Lissosabinea Christoffersen, 1988

Komai, Tomoyuki, 2006, A review of the crangonid genus Lissosabinea Christoffersen, 1988 (Crustacea, Decapoda, Caridea), with descriptions of three new species from the western Pacific, Zoosystema 28 (1), pp. 31-59 : 33-37

Genus Lissosabinea Christoffersen, 1988

Sabinea – Pequegnat 1970: 115 (part).

Lissosabinea Christoffersen, 1988: 46 , 48. — Holthuis 1993: 290.

TYPE SPECIES. — Sabinea tridentata Pequegnat, 1970 . Original designation.

OTHER SPECIES INCLUDED. — Lissosabinea indica ( De Man, 1918) , L. armata n. sp., L. ecarina n. sp. and L. unispinosa n. sp.

DIAGNOSIS. — Body moderately robust; integument not particularly firm; small scales present on carapace, telson, antennae and pereopods. Cephalothorax subcylindrical or slightly compressed laterally. Rostrum variable in shape, but always with one pair of distinct lateral teeth. Carapace with low, usually indistinct epibranchial carina, but other lateral carinae absent; epigastric tooth always present; antennal tooth sharp; branchiostegal tooth moderately small to large; tiny pterygostomian tooth usually present; hepatic tooth always present. Abdomen more or less hump-backed, as tergum of third somite slightly to strongly elevated. First and fourth to sixth abdominal somites smooth on dorsal surface; third somite with tergal surface elevated in posterior part or bearing median carina. Eye with well developed cornea; eye-stalk without dorsal tubercle. Antennal scale with conspicuous distolateral tooth distinctly overreaching distal margin of blade. First pereopod without exopod; merus with lamelliform carina on proximal half of ventral surface. Second pereopod very short, simple, not chelate, not reaching midlength of merus of first pereopod. Two arthrobranchs present above third maxilliped.

DISTRIBUTION. — Tropical to warm temperate waters in the western Pacific and western Atlantic ; upper bathyal, 146-830 m.

GENERAL DESCRIPTION

Body moderately robust for crangonids. Integument of body not particularly firm; tegumental scales present on carapace, telson, antennae and pereopods.

Rostrum variable in shape, but armed with one pair of small to large lateral teeth. Carapace always longer than wide postorbitally, subcylindrical or slightly compressed laterally; surface with paired longish plumose setae particularly on dorsal side; middorsal line distinctly carinate at least in anterior half, bearing one to three teeth including epigastric tooth; orbital margin evenly concave, without cleft; anterolateral margin terraced anteriorly, armed with sharp antennal tooth, small to large branchiostegal tooth and tiny pterygostomian tooth; lateral surface of carapace always with hepatic tooth accompanied by shallow hepatic groove and occasionally with posthepatic tooth; postorbital carina absent; epibranchial carina usually low, inconspicuous; longitudinal suture absent.

Thoracic sternum widened posteriorly, fourth sternal plate with elongate median spur arising from anterior margin and reaching to midlength of basis of first pereopod; in males and non-spawning females sternal plates on fifth to eighth thoracic somites slightly elevated in midline, each with sharp median tooth, size of median teeth decreasing in size posteriorly ( Fig. 2G ); in spawning females thoracic sternum nearly flat or concave, median teeth on fifth and sixth somites completely absent ( L. ecarina n. sp., L. indica , L. tridentata and L. unispinosa n. sp.) or only that on sixth somite absent ( L. armata n. sp.).

Abdomen more or less gibbous, with first, fourth, fifth and sixth somites rounded or faintly sulcate on dorsal surface; second somite without distinct middorsal carina, but occasionally with low, flat triangular plateau lined by row of longish plumose setae; third somite with weakly to strongly elevat- ed, occasionally sharply carinated tergum. Pleura of anterior fifth somites broadly rounded. Sixth somite with posterolateral process sharply pointed; posteroventral angle blunt; ventral surface rounded in anterior part, shallowly convex in posterior part. Telson slender, tapering posteriorly, armed with two pairs of tiny dorsolateral spines on posterior half; dorsal surface shallowly sulcate medially in anterior half; posterior margin with one lateral pair of spinules and two pairs of long spines, flanking posteromedian projection.

Abdominal sternum flattened on anterior three somites, fourth and fifth somites each with low, blunt median carina.

Cornea distinctly wider than eye-stalk, well faceted.

