Plesiomenaeus poorei, Bruce, 2009

Bruce, A. J., 2009, Plesiomenaeus poorei gen. nov., sp nov., (Crustacea: Decapoda: Pontoniinae) from Zanzibar, Memoirs of Museum Victoria 66 (1), pp. 25-34 : 26-34

publication ID	https://doi.org/ 10.24199/j.mmv.2009.66.4
DOI	https://doi.org/10.5281/zenodo.12212206
persistent identifier	https://treatment.plazi.org/id/621D87EC-FFC4-FF92-B6FE-F89495019BB4
treatment provided by	Felipe
scientific name	Plesiomenaeus poorei
status	sp. nov.

Treatment

Plesiomenaeus poorei View in CoL sp. nov.

Figures 1–7 View Figure 1 View Figure 2 View Figure 3 View Figure 4

Material examined. 1 ovig., holotype, Chukwani , Unguja, Zanzibar, 6° 13' 60"S 30° 13' 00"E, 0.1m at low water spring tide, 4 December 1960, coll. A.J. Bruce, #271, NMV J59993 View Materials GoogleMaps . 1, allotype, idem, NMV J59994 View Materials GoogleMaps . Ovig. , dissected, idem, NMV J59995 View Materials GoogleMaps . 1, 1 ovig., paratypes, idem, MNHN-Na17209. 1, 1 ovig., paratypes, idem, QM W28956 GoogleMaps . 1, 1 ovig., paratypes, idem, OUMNH. ZC GoogleMaps . 2009-12-001. 1, 1 ovig., paratypes, idem, RMNH D 53113 View Materials GoogleMaps .

Diagnosis. With the characters of the genus. Very short rostrum generally with single dorsal tooth only, proximal segment of antennular peduncle distolaterally rounded, without acute tooth, ventral border of second pereiopod merus non-tuberculate.

Description. A stoutly built shrimp of subcylindrical body form (fig. 1).

Rostrum (fig. 6A) very short, about 0.06 of CL, compressed, triangular, acute, with singe acute dorsal tooth, carapace (fig. 2A) smooth, without supraorbital, epigastric, hepatic or antennal spines, inferior orbital angle (fig. 2B) acute, pterygostomial angle strongly produced, rounded.

Abdomen smooth, first segment without anterior median dorsal lobe, pleura rounded, sixth segment (fig. 2C) depressed, about 0.24 of CL, with small subacute posterolateral tooth and much larger, acute posteroventral tooth; telson (fig. 2D) about 0.35 of CL, 2.15 times longer than anterior width, lateral margins slightly convex, tapering posteriorly, posterior margin rounded (figs 2E, 6J) two pairs of small submarginal dorsal spines, about 0.08 of telson length, anterior pair at 0.65 of telson length, posterior pair at about 0.96 (see Remarks), with three pairs of marginal spines, lateral spines similar to dorsal spines, intermediate spines about 0.1 of telson length, submedian spines more slender, finely setulose, about 0.8 of intermediate spine length.

Antennule (fig. 2F) with proximal segment of peduncle (fig. 2G) about twice as long as proximal width, lateral margin straight, non-setose, without ventromedial tooth, lateral margin angular, distolateral angle rounded (fig. 6B) with 1–2 short plumose setae, sometimes acute, stylocerite acute, projecting laterally, reaching to about half segment length, statocyst poorly developed, without statolith, intermediate and distal segments short and broad, combined length about 0.4 of proximal segment length, upper flagellum short, biramous, with proximal 8 segments fused, short free ramus with single long segment, with 2 groups of aesthetascs, longer free ramus with 5 slender segments, lower flagellum short, filiform with 10 segments.

Antenna (fig. 2H) with carpocerite subcylindrical, about 3.0 times longer than wide, basicerite robust, without lateral tooth, with large rounded protuberant antennal gland process medially; scaphocerite (fig. 2I) small, subequal to carpocerite length, about 2.7 times longer than wide, distally rounded, lateral margin straight with small acute distal tooth, at about 0.9 of scaphocerite length, well short of margin of lamella, distal and medial margins with numerous short plumose setae.

Epistome unarmed, without special features.

Eye, (fig. 2J), with hemispherical cornea, well pigmented, diameter about 0.13 of CL, without accessory ocellus, stalk globular, about 1.1 times longer than wide.

Mandible (fig. 3A) small, without palp, molar process (fig. 6D) subcylindrical, tapering distally, distally obliquely truncate with two small teeth and numerous rows of short spiniform setae, incisor process small (fig. 6E) narrow, distally rounded with three small acute teeth laterally, two smaller teeth medially.

Maxillula (fig. 3B) with bilobed palp (fig. 6F), upper lobe larger than lower, lower tapering with distal tubercle with short slender terminal seta, upper lacinia (fig. 6G) short and broad, upper margin emarginate, distal margin broadly truncate with about 16 short simple spines and scattered setae, lower lacinia tapering distally with six terminal spines and numerous spiniform setae.

