not exceeding lamella; incisor process of mandible multidentate; first pereiopod fingers narrow, spatulate, edges entire; second pereiopod chelae small, smooth, major dactyl with well developed molar process, cutting edge posteriorly finely denticulate, anterior cutting edge entire, merus with acute tubercles ventrally, minor second pereiopod dactyl with denticulate, feeble molar process proximally, fixed finger with proximal fossa, long denticulate lateral cutting edge; third pereiopod with dactyl pseudo-tuberculate, densely finely denticulate; third pereiopod with dactyl simple, carpus not swollen; telson with robust dorsal spines at 0.1 and 0.5 of telson length.

Description. Ovigerous ♀, holotype, complete.

Rostrum (Fig. 1 C) slender, compressed, short, about 0.43 of CL, reaching to end of proximal segment of antennular peduncle, dorsal carina with six similar slender acute teeth over full length, numerous interdental setae, ventral carina obsolete, unarmed.

Carapace (Fig. 1 A) smooth, glabrous, slightly compressed, without supraorbital teeth or tubercles (Fig. 1 B), antennal tooth well developed, inferior orbital angle obsolete, anterolateral carapace margin advanced, broadly rounded.

Abdomen well developed, without antero-median dorsal lobe on first segment, pleura of first three segments enlarged, broadly rounded, fourth and fifth angular, subacute, sixth segment (Fig. 1 H) with well developed posterolateral and posteroventral teeth.

Telson (Fig. 1 I) about 0.6 of CL, twice as long as anterior width, lateral margins straight, convergent, distal margin broadly angular (Fig. 4 K), without median point, with short stout subequal dorsal spines (Fig. 5L) at 0.1 and 0.5 of telson length, about 0.11of telson length, lateral posterior spines (Fig. 4 K) well developed, about as long as anterior dorsal spines, intermediate spines robust, slightly longer than anterior dorsal spines, submedian spines slender, about as long as posterior dorsal spines.

Antennule (Fig. 1 D) with proximal segment of peduncle (Fig. 4 A) about 2.2 times longer than central width, medial margin straight, with acute ventral tooth at about 0.5 of length, lateral margin produced, distally concave, with small acute distolateral tooth (Fig. 4 A), stylocerite acute, phylliform, statocyst with granular statolith, intermediate and distal segments short, subcylindrical, subequal, about 0.5 of proximal segment length, upper flagellum biramous, proximal five segments fused, short free ramus with single segment, with twelve groups of aesthetascs, longer free ramus with four segments; lower flagellum short, filiform, with eight segments.

Antenna (Fig. 1 E) with basicerite unarmed; carpocerite reaching to middle of intermediate segment of antennular peduncle, far exceeding scaphocerite, subcylindrical, about 5.0 times longer than wide; merocerite and ischiocerite without special features; scaphocerite (Fig. 1 F) reduced, reaching to 0.6 of carpocerite length, about 2.5 times longer than wide, distal lamella rounded, lateral margin straight with robust distolateral tooth at 0.9 of length, 0.16 of lateral margin length, slightly exceeding distal margin of lamella.

Eye (Fig. 1 G) with cornea globular, oblique, diameter about 0.19 of CL, without accessory pigment spot, stalk about as long as deep, swollen.

Mouthparts, right side.

Mandible (Fig. 2 A) with corpus robust, without palp, molar process (Fig. 4 B) subcylindrical, obliquely truncate distally, densely setulose, with stout distolateral tooth; incisor process (Fig. 4 C) normal, tapering to oblique tip with five small acute subequal teeth and single larger lateral tooth.

Maxillula (Fig. 2 B) with feebly bilobed palp (Fig. 4 D), lower lobe slightly produced with simple terminal seta on small tubercle; upper lacinia (Fig. 4 E) short and broad, distally truncate, straight, with ten simple teeth, medial and lateral similar spines, sparse ventral setae; lower lacinia short, stout, subcylindrical, distally rounded with several long slender serrulate spiniform setae.

Maxilla (Fig. 2 C) with flattened tapering palp, about 3.5 times longer than basal width, non-setose, basal endite with lobes fused, broadly rounded distally with seven slender setae, coxal endite with medial margin convex, nonsetose, scaphognathite normal, broad, about 3.4 times longer than central width, anterior lobe 1.6 times longer than wide, medial margin slightly concave, posterior lobe 2.0 times longer than basal width, all margins setose.

First maxilliped (Fig. 2 D) with flattened palp without terminal seta, basal and coxal endites fully fused, distally rounded, medial margin straight with numerous slender setae, decreasing proximally, exopod normal, flagellum slender, with four plumose distal setae, caridean lobe large, about 2.0 times longer than central width, epipod well developed, rounded, bilobed.

Second maxilliped (Fig. 2 E) with normal endopod, dactylar segment narrow, 3.2 times longer than broad, with numerous long slender serrulate marginal spines, propodal segment antero-medially rounded, not produced, with seven long slender marginal spines, carpus, merus and ischiobasis without special features, exopod with slender flagellum with four long plumose terminal setae, coxa not produced medially, without epipod.