Antennular peduncle not reaching midlength of antennal scale. First segment longer than distal two segments combined, dorsal surface excavated to receive eyes; ventral surface bluntly ridged, with distinct spine arising from midlength of first segment; stylocerite well developed, sharp. Second segment slightly longer than wide, subcylindrical. Third segment shorter than second segment. Flagella sexually dimorphic as in other crangonids, lateral flagellum much stouter and longer and bearing much more numerous aesthetascs in males than in females.

Antenna with second segment (= basicerite) stout, always with spine at ventrolateral distal angle; fifth segment (= carpocerite) subcylindrical. Antennal scale wel developed, exceeding half length of carapace, bearing distinct distolateral tooth distinctly overreaching rounded or truncate distal margin of blade; dorsal surface with short, oblique median ridge extending from base of antennal scale.

Mouthparts typical of family.Mandible ( Fig. 15A ) slender, divided distally in two principal teeth, margins of principal teeth each with one small accessory tooth. Maxillule ( Fig. 15B ) with small, narrowly subovate coxal endite bearing some long setae distally; basial endite notably curved mesially, with six to eight long spines arranged in double row on truncate mesial margin; palp directed laterally, slightly curved distally, bearing one setae terminally. Maxilla ( Fig. 15C ) with coxal and basial endites strongly reduced, each represented by very narrow convexity; palp relatively slender, tapering distally, weakly curved mesially; scaphognathite broad, anterior lobe rounded, posterior lobe also rounded, fringed with moderately long setae. First maxilliped ( Fig. 15D ) with endites poorly developed, with few unequal setae; endopod slender, not reaching distal margin of exopod, with row of sparse setae on mesial margin; exopod with narrow caridean lobe, and with well developed flagellum; epipod large, subtriangular, faintly bilobed. Second maxilliped ( Fig. 15E ) with endopod composed of seven segments, but basis and ischium partially fused; dactylus small, obliquely articulated to propodus, armed with two long spines and numerous setae of various length; propodus elongate, with row of bristle-like long setae on mesial margin; exopod far overreaching carpus of flexed endopod, bearing well developed flagellum; epipod rounded, lacking podobranch.

Third maxilliped apparently composed of four segments. Distal two segments narrow, but somewhat flattened dorsoventrally; ultimate segment tapering distally to blunt tip, with numerous setae on lateral and mesial margins; carpus (= penultimate segment) also with long setae on lateral and mesial margins. Antepenultimate segment (merusischium-basis fused segment) subequal in length to distal two segments combined, slightly sinuous in dorsal view, dorsally curved in lateral view, with two or three subdistal spinules on ventral surface. Coxa with rounded lateral process presumably originated from epipod; dorsodistal, lateral and mesial margins of antepenultimate segment with numerous long plumose setae; exopod reaching midlength of antepenultimate segment, bearing well developed flagellum.

First pereopod overreaching antennal scale. Palm somewhat depressed dorsoventrally, distomesial spine (= thumb) always fixed, cutting edge more or less oblique, bearing submarginal row of sinuously curved setae on both dorsal and ventral surfaces. Carpus armed with two spines on distolateral margin. Merus with sharply carinate dorsal margin terminating in strong dorsodistal spine; ventral surface with sharp, occasionally lamelliform carina in proximal half, terminating distally in blunt or sharp spine. Exopod absent.

Second pereopod simple, short, reaching midlength of merus of first pereopod. Dactylus less than half of propodus length, with three or four long spiniform bristles distally; propodus shorter than carpus, with one or two long bristles on dorsal and ventral margins and two long bristles on each distal angle; carpus somewhat broadened distally. Merus slightly longer than ischium, and subequal in length to distal three segments combined. Ischium not strongly curved inward, with row of long setae on ventral margin. Basis setose on ventral margin. Coxa devoid of lateral process.

Third pereopod very slender, distinctly overreaching antennal scale. Dactylus needle-like, exceeding half-length of propodus, apparently lacking terminal tuft of setae. Propodus tapering distally. Carpus distinctly longer than distal two segments combined. Merus much shorter than carpus. Ischium distinctly longer than merus. Coxa without lateral process.

Fourth and fifth pereopods similar; propodi each with setal tuft dorsodistally; carpi shorter than propodi, each with small dorsodistal projection; meri longer than ischia.

