Dactylonia carinicula, Bruce, A. J., 2006

Bruce, A. J., 2006, Pontoniine shrimps (Decapoda: Palaemonidae) from the island of Socotra, with descriptions of new species of Dactylonia Fransen, 2002 and Periclimenoides Bruce, 1990, Zootaxa 1137, pp. 1-36 : 4-13

Dactylonia carinicula sp. nov.

Figures 2–5

Diagnosis. Rostrum narrowly triangular, much shorter than antennular peduncles, dorsally carinate, unarmed; maxilla with basal laciniae obsolete; ambulatory dactyls biunguiculate, with corpus bearing large blunt, distal tooth and several smaller acute ventral denticles, with large acute central accessory tooth, smaller interposed denticles distally, larger anteroverted denticles proximally; telson with two pairs of large dorsal spines.

Material examined. 1 ovig. Ψ, holotype, reg. N o. SMF 29116, 1 Ψ, paratype, dissected, SMF 29117, MAP­137, ST­067, 12°40.429’N 54°11.731’E, Rhyi di Hamri, E of Hawlaf, N coast, 7–9 m, 19 March 1999, “from dead Acropora ”.

Description: Small sized pontoniine shrimp of stout subcylindrical body form.

Rostrum: ( Figure 5 A) about 0.19 of carapace length, depressed, reaching to about 0.8 of proximal segment of antennular peduncle, subequal to anteroverted corneal margin ( Figure 2 B), acute, about 1.8 times longer than basal width, distally rounded, inclined ventrally, with two upper setae, one lower seta, dorsally convex, carinate, without teeth, lateral carinae distinct, merging posteriorly with orbital margin, ventral carina concave, without subapical tooth.

Carapace: ( Figure 2 A) smooth, subcylindrical, glabrous, orbit moderately developed, with broadly rounded inferior orbital angle, acute marginal antennal spine, anterolateral margin of branchiostegite slightly produced, broadly rounded.

Abdomen: well developed, feebly swollen, sixth segment short, about 0.29 of carapace length, 1.5 times length of fifth, about 1.8 times wider than long, depressed, with acute posteroventral angle, lateral posterolateral angle reduced, rounded, pleura of first three segments large, broadly rounded, fourth and fifth small, rounded, not produced.

Telson: ( Figure 2 G) about 0.33 of CL, about 2.1 times longer than maximal width at 0.3 of length, lateral margins feebly convex and posteriorly convergent, with 2 pairs of large submarginal dorsal spines at about 0.2 and 0.55 of length, anterior spines slightly longer than posteriorly, about 0.23 of telson length, posterior margin broadly convex, without median point, about 0.3 of maximal width, with 3 pairs of spines ( Figure 2 H), lateral spines small, about 0.25 of intermediate spine length, intermediate spines robust, proximally slightly swollen, about 0.18 of telson length, submedian spines more slender subequal to intermediate spine length, setulose. Antennule: ( Figure 2 C) small, exceeding rostrum by about 0.25 of proximal segment length, proximal segment about 1.3 times longer than basal width, with small ventromedial tooth, anterolateral angle acute, reaching to about middle of intermediate segment length, lateral margin convex, stylocerite phylliform, slightly exceeding half segment length, statocyst normally developed with circular statolith; intermediate and distal segments short, stout, of subequal length, combined length about 0.9 of proximal segment length; upper flagellum short, subequal to peduncle length, fused rami with four stout segments, with about eight groups of aesthetascs, shorter free ramus single segmented, longer ramus with six slender segments.

Antenna: ( Figure 2 D) short, with carpocerite reaching to about distal margin of distal segment of antennular peduncle; basicerite normal, unarmed, antennal gland aperture tuberculate; carpocerite subcylindrical, 5.2 times longer than distal width, reaching to distal margin of scaphocerite; flagellum short, reaching to about posterior carapace margin, scaphocerite ( Figure 2 E) normal, reaching to distal end of carpocerite, about two times longer than wide, maximal width distally at about half length, lamella broadly rounded distally, lateral margin feebly convex, with small stout acute tooth distally, falling distinctly short of distal margin of lamella ( Figure 5 B).

Eye: ( Figure 2 F) small, with cornea hemispherical, well pigmented, transverse, diameter about 0.15 of CL, without accessory pigment spot, stalk, subcylindrical, swollen, medially flattened, about 1.2 times longer than wide.

