Odontonia plurellicola, Gier, Werner de & Fransen, Charles H. J. M., 2018

Gier, Werner de & Fransen, Charles H. J. M., 2018, Odontoniaplurellicola sp. n. and Odontoniabagginsi sp. n., two new ascidian-associated shrimp from Ternate and Tidore, Indonesia, with a phylogenetic reconstruction of the genus (Crustacea, Decapoda, Palaemonidae), ZooKeys 765, pp. 123-160 : 123

Odontonia plurellicola sp. n. Figs 1, 2, 3, 4, 5, 6, 7, 15 A–D, 16F, 17E

Material examined.

Type series. 1 ovigerous female (holotype), PoCL 1.55 mm (MZB Cru 4734), Tarau, W Halmahera, Ternate, Indonesia, 0°50'30"N, 127°22'38.5"E, shallow area with coral followed by sandy slope with coral gardens, 9 m depth, scuba diving, 2-11-2009; in ascidian Plurella sp. (Asc. 68), leg. C.H.J.M. Fransen, photo TER.17.0049 - 76; 1 male, PoCL 1.30 mm, 1 ovigerous female, PoCL. 1.50 mm, 2 non-ovigerous females PoCL 0.90-1.05 mm (paratypes) (RMNH.CRUS.D.53554), same data as holotype.

Diagnosis.

Rostrum as long as antennular peduncle, with distoventral tooth. Pterygostomial angle produced. Basal segment of antennular peduncle with distolateral tooth minute, medioventral tooth strong, acute. Distolateral tooth of scaphocerite robust, 0.3 length of lamina. Dactylus of ambulatory pereiopods with flexor margin of corpus with few (usually 3) short teeth but without accessory tooth; unguis without terminal scales. Telson with two pairs of medium sized (approx. 0.17 of telson length) submarginal dorsal spines at 0.20 and 0.54 of telson length.

Description.

Body (Figs 1, 2A) subcylindrical, depressed. Carapace smooth. Rostrum well developed, approx. 0.45 of post-orbital carapace length, as long as antennular peduncle, falling short of distal margin of scaphocerite, approximately 1.8 times longer than diameter of hemispherical cornea, with broad shallow indistinct dorsal carina, with acute lateral carinae, with straight ventral carina; with distal ventral tooth, with distal setae, bluntly acute in dorsal view, broadened at base. Inferior orbital angle not produced, straight. Antennal spine reduced to blunt process. Pterygostomial of carapace straight, anterolateral angle slightly produced, rounded.

Abdomen smooth, sixth segment 1.4 times longer than fifth, 1.4 times wider than long, posterolateral angle blunt, slightly produced, posteroventral angle blunt, not produced; pleura of first five segments broadly rounded.

Telson (Fig. 2 B–D) 1.6 times as long as sixth abdominal segment, 2.3 times longer than proximal width; lateral margins almost straight, slightly tapering posteriorly; posterior border without median process; two pairs of medium-sized submarginal dorsal spines at 0.20 and 0.54 of telson length; distal and proximal pair of spines of equal length, 0.17 of telson length; posterior margin with three pairs of spines, lateral spines small, marginal, 0.06 times telson length; submedian spines about as long as intermediate spines, lateral spines 0.23 of submedian and intermediate spines; both intermediate and submedian spines approx. 0.75 of dorsal spine length, but more slender.

Eyestalk short, broader than long, slightly broader than diameter of hemispherical cornea.

Antennula (Fig. 3B) with peduncle and flagella short. Basal segment as long as proximal width, with feebly produced distolateral tooth just reaching beyond proximal margin of intermediate segment, anterior margin not developed, oblique; medioventral tooth strongly developed, acute, submarginal, situated halfway basal segment; stylocerite short, reaching halfway basal segment, with acute tip, lateral margin with few plumose setae. Intermediate segment short, broader than long, medial margin with single long distal plumose seta. Distal segment broader than long, upper flagellum short, biramous, with three fused segments; short free ramus one-segmented; longer free ramus with three or four segments. Lower flagellum with four segments; upper ramus carried reflexed beneath lateral rostral carina.

Antenna (Fig. 3C) with basicerite short, laterally unarmed, with large gland tubercle medially; ischiocerite and merocerite normal; carpocerite extending to distal end of distolateral tooth of scaphocerite, rather slender, 4.5 times longer than distal width; flagellum short, slender, nearly as long as postorbital carapace length; scaphocerite with lamina almost twice as long as wide, anterior margin small, rounded, lateral margin broadly convex; distolateral tooth robust, 0.3 length of lamina, reaching beyond lamina, curved medially.