Third maxilliped (Fig. 2 F) with ischiomerus and basis fully fused, combined segment 2.2 times longer than basal width, tapering distally, sparsely setose distomedially, merus subcylindrical, 2.0 times longer than ischiomerus, 2.8 times longer than wide, with few groups of spiniform setae medially, terminal segment subequal to meral length, 3.0 times longer than proximal width, tapering distally, with numerous spiniform setae, coxa robust, medial margin straight, non-setose, lateral margin with well developed low rounded lateral plate, without arthrobranch.

Thoracic sternite s narrow, unarmed.

First pereiopod (Fig. 3 A) normal, chela (Fig. 3 B) about 0.28 of CL, palm subcylindrical, slightly compressed, twice as long as deep, with few short cleaning setae proximo-ventrally, fingers about 0.85 of palm length, slender, spatulate, cutting edges entire, tips rounded with dactyl with three terminal teeth (Fig. 4 F), central tooth larger than adjacent teeth, fixed finger with two distal teeth only; carpus 1.2 times chela length, 4.1 times longer than distal width, tapering strongly proximally; merus about 1.4 times chela length, 5.1 times longer than maximal width, subcylindrical; ischium 0.5 of meral length, 0.6 of palm length; basis without special features; coxa normal, without ventral process.

Second pereiopods unequal, feebly dissimilar.

Major second pereiopod (Fig. 3 C) with chela about 2.1 times CL, palm subcylindrical, slightly swollen centrally, compressed, about 2.0 times longer than proximal depth, distal depth 0.6 of proximal width, smooth, glabrous; fingers (Fig. 3 D) 0.38 of palm length, gaping, dactyl (Fig. 3 D) about three times as long as central depth, compressed, dorsal margin strongly convex, tip acute, cutting edge with small molar process proximally, ventrally concave with posterior margin thickened and finely tuberculate, distally concave, unarmed; fixed finger (Fig. 3 D) about 1.5 times as long as proximal depth, proximal third of cutting edge with fossa for reception of dactylar molar process, flanked medially by low raised tooth densely covered with minute tubercles (Fig. 3 E), with similar tooth laterally and distally, distal third of cutting edge concave, unarmed; carpus 0.55 of palm length, distally expanded, 3.0 times longer than distal width, unarmed; merus 0.5 of palm length, 2.0 times longer than wide, slightly expanded central with four minute acute ventral tubercles; ischium subequal to meral length, tapering proximally, 2.1 times longer than distal width; basis and coxa very robust, without special features.

Minor second pereiopod (Fig. 3 F) with chela about 1.64 of CL, 0.72 of major chela length, palm subcylindrical, uniform, compressed, about 2.0 times longer than depth, smooth, glabrous; fingers (Fig. 3 GH) gaping, sparsely setose, about 0.5 of palm length, dactyl (Fig. 3 G) compressed, dorsal margin convex, 4.0 times longer than centrally depth, tip acute, crossing with fixed finger tip, cutting edge (Fig. 3 I), with low rounded tooth proximally, compressed, densely covered with small short acute erect denticles, distal two thirds of cutting edge concave, entire, fixed finger about 1.6 times as long as proximal depth, cutting edge longitudinally grooved proximally with small fossa to accommodate dactylar tooth, cutting edge sinuous, proximal two thirds convex, with densely covered with small denticles similar to those of the dactylus, proximal third concave, unarmed, tip acute, feebly hooked; carpus 0.4 of palm length, distally expanded, 1.8 times longer than wide, unarmed; merus 0.65 of palm length, twice as long as central width, with four small acute distally directed denticles ventrally; ischium subequal to meral length, tapering proximally, unarmed; basis and coxa robust, without special features.

Third pereiopod (Fig. 3 I) robust, dactyl (Fig. 4 H) short and stout, about 0.18 of propod length, compressed, unguis short, curved, unarmed, 2.0 times longer than basal width, 0.5 of corpus length, dorsal margin convex, without ornamentation, corpus with dorsal margin convex, about twice length of unguis, 11.3 times longer than maximal depth, without distal accessory tooth, distal half of ventral margin feebly convex, entire, proximal half concave, with large angular tooth, sparsely setose; propod (Fig. 4 G) about 0.6 of CL, subcylindrical, tapering slightly distally, compressed, 3.5 times longer than proximal depth, with pair of short stout distoventral spines, sparsely setose; carpus similar to propod, not swollen, compressed, about 0.7 of propod length, unarmed; merus robust, 1.1 times propod length, compressed, centrally swollen, 2.6 times longer than central width, unarmed; ischium 0.8 of meral length, unarmed; basis and coxa stout, coxa with long setae ventrally, without special features.

Fourth and fifth pereiopods similar to third, dactyls (Fig. 4 J) similar, unguis simple, corpus without accessory tooth, ventral margin unarmed, broadly rounded proximally; propod of fifth (Fig. 4 I) longer than third.

