Hexapleomera satella, Bamber, Roger N., 2012

Bamber, Roger N., 2012, A re-assessment of Hexapleomera Dudich, 1931 (Crustacea: Tanaidacea: Tanaidae), with designation of three new species, Zootaxa 3583, pp. 51-70 : 63-68

Hexapleomera satella sp. nov.

( Figs 6–8 )

Hexapleomera robusta Bamber et al., 2009: 10 . (non- Tanais robustus Moore )? Anatanais robustus Riggio, 1976: 503 , figs 4–5.

? Hexapleomera robusta Riggio, 1996: 644 –648, figs 20–21.

Type material: brooding Ƥ, holotype ( BMNH.2012.654), 1 adult 3, paratype ( BMNH.2012.655), 1 subadult 3, 4 Ƥ (two brooding), four juveniles, paratypes ( BMNH.2004.1795-1804), Tripoli Port, ca 34°27'N 035°49'E; surface concretion of Spirobranchus kraussii (Baird, 1865) (Annelida: Serpulidae ). 19 September 2002; coll. Helmut Zibrowius. 1 Ƥ ( TAU AR 28449), off Israel, Station MI 3, 31°51.472'N 034°39.553'E, 4.7 m depth, sand; 2 Ƥ ( BMNH.2008.4911-4912), off Israel, Station MI 4, 31°51.733’N 034°39.699’E, 4.4 m depth, sand; both 0 2 May 2007.

Other material: 11 specimens, Tripoli Harbour, ca 34°27'N 035°49'E; 2 m depth, 19 September 2002. 2 specimens, Tripoli Harbour, ca 34°27'N 035°49'E; 2–5 m depth, 0 8 July 2003. 56 specimens, Beirut, harbour jetty, inner side, ca 33°54'N 035°31'E; 1–2m with ascidians, 0 9 July 2003. 9 specimens, Beirut, harbour jetty, outer side, ca 33°54'N 035°31'E; 5–8m ,, 0 9 July 2003. All coll. Helmut Zibrowius. 1 3, north-east Il Ramkine Island, Tripoli, ca 34°29.8'N 035°45.7'E; amongst Dictyopterus and Sargassum , 0.5 m depth, 0 1 June 2000, coll. Ghazi Bitar.

Diagnosis: Adult uropod with four segments; dorsum of pereonites and margins of pleotelson with unequal paired setae; pleopod endopod with one subdistal inner marginal seta, pleopod 3 basis with no inner seta; coxa of pereopod 1 with apophysis; maxillule palp with four distal setae; maxilliped basis with two unequal distal setae, coxa with two setae, endite with no distal spines; cheliped fixed finger with three ventral setae; dactylus of male cheliped with spinulation along cutting edge; fixed finger with ventroproximal apophysis but no tooth-like proximal apophysis on cutting edge.

Description of female: body ( Fig. 6 A) 4.5 times as long as wide, dorsally with diffuse pale-brown pigmentation on cephalon, all pereonites and whole pleon, and chelipeds (after preservation in alcohol); length of holotype 2.0 mm. Cephalothorax stout, pear-shaped, tapering towards anterior, 0.9 times as wide as long, with slight rounded frons but no distinct rostrum, eyes present, pigmented; unequal paired setae behind ocular lobes, single midlateral setae on each side. Cephalothorax as long as pereonites 1–3 together. Each pereonite armed with one (pereonite 1) or two (pereonites 2 to 6) mid-lateral setae, and four pairs of one longer seta and one shorter seta across dorsum towards frontal edge. Pereonites 1 to 3 subequal in length, together 0.9 times as long as wide, rounded laterally, each three times as wide as long. Pereonites 4 and 5 wider posteriorly, with concave anterolateral margins; pereonite 4 twice as long as pereonite 3 and 1.5 times as wide as long, pereonite 5 just shorter, 1.8 times as long as pereonite 3 and 1.7 times as wide as long; pereonite 6 shorter, 1.5 times as long as pereonite 3 and twice as wide as long. Pleon of five free pleonites, pleonites 1 and 2 with tufts of plumose lateral setae, each pleonite half as long as pereonite 6 and about four times as wide as long; pleonite 3 shorter, 0.7 times as long as pleonite 2; pleonites 4 and 5 subequal, 0.4 times as long as pleonite 2 and seven times as wide as long, with unequal paired mid-lateral setae, without pleopods. Pleotelson ( Fig. 6 B) pentagonal, twice as wide as long, with unequal paired lateral and laterodistal setae on each side and one longer and one shorter pair of distal setae.

