Apopontonia seticauda, Bruce, 2008

Bruce, A. J., 2008, Palaemonoid shrimps from the Australian north west shelf, Zootaxa 1815, pp. 1-24 : 3-9

Apopontonia seticauda sp. nov.

( Figs 2–5, 14A)

Material examined. 1 ♀, holotype, CL 3.0, CMAR Cruise, SS 05/2007, stn 082, Imperieuse transect L23, 18° 27’37”S 120°08’41”E, 80m, Sherman sled, 19 July 2007, NMV J56496

Diagnosis. An Apopontonia with well developed compressed straight rostrum with a dorsal dentition of seven acute teeth, ventrally unarmed, with feebly developed orbit and without supraorbital teeth, second pereiopods unequal and dissimilar, major chela fingers with molar process on fixed finger, dactylus with fossa, minor chela fingers simple, caudal fan ( Fig. 3K) densely covered with numerous slender spiniform setae, telson with large dorsal spines on anterior half, intermediate and submedian posterior spines very long, about 0.4 of telson length, endopod of uropod far exceeding telson, longer than exopod, exopod with 8–9 lateral spines.

Description. A small pontoniine shrimp ( Fig. 2) of subcylindrical body form.

Rostrum ( Fig. 3C) short, straight, acute, reaching to end of antennular peduncle, about 0.45 of CL, dorsal carina not extending on to carapace, distally compressed, with 7 small acute teeth on distal two thirds, ventrally unarmed, non-setose, proximally with lateral carinae slightly broadened forming small supraocular carina covering bases of eye stalks only.

Carapace ( Fig. 3 AB) smooth, glabrous, without supraocular teeth, supraorbital, epigastric or hepatic spines, orbit feebly developed, inferior orbital angle ( Fig. 5A) feebly developed, rounded, antennal spine robust, marginal, reaching to distal margin of basicerite, pterygostomial angle rounded, not produced.

Abdomen normal, smooth, mainly glabrous, third segment not posterodorsally produced, sixth segment ( Fig. 5F) about 0.25 of CL, 2.5 times longer than central depth, sparsely setose with spiniform setae dorsally, pleura rounded.

Telson ( Fig. 5 FG) about 2.5 times longer than anterior width, twice sixth abdominal segment length, sides straight, converging to triangular apex, about 0.25 of anterior width, with minute acute median point, covered with numerous spiniform setae ( Fig. 5I), with two pairs of large robust erect dorsal spines ( Fig. 5H), about 0.2 of telson length, at about 0.13 and 0.32 of telson length, posterior spines ( Fig. 5) with lateral posterior spines small, about 0.22 of intermediate spine length, intermediate spines very long, 0.38 of telson length, slender, about 15.0 times longer than basal width, submedian spines subequal to intermediate spines, slightly more slender, non-setulose.

Antennule ( Fig. 3D) with proximal segment ( Fig. 3E) broad, about 2.5 times longer than proximal width, tapering distally, medial margin straight, non-setose, with acute submarginal ventral tooth at 0.5 of length, lateral margin with strong acute distolateral angle extending almost to level of base of distal peduncular segment, stylocerite large acute, reaching to 0.6 of proximal segment length, statocyst normal, intermediate and distal segments short, combined length about 0.4 of proximal segment length, upper flagellum biramous, proximal three segments fused, shorter ramus with one free segment with four groups of aesthetascs, longer ramus filiform, lower flagellum also filiform.

Antenna ( Fig. 3F) with basicerite robust, distolaterally unarmed, carpocerite subcylindrical, about 3.2 times longer than wide, flagellum well developed, scaphocerite ( Fig. 3G) with lamella slightly exceeding car- pocerite, 2.75 times longer than central width, maximum width at about 0.4 of length, distally rounded, lateral margin straight, with short stout distal tooth ( Fig. 5B), 0.07 of scaphocerite length, slightly everted.

Ophthalmic somite without medial dorsal process.

Eye ( Fig. 5C) with hemispherical pigmented cornea, about 0.14 of CL, with small marginal accessory pigment spot, stalk about 1.25 times corneal diameter.