Pleopods without special features.

Uropods (Fig. 1 J) with protopodite unarmed; exopod about 0.85 of telson length, 2.4 times longer than wide, lateral margin mainly straight, with small distal tooth and longer mobile spine medially (Fig. 4 M), without diaeresis; endopod subequal to exopod length, 3.0 times longer than wide.

Ova numerous and small.

Measurements. Holotype female — post-orbital carapace length, 1.75 mm; carapace and rostrum, 2.5 mm; total body length (approx.), 8.5 mm; major second pereiopod chela length, 2.7 mm; minor second pereiopod chela length, 1.9 mm; length of ovum, advanced, 0.7 mm.

Host. Unidentified ascidian.

Colouration. Semi-transparent, finely speckled with small uniform white dots over body, antennae, second pereiopods and caudal fan with smaller red dots in interspaces..

Etymology. From dens, (Latin), tooth, and digitus, (Latin), finger, with reference to the second pereiopod fingers.

Systematic position. The five species of indo-West Pacific Periclimenaeus species known to have a fully simple ambulatory dactyl on the third pereiopod are P. calmani Bruce 2012, P. h e c a t e (Nobili, 1904), P. serenei Bruce, 2012, P. serrula Bruce & Coombes, 1995 and P. denticulodigitus sp. nov. The species do not appear to be closely related but can be readily identified from the following key:

1. Third ambulatory dactyl with oblique oval flattened area distomedially on corpus........................... P. calmani

- Third ambulatory dactyl without oblique oval flattened area distomedially on corpus................................ 2

2. Minor second pereiopod dactyl with denticulate pseudo-molar process with opposing depression on fixed finger................................................................................................. P. denticulodigitus

- Minor second pereiopod dactyl without denticulate pseudo-molar process with opposing depression on fixed finger........ 3

3. Dactyl of minor second pereiopod with cutting edge entire, of major second pereiopod minutely denticulate; R 4/0...................................................................................................... P. serrula

- Dactyl of minor second pereiopod with cutting edge denticulate................................................. 4

4. Third ambulatory dactylar corpus pitted, minor second pereiopod dactyl cutting edge slenderly denticulate, about 15 teeth; fixed finger cutting edge coarsely denticulate; R 4/0................................................... P. serenei

- Third ambulatory dactylar corpus smooth, minor second pereiopod dactyl cutting edge finely denticulate, about 40 teeth; fixed finger cutting edge entire; R 4–5/0.................................................................. P. hecate

The minor second pereiopod in P. denticulodigitus is unique in this genus and suggests an isolated systematic position for this species. The incipient molar process and fossa show a small resemblance to P. parkeri Bruce, 2012, and Isopericlimenaeus gorgonidarum (Balss, 1913) (Bruce, 2012; Marin, 2012). In both of these species the fingers resemble those of the major pereiopod, unlike all other species of the genus in which they are of markedly contrasting morphology. The former species has a third ambulatory dactyl that is biunguiculate with a large acute proximal tooth on the corpus and the minor second pereiopod has a dactyl that far exceeds the fixed finger with a well developed molar process proximally and the distal cutting edge minutely denticulate and bluntly rounded distal tip (Bruce, 2012). The latter species has a rostral dentition of 7-8/1-2, carapace with supraorbital teeth, caudal fan with lateral margin of exopod dentate and spinulate and telson with very large anterior dorsal spines and small posterior dorsal spines and the ambulatory dactyls are biunguiculate with ventral margins of unguis and corpus minutely denticulate (Marin, 2013). These major differences indicate no close relationship to P. denticulodigitus. The denticulations of the minor second pereiopod fingers are unique but some species, such as P. heronensis Bruce, 2012, do show traces of minute tuberculations in this position (Bruce, 2012: 24, Fig. 3), with feeble indications of a fossa on the fixed finger. Periclimenaeus usitatus Bruce, 1969 is also noteworthy as although the cutting edge of the minor second pereiopod dactyl has an entire cutting edge the fixed finger has the cutting edge grooved and in the holotype specimen “Indeed the fixed finger has this minute denticulation on the higher medial edge of the groove. It is not a single row of denticles however, but extends into the groove with obtuse denticles forming a granular longitudinal band. I also checked the major second chela, which has the same structure on the fixed finger”, as reported by Dr C.H.J.M. Fransen (Bruce, 2010). A similar structure can also be found in other genera such as the sponge associate Nippontonia (Bruce & Bauer, 1997; Fransen, 2013).

Remarks. It is remarkable that despite several years of detailed shrimp collecting on Heron Island, no further specimens of this shrimp were obtained although numerous examples of Periclimenaeus species were collected from ascidians and sponges. Heron Island now has a Periclimenaeus shrimp fauna of 18 species, with a further 2 species from the adjacent Capricorn Islands. The Great Barrier Reef supports no further species but 28 of the 61 Indo-West Pacific species are known from Australian waters.