Antennule ( Fig. 6 C) proximal article about 1.5 times as long as distal articles together, 2.8 times as long as wide, mid-inner and outer-distal margins with tufts of three penicillate setae, distally with inner, mid-dorsal and outer simple setae; second article one-third as long as first, distally with inner and dorsal tufts of simple setae and outer tuft of three penicillate setae; third article three-quarters as long as second, distally with dorsal pair of simple setae and inner and outer fine simple setae; distal article (flagellum) very small, with six distal setae and three aesthetascs.

Antenna ( Fig. 6 D) first article naked, half length of second; second article with paired mesial simple setae and single dorsodistal and ventrodistal simple setae; third article 0.6 times as long as second article, naked; fourth article longest, twice as long as third article and twice as long as wide, with three simple distal setae; fifth article 0.8 times as long as fourth, with four simple distal setae; sixth article one-third as long as fifth article, with ten distal setae.

Labrum ( Fig. 6 E) rounded, setose. Left mandible ( Fig. 6 F) with wide, robust, distally denticulate lacinia mobilis with adjacent seta, pars incisiva stout, smooth; right mandible ( Fig. 6 G) with much narrower lacinia mobilis, pars incisiva distally inflected; pars molaris of each mandible robust, rugose. Labium ( Fig. 6 I) wide, all lobes finely setose distally; labial palp present, about as long as wide. Maxillule ( Fig. 6 H) with eight distal spines, each spine finely denticulate, endite with distal tuft of setules on outer margin, palp with four distal setae. Maxilla ovoid, simple. Maxilliped ( Fig. 6 J) generally typical of genus; coxa with two inner setae; basis with one shorter and one longer distal setae, latter reaching distal margin of palp article 1; proximal palp article with slender, curved outer-distal spine, second palp article with slender outer-distal spine, and four slender and three stouter, recurved inner setae; third article with fourteen inner setae in two rows; fourth article with nine inner-distal and two outer subdistal finely-denticulate setae. Maxilliped endites ( Fig. 6 K) with setose distal margins, two longer coarselyplumose setae, but no spines. Epignath ( Fig. 6 L) typical of genus, elongate with distal spine and finely setose margins.

Cheliped ( Fig. 7 A) comparatively stout, rounded, basis 1.4 times as long as wide with single dorso-subdistal seta and unequal paired ventrodistal setae; merus ventrally with two subdistal seta and unequal paired setae towards dorsal margin; carpus 1.4 times as long as wide, with single proximo-dorsal, three dorsodistal, and three midventral setae; propodus shorter than wide with two inner and one outer setae distally near dactylus insertion; fixed finger 0.75 times as long as propodus, with three ventral setae, three outer distal setae, and five setae along cutting edge, cutting edge distally expanded into rounded lamella; dactylus with seven fine spinules along cutting edge.

