Odontonia kerangcaris Fransen & Groenhof & Gier 2021, sp. nov.
Creators: name: Fransen, Charles H. J. M.
name: Groenhof, Mike
name: Gier, Werner De
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Palaemonidae
Odontonia
Odontonia kerangcaris

description: Odontonia kerangcaris sp. nov.   
(Figs. 1–8)  
urn:lsid:zoobank.org:act: 197FDE7A-BDDD-4162-8412-FEC59D128460  
 Material examined. Holotype male, pocl. 2.1mm, MZB 5341, stn BER.39, Indonesia, NE Kalimantan, Berau Islands, Baliktaba reef, SW-side (N of Panjang Isl.), 02˚34’43.3”N 118˚00’48.2”E, 24.x.2003, depth 33m, SCUBA diving, in Chama lazarus Linnaeus, 1758, collected by C.H.J.M. Fransen.   
 Diagnosis. Rostrum short, not overreaching antennular peduncle, without ventral tooth. Pterygostomial angle broadly rounded, slightly produced. Basal segment of antennular peduncle with strong, acute medioventral tooth, with distolateral tooth reaching distal margin of intermediate segment. Carpocerite just falling short of distal margin of lamina of scaphocerite; distolateral tooth of scaphocerite robust, 0.15 times length of lamina (incl. distolateral tooth), almost twice as long as distal lamina; incision between distolateral tooth and lamina rather deep. Dactylus of ambulatory pereiopods with acute distoventral accessory tooth, perpendicular to flexor margin; ventral margin of corpus with one rounded protuberance at 2/3rd and one rounded protuberance proximally, without denticles in between; unguis strongly curved, 0.5 times corpus length, with large scales distally on outer margin, gradually decreasing in size proximally. Telson with two pairs of submarginal dorsal spines at 0.3 and 0.7 of telson length; distal and proximal pair of spines of equal length, 0.14 times telson length.   
 Description. Body (Fig. 1) subcylindrical, somewhat depressed. Carapace (Fig. 1) glabrous with a few scattered simple setae. Rostrum (Fig. 2A, B) well developed, without dorsal teeth, reaching half of distal segment of antennular peduncle, with broad, indistinct, shallow dorsal elevation over entire length and acute lateral carinae, with slightly concave ventral carina in distal part; distal end rounded in lateral view, without subdistal ventral tooth, with few distal setae, blunt in dorsal view, broadened at base. Inferior orbital angle (Fig. 2B) produced, directed inward. Antennal spine (Fig. 2B) blunt, protruding rounded process, not separated by notch from inferior orbital angle. Anterolateral margin straight, pterygostomial angle slightly produced, rounded.   
Abdomen (Fig. 1) smooth; sixth segment 1.3 times longer than fifth, 1.3 times broader than long, posteroventral angle rounded, posterolateral angle feebly produced, blunt; pleura of first five segments broadly rounded.  
Telson (Fig. 2C, D) almost twice as long as sixth abdominal segment, about twice as long as proximal width; lateral margins slightly convex, almost straight, convergent posteriorly; posterior border without median process; two pairs of submarginal dorsal spines at 0.3 and 0.7 of telson length; distal and proximal pair of spines of equal length, 0.14 times telson length; posterior margin (Fig. 2E) with three pairs of spines, lateral spines small, marginal, about 1/3 of length of intermediate spines; submedian spines slightly shorter than intermediate spines; both intermediate and submedian spines about as long as dorsal spines, but more slender.  
Eyestalk (Fig. 2A, B) short, about as long as broad, broader than diameter of hemispherical cornea.  
Antennula (Fig. 3A, B) with peduncle and flagella short. Basal segment 1.4 times as long as proximal width, with acute produced distolateral tooth reaching distal margin of intermediate segment, anterior margin oblique; ventromedial tooth large, acute, at midlength of basal segment, submarginal; stylocerite short, reaching halfway basal segment, tip acute, distolateral margin with 4 short plumose setae; statocyst with statolith present in proximal part. Intermediate segment short, slightly broader than long; distal segment broader than long. Upper flagellum short, biramous, with 3 segments fused; short free ramus one-segmented; longer free ramus 3-segmented. Lower flagellum with 5 segments.  
Antenna (Fig. 3C) with basicerite short, laterally unarmed, with large rounded antennal gland tubercle medially; ischiocerite and merocerite normal; carpocerite just falling short of distal margin of lamina of scaphocerite, slender, 3.7 times longer than distal width; flagellum about as long as post-orbital carapace length; scaphocerite with lamina twice as long as wide, anterior margin rounded, lateral margin broadly convex; distolateral tooth robust, 0.15 times length of lamina (incl. distolateral tooth), almost twice as long as distal lamina length, somewhat curved inward; incision between distolateral tooth and lamina rather deep.  
