Aatolana Bruce, 1993

Keable, Stephen J., 1998, A third species of Aatolana Bruce, 1993 (Crustacea: Isopoda: Cirolanidae), Records of the Australian Museum 50 (1), pp. 19-26 : 20-21

Aatolana Bruce

Aatolana Bruce, 1993b: 2 .-Brusca et aI., 1995: 96.

Type species: Aatolana rapax Bruce, 1993b (by original designation).

Diagnosis: Frontal lamina: short, length approximately 1.3-2.5 x basal width; anterior margin convex with a dorsally deflected apical point, or with an excavate extension; ventral surface flat, or with the posterior section projecting. Clypeus: ventral surface not projecting relative to frontal lamina. Antenna: peduncular articles 1 and 2 shortest, subequal; peduncular article 4 longer than article 3; peduncular article 5 longer than article 4 and all other articles. Pereon and pleon: dorsal surfaces without setae, tubercles, processes orfurrows. Pleonite 3: epimera broader than that of other pleonites, with lateral row of slender setae; dorsal and ventral posterolateral margins convex, converging smoothly to a point, posteroventral excision absent; enclosing but not covering epimera of pleonite 4; extending to or beyond posterior of pleonite 5. Pleonite 5: posterolateral margins encompassed by pleonite 4. Pereopods 1-7: dactylus with secondary unguis present or absent; secondary unguis not large and strongly sclerotized when present. Pereopod 1: merus anterodistal angle not produced to posterodistal extent of carpus or beyond. Pereopod 7: basis, ischium and merus with or without plumose setae. Penes: present; short, approximately 2 x width; forming well separated flattened lobes. Pleopod 2 appendix masculina: arising basally; longer than endopod in fully developed specimens; slender. Pleopods 1-5: endopod plumose setae present across distal margins of pleopods 1-4 and absent on pleopod 5.

Additional characters: Body: narrow, length 2.0-3.5 x greatest width; lateral margins sub-parallel in dorsal view. Cephalon: broad, width greater than 60% of pereonite 1; moderately enclosed by pereonite 1; without tubercles or processes; anterior margin with medial indentation, not extending to cover proximal articles of antennule; rostrum not prominent. Eyes: well developed, ommatidia clearly defined, pigmented; elongate, length approximately 3 x width; not divided by unfaceted band. Frontal lamina: visible in dorsal view; forming an angle of 90° or of less than 45° with clypeus; not fused to cephalon. Antennule: colinear, peduncular article 2 not at right angles to article 1; much shorter than antenna, just reaching pereonite 1. Peduncular articles 1-3 not fused; article 3 well developed, longer than articles 1-2, or subequal to article 1 with article 2 shortest. Accessory flagellum absent. Primary flagellum longer than peduncle; callynophore absent. Antenna: not sexually dimorphic. Peduncle comprised of 5 articles. Flagellum much longer than peduncle.

Mandible: molar well developed; medial surface with slender setae; marginal robust setae present, numerous. Incisor broad, wider than narrowest part of mandible; serrate; not quadridentate on left mandible. Lacinia mobilis absent orpresent onleft mandible as a triangular sclerotized process embedded between the setal row and the incisor. Setal row present, well developed, with numerous robust setae; intermediate slender setae absent. Palp 3-articulate; inserted adjacent to molar; article 3 distally narrow. Maxilla: lateral lobe and middle lobe subequal; medial lobe short and broad; lateral, middle and medial lobes with numerous setae. Maxilliped: palp medial margin with slender setae on more than half the length of articles 2-5; lateral margin with slender or plumose setae along most of the length of articles 2-5; article 3 with distal margin width greater than proximal margin of article 4; article 4 with distal margin width greater than proximal margin of article 5. Endite with coupling hooks.

Pereon: pereonite 1 distinctly longer than pereonite 2. Coxae: not forming sternal plates.

Pleon: not sexually dimorphic; five unfused se<gments present, all equally visible along dorsal margin, or pleonite 1 partially or completely concealed by pereonite 7, in dorsal view all appearing broader than pleotelson.

Pleotelson: dorsal surface smooth with anterodorsal depression, tubercles, pits and ridges absent, setae present or absent; margins convex, meeting at an acute apex; marginal robust setae present; marginal plumose setae present, restricted to posterolateral margins, abundant; marginal teeth-like serrations absent.

Pereopods 1-3: ischium anterodistal angle produced subequally. Merus anterodistal angle more produced on pereopods 2 and 3. Dactylus not longer than propodus. Pereopod 7: coxa not extending beyond posterior of pleon. Basis not noticeably broader in distal half compared to proximalhalf; anteriormargin withlong plumose or slender setae along entire length (using the conventions for pereopod orientation outlined by Bruce (1993b), not the posterior margin as he states); medial carina with plumose or slender setae along most of length of article, or slender setae only distally; posterodistal angle without long plumose setae. Ischium anterior margin with plumose and slender setae present or absent, setae abundant and occurring along entire length when present; posterior margin with plumose and slender setae absent. Merus anterior margin with slender setae absent, plumose setae present or absent; posterior margin with plumose and slender setae absent.

Pleopods: peduncle respiratory branchiae absent; accessory lobe well developed, with complex folding. Pleopods 1-4: exopods with slender accessory lamella at posterior proximolateral angle; endopods with elongate laterally curving lobe arising from proximomedial angle. Pleopod 1: not operculate to posterior pleopods; peduncle length shorter than breadth; exopod and endopod narrow, length greater than 2 x width; exopod medial margin convex, narrow at apex, lateral margin relatively straight; endopod width greater than 0.5 x width of exopod.

