Periclimenaeus cloacola Fransen 2023, spec. nov.

Periclimenaeus cloacola spec. nov.

(Figs. 21–29, video 8)

Material examined. Curaçao: RMNH. CRUS.D.58145: 1 ovigerous female, pocl. 1.8 mm, R =2/0, damaged, all pereiopods missing; Piscaderabaai, 05.i.1964, 1.5–2 m depth, collected by P. Wagenaar Hummelinck (fcn. 1457). RMNH.CRUS.D.58146: 1 female, R =2/0, pocl. 1.6 mm; stn COA. 14, Playa Boka Sami, 12°08′51.40″N 68°59′55.50″W, 05.xi.2013, depth 5 m, scuba diving, in compound ascidian under stone, Diplosoma aff. listerianum (H. Milne Edwards, 1841) (photo COA.14 108–111), collected by B. T. Reijnen (photo COA.14 116–124). Bonaire: RMNH. CRUS.D.57868: 1 specimen, probably a male (first and second pleopods missing), pocl. 1.5 mm, R =2/0; 1 ovigerous female, pocl. 2.1 mm, R = 2/0; stn BON.05, Corporal Meiss, 12°07.888′N 068°16.996′W, 24.x.2019, depth 2 m, in greyish compound ascidian under stone, Diplosoma sp., collected by C.H.J.M. Fransen (fcn. BON.05- 1) (photo). RMNH. CRUS.D.58147: 1 ovigerous female, pocl. 2.0 mm, R = 1/0; stn BON.06, Oil Slick Leap, 12°12.029′N 068°18.512′W, 25.x.2019, depth 8 m, in greyish compound ascidian under stone, D. aff. listerianum, collected by C.H.J.M. Fransen (fcn. BON.06-1) (video 8). RMNH. CRUS.D.57883: 1 ovigerous female, pocl. 2.9 mm, R =2/0; stn BON.21, Something Special (Pali Grande), 12°09.696′N 068°17.016′W, 31.x.2019, depth 1 m, scuba diving, in greyish compound ascidian under stone, D. aff. listerianum, collected by C.H.J.M. Fransen (fcn. BON.21-1) (video 8).

Description. Small shrimp with subcylindrical body (Fig. 21A). Rostrum short, dorsal carina well marked, directed downwards with 1–2 dorsal teeth placed distinctly in advance of posterior margin of orbit, with short setae interspersed proximally; apex of rostrum slender and curved upwards, reaching distal margin of basal segment of antennular peduncle; ventral margin convex, unarmed, devoid of setae; lateral carina obsolete (Fig. 21A–E). Carapace smooth, glabrous, without epigastric, supraorbital or hepatic spine, antennal tooth strong, marginal, at level of produced inferior orbital angle; inferior orbital angle moderately produced (Fig. 21C); orbital ridge present; pterygostomial angle broadly rounded, distinctly produced (Fig. 21A, B).

Epistome and labrum normal.

Sternites small; second thoracic sternite unarmed; third thoracic sternite with median rounded shallow plate; fourth to eighth thoracic sternites unarmed.

Abdomen smooth, first abdominal segment without median anterior dorsal lobe, third segment not produced posteriorly; pleura of first five pleonites broadly rounded, sixth pleonite as long as fifth, somewhat more than half as long as telson, with posteroventral angle feebly produced, angular, posterolateral angle rounded (figs. 21A, 22A).

Telson twice as long as maximal width, about 3.3 times as broad as posterior width, lateral margins converging; dorsal spiniform setae stout, large, 0.2 of telson length, anterior pair placed at 0.15 of telson length, of considerable distance from lateral margin of telson, posterior pair placed at 0.5 of telson length, submarginal; three pair of terminal spiniform setae; lateral pair short, slightly shorter than dorsal spiniform setae, placed subdistally, marginal; intermediate pair longest, slightly more than twice as long as lateral pair, submedian pair slightly shorter than intermediate pair, plumose (Fig. 22A, B).

Eyes with cornea hemisperical, slightly shorter than the stalk, without Nebenauge; stalk slightly swollen proximally (Fig. 21B, C).

