Alainodromia dambimangari, Mclay & Hosie, 2022

Mclay, Colin L. & Hosie, Andrew M., 2022, The sponge crabs of Western Australia and the Northwest Shelf with descriptions of new genera and species (Crustacea: Brachyura: Dromiidae), Zootaxa 5129 (3), pp. 301-355 : 305-307

Alainodromia dambimangari sp. nov.

( Fig. 1A–E )

Type material. Holotype: WAM C69971, ovig. female 15.2 × 14.9 mm, Camden Sound , Western Australia, 47–49 m, 18°18’50.15”S, 124°06’45.05”E, 03-2015 . Paratype: WAM C69970, male 9.3 × 10.2 mm, Eclipse Islands , Western Australia, 42 m, 13°29’37.61”S, 125°51’06.88”E, 2-03-2016 .

Other material Examined. WAM C69972, Camden Sound , Western Australia, 36 m, 18°26’55.47”S, 124°09’13.06”E, 20-03-2015: female 7.6 × 7.3 mm ; WAM C71297, Camden Sound , Western Australia, 42 m, 18°24’23.11”S, 124°07’33.34”E: male 6.8 × 6.5 mm .

Etymology. The specific name for this new species acknowledges the Dambimangari, traditional owners of Camden Sound, where the species was first discovered. It is a noun used in apposition.

Description. Carapace as wide as long or slightly wider, weakly convex, weak frontal groove, cardiac area well defined, branchial groove marked; surface covered in low subacute scattered tubercles of different sizes with larger tubercle roughly behind supraorbital tooth, surface between them smooth. Rostrum strongly tridentate; subacute median tooth shorter than flattened lateral teeth but visible dorsally; supraorbital margin interrupted by strong blunt tooth, postorbital tooth absent, suborbital tooth not visible dorsally. Anterolateral carapace margin armed with 2 prominent flattened teeth, second tooth bifid, smaller blunt posterolateral tooth behind branchial groove; posterolateral margin convergent, occasionally with several smaller blunt tubercles; posterior carapace margin sinuous. Subhepatic area flat with pair of tubercles beneath anterolateral teeth and broken “saw-tooth”-like ridge extending from buccal corner, epistome plate-like. Female sternal grooves ending apart but in close proximity on elevated humps at either end of ridge lying between boundary between chelipeds and P2. When closed, telson lying directly over (in ventral view) termini of sternal grooves.

Chelipeds and P2 and P3 elongate, not massive, sparse small rounded tubercles, dorsal distal borders of merus, carpus and propodus produced as prominent blunt lobes. Inner margins of P2 and P3 dactyli armed with 3 or 4 evenly spaced stout spines. Cheliped fingers flattened, gaping, with 7 or 8 small teeth. P4 and P5 both dorsal, P4 shortest, P5 reaching almost to second anterolateral tooth when extended anteriorly. P4 and P5 dactylus short stout acute bent into right-angle shape and twisted upwards at around 45°; opposed by single stout propodal spine.

Abdomen strongly ornamented and sculptured, segments immobile. Female segments with large blunt tubercles tending to be arranged in pairs: medially with two adjacent pairs on first segment, becoming merged into single ridge on posterior segments; laterally with pair, one behind the other, becoming larger posteriorly. Telson triangular, tip rounded, basal width about twice length, centrally 2 pairs of small blunt tubercles, small angled ridge is suggestive of uropods often present in dromiids but these are absent here.

Male abdomen ornamentation similar to that of females but tubercles much less prominent; telson trapezoidal in shape, length slightly more than half basal width, tip truncate posterior corners end in subacute lobes. Abdominal locking mechanism consisting of lateral projections from margins of penultimate segment fitting in front of tubercles on P2 coxae. Male G1 flattened, setose tube, G2 longer than G1, needle-like.