Branchial formula summarized in Table 1. Two greatly unequal arthrobranchs above third maxilliped (dorsal gill much smaller than ventral gill, hidden by latter). One pleurobranch on each fourth to eighth thoracic somites; ventral apices of gills directed backwards.

Male first pleopod with endopod about 0.60 times as long as exopod, broad, strongly sinuous, terminating in triangular lobe bearing row of cincinnuli on distomesial margin; female first pleopod with spatuliform endopod. Male second pleopod with appendix masculina moderately stout, distinctly longer than appendix interna. Appendices internae on second to fifth pleopods well developed in both male and female, not tapering distally, each with cluster of cincinnuli at distomesial portion. Protopods of first to fifth pleopods distally widened in females, not widened in males; rami broad, foliaceus in females, moderately narrow in males. Uropod ( Fig. 2H ) with endopod narrower than exopod; endopod with shallow depression bearing setae on dorsal surface proximally; exopod not reaching endopod, lateral margin nearly straight, terminating in small tooth; terminal margin of exopod rounded or subtruncate; no diaeresis on exopod; protopod with small posterolateral tooth.

Eggs large, measuring about 1.3-1.7 × 1.2-1.4 mm, few in number.

REMARKS

Christoffersen (1988) investigated the phylogenetic relationships among the genera of the Crangonidae based on morphological characters using parsimony analysis. He hypothesized that the sister group of Lissosabinea was a clade composed of Paracrangon + Vercoia + Prionocrangon , and these four genera were assigned to a new subfamily Paracrangoninae Christoffersen, 1988 . This hypothesis is derived from the shared apomorphies, including the trend toward reduction and loss of arthrobranchs on the third maxilliped (at a node of Philochelinae + Pontophilinae + Paracrangoninae + Crangoninae) and the simple second pereopod (at a node of Paracrangoninae ) ( Christoffersen 1988). Christoffersen’s (1988) cladogram indicates that Lissosabinea possesses only a single arthrobranch on the third maxilliped. Furthermore, he clearly mentioned that there was only a single arthrobranch on the third maxilliped in the specimens he referred to L. cf. tridentata from off Uruguay. However, it has been found that the species of Lissosabinea all possess two arthrobranchs on the third maxilliped, a character state shared with Aegaeon Agassiz, 1846 , Parapontocaris Alcock, 1901 , Pontocaris Bate, 1888 and Sabinea Ross, 1835 . According to Christoffersen (1988: 54), his specimens of L. cf. tridentata were different from the descriptions of L. tridentata given by Pequegnat (1970) and Dardeau & Hard (1983) (as Sabinea ) in the presence of two submedian carinae on the sixth abdominal somite, each bearing a small submarginal denticulation on the posterior third. It has been confirmed that the sixth abdominal somite of L. tridentata is only faintly sulcate medially, lacking submedian carinae or denticulation. Since the specimens used by Christoffersen were in poor condition ( Christoffersen 1988), it is reasonable to consider that his identification was wrong. It seems that Christoffersen (1988) did not actually examine specimens of L. indica . Komai (1995) questioned the homology of the simple, non-chelate second pereopod found in Lissosabinea , Sabinea , Vercoia and Prionocrangon , because of the great structural differences observed among them, suggesting a different origin of the non-chelate condition. The non-chelate second pereopod accompanied by a great reduction of its size is found only in Lissosabinea and Sabinea within the Crangonidae . Furthermore, one more plesiomorphy, the lack of elongate setae on the posterior lobe of the scaphognathite, also excludes Lissosabinea from the clade composed of Philochelinae + Pontophilinae + Paracrangoninae + Crangoninae ( Christoffersen 1988: fig. 1; Komai unpubl. data). This plesiomorphic character is also seen in Aegaeon , Pontocaris , Parapontocaris and Sabinea . The sister group of Lissosabinea is thus most probably Sabinea , as the reduced, non-chelate second pereopod links the two genera. Although the original definition of Lissosabinea was based on an insufficient character analysis and a possible misidentification of material, full generic status for Lissosabinea is maintained because of the large morphological gap between the species assigned to Sabinea s.s. and those assigned to Lissosabinea , as discussed below.