Mandible: (right) ( Figure 3 A) with corpus robust; incisor process ( Figure 5 E) normal, distal margin oblique with stout medial and lateral teeth, with three smaller intermediate teeth, medial margin laminar with five small denticles distally; molar process ( Figure 5 C, D) stout, subcylindrical, distally trullate, anterior margin laminar, with band of short setae ventrally, two stout teeth posteriorly; without palp.

Maxillula: ( Figure 3 B) with palp ( Figure 5 F) normal, feebly bilobed, with small ventral tubercle with minute simple terminal seta; upper lacinia suboval about seven short submarginal spines distally, four longer distomarginal spines, densely setose ventrally; lower lacinia short, broad based, tapering strongly, distally acute, densely setose.

Maxilla ( Figure 3 C) with simple non­setose tapering palp, basal endite with laciniae obsolete, with short, simple preterminal and terminal simple setae only ( Figure 5 G), proximal margin broadly rounded, non­setose; scaphognathite normal, three times longer than central width, anterior lobe tapering, medially concave.

First maxilliped: ( Figure 3 D) with slender palp, with single simple terminal seta; basal and coxal endites completely fused, basal portion narrow, medial margin concave, densely fringed with long, finely plumose setae; exopod well developed, with slender ramus with numerous plumose setae distally, caridean lobe large narrow; epipod well developed feebly bilobed, anterior lobe much larger than posterior.

Second maxilliped: ( Figure 3 E) with normal endopod, dactylar segment about four times longer than central width, densely fringed with robust spines medially, propodal segment with anterior margin broadly rounded with numerous spiniform setae; endopod similar to first maxilliped without caridean lobe; coxa with feeble medial process, epipod small, rounded, without podobranch.

Third maxilliped: ( Figure 3 F) reaching anteriorly to middle of carpocerite; endopod with ischium and merus completely fused, antepenultimate segment deeply bowed ventrally, sub­operculate, 1.7 times longer than central width, tapering distally, basal width three times distal width, lateral margin feebly convex, medial margin strongly convex, ventomedial surface densely setose, with long silky finely plumose setae, carpal segment subcylindrical, 3.4 times longer than width, about 0.5 of ischiomeral segment length, with numerous long slender setae ventromedially, terminal segment tapering distally, subequal to carpal segment length, about 3.6 times longer than basal width, with long spiniform terminal seta, dense ventromedial setae; basal segment broadly convex medially, without medial process, densely setose, exopod well developed, slender, with numerous plumose setae distally; coxa stout, feebly concave medially, non­setose, with well developed rounded lateral plate, without arthrobranch.

Thoracic sternites: third and fourth broad, unarmed.

First pereiopod: ( Figure 4 A) normal, neither long nor short, moderately robust, exceeding proximal segment of antennular peduncle by distal third of merus, carpus and chela; chela ( Figure 4 B) with palm about 1.3 times longer than deep, compressed, dorsal margin feebly convex, ventral border straight, sparsely setose, fingers slender, tapering, with numerous groups of long setae, dactylus about 1.2 of palm length, straight, four times longer than basal width, tapering strongly to slightly dilated tip with single small acute hooked tip, cutting edges straight, sharp, entire, fixed finger similar to dactylus, 2.7 times longer than basal width, cutting edge sharp, entire, tip with small hooked tooth; carpus subequal to chela length, about 3.6 times longer than central width, tapering proximally, merus moderately slender, 6.2 times longer than central width, situated at 0.5 of length, tapering distally and proximally, about 1.2 times carpus length, unarmed; ischium short, 0.5 of merus length, robust, unarmed; basis and coxa short, stout, ventrally setose, without special features; coxa without ventral process.

