Kaviengella, Šobáňová & Ďuriš, 2018

Šobáňová, Anna & Ďuriš, Zdeněk, 2018, Kaviengella jeffkinchi, a new genus and species of symbiotic shrimp (Crustacea: Decapoda: Palaemonidae) from Papua New Guinea, Zootaxa 4415 (1), pp. 118-134 : 121-125

Genus Kaviengella gen. n.

( Figs 1–5 )

Diagnosis. Small-sized shrimp with vermiform subcylindrical body shape. Carapace smooth, glabrous, without antennal, hepatic, epigastric or supraorbital teeth; rostrum greatly reduced, slightly overreaching proximal margins of eyestalks, with single dorsal tooth; orbit obsolete, inferior orbital angle produced, acute. Pleon smooth, glabrous, pleura rounded. Telson with two pairs of closely set dorsal spines anteriorly, posterior margin with 5 elongate, cuspidate setae, median and intermediate spines long, hooked. Antennule with short stylocerite, ventromedial tooth on basal segment obsolete; flagella with segments elongate. Antenna with basicerite unarmed, scaphocerite with lamella acutely produced, non-setose, lateral tooth strong, placed at midlength of scaphocerite; carpocerite long, overreaching end of scaphocerite. Eyes long, subcylindrical, cornea oblique. Mandible without palp; molar process reduced, slender, apex surrounded by spiniform teeth; incisor process narrow, bidentate. Maxillula with bilobed palp and well-developed laciniae. Maxilla normal, with simple palp, simple basal endite and obsolete coxal endite. First maxilliped with simple palp, basal and coxal endites fused, exopod with reduced flagellum, caridean lobe broad, epipod small, cordiform. Second maxilliped with normal stout endopod, dactylar segment moderately broad, exopod well developed, epipod small, without podobranch. Third maxilliped normal, moderately slender, ischiomerus fused to basis, exopod well developed but failing to reach distal end of ischiomerus, coxa without both lateral plate and arthrobranch. Thoracic sternites narrow, unarmed. First pereiopod moderately stout, chela with movable finger broadly spatulate, with denticulate margins thoughout; fixed finger tridentate distally, with series of smaller teeth distodorsally. Second pereiopods missing; coxae with bases intact, segments unequal. Ambulatory pereiopods normal, smooth, dactyls with distoventral accessory tooth, without ornamentation, propodus with single ventral spine posterior to distoventral pair. Uropods with protopodite unarmed; exopod distolaterally strongly produced and far overreaching both lamina and large medial mobile spine.

Etymology. Derived from the name of the type locality, Kavieng Lagoon, New Ireland, Papua New Guinea; gender feminine.

Type-species. Kaviengella jeffkinchi gen. & sp. n., by monotypy and present designation.

Included species. Only one- Kaviengella jeffkinchi gen. & sp. n.

Systematic position. Some important structures might allow to placing Kaviengella gen. n. in the family Anchistioididae rather than Palaemonidae . As pointed out by Chace (1992), the family-level separation of Anchistioides , first proposed by Gurney (1938) on larval characters, is evident also in the first maxilliped with a reduced exopod, the flared molar process of the mandible, and the reduced number of posterior cuspidate setae on the telson. Indeed, the ‘corona-like‘ arrangement of the mandibular molar proces in the specimen of the present new genus somewhat resembles the molar apex of Anchistioides antiguensis ( Schmitt, 1924) with its 3–4 elongate and widely spaced teeth (Ashelby et al. 2015: 11, Fig. 7D–F). The first maxilliped has the exopodal flagellum reduced in both genera. The scaphocerite of, e.g., A. compressus Pauľson, 1875 , is acutely produced distomedially, with the anterior margin obliquely retreating back to a small distolateral tooth, thus, somewhat resembling the bispinose scaphocerite of Kaviengella gen. n. However, the scaphocerite blade is marginally setose and not reduced in size, and the lateral tooth is otherwise distally placed ( Gordon 1935), not with a non-setose blade and reduced in width and with a proximal lateral tooth. The posterior telson margin is variable in Anchistioides spp. in regards of the number, size, and arrangement of the cuspidate setae. Generally there are two pairs of short, but stout lateral ones, and minute submedian ones; in some specimens the submedian pair is lacking or replaced by a single cuspidate seta ( Gordon 1935). The latter state might also resemble that of Kaviengella gen. n. However, the telson is narrow, elongate, with widely spaced dorsal pairs of spines in Anchistioides spp., not broad, with anteriorly placed and closely set dorsal spines, and with five posterior cuspidate setae from which three medial ones are extremely long and hooked in the new genus. All species of the genus Anchistioides clearly differ from Kaviengella gen. n. by a well-developed, large and strongly dentate rostrum, moderately sized eyes, a short carpocerite, the presence of a pleurobranch above the third maxilliped, a complete reduction of maxillar endites, and by other characters, as highlighted by Gordon (1935). The similarities with Kaviengella gen. n. mentioned above are superficial, perhaps convergent to some extent, and the present new genus thus cannot be placed in the family Anchistoididae.