One of the features that distinguish Lissosabinea from Sabinea is the absence of strongly denticulate lateral carinae on the carapace. All three species of Sabinea have three pairs of strongly denticulate carinae on the carapace. The abdomen of Lissosabinea is dorsally rounded except for a more or less gibbous third somite, while that of Sabinea is provided with sharp median or submedian carinae on the first to sixth somites. The posterior margin of the orbit is smooth in Lissosabinea , instead of having a distinct cleft as in Sabinea . Furthermore, the armature of the second pereopod is characteristic and constant in species of Lissosabinea (see above). In contrast, in the species of Sabinea , the propodus and dactylus of the second pereopod have only scattered setae. Other characters shared by all species of Lissosabinea include: rostrum is armed with a pair of conspicuous lateral teeth; lateral carinae on the carapace are poorly developed, only a rather inconspicuous epibranchial carina is recognizable; and the merus of the first pereopod is provided with a distinct, occasionally lamelliform ventral carina in the proximal half, which terminates in an acute or blunt tooth. Of the characters enumerated above, at least the more or less gibbous third abdominal somite and the distinct ventral carina are apomorphic, suggesting monophyly of Lissosabinea .

This study demonstrates that the species of Lissosabinea all have tegumental scales on their carapace, telson, antennae and/or pereopods. The presence of tegumental scales is well known in species of the Oplophoridae and Pandalidae within the Caridea ( Mauchline et al. 1977; Chace 1985). In Crangonidae , however, the possession of the tegumental scales has only been recently documented for two species of Aegaeon , A. lacazei (Gourret, 1887) and A. rathbuni ( De Man, 1918) (see Komai 2000), and Pseudopontophilus serratus Komai, 2004 . Komai (2000) suggested a possibility that the presence or absence of the tegumental scales is indicative of presumed phylogenetic relationships among the crangonid genera, but later Komai (2004) suggested that the presence of the tegumental scales was homoplastic because of the character incongruence observed among the genera. As noted above, a sister relation between Lissosabinea and Sabinea is suggested in this study, but species of Sabinea do not have tegumental scales. Further Aegaeon shares only plesiomorphic characters with Lissosabinea but not the possession of the tegumental scales ( Christoffersen 1988; Chan 1996; pers. obs.).

No information on larval development is available for the species of Lissosabinea . Nevertheless, because of the large and few eggs, it can be assumed that the larval development of Lissosabinea species is highly abbreviated.

KEY TO SPECIES OF LISSOSABINEA CHRISTOFFERSEN, 1988

1. Carapace with only one tooth (epigastric tooth) on dorsal midline ... L. unispinosa n. sp.

— Carapace with two or three teeth on dorsal midline .................................................... 2

2. Carapace with two teeth on dorsal midline and one or two posthepatic teeth ............. 3 — Carapace with three teeth on dorsal midline, but without posthepatic tooth .............. 4

3. Third abdominal somite with distinct median carina; dactylus of fourth pereopod less than half of propodus in length ...................................................................... L. indica

— Third abdominal somite weakly elevated medially, but without distinctly delineated median carina; dactylus of fourth pereopod more than half of propodus in length ............. ............................................................................................................ L. ecarina n. sp.

4. Carapace with small median teeth, epigastric tooth not reaching base of rostrum; epibranchial tooth present; median carina on third abdominal somite not extremely high; fourth and fifth pereopods slender ............................................................ L. tridentata

— Carapace with large median spines, epigastric tooth overreaching base of rostrum; epibranchial tooth absent; median carina on third abdominal somite extremely high; fourth and fifth pereopods very stout ............................................................. L. armata n. sp.

Figures

FIG. 2. — Lissosabinea indica (De Man, 1918), Banda Sea, Indonesia, KARUBAR,stn CP 17, ♀ cl 9.0 mm (MNHN-Na 15152): A, carapace and cephalic appendages, dorsal view (tegumental scales omitted); B, anterior part of carapace and cephalic appendages, lateral view; C, abdomen, dorsal view; D, telson, dorsal view; E, posterior part of telson, dorsal view; F, left antennal scale, dorsal view; G, thoracic sternum, ventral view; H, left uropod, dorsal view. Scale bars: A-D, F, H, 2 mm; E, 0.5 mm; G, 1 mm.

FIG. 15. — Lissosabinea unispinosa n. sp., left mouthparts, New Caledonia, BIOCAL, stn CP 45, paratype ovigerous ♀ cl 4.3 mm (CBM-ZC 8341): A, mandible, ventral view, inset, distal part, inner view; B, maxillule; C, maxilla; D, first maxilliped; E, second maxil- liped. Scale bar: 0.5 mm.