Maxilla (fig. 3C) with simple tapering palp, with few short plumose setae proximo-laterally, basal endite simple, short and broad, with 10 slender sparsely setulose terminal setae, coxal endite obsolete, medial margin broadly rounded, non-setose, scaphognathite well developed, about 2.6 times longer than wide, anterior lobe as long as wide, medial margin concave, posterior lobe about 0.8 of anterior lobe length.

First maxilliped (fig. 3D) with palp (fig. 6H) about 2.5 times longer than wide, distally rounded, with two preterminal feebly setulose setae disto-medially, basal and coxal endites fused, distally rounded medial margin straight, with numerous slender sparsely setulose marginal setae, exopod with well developed caridean lobe, flagellum slender with four long plumose terminal setae, epipod well developed, bilobed.

Second maxilliped (fig. 3E) with endopod normally developed, dactylar segment about 3.4 times longer than broad, medial margin with numerous long slender coarsely setulose or finely denticulate spines, propodal segment distomedially produced, with numerous long slender sparsely setulose marginal spines, proximal endopod segments normal, basis with slender flagellum, coxa with small suboval epipod, without podobranch.

Third maxilliped (fig. 3F) with ischiomerus and basis fully fused, combined segment about 3.0 times longer than maximal width, tapering distally, medial margin straight with numerous long slender simple setae,carpus subcylindrical,half ischiomerusbasis length, 4.0 times longer than wide, with numerous spiniform setae medially, distal segment missing in dissected specimen, exopod with slender flagellum, slightly exceeding distal merus, with four major plumose terminal setae (broken off in dissected specimen), coxal with well developed low rounded lateral plate, without arthrobranch. Paragnaths (fig. 6C) deeply bilobed.

Thoracic sternites unarmed, narrowest at fourth and fifth segment levels and broadening anteriorly and posteriorly.

First pereiopod (fig. 4A) short, robust, chela (fig. 4B) with palm 1.5 times longer than deep, compressed, with numerous short simple cleaning setae proximo-ventrally, fingers subspatulate, with numerous groups of short simple setae, cutting edges entire, dactyl with tridentate tip (fig. 6I) medial and lateral teeth posteriorly tuberculate, fixed finger distally deeply bidentate (fig. 6I) simple; carpus 0.59 of chela length, 2.9 times longer than distal width, with transverse row of distal marginal cleaning setae with 3 long distoventral setae; merus 1.3 times longer than chela, 5.7 times longer than wide, uniform, slightly bowed; ischium 0.33 of chela length, 0.28 of meral length, basis subequal to ischial length; coxa robust, without ventral process, with dorsal flange.

Second pereiopods well developed, unequal, similar, fingers up-curved. Major chela (fig. 4C) length subequal to CL, palm smooth, oval in section, about 2.1 times longer than deep, tapering distally, distal width about 0.6 of maximal width, non-setose; fingers (fig. 4CDE) 0.25 of palm length, dactyl about 3.0 times longer than proximal depth, dorsal margin convex, with strong acute tip, cutting edge without molar process, unarmed, feebly convex, entire, sharp, fixed finger about 1.8 times longer than proximal depth, ventral margin convex, with acute tip distally, occlusal edge longitudinally grooved throughout length with deep depression proximally, dorsal margin with bluntly triangular tooth proximally, with sharp entire cutting edge, ventral cutting edge similar, without proximal tooth, carpus robust, about 0.4 of palm length, distally expanded, 1.5 times longer than distal width, tapering strongly proximally, unarmed, merus about 0.5 of palm length, 3.0 times longer than wide, unarmed, ventrally non-tuberculate; ischium 0.8 of merus length, 0.4 of palm length, 2.4 times longer than distal width, tapering proximally, unarmed, basis and coxa robust, without special features. Minor second pereiopod chela (fig. 4G) similar to major chela, subequal to palm length of major chela, palm 3.5 times longer than depth, tapering slightly distally, fingers (fig. 4H) 0.25 of palm length, similar to major chela, carpus 0.33 of palm length, 2.0 times longer than distal width; proximal segments as for major chela but smaller.