As is plainly evident from the present molecular analysis ( Fig. 6 ), Kaviengella gen. n. occupies a position among symbiotic palaemonid shrimps, showing a closer relation to the spongobiotic genera Nippontonia and Thaumastocaris ; which of those genera is sister positioned to the new genus remains unresolved due to their low basal supports in ML or BI analyses, in turns, and due to the uncomplete dataset of gene sequences for the new genus.

Based on the general shape of the body and some partial characters, the new genus is most similar to species of a vermiform body shaped genus, Nippontonia . Both the rostrum and scaphocerite are reduced and unsetose in either genus. The scaphocerite is acutely produced in both genera, but their apices are not similar; in Kaviengella gen. n., the apex formed by an acutely produced non-setose lamella, with a strong proximally placed lateral tooth; in Nippontonia , the apex is formed by a well-developed distolateral tooth, but the lamina is strongly reduced medially. The mandibular molar process is slender with a unique apical corona of spiniform teeth in the new genus, while it is deply reduced in Nippontonia ; instead, the incisor process in the new genus is somewhat reduced, i.e. slender, bidentate, whereas in Nippontonia it is broadly expanded, rounded, spoon-like, and finely denticulate. The distolateral angle of the uropodal exopod is strongly produced, elongate, in both genera; but laterally entire, leaflike, and longer than the medial spine in Kaviengella gen. n.; that lobe, as well as the distal part ot the lateral margin of the exopod, are strongly dentate, but surpassed by a long and slender medial movable spine in Nippontonia spp. (Bruce & Bauer 1997; Bruce 2014; Fransen 2013). Kaviengella gen. n. is also easily distinguished from Nippontonia and other palaemonid genera by the unusual shape of the first pereiopod chelae with a broadly spoon-like dactylus possessing marginal denticulation, and with a distodorsally toothed fixed finger. Nippontonia spp. have simple fingers on the first pereiopod chelae, with poorly developed simple lateral cutting edges; only the projecting terminal teeth on the fixed finger (see: Bruce & Bauer 1997) remotely resemble those of Kaviengella n. gen.

Both these genera, Nippontonia and Kaviengella n. gen., show also some resemblance to the genera Onycocaridella and Orthopontonia . The genus Onycocaridella is also confirmed by BI analysis of the phylogenetic tree ( Fig. 6 ) as sister positioned to the three genera discussed above. Onycocaridella , currently comprising three spongobiotic species, is another genus which possesses a vermiform body, reduced rostrum, stout first pereiopods with spatulate fingers, large unequal second pereiopods, and biunguiculate ambulatory dactyli, all similar to Kaviengella gen. n. The first pereiopod fingers are however both spatulate, subequal, with simple margins (vs dactylus broadly spatulate with dentate margins, and fixed finger strongly dentate dorsally in the new genus). Onycocaridella is also easily distinguishable from the new genus by a normally developed scaphocerite, posterior telson setae, and uropodal exopod posterior ornamentation (e.g. Bruce 1981, 1995).