Epistome unarmed.

Mouthparts not dissected. Maxillipeds with slender flagella, each with four terminal plumose setae. Third maxilliped ( Fig. 3H) slender, with ischiomerus and basis completely fused, coxa with acute medial process, lateral plate semicircular, without arthrobranch.

Thoracic sternites unarmed.

First pereiopod ( Fig. 3I) of normal form, merus falling slightly short of distal end of carpocerite; chela ( Fig. 3J) with palm oval in section, short, about as long as deep, sparsely setose with four rows of short cleaning setae proximoventrally, fingers about twice palm length, dactylus 4.0 times longer than proximal depth, dorsal margin convex, cutting edge straight, entire, blunt, tip not hooked, dorsal surface densely covered with long simple setae, cutting edge with short setae, fixed finger similar, twice as long as proximal depth, similarly setose, many setae finely serrulate; propod about 1.3 times chela length, 4.4 times longer than distal width, tapering proximally, few cleaning setae proximoventrally, otherwise glabrous; merus subequal to propod length, 4.0 times longer than central width, glabrous; ischium, about 0.5 of meral length, medial margin with numerous long simple setae, otherwise glabrous; basis normal; coxa with small acute setose medial process.

Second pereiopods ( Fig. 4) unequal, dissimilar, dactylus held ventrally.

Major chela (right) ( Fig. 4A) well developed, robust, about 1.5 times CL, articulating obliquely with carpus ( Fig. 5D), chela ( Fig. 4B) with palm mainly smooth, ventral border finely tuberculate, glabrous, oval in section, about 2.2 times longer than central depth, dorsal margin convex, ventral margin straight, fingers ( Fig. 4 CDE) sparsely setose, dactyl about 0.5 of palm length, about 3.0 times longer than proximal depth, proximal two thirds swollen, distally compressed, dorsal margin strongly curved, tip acute, ventral margin with cutting edge distally concave, entire, central third with well developed deep oval fossa, with small subacute tooth proximally; fixed finger stout, about as long as proximal depth, ventral margin straight, continuous with ventral margin of palm, distally acute with tip directed distally, distal half of cutting edge concave sharp, entire, proximal half with large irregular molar process distally, with deep concavity proximally; carpus stout, smooth, distally expanded, excavate, about 0.25 of palm length, unarmed; merus about 0.6 of palm length, 2.3 times longer than central depth, most strongly tapered proximally, unarmed; ischium short, unarmed, about 1.5 times longer than distal width, tapering strongly proximally, subequal to carpal length, 0.25 of palm length; basis and coxa robust, without special features.

Minor chela (left) ( Fig. 4F) well developed, more slender than major chela, about 1.3 times CL, about 0.88 of major chela length, articulating obliquely with carpus ( Fig. 5E), chela ( Fig. 4G) with palm smooth, glabrous, compressed, ventrally carinate, lateral surface concave, medial surface convex, about 2.2 times longer than central depth, dorsal margin feebly convex, ventral margin straight, subcarinate, tuberculate; fingers ( Fig. 4H) sparsely setose, dactyl about 0.8 of palm length, slender, scaphoid, about 6.5 times longer than proximal depth, dorsal margin feebly convex, tip ( Fig. 4I) bluntly bifid (? damaged), ventral margin with cutting edge distally straight, sharp, entire, with small subacute tooth proximally; fixed finger stouter, about 2.2 times longer than basal depth, extending beyond closed dactyl, ventral margin straight, continuous with ventral margin of palm, distally acute with tip directed distally; carpus stout, smooth, distally expanded, excavate, about 0.37 of palm length, unarmed; merus about 0.75 of palm length, 2.0 times longer than central depth, unarmed; ischium short, unarmed, about 1.5 times longer than distal width, tapering strongly proximally, subequal to carpal length, 0.4 of palm length; basis and coxa robust, without special features.

Ambulatory pereiopods not preserved.