Third ambulatory pereiopod (fig. 4I) moderately slender, reaching beyond carpocerite by propod and dactyl; dactyl short, stout, compressed, about 0.12 of propod length, unguis well developed, curved, 2.2 times longer than basal width, 0.33 of corpus length, unarmed, corpus 1.2 times longer than proximal depth, with dorsal margin strongly convex, ventral margin sinuous, distally concave, sharp, unarmed, with acute distal accessory tooth, about 0.5 of unguis length, with several simple ventral sensory setae; propod about 0.3 of CL, 5.5 times longer than proximal width, tapering distally, distal width 0.66 of proximal width, with three stout spines distally, medial, lateral and ventral, medial spine longest, 3.7 times longer than basal width, projecting beyond dorsal margin of flexed dactyl, ventral spine shortest, 0.8 of medial spine length, ventral margin of propod otherwise without spines; carpus 0.8 of propod length, 4.0 times longer than distal width, slightly tapering proximally, unarmed; merus subequal to propod length, 3.4 times longer than wide, unarmed; ischium 0.55 of propod length, twice as long as distal width, tapering proximally, unarmed; basis and coxa without special features. Fourth pereiopod similar, propod subequal in length but more swollen, 3.6 times longer than proximal depth, maximal width 3.0 times distal width, with shorter, more slender medial, lateral and ventral spines, dactyl with corpus 1.6 times longer than proximal depth, unguis 0.2 of corpus length, accessory tooth smaller. Fifth pereiopod similar, propod subequal in length but propod more swollen than fourth, 3.2 times longer than proximal depth, maximal width 2.8 times distal width, with single small ventral spine and numerous distoventral setae, dactyl about 0.12 of propod length, with corpus 1.5 times longer than proximal depth, unguis 0.2 of corpus length, accessory tooth smaller.

First pleopod (fig. 7C) male paratype (CL 3.4mm) with protopod about 2.5 times longer than broad, exopod subequal to protopod length, 5.0 times longer than wide with numerous plumose marginal setae, endopod, 0.7 of exopod length, 5.0 times longer than proximal width, tapering distally, without medial accessory lobe, with numerous, about 20, simple spiniform setae scattered along medial border. Second pleopod (fig. 7D) with protopod 2.0 times longer than wide, greatest width centrally, 1.2 times longer than first pleopod protopod, exopod similar to first pleopod, endopod (fig. 7E) subequal exopod length, 4.4 times longer than central width, with numerous plumose marginal setae distally, appendices (fig. 7F) at 0.55 of medial margin length, appendix masculina subcylindrical, 2.5 times longer than wide, about 0.16 of endopod length, with 5 setulose setae of increasing length distally along medial margin, terminal seta longest, about twice corpus length’ appendix interna slightly longer than appendix masculina, with few terminal cincinnuli.

Uropod (fig. 2K) with protopod unarmed; exopod broad, about 1.6 times longer than broad, lateral margin feebly convex, non-setose with small acute distal tooth (fig. 6K) with small spine medially (see Remarks); endopod 0.95 of exopod length, 2.0 times longer than wide.

Measurements (mms). Holotype, ovigerous female, postorbital carapace length, 6.0; carapace and rostrum, 6.4; total body length (approx.) 17.0; second pereiopod, major chela, 6.0; minor chela, 5.0; length of ovum, 0.55.

Etymology. Named for Dr Gary C.B. Poore, Principal Curator (Marine Biology), Museum of Victoria, in recognition of his major contributions to Australian and wider carcinology over many years.

Host. Unidentified sponge encrusting round the base of a coral colony.

Colouration. No data.

Remarks. The telson of the holotype is slightly abnormal in that the posterior pair of dorsal spines are placed on the posterior margin of the telson which thus presents the appearance of having four pairs of posterior marginal spines, with only a single pair of dorsal spines. One female (fig. 7A) was without a rostrum, the absence appearing congenital rather than traumatic. Two of the male specimens (fig. 7B) had two rostral teeth. Some specimens had a small acute distolateral tooth on the proximal segment of the antennular peduncle, usually asymmetrically.

The presence of slender propods on the third pereiopod and stouter propods on the posterior limbs is unusual in pontoniine shrimps. In some species of the closely related genus Periclimenaeus the propods are not greatly different but in others, such as P. crassipes Calman and P. trispinosus Bruce , the third pereiopod propods are particularly short and stout and the posterior propods longer and more slender, in contrast to their development in P. poorei sp. nov.

Despite intensive collecting over the coral reefs of Zanzibar, and similar reefs in Tanganyika and Kenya, over several years, resulting in numerous other sponge associated shrimps, no further specimens of this species were ever collected.

The resemblance of P. poorei sp. nov. to Periclimenaeus bouvieri (Nobili) is remarkable. Holthuis’s statement that “a strong hammer shaped tooth fitting into a cavity on the fixed finger”, leaves little doubt concerning these features and the placement of Nobili’s species in Periclimenaeus . Re-examination of the type material of Nobili’s species may shed further light on the detailed morphology of the fingers of the major second pereiopod and hence its exact systematic position. Plesiomenaeus poorei sp. nov. is readily distinguished from Periclimenaeus bouvieri by having only a single dorsal rostral tooth in females and a non-tuberculate second pereiopod merus as opposed to two dorsal rostral teeth and a ventrally tuberculate merus in addition to the absence of a molar process and fossa on the major second pereiopod fingers. The type material of Typton bouvieri is held in the collections of the Museo Regionale di Scienze Naturali, Torino.