Pereopod 1 ( Fig. 7 B) coxa with blunt apophysis bearing two setae; ischio-basis 3.7 times as long as wide, dorsoproximally with one simple and one penicillate setae; merus 0.3 times length of ischio-basis with one ventrodistal seta; carpus 1.5 times as long as merus with single dorsodistal and ventrodistal setae; propodus 1.5 times as long as carpus, with subdistal dorsal seta, two ventrodistal simple setae; dactylus with dorsoproximal seta and distinct, slender, longer claw, both together about half as long as propodus. Pereopod 2 ( Fig. 7 C) ischio-basis 2.3 times as long as wide, dorso-proximally with one simple seta, one ventrodistal seta; merus half length of ischiobasis with one ventrodistal seta and short tooth-like spine, one dorsodistal seta, ventral margin with microtrichia; carpus compact, shorter than merus, with dorsal seta, three posterodistal and one anterodistal short tooth-like spines, ventral and distal margins with microtrichia; propodus 1.6 times as long as carpus, one dorsodistal and one ventro-subdistal setae, ventral margin with microtrichia; dactylus plus claw just shorter than carpus. Pereopod 3 ( Fig. 7 D) similar to pereopod 2 but basis with additional dorsoproximal penicillate seta, propodus with two ventrosubdistal setae.

Pereopod 4 ( Fig. 7 E) ischio-basis three times as long as wide, with two ventrodistal setae; merus one-third as long as ischio-basis, with paired subdistal ventral short spines, single dorsodistal and ventrodistal setae, ventral margin with microtrichia; carpus as long as merus, with crown of three posterodistal and two anterodistal short tooth-like spines, ventral and distal margins with microtrichia; propodus just longer than carpus, with two dorsodistal and one ventrosubdistal setae but apparently without mid-dorsal penicillate seta,, ventral margin with microtrichia; dactylus and unguis fused into a claw, curved, with lateral comb of six lanceolate spinules, heel of unguis finely denticulate. Pereopod 5 (not figured) as pereopod 4. Pereopod 6 ( Fig. 7 F) as pereopod 4, but merus with two dorsodistal and two ventrodistal setae, propodus with three dorsodistal setae and distal row of seven leaf-like spines.

Pleopods 1 and 2 ( Fig. 7 G) basis with one inner and five outer plumose setae, pleopod 3 ( Fig. 7 H) basis with no inner and 3 outer plumose setae; exopods with about 19 plumose setae along outer edge; endopods with one inner and nine outer plumose setae, distally with shorter, stout seta.

Uropod ( Fig. 7 I) of three segments plus basis, ramus segments 1.5–2 times as long as wide, subequal in length.

Juvenile: Body lengths between 1.2 and 1.5 mm; similar overall to mature female, but with only three (in total) uropod segments and two aesthetascs.

Adult male: body ( Fig. 8 A) 3.8 times as long as wide, dorsally with diffuse pigmentation as in female (in preserved material); length of allotype 2.0 mm. Cephalothorax onion-shaped, tapering towards anterior, as wide as long, parallel-sided anterior part 0.4 times as wide as posterior width; with slight rounded rostrum, eyes present, pigmented. Cephalothorax 1.25 times as long as pereonites 1–3 together, and one-quarter of total body-length. Pereonites rounded laterally, setation as in female; pereonites 1 to 3 together 0.8 times as long as wide; pereonites 1 and 2 equal in length, 4.3 times as wide as long; pereonite 3 about 1.4 times as long as pereonite 2 and three times as wide as long; pereonites 4 and 5 both narrower anteriorly, longest, twice as long as pereonite 2 and twice as wide as long; pereonite 6 as long as pereonite 3. Pleon comprising some 22% of total body length.

Appendages similar to those of female except for antennules, antennae and chelipeds.

Antennule ( Fig. 8 B) longer than cephalothorax, elongate, proximal peduncle article 0.8 times as long as cephalothorax, six times as long as wide, with proximal tuft of penicillate setae, one longer and one shorter simple mesial setae, and distal tuft of three simple and one penicillate setae; second article one-third as long as first, with distal crown of five simple and two penicillate setae; third article 0.7 times as long as second, with one penicillate and two longer and two shorter simple distal setae; distal article (flagellum) very short, with six simple setae and four aesthetascs.

Antenna ( Fig. 8 C) more elongate than that of female, proximal article compact, naked; second article three times as long as first and nearly three times as long as wide, with dorsal and ventral proximal, mesial and distal simple setae; third article 1.5 as long as first, naked; fourth article longest, twice as long as third article, with four distal setae of varying lengths, the longest longer than fifth article; fifth article 0.7 times as long as fourth article, distally with two simple setae; sixth article one-third as long as fifth article, with one short penicillate seta and nine longer simple setae.