Uropod ( Fig. 5 FK) with protopodite distolaterally rounded; exopod subequal to telson length, twice as long as broad, proximal two thirds of lateral border expanded, convex, with small acute tooth at half length, 8–9 marginal spines ( Fig. 5L), short proximally, becoming large and subdorsal distally, distally rounded, medial margin with very long densely plumose setae, lateral margin with similar submarginal ventral setae, setae held perpendicular to margin, dorsolateral surface covered with dense setae, long laterally, shorter medially, mainly erect; endopod 3.3 times longer than width, distally pointed, greatly exceeding telson, exceeding endopod by about one fourth of its length, medial and lateral margins with numerous very long densely plumose setae, dorsal surface covered with dense long erect spiniform setae.

Measurements (mms). Postorbital carapace length, 3.0; carapace and rostrum, 4.3; total body length (approx.), 9.7; second pereiopod, major chela, 4.8; minor chela, 4.2.

Systematic position. Most similar to A. dubia Bruce, 1981 , which it resembles particularly in the absence of large supraocular teeth and deep orbits. It differs in (i) more numerous rostral teeth, 7 vs 5, (ii) less expanded lateral rostral carinae, scarcely covering bases of eyestalks, (iii) distolateral tooth of the scaphocerite not markedly exceeding the lamella, (iv) more slender endopod of third maxilliped, (v) first pereiopod chela with fingers longer than palm, second pereiopod with palm of chela laterally concave, vs convex, (vi) dense setation over dorsal surface of caudal fan, (vii) stronger dorsal telson spines, all on anterior half of tel- son, (viii) longer intermediate and submedian posterior telson spines, (ix) uropod with exopod proximally expanded, with 8–9 distolateral spines, preceded by a small tooth, vs not broadened, with about 12 less robust spines, without proximal tooth, (x) uropod with long narrow endopod markedly exceeding endopod and telson. Apopontonia seticauda differs strongly from A. falcirostris Bruce, 1976 , the type species of the genus, in the more robustly developed second pereiopods and, particularly in the dactylar fossa and fixed finger molar process of the major second pereiopod which are unarmed in A. falcirostris .

Etymology. From seta (Latin), a bristle, and cauda (Latin), a tail, with reference to the setation of the telson.

Colouration ( Fig. 9A). (From colour photo). Uniform deep red over whole body and all appendages.

Host. Unknown, presumably a sponge.

Remarks. Three species of Apopontonia Bruce, 1976 , have been described: A. dubia Bruce, 1982 , A. falcirostris Bruce, 1976 , and A. orbitospinata ( Bruce, 1969) . These species and A. seticauda may be distinguished by the following key.

1. Supraocular teeth absent, without deep orbits.............................................................................................2

- Large supraocular teeth present, with deep orbits.......................................................................................3

2. Caudal fan sparsely setose, dorsal telson spines at 0.33 and 0.66 of telson length, intermediate posterior spines 0.28 of telson length, uropodal endopod not elongate, subequal to exopod, R. 5/0 .. A. dubia Bruce

- Caudal fan conspicuously setose, dorsal telson spines at 0.13 and 0.32 of telson length, intermediate posterior spines almost 0.4 of telson length, uropodal endopod elongate, much exceeding exopod, R. 7/0...... ..................................................................................................................................... A. seticauda sp. nov.

3. Rostrum with deflexed bifid tip, otherwise edentate ............................................. A. orbitospinata (Bruce)

- Rostrum not distally deflexed, with strong, recurved ventral tooth; R. 4/1… .............. A. falcirostris Bruce

Apopontonia dubia has been found in sponges of the genera Spongia and Ircinia and it is therefore likely that A. seticauda will have similar associations (Bruce, 1976, 1983). Apontonia falcirostris has been found at 10–73m ( Marin, 2007; Bruce, 1976b), A. dubia from 10–43 m ( Bruce, 1991b; De Grave, 2000); and A. orbitospinata from 18–27m, 54m and 60m ( Bruce, 1969, 1983; Debelius, 1999). The latter species has also been reported from the North West Shelf (Bruce, 2008) and Gulf of Carpentaria.