Orthopontonia ornata (Bruce, 1970) , a single representative of the genus, also has an elongate subcylindrical body, stout first pereiopods with apically dentate fixed fingers, ambulatory dactyli with at least one accessory distoventral tooth, and a produced distolateral angle on the uropodal exopod. In O. ornata , however, the rostrum is well-developed, dorsally dentate (vs reduced in the new genus), the scaphocerite is not reduced, the mandibles are well-developed but not specialized (vs rostrum reduced and mandibular molar uniquely shaped in both former genera), and both pairs of the dorsal spines are situated on the distal half of the telson (vs anteriorly in the new genus, or both anteriorly and distally in Orthopontonia ) (see Bruce 1970b; 1982). The species of both Nippontonia and Orthopontonia have similarly shaped large, unequal and dissimilar second pereiopods. Their subapical carpopropodal articulation allowing for higher flexibility of those otherwise robust chelipeds are remarkable adaptations for life in narrow spaces inside their sponge hosts, and clear example of convergence with similarly built second chelipeds of Ischnopontonia Bruce living in narrow spaces among corallites of the scleractinian coral Galaxea Oken. The latter shrimp genus is however unrelated to these spongobiotic shrimps, as demonstrated in the recent phylogenetic study ( Horká et al. 2016).

Surprisingly, among the examined genera, Kaviengella n. gen. shows the lowest genetic divergence ( Tab. 2) on the 16S rRNA from the genus Thaumastocaris . The latter, together with species of the more remorely related genus Periclimenaeus , generally have a well-developed dentate rostrum and normally shaped the scaphocerite, posterior telson setae, and uropodal exopod. Thaumastocaris streptopus Kemp, 1922 , the only species of the genus, has subsegmented carpi and meri on the first pereiopod, and representatives of the highly speciose genus Periclimenaeus display a wide variability in the shape of the first and second periopods chelae, as well as of the ambulatory dactylar ventral ornamentation (e.g. Kemp 1922; Fransen 2006; Bruce 2013). The shapes of the first pereiopod chela, the scaphocerite, and the posterior telson setae of the single representative of Kaviengella n. gen., are highly distinctive from any species of the genera Periclimenaeus or Thaumastocaris .

Figures

FIGURE 1. Kaviengella jeffkinchi gen. & sp. n. female holotype, habitus, lateral aspect.

FIGURE2. Kaviengella jeffkinchigen.& sp.n.,female holotype. A, anterior carapace and antennae, dorsal.B, same, lateral. C, posterior sixth pleonal segment, telson, and left uropod, dorsal. D, telson, lateral. E, distal endo of telson, dorsolateral. F, right antennule, dorsal. G, same, lateral. H, left antenna, ventrolateral.I, distolateral angle of exopod of right uropod, dorsal. J, same, right uropod.

FIGURE 3. Kaviengella jeffkinchi gen. & sp. n., female holotype, mouthparts (from left side, except maxillula). A, mandible, inner aspect.B, same, outer aspect.C, distal end of molar process.D, same, outer aspect. E, maxillula. F, maxilla.G, first maxilliped.H, second maxilliped. I, third maxilliped.

FIGURE 4. Kaviengella jeffkinchi gen. & sp. n., female holotype. A, right first pereiopod, lateral. B, right third pereiopod, lateral. C, same, distal segments. D, same, distal propodus and dactylus, lateral. E, same, ventromedial. F, fifth pereiopod, lateral.G, same, distal segments. H, same, dactylus and distal propodus, lateral.

FIGURE 5. Kaviengella jeffkinchi gen. & sp. n., female holotype. A, right first pereiopod, chela and distal propodus, lateral. B, left first pereiopod, chela and distal propodus, medial.C, same, ventromedial.

FIGURE 6. Phylogenetic position of Kaviengella jeffkinchi gen. et sp. n. revealed by Bayesian Inference (BI) analysis of combined 16S rRNA and H3 gene sequences of selected palaemonid and anchistioidid shrimps (with a pandalid and a stenopodid species as ougroup). Maximum Likelihood (ML) bootstrap supportand Bayesian(BI) posterior probabilities (ML/ BI) expressed as percentages indicated in nodes (dash indicates basal support <50); asterisk points on different ML topology. A, BI tree topology; B, respective part of ML tree showing different topology.