Cheliped ( Fig. 8 D) much stouter than that of female, in life reaching well-forward of rostrum; basis compact, about 1.2 times as long as wide, with two unequal ventrodistal setae and one outer submarginal dorsodistal seta; merus triangular, with two unequal mesial setae and two ventral setae; carpus short, 0.9 times as long as wide, just shorter than basis, ventral margin very short, with two dorsodistal, one mid-distal and three mid-ventral setae. Propodus wider than long, with conspicuous blunt ventroproximal apophysis, one inner seta (comb-row?) adjacent to dactylus attachment, row of three outer setae adjacent to fixed finger origin, and three setae distally between fingers; fixed finger shorter than palm, with three ventral setae, three inner-distal setae and row of eleven setae alongside cutting edge; dactylus arcuate, with inner seta in distal half, and row of eleven tooth-like spinules along cutting edge.

Etymology: From the Latin satelles —a companion, and -ella, a diminutive ending, with reference to the unusual small companion setae occurring with the setae on the pereonite terga, the pleotelson, and the cheliped basis and merus.

Remarks: H. satella sp. nov. is the smallest of those taxa analyzed herein, which may account for the lowerthan-usual numbers of setae on, for example, the cheliped fixed finger, the maxillule palp, and the antennules (where there are also the fewest aesthetascs) and antennae. Reduced setation has been cited previously as an almost inevitable feature of smaller species (e.g. Bamber et al. 2009; Bamber & Chatterjee 2010). Unique features of the present species include the pairs of unequal setae on the pereonite terga, the margins of pleonites 4 and 5, the pleotelson, and the cheliped basis and merus; the slender outer spines on proximal two articles of the maxilliped palp; the very narrow lacinia mobilis on the right mandible; and in particular the ventroproximal apophysis on the male cheliped propodus. H. satella shares only with the two Australian species the apophysis on the coxa of pereopod 1.

Riggio (1976, 1996) recorded “ Hexapleomera robusta ” from epilithic and algal habitats around Italy, giving little useful description, but did figure six distal spines on the maxillule endite ( Riggio 1996, fig. 21) and a small ventroproximal apophysis on the male cheliped propodus ( Riggio, 1976, fig. 5; 1996, fig. 20a). While the former is likely to be a misinterpretation, the latter feature appears to coincide with the cheliped morphology of H. satella , as does the habitat, so it is likely that these two may be the same species.

Riggio’s (1975, 1996) description and figures of “ Hexapleomera crassus ”, also taken from benthic habitats, are even more inadequate. His distinguishing of this species from his Italian “ Hexapleomera robusta ” material suggests it is not the same as the present species (see below).

Hexapleomera satella is presently known from shallow benthic habitats along the eastern coastline of the Mediterranean.

Figures

FIGURE 6. Hexapleomera satella sp. nov., female: A, holotype, dorsal; B, pleotelson, dorsal; C, antennule; D, antenna; E, labrum; F, left mandible; G, right mandible; H, maxillule and maxilla; I, labium; J, maxilliped; K, maxilliped endites; L, epignath. Scale line = 1 mm for A, 0.4 mm for B, 0.2 mm for C – L.

FIGURE 7. Hexapleomera satella sp. nov., female: A, cheliped; B – D, pereopods 1 to 3 respectively; E, pereopod 4, with detail of claw; F, pereopod 6; G and H, pleopods 2 and 3 respectively (plumose mature of all setae not shown; most setae of rami shown only by their bases); I, uropod. Scale line = 0.2 mm for A to H, 0.15 mm for I.

FIGURE 8. Hexapleomera satella sp. nov., male allotype: A, habitus; B, antennule; C, antenna; D, right cheliped. Scale line = 1 mm for A, 0.3 mm for B – D.