Epistome with blunt anterior median carina; labrum normal, oval.  
Paragnaths well developed, alae with broad transverse more or less rectangular distal lobes, and small rounded more or less triangular ventromesial lobes; corpus very short, with shallow median excavation, bordered laterally by non-setose, oblique, carinae.  
Second thoracic sternite with shallow indistinct rounded median elevation, without setae.  
Third thoracic sternite unarmed.  
Fourth thoracic sternite with low, medially notched, triangular plate formed by the fused lateral carinae.  
Fifth thoracic sternite with well-developed lateral plates with shallow central slit posteromedial to second pereiopod coxae; coxae almost against each other.  
Sixth to eighth thoracic sternites unarmed, broadening posteriorly.  
Mandible (Fig. 3D) with incisor process with 5 acute distal teeth, small denticles along medioventral margin absent; molar process robust with several blunt teeth, some fringed with setal brushes.  
Maxillula (Fig. 3E) with upper and lower lacinia rather small; distal lacinia rectangular with two rows of about 8 stout distal spines, almost devoid of setae; lower lacinia slender, triangular, with few short serrulate setae in distal part; palp feebly bilobed, large lobe with small ventral tubercle with single short recurved seta.  
Maxilla (Fig. 3F) with basal endite well developed, with distal lobe and proximal lobe distinct, each with one long, simple distal seta; coxal endite obsolete, medial margin convex, non-setose; scaphognathite of moderate size; palp simple, longer than basal endite, blunt distally, non-setose.  
First maxilliped (Fig. 3G) with coxal and basal endite partly fused, broad; basal endite fringed with scattered, rather short simple and finely serrulate setae along medial and distal margins; coxal endite convex, indistinctly separated from basal endite, with few simple setae medially; exopod well developed, flagellum with 4 long plumose setae distally; caridean lobe rather small, narrow; epipod bilobed; palp simple, rather short, non-setose.  
Second maxilliped (Fig. 4A) with endopod short, stout; dactylar segment 3.0 times broader than long, 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 distomedial margin; one seta in distal part of ventrolateral margin; carpal segment short, broader than long, unarmed; meral segment without setae; ischial and basal segment completely fused, medially somewhat excavate, without setae, basal part strongly convex medially; exopod long, with 4 long plumose setae distally; coxal segment medially slightly produced, with few short simple setae, with expanded epipod laterally.  
Third maxilliped (Fig. 4B) short; with ischiomerus partly fused to basis, not broadened, 2.3 times as long as broad, not tapered distally, somewhat flattened, with row of long simple setae along medial margin, lateral margin with few simple setae; basal segment medially convex with few long simple setae on medial margin; exopod well developed, reaching distal margin of ischiomerus, with 4 long plumose setae in distal part; coxal segment without medial process, with large lateral plate with one short simple seta laterally; without arthrobranch; ultimate and penultimate segments of equal length; penultimate segment as long as broad, somewhat flattened, with few long finely serrulate setae ventromedially; ultimate segment more slender, with groups of long coarsely serrulate setae ventromedially and distally.  
First pereiopod (Fig. 4C) stout, exceeding carpocerite with chela and half of carpus; chela 3.0 times longer than deep, slightly compressed; fingers as long as palm, cutting edges entire, with groups of serrulate setae, tips slightly hooked; cleaning organ absent; carpus 0.8 times length of chela, 2.4 times longer than distal width, tapering proximally, unarmed; merus as long as chela, 3.3 times longer than central width, somewhat curved, with few setae medially; ischium 0.5 times merus length, slightly expanded medially, with few setae medially; basis as long as ischium, with few setae medially; coxa with small ventral lobe with few short simple setae.  
Second pereiopods (Fig. 5A, B) subequal, similar. Major right chela (Fig. 5C) with palm slightly compressed, without carinae, with few scattered simple setae; fingers with simple setae; dactylus 0.6 of palm length, 3.2 times longer than deep, with one large triangular tooth at 1/3 of cutting edge, distal part of cutting edge entire, straight, tip strongly hooked; fixed finger 2.1 times as long as deep, with broad flattened tooth with row of small denticles in proximal part, separated by shallow notch from triangular acute tooth at midpoint of cutting edge, distal part of cutting edge entire, straight, tip strongly hooked; carpus 0.55 of palm length, 1.5 times longer than distal width, strongly tapering proximally; merus as long as carpus, 1.8 times longer than central width, distomedially excavate; ischium as long as merus, somewhat tapering proximally, with slightly protruded distomedial angle; basis and coxa without special features. Minor cheliped (Fig. 5B) similar, dactylus slightly longer in relation to palm than in major chela.  