Second pereiopods: well developed, unequal in length, dissimilar in shape. Major second pereiopod: ( Figure 4 C) about 1.75 of CL (holotype); chela ( Figure 4 D) with palm, compressed, smooth, two times longer than deep, slightly swollen centrally, strongly carinate ventrally, feebly dentate with numerous very long rigid simple setae, fingers about 0.28 of palm length, dactylus ( Figure 4 F) compressed, slightly overreaching tip, cutting edge concave, sharp, entire, with single large acute tooth at about half length; fixed finger, three times longer than deep, dorsal margin moderately convex, with acute tip, cutting edge concave, sharp, entire, with single large acute tooth at about half length, ventrally carinate continuously with palm, with numerous very long rigid simple setae, with acute feebly hooked tip, cutting edge with distal third sharp, entire, as on dactylus, proximal two thirds with two low distal teeth and larger more acute proximal tooth; carpus articulating obliquely with propod, about 0.27 of palm length, 1.5 times longer than distal width, tapering strongly proximally, distally excavate, unarmed; merus about 0.36 of palm length, two times longer than central width, unarmed, ischium 0.75 of meral length, 1.8 times longer than distal width, tapering strongly proximally, unarmed; basis and coxa robust, without special features.

Minor second pereiopod: ( Figure 4 E) with chela about 1.3 times CL (holotype), 10.5 times (paratype) 0.75 of major chela length (paratype): with palm, compressed, smooth, 1.8 times longer than deep, slightly swollen distally, strongly carinate ventrally, feebly dentate with numerous very long rigid setae, fingers about subequal to palm length, dactylus slender, compressed, slightly overreaching fixed finger, about six times longer than deep, dorsal margin convex, with acute tip, cutting edge concave, sharp, entire, with single small acute tooth proximally; fixed finger about 2.7 times longer than basal width, ventrally carinate continuously with palm, with numerous very long rigid simple setae, with acute feebly hooked tip, cutting edge proximally cannulate ( Figure 4 F), distally sharp, entire, proximally with two small blunt teeth, inner edge with three smaller rounded teeth; carpus articulating transversely with propod, robust, about 0.38 of palm length, 1.1 times longer than distal width, unarmed; merus about 0.66 of palm length, 1.7 times longer than distal width, tapering slightly proximally, unarmed, ischium 0.9 of meral length, 48 times longer than distal width, tapering strongly proximally, unarmed; basis and coxa robust, without special features.

Third pereiopod: ( Figure 4 G) exceeding basicerite by distal fourth of merus, dactylus ( Figure 5 I) about 0.25 of propod length, with unguis distinctly obliquely demarcated, about 0.7 of length of dorsal corpus length, slender, curved, acute, about 1.8 times longer than basal width, with minute accessory denticle distodorsally ( Figure 5 J), corpus strongly compressed, dorsal border feebly convex, ventral margin with stout blunt curved tooth distally, ventral margin feebly convex otherwise, with small acute anteroverted tooth at about half length, with two very small acute denticles distally, three small acute teeth, of decreasing size, proximally; propod ( Figure 4 H) about 0.42 of CL, compressed, sparsely setose, five times dactylus length, 7.25 times longer than maximal width, subuniform, feebly bowed, ventral border concave, with stout subequal medial and lateral distoventral spines ( Figure 5 H), similar subterminal ventral spine, single distal ventral spine at about 0.7 of propod length, about 0.8 of corpus length, ventral border straight, unarmed; carpus 0.5 of propod length, slender, four times longer than distal width, tapering proximally, unarmed; merus robust, subequal to propod length, 5.2 times longer than central width, compressed, subuniform, unarmed; ischium equal to 0.8 of propod length, 4.7 times longer than distal width, tapering proximally; basis and coxa robust, without special features. Fifth pereiopod: more slender, generally similar to third pereiopod, propod about 0.57 of CL, 1.2.times third pereiopod propod length, slightly tapering distally, 9.0 times longer than wide, ventral margin with distoventral spines and setae, 3 ventral spines.

Pleopods: without special features.

Uropod: ( Figure 2 I) with protopod unarmed posterolaterally; e ndopod slightly exceeding posterior telson margin, exopod slightly shorter; exopod broad, about two times longer than wide, lateral margin convex, sparsely setose, unarmed, with minute acute distolateral tooth with larger stout mobile spine medially ( Figure 5 K), not reaching level of distal border of exopod, without distinct diaeresis; endopod 1.1 times exopod length, 2.4 times longer than broad, slightly exceeding endopod.

Ova : numerous and small, about 50.

Measurements. Holotype; carapace 3.5 mm, carapace and rostrum 3.9 mm, total body length (approx.) 10.5 mm, major second pereiopod chela 4.8 mm, minor second pereiopod chela 4.2 mm: paratype; carapace 3.8 mm, carapace and rostrum 4.6 mm, total body length (approx.) 120.0 mm, minor second pereiopod chela 3.7 mm, length of ovum 0.5 mm.