Antennula with peduncle almost as long as scaphocerite, stylocerite broad, short and pointed, almost reaching middle of basal segment, lateral margin of basal segment slightly concave, forming blunt angle with rounded tip at about level of tip of stylocerite, anterior margin not developed, small distolateral tooth present; intermediate segment short, about as long as broad, unarmed; distal segment slightly longer than intermediate segment; outer upper antennular flagellum with rami fused for about six joints, free part of shorter ramus unsegmented, fused part and shorter ramus both with many aesthetascs, longer ramus short, about 7-segmented; inner lower flagellum about als long as outer antennular flagellum, filiform (Fig. 23A).

Antennal basicerite unarmed; carpocerite reaching distal margin of scaphocerite lamella, about four times longer than distal width; scaphocerite small, just overreaching antennular peduncle, about twice as long as broad, outer margin is slightly convex, distolateral tooth distinct, not overreaching lamella, lamella rounded distally, narrowing posteriorly (Fig. 18B).

Mandible incisor process with four teeth; molar process with one strong rather acute tooth and brush of setae (Fig. 23C).

Maxillula with palp distally bilobed, upper lobe rounded, short; inferior rounded with one distal recurved spinule with globose base; upper lacinia of endite broad with series of cuspidate and simple setae on slightly convex mesial margin; lower lacinia of endite more slender, curved, with slender pappose setae (Fig. 23D).

Maxilla with scaphognathite ovoid, anterior lobe about as broad as posterior lobe, margins covered by dense plumose setae; palp simple, reaching to 2/3 rd of length of scaphognathite anterior lobe; distal endite entire, with about 12 long slender simple distomarginal setae; basal endite not developed, slightly convex (Fig. 23E).

First maxilliped with simple elongated palp reaching anterior margin caridean lobe; exopodal flagellum long and slender with four long plumose setae distallu and one shorter plumose seta subdistally; caridean lobe longer than broad, margin covered by dense plumose setae; epipod distinctly bilobed; endite ovoid, without clear division between distal and proximal endites, with simple and plumose setae along distal and median margins (Fig. 24A).

Second maxilliped with dactylar segment elongated, ovoid, furnished with many simple, and plumose setae; propodal segment with superior margin produced with long simple and plumose setae; carpal segment cu shaped, without setae; merus slightly longer than broad, without setae; ischio-basis excavate medially, with few short simple setae along median margin; exopod elongated, with four long plumose setae distally and one short seta subdistally; median margin of coxa not produced, furnished with one simple seta; epipod recangular (Fig. 24B).

Third maxilliped short, reaching with ultimate segment to basis of carpocerite; ultimate segment about 0.6 times as long as the penultimate segment, slightly tapering distally, distal end rounded, covered with abundant plumose setae; penultimate segment about 0.8 times as long as ischio-meral segment, about 2.8 times as long as wide, ventral margin with rows of long plumose setae; ischio-meral segment partly fused with basal segment, with simple and plumose setae along straight median margin; basal segment slightly convex medially with row of simple setae; exopod elongate, about 1.5 times longer than ischio-meral segment, with four long plumose setae distally and two short setae subdistally; coxa not produced medially, unarmed, lateral plate rounded; without arthrobranch (Fig. 24C).

First pair of pereiopods reaching with merus to distal margin of scaphocerite; coxa and basis unarmed; ischium twice as long as basis, about 3.2 times as long as broad, unarmed; merus twice as long as ischium; carpus slightly shorter than merus; carpo-propodal cleaning apparatus well developed; chela 0.8 times carpus length fingers; finger 0.6 times chela length, with entire cutting edges, with several rows of plumose setae on median margin, tips of fingers bifid (Fig. 25A–C).

Second pair of pereiopods dissimilar in shape and size. Left major second pereiopod robust (Fig. 21A); ischium 0.6 times as long as merus; merus slightly gurved with ventral margin concave; carpus cup shaped; chela robust, 2.5 times longer than wide; palm slightly swollen proximally, without tubercles; fingers about 0.25 of chela length, fixed finger slighly longer than movable finger, with tip strongly hooked, with distal half of cutting edge entire, with proximal fossa to receive dactylus plunger flanked by proximal blunt triangular knob medially; movable finger compressed, rounded, almost circular, dorsally carinate with acute hooked tip, with cutting edge minutely denticulate in distal part and plunger proximally (Fig. 26A).