Ambulatory pereiopods (Figs. 6, 7) short, stout. Dactylus of third pereiopod (Fig. 6A, B) with corpus moderately compressed, about 1.2 times longer than proximal width, with single row of few simple setae along ventral margin and in distal part, distoventral accessory tooth acute, perpendicular to flexor margin, ventral margin with one rounded protuberance at 2/3rd of ventral margin and one rounded protuberance proximally, without denticles in between; unguis strongly curved, about 0.5 of corpus length, distally with large dorsal scales, gradually decreasing in size proximally; propodus 2.8 times dactylus length, 4.7 times longer than proximal width, with one short, blunt, spine in distal part of flexor margin, with few long slender simple setae; carpus 0.64 of propodus length, 2.25 times longer than distal width, slightly tapering proximally, with indistinct distal lobe, unarmed; merus about as long as propodus, slightly swollen, about 2.8 times longer than central width, cylindrical; ischium 0.66 of merus length, 2.2 times longer than distal width; basis and coxa without special features. Fourth and fifth (Fig. 7A, B) pereiopods similar.  
Male first pleopod (Fig. 8A) with endopod 0.4 times as long as exopod, with 2 long distal setae, with row of 5 small simple setae on lateral margin.  
Male second pleopod (Fig. 8B, C) with endopod slightly shorter than exopod, with appendix masculina, equal to about half length of appendix interna, reaching halfway endopod, with 3 very long setulose setae distally.  
Uropods (Figs. 2D, 8D) normal, with short unarmed protopodite; exopod broad, 2.0 times longer than central width, lateral margin strongly convex, without distolateral tooth, with minute spinule distolaterally; endopod slightly exceeding exopod, reaching posterior margin of telson, 2.4 times longer than wide.  
 Size. This is a small sized species, pocl. is 2.1 mm.   
 Coloration. Not known.   
 Host. Mollusca, Bivalvia, Chamidae, Chama lazarus Linnaeus, 1758.   
 Distribution. Only known from the type locality: Berau Island, NE Kalimantan, Indonesia.   
 Etymology. From the Indonesian word ‘kerang’, which translates to “bivalve”, combined with the Latin ‘ caris ’ referring to shrimp.   
 Remarks. The species falls within the genus definition for Odontonia provided by Fransen (2002) and modified by De Gier & Fransen (2018). The new species has the accessory tooth on the dactyli of the ambulatory pereiopods similar to the ones found in O. rufopunctata, O. bagginsi, O. sibogae, O. compacta, and O. katoi. It differs from these species in the absence of a forward directed proximal tooth on the flexor margin of the corpus of the ambulatory dactyli. It also lacks the small denticles posterior to the distoventral accessory tooth on the dactylar corpus.   
 Species of Odontonia are known as endosymbionts of solitary ascidians (De Gier & Fransen 2018). Odontonia kerangcaris sp. nov. is the first species within the genus recorded from a bivalve mollusk. The species has affinities with species of the closely related bivalve mollusk dwelling genus Conchodytes Peters, 1852 (Horká et al. 2016; Chow et al. 2021). The accessory tooth and protuberances on the flexor margin of the ambulatory pereiopods resemble almost all Conchodytes species except for C. chadi (Marin, 2011) and C. monodactylus (Holthuis, 1952).   
 Other palaemonid endosymbionts known from chamid bivalves are Pontonia pilosa Fransen, 2002 and Bruceonia ardeae (Bruce, 1981). The East Atlantic P. pilosa has been recorded as an endosymbiont of Pseudochama cristella (Lamarck, 1819). B. ardeae has been recorded from the Great Barrier Reef, Australia, as an endosymbiont of Chama pacifica Broderip, 1835. Both P. pilosa and B. ardeae have the furry appearance shared with another palaemonid endosymbiont of bivalves: Pinnotherotonia rumphiusi Marin & Paulay, 2010, hosted by the venerid bivalve Periglypta crispata (Deshayes, 1854). A dense setal coverage has also been noted for several pinnotherine crabs infesting bivalves (De Gier & Becker 2020).   
 The phylogenetic position of the new species seems to be at the base of the Odontonia clade and as sister of the Conchodytes clade (De Gier, Groenhof & Fransen, in prep.), revealing intrageneric host switching.
description: Published as part of Fransen, Charles H. J. M., Groenhof, Mike & Gier, Werner De, 2021, Odontonia kerangcaris sp. nov., a new bivalve-associated shrimp (Crustacea, Decapoda, Palaemonidae) from East Kalimantan, revealing intrageneric host switching, pp. 275-285 in Zootaxa 5081 (2) on pages 276-283, DOI: 10.11646/zootaxa.5081.2.6, http://zenodo.org/record/5771777