Colour pattern. Not noted.

Host/Habitat: Not identified, presumably from encrusting tunicate (Ascidiacea).

Etymology: From carina (Latin), a keel, diminutive.

Distribution: Known from the type locality only.

Sy stematic Position: Dactylonia carinicula appears to be most closely similar to Dactylonia anachoreta Kemp which has relatively few teeth on the flexor margin of the ambulatory dactyls, a short dorsally carinate rostrum, but which lacks a distinct ventral carina and has no significant orbital development. The figures of D. anachoreta provided by Fransen (1994, 2002) shows a shorter broader rostrum with a shorter, lower dorsal carina, and which bears a minute distal subapical ventral tooth, lacking in D. carinicula . In D. carinicula the scaphocerite extends distinctly beyond the end of the carpocerite but is subequal in D. anachoreta . The ambulatory dactyls are similar in general shape but differ in several details. In D. carinicula the corpus has the distal (primary) tooth blunt, the next largest (secondary) tooth at about half the ventral margin length, with two small denticles between it and the primary tooth, with four small acute teeth proximally (in D. anachoreta the secondary tooth is long and acute, close to the primary tooth, without intervening denticles, with about five smaller teeth proximally, these teeth finely denticulate distally, a feature not present in D. carinicula .

Dactylonia carinicula appears also to be closely similar to D. ascidicola Borradaile in many of the features of its general morphology. Common features include a short rostrum, narrow in dorsal view, with a dorsal median carina, unequal dissimilar second pereiopod chelae, with two pairs of large dorsal telson spines. Borradaile (1898) does not mention the dorsal rostral carina in his descriptions (1898, 1899), although he notes the absence of a ventral carina, which is distinct in D. carinicula . Its presence is indicated by Holthuis (1952), although it is not shown in his figure 79b. Dactylonia carinicula differs particularly in the complete absence of laciniae on the basal endite of the maxilla and the quite different dactyl of the third pereiopod which is elongate, biunguiculate, with a series of numerous blunt ventral accessory denticles of progressively diminishing size proximally. The fingers of the minor second pereiopod are distinctly longer than the palm, but markedly shorter in D. ascidicola . Dactylonia carinicola also resembles D. monnioti Bruce, 1990 , but which has a much narrower rostrum in dorsal view, with feebly developed orbits, and the carinate rostrum, which well exceeds the anteroverted corneal margin, and bears a small distoventral tooth. The maxilla has two small laciniae and the ambulatory dactyl resembles that of D. ascidicola .

Remarks: The recognition of Dactylonia carinicula sp. nov. raises to 8 the number of Indo­West Pacific species of this genus. All are probably associates of tunicate hosts. A key for the preliminary identification of these species is presented below.

As noted for D. okai by Holthuis (1952) the upper antennular flagella of D. carinicula are carried in a reflexed position, a common feature of many ” Pontonia ”­ like specimens.

Figures

FIGURE 2. Dactylonia carinicula sp. nov., paratype. (A), carapace and appendages, lateral. (B), anterior carapace and appendages, dorsal. (C), antennule. (D), antenna. (E), scaphocerite. (F), eye, dorsal. (G), telson. (H), same, posterior spines. (I), uropod.

FIGURE 3. Dactylonia carinicula sp. nov .. paratype. (A), mandible. (B), maxillula. (C), maxilla. (D), first maxilliped. (E), second maxillped. (F), third maxilliped.

FIGURE 4. Dactylonia carinicula sp. nov. (A), first pereiopod. (B), same, chela. (C), major second pereiopod, ventral. (D), same, chela, medial. (E), minor second pereiopod. (F), same, hinge region of fingers. (G), third pereiopod. (H), same, propod and dactyl. (ABG), paratype; (C – F), holotype.

FIGURE 5. Dactylonia carinicula sp. nov., paratype. (A), rostrum. (B), scaphocerite, distal margin. (C), right mandible, molar process, lateral. (D), same, medial. (E), incisor process. (F), maxillula, palp. (G), maxilla, palp and endites. (H), third pereiopod, distal propod and dactyl. (I), same, dactyl. (J), same, tip of unguis. (K), exopod of uropod, posterolateral spine.