Right minor second pereiopod with merus ventrally not concave; carpus more oblong than in major second pereiopod; palm slightly more compressed than in major chela, without tubercles; fingers of equal length, 0.36 of chela length; fixed finger with tip strongly hooked, with distal part of cutting edge with row of small blunt teeth followed by oblong excavation to receive broad tooth of dactylus, flanked by broad triangular minutely granulated tooth, with proximal third of cutting edge minutely granulate as well; movable finger slightly compressed, with tip strongly hooked, distal half of cutiing edge minutely denticulate, with broad minutely granulated tooth at proximal third (Fig. 26B, C).

Third pereiopod overreaching tip of rostrum by dactylus and propodus, compressed, distinctly more robust than fourth and fifth propodi; basis unarmed; ischium twice as long as distal width, oblong; merus about twice as long as ischium, about three times longer than maximum width, slightly swollen proximally; carpus half length of merus, twice as long as wide; propodus strongly compressed, 1.7 times longer than carpus, three times longer than proximal width, slighly tapering distally, with pair of distoventral cuspidate setae and one subdistal cuspidate setae on ventral margin; dactylus short, 0.16 of propodus length, with unguis curved, slightly shorter than corpus length, flexor margin of corpus without distal accessory tooth, with strong acute posterior tooth perpendicular to corpus margin (Fig. 27A, B).

Fourth pereiopod similar to third, more slender; dactylus without posterior tooth on flexor margin of corpus (Fig. 27C, D).

Fifth pereiopod similar to fourth; propodus distoventral pair of cuspidate setae, without subdistal ventral cuspidate seta, with rows of serrulate setae ventrolaterally in distal fifth (Fig. 28A, B).

Pleopods normal in shape (Fig. 28C).

Uropods broadly ovate; endopod overreaching telson; exopod about as long as telson, with lateral margin convex, ending in distinct tooth flanked by one (seldom two) mobile spine, slightly bent inward, about twice length of distolateral tooth; diaeresis slightly curved (Fig. 22A).

Eggs about 0.4 to 0.5 mm in diameter, rather numerous, over a hundred.

Colour (Fig. 29). Body and appendages speckled with small white and brownish chromatophores. Pereiopods with a more dense cover of chromatophores at joints. Carpi and propodi of ambulatory pereiopods without chromatophores, except for second chelipeds in female.

Ecology. Living as endosymbiont in the cloacal cavities of the didemnid ascidian Diplosoma aff. listerianum (Milne Edwards, 1841).

Etymology. The specific epithet cloacola derives from the Latin word cloaca, meaning ‘sewer’, and the Latin suffix - cola, meaning ‘dweller’ or ‘inhabitant’, and refers to the habitat of the species, found living in the cloacal cavity of compound ascidians.

Distribution. Known only from the type material from Curaçao and Bonaire.

Systematic position. The new species is morphologically most similar to Periclimenaeus ascidiarum. The two can be separated by the following characters: 1) in the new species the rostrum has two (seldom one) dorsal teeth whereas three in P. ascidiarum; 2) the rostrum does not exceed the basal segment of the antennular peduncle whereas it overreached the basal segment in P. ascidiarum; 3) the inferior orbital angle is moderately produced whereas strongly produced in P. ascidiarum; 4) the carpocerite reaches the distal lamina of the scaphocerite whereas it distinctly overreaches the distal lamina of the scaphocerite in P. ascidiarum; 5) the fingers of the first pereiopods bear several rows of many serrulate setae medially whereas these are much les abundant in P. ascidiarum; 6) proximal tooth of fixed finger of minor second pereiopod broad wheres small in P. ascidiarum; 7) ambulatory pereiopods without subdistal assessory tooth on corpus of dactylus whereas a distinct tooth is present in P. ascidiarum; 8) acute posterior tooth on corpus of dactylus only present in third pereiopod, absent in fourth and fifth whereas present on all ambulatory pereiopods in P. ascidiarum; 9) fifth pereiopod with distolateral fifth covered with rows of serrulate setae whereas covered by these rows of setae in distolateral half in P. ascidiarum; 10) posterolateral margin of sixth abdominal somite rounded wheras with a small tooth in P. ascidiarum.