Epistome with rather sharp anterior carina; labrum normal.

Paragnath well developed, alae with broad transverse more or less rectangular distal lobes, and small rounded more or less triangular ventromedial lobes; corpus very short, with shallow median excavation, bordered laterally by non-setose, small, oblique, carinae.

Second thoracic sternite (Fig. 3A) with anterior margin broadly rounded; without median process.

Third thoracic sternite with indistinct shallow lateral carinae.

Fourth thoracic sternite with shallowly developed, medially notched plate formed by the lateral carinae.

Fifth thoracic sternite with well-developed lateral plates with medial broadened deep slit, posteromedial to second pereiopod coxae.

Sixth to eight thoracic sternites unarmed, broadening posteriorly.

Mandible (Fig. 3E) with incisor process with five terminal teeth and one large teeth-like ventromedial denticle; molar process robust, with several blunt teeth, some fringed with setal brushes.

Maxillula (Fig. 3D) with upper lacinia rather small, rectangular with about nine distal spines in two rows, with only few simple setae in distal part; lower lacinia lost in dissection; palp feebly bilobed, larger lobe with small ventral tubercle with single short recurved simple seta.

Maxilla (Fig. 4A) with basal endite well developed, bilobate, distal and proximal lobe short, distal lobe with two distal seta of unequal length, proximal lobe with two distal setae; coxal endite obsolete, median margin convex, without setae, scaphognathite large, 2.3 times longer than wide, posterior lobe large, 2.3 as long as anterior width, anterior lobe 1.4 times longer than proximal width; palp simple, subquadrate distally, longer than basal endite, not expanding proximally, without row of plumose setae along lateral margin.

First maxilliped (Fig. 4B) with coxal and basal endite partly fused, broad; basal endite fringed with scattered, rather short simple and finely serrulate setae along median and distal margins; coxal endite convex, separated from basal endite, with few simple setae medially; exopod well developed, flagellum with four plumose setae distally; caridean lobe rather small, narrow; epipod bilobate, lobes rounded; palp simple, rather short, non-setose.

Second maxilliped (Fig. 4C) with endopod short, compact; dactylar segment 2.4 times longer than broad, fringed with short, coarsely serrulate, spiniform, and longer curled, finely serrulate setae medially; propodal segment with row of robust spines and few simple setae along expanded distomedian margin; one seta in distal part of ventrolateral margin; carpal segment short, broader than long, unarmed; meral segment without setae, ischial and basal segments partly fused, without setae, basal part angular produced medially; exopod long, with four long plumose setae distally; coxal segment not medially produced, without setae, with proximally expanded epipod laterally.

Third maxilliped (Fig. 4D) short; with ischiomerus distinct from basis, 2.5 times as long as broad, not tapered distally, somewhat flattened, with row of long simple setae along median margin, lateral margin with few simple setae; basal segment medially convex with few simple setae on medial margin; exopod well developed, reaching just beyond distal margin of ischiomerus, with about four long plumose setae in distal part; coxal segment with small median process, with large lateral plate without setae; without arthrobranch; penultimate segment 1.3 times longer than broad, somewhat flattened, with few long finely serrulate setae ventromedially; ultimate segment slightly shorter than penultimate segment, more slender, with groups of long coarsely serrulate setae ventromedially and distally.

First pereiopod (Fig. 5C) stout, exceeding carpocerite with chela and carpus, chela 2.8 times longer than deep, subcylindrical, slightly compressed; fingers as long as palm, stout, with lateral entire cutting edges, with groups of many serrulate setae, tips slightly hooked, suture of unguis visible; carpo-propodal brush present, serrulate setae in distal part of carpus, no setae in proximal part of palm; carpus 1.2 length of chela, 3.7 times longer than distal width, tapering proximally, unarmed, with medially and laterally few simple setae; merus as long as carpus, 3.7 times longer than central width, somewhat bowed, with few simple setae medially; ischium 0.5 times merus length, slightly expanded medially, with few simple setae medially; basis slightly smaller than ischium, with few simple setae medially; coxa with small ventral lobe with few short simple setae.