Uropods: inserted ventrolaterally on pleotelson; extending posteriorly beyond pleotelson. Peduncle strongly produced along medial margin of endopod. Endopod and exopod margins with robust setae; plumose setae present on most of margin length; apices sub-bifid, without robust setae. Endopod lateral margin sinuate, straight or slightly convex (not concave); without prominent lateral excision; without distinct pit. Exopod dorsoventrally flattened, not extending posteriorly beyond endopod.

Remarks. The diagnosis and description of Aatolana provided by Bruce (1993b) is emended here based on the material of Aatolana examined in this study and in that of Keable (1997). Particularly important changes to the original diagnosis of Aatolana include: the recognition of a small secondary unguis on the dactylus of pereopods 1-7 in the species described here; variation in the form of the frontal lamina; and variation in the setation of pereopod 7.

Three uniqu.e apomorphies characterising species of Aatolana were recognised by Bruce (1993b): the prominent, posteriorly acute epimera of pleonite 3; the complexrefolded lobe on the lateral margin of the peduncle of pleopods 1-5; and the structure of the frontal lamina. Of these suggested apomorphies, only the enlarged epimera of pleonite 3 (which is made additionally distinctive by having a row of slender setae along the medial longitudinal carina of the lateral surface) is shared exclusively between species of Aatolana and remains as a putative unique synapomorphy of these species that unambiguously defines the genus. Examination of all three species of Aatolana and also the figures ofA. rapax Bruce, 1993b , shows that the refolding of the lobe on the lateral margin of the pleopod peduncle is poorly developed on pleopod 1 but characteristic of pleopods 2-5 ( Keable, 1996b). On these pleopods the lobe extends distally on the peduncles (see Fig. 2). Furthermore, examination of specimens of species of Bathynomus A. Milne Edwards, 1879 , Booralana Bruce, 1986 and an undescribed taxon similar to Dolicholana elongata (H. Milne Edwards, 1840) show that they have a comparable lobe on the lateral margin of the peduncle of the pleopods ( Keable, 1996b). Additionally, the structure of the frontal lamina cannot be recognised as a unique synapomorphy shared by species ofAatolana because this character varies considerably among the three species now placed in this genus and can actually be used to discriminate these species (Keable, 1997; this study). However, the variation in structure of the frontal lamina found in these species is relatively simple and it may be possible to hypothesize a transformation series for this character when the phylogeny of the Cirolanidae is better understood.

Bruce (1993b) suggested that species of Aatolana were similar only to species of Booralana , with which they share comparable elongate eyes, prominent flattened penes, a medially indented cephalon and prominent epimera on pleonite 3. Bruce (1993b) further noted that the structure of the frontal lamina differed between species placed in these two genera. However, the frontal lamina of species of Booralana has been described as being formed from two parts, an anterior half and a posteroventral section which projects ( Bruce, 1986; Camp & Heard, 1988). This description matches that of the frontal lamina of the species of Aatolana described here. Furthermore, an additional character shared between species placed in these two genera, which has not been remarked upon previously, is the slender accessory lamella at the posterior proximolateral angle of the exopod of pleopods 1-4 which has been described in species of Aatolana ( Holdich et al. 1981; Bruce, 1986, 1993b; this study). The shape and position of this lamella indicates its homology with the upturned lobe found in this location in species of Booralana (see Camp & Heard, 1988, figs 4A-E; Keable, 1996b). While Aatolana has not been placed in a subfamily these additional characters further suggest a close relationship with Booralana . Booralana has also beenlinked withBathynomus, Parabathynomus Barnard, 1924 and Cirolana quadripustulata Hurley, 1957 ( Bruce, 1981a, b, 1986; Botosaneanu et aI., 1986; Wagele, 1989). Bathynomus and Parabathynomus have been placed in the subfamily Cirolaninae Dana, 1852 while C. quadripustulata remains incertae sedis. However, according to Bruce (1986: 223) C. quadripustulata also shares characters found in Natatolana Bruce, 1981a which is placed in the Conilerinae Kensley & Schotte, 1989.

An additional noteworthy character found in species of Aatolana , which has not been remarked upon previously, is the presence of a large, triangular, highly sclerotized structure imbedded in the body of the left mandible between the setalrow and the incisor ( Fig. 1 ). This structure occurs in A. rapax and the species described here but not A. schioedtei . A similar large triangular structure is found partially fused to the distal side of the setal row on the left mandible of species of Bathynomus (see illustrations of B. giganteus A. Milne Edwards, 1879 by A. Milne Edwards & Bouvier (1902, plate 4) and also B. immanis Bruce, 1986 and B. pelor Bruce, 1986 by Bruce (1986, figs 90F, 91F); Keable (1996b, plate 2.2.2). This structure appears to be absent in many other genera of the Cirolanidae ( Keable, 1996b) . The function and phylogenetic significance of this structure is unknown. Although Brusca et al. (1995) concluded that a lacinia mobilis is absent in the Cirolanidae , the morphology and position of this structure in Bathynomus suggest it is homologous to the lacinia mobilis of other peracaridan crustaceans. It also appears to play a similar role as a guiding and locking mechanism for the mandible ( Dahl & Hessler, 1982). This structure cannot act in the same way as a lacinia mobilis in species of Aatolana because it is embedded in the mandible surface. However, this may represent a transition from the condition found in Bathynomus .

Figures

Fig. 1. Aatolana springthorpei, holotype. CE a, band c are dorsal, anterior and lateral views of cephalon, respectively. Scales = 0.5 mm.