Remarks. The major differences between Alainodromia dambimangari sp. nov. and A. timorensis are as follows: lateral rostral teeth broader (less flattened in A. timorensis ); median rostral tooth prominent (deflexed less prominent); only second anterolateral tooth deeply bifid (both teeth bifid); frontal carapace surface covered in low subacute scattered tubercles of different sizes with one larger tubercle roughly behind supraorbital tooth (surface covered with scattered small tubercles but prominent row of five larger tubercles at level of first anterolateral tooth) ( Fig. 1 ).

McLay (1998) stated that the abdominal segments of the type male were “free”, but while there are sutures present between them, there is very little flexibility and the abdomen as a whole only articulates with the thorax. When specimens are preserved in formalin it can be difficult to determine whether inflexibility is a result of preservation or a natural condition. The present material allows us to show that in both males and females, segment immobility is the natural condition and that the abdomen has a largely fixed shape in both sexes articulating with the thorax. In males, the abdomen is approximately linear, retained by the abdominal locking mechanism, whereas in females, it is rounded, forming a brood chamber held closely against the sternum by musculature. The female abdomen does not have abdominal locking mechanism. The plesiomorphic condition in decapods is to have all segments free, but in Brachyura the ventrally folded abdomen requires some holding mechanism: segment immobility (resulting from fusion or ankylosis) or a locking mechanism are alternatives. Partial ankylosis of abdominal segments is a feature of species of Dromidiopsis Borradaile, 1900 and Lauridromia McLay, 1993 .

When describing Alainodromia timorensis McLay (1998) speculated that this species may carry pieces of sponge, but both P4 and P5 are dorsal in this genus, unlike most other dromiid genera where P4 is directed ventrally and P5 is sub-dorsal. In A. timorensis they both lie in the same horizontal plain so that their movements are only anterior/posterior, linked to the weakly convex shape of the carapace. The dactyli are unusual in being short, stout and bent into a right angle and oriented vertically at approximately 45° so that neither are directed ventrally as might be found in a sponge-carrying dromiid. They show closest resemblance to the P4 and P5 of Desmodromia McLay, 2001 , which is a bivalve shell-carrier also found in northwest Australia (see McLay & Hosie 2012). Desmodromia has a more convex carapace and the P5 is subdorsal, whereas the P4 is directed ventrally and has been found with cockle shells. However, the P4 and P5 dactyli of Alainodromia dambimangari sp. nov. are opposed by a small propodal spine not found in Desmodromia . Both of these genera have distinctive lamellate anterolateral carapace margins, which may be related to the use of shells for camouflage. These structures would increase the amount of carapace surface in contact with the inner surface of the shell. The carapace of species of Alainodromia is only weakly convex, so it may utilize more flattened shells.

The ovigerous female of A. dambimangari sp. nov. had approximately 100 large eggs of diameter 1.5 mm. The small brood-large eggs strategy is a feature shared with Desmodromia tranterae whose females have been recorded with ~ 20 eggs, 0.8–0.9 mm diameter. The difference in brood size is probably a reflection of female size, but egg size of A. dambimangari is considerably larger, having 4.7 × the volume of those of Desmodromia tranterae . On this basis A. dambimangari possibly has direct development and D. tranterae abbreviated development. Direct or abbreviated development is apparently a feature of the Australian dromiid crab fauna (see McLay 1993; McLay et al. 2001; Morgan 1987). The type female of A. dambimangari had a tubiculous polychaete, 3 mm diameter, attached to the left third maxilliped suggesting that it may not have moulted recently.

The other species in the genus, Alainodromia timorensis has been collected from 27–44 m in the Timor Sea.

Distribution. Known only from northwestern Australia. Depth 36– 49 m.

Figures

FIGURE 1. Alainodromia dambimangari sp. nov.: A–C, ovigerous female holotype, 15.2 × 14.9 mm (part of left rostral tooth missing) (WAM C69971):A, dorsal view; B, frontal view (note a tubiculous polychaete has attached to the left third maxilliped); C, ventral view; F, dorsal view left P4 and P5. D–E, paratype male 9.3 × 10.2 mm (WAM C69970): D, dorsal view; E, ventral view.