Second pereiopods (Fig. 5 A–B) subequal, similar. Chela 0.8 times postorbital carapace length in females, major chela about as long as the postorbital carapace length in females, palm smooth, compressed, without carinae, non-setose; fingers with few simple setae in distal part; dactylus 0.39 of palm length, 3.2 times longer than deep, with low, triangular tooth halfway of cutting edge, distal part of cutting edge entire, tip strongly hooked; fixed finger 1.7 times as long as deep, with broad flattened tooth, separated by shallow notch from triangular, small acute tooth at around midpoint of cutting edge, distal part of cutting edge entire, straight, tip strongly hooked; carpus 0.5 of palm length, 1.5 times longer than distal width, strongly tapering proximally; merus as long as carpus, 1.5 times longer than central width, distomedially excavate; ischium slightly shorter than merus, somewhat tapering proximally, with slightly protruded distomedial angle; basis and coxa without special features. Minor cheliped similar, dactylus slightly longer in relation to palm than in major chela; palm less swollen than in major chela.

Ambulatory pereiopods short, stout. Dactylus of third pereiopod (Fig. 6A, B, 16F, 17E) with corpus compressed, 2.2 times longer than proximal width, with about three small proximal ventrally directing teeth, without accessory tooth, with few simple setae along dorsal margin, with row of simple short setae along flexor margin; unguis long and slender, acute, 0.45 of corpus length, without terminal scales; propodus stout, compressed, 3.7 times length of dactylus, 3.7 times longer than deep, with minute lateral distoventral spinules, and distal ventral spinule with sparse simple setae and one plumose distodorsal setae, carpus 0.6 of propodus length, unarmed, merus subequal to propodus length, 2.2 times longer than central depth, unarmed; ischium 0.6 of merus length, slightly tapering proximally; basis and coxa without special features. Fourth and fifth pereiopods similar, but fifth pereiopod (Fig. 6C) with slightly bigger dactylus, with single lateral pectinate spine.

First pleopod of female (Fig. 7A) with endopod, more than 1/3 as long as exopod, with two long plumose distal setae when ovigerous, with two lateral simple setae. Male first pleopod (Fig. 7B) with endopod about three times as long as proximal width, distinctly tapering distally; median margin straight with single simple setae, with few plumose long setae along lateral and distal margin.

Endopod of second pleopod (Fig. 7C) with appendix masculina about 2/3 length of appendix interna, with three very long setulose setae distally.Uropods (Fig. 7D), with short unarmed protopodite; exopod broad, 2.2 times longer than central width, lateral margin feebly convex, without distolateral tooth, with minute spinule distolaterally; endopod exceeding exopod, about as long as telson, 2.8 times longer than wide.

Number of eggs approximately 11.

Size.

This is a small sized species. The maximum PoCL is 1.55 mm in adult females, 1.30 mm in adult males. The minimal PoCL in ovigerous females is 1.50 mm.

Colour in life

(Fig. 15 A–D). Body with small white chromatophores and scattered larger white spots. Carapace with white chromatophores at base of rostrum and in posterior part, central part without white spots or chromatophores. Laterally covered with white chromatophores and big large white spots. Eyestalks with some big dorsal white spots, cornea with white spots. Antennular peduncle with large white spots distally. Pereiopods without small white chromatophores, with white spots at joints. Palm of chela of second pereiopods with scattered white spots. Abdominal pleura with many small white chromatophores and large white spots dorsally and laterally at fixed distances; in dorsal view, each tergum with a transverse row of white spots anteriorly. First abdominal segment covered with large white spots as fixed distances. Tailfan without chromatophores. Thoracical appendages and tailfan appear to be translucent; carapace, eyestalks, corneas and abdominal segments appear to be darker in colour.

Host.

Specimens were found inside a colonial ascidian of the genus Plurella Kott, 1973 ( Plurellidae , Phlebobranchia).

Distribution.

Only known from the type locality.

Etymology.

The species is named plurellicola after the colonial ascidian genus Plurella Kott, 1973 in which it was found.

Remarks.

The species resembles O. simplicipes , known only by the holotype, in morphological characters. It differs from this species in the length and shape of the rostrum (most notably, O. simplicipes has no distal tooth on its rostrum, while O. plurellicola bears a small distal tooth), in the size of the ventromedial tooth on the basal segment of the antennular peduncle which is larger in O. seychellensis than in the new species, in the distolateral tooth of the basal segment of the antennular peduncle which is well developed in O. seychellensis while minute in the new species, in the amount of plumose setae on the three maxillipedes and the antennular peduncle.

Thus far this is the only species of Odontonia living inside a colonial ascidian. The ascidian genus Plurella has also been recorded as host for Dactylonia holthuisi Fransen, 2002, another symbiotic palaemonid shrimp ( Fransen 2002, 2006).