Austrodromidia octodentata (Haswell, 1882)

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 : 309-315

Austrodromidia octodentata (Haswell, 1882)

( Figs. 4–7 )

Dromia octodentata Haswell, 1882a: 755 ; 1882b: 140.— Fulton & Grant, 1906 b: 20.— Baker, 1907: 179, pl. XXIII fig. 4.

Cryptodromia octodentata . — Rathbun, 1923a: 151, pl. 41.— Hale, 1925: 406, pls. 39, 40, text figs 1–5; 1927a [Handbook]: 107, figs. 103–105; 1927b: 310.— Griffin, 1972: 53.

Austrodromidia octodentata . — McLay, 1993: 185.— Davie, 2002: 159.— Poore, 2004: 304, fig. 87e, pl. 17e.— Farrelly & Ahyong, 2019: 72, fig. 139 (not fig. 138 = Stimdromia lateralis ( Gray, 1831)) .

Material examined. Western Australia: WAM C3464 , Middleton Beach , (metal tag 15581): male 46.0 × 42.8 mm ; WAM C39957, Recherche Archipelago, Wickham Island , 34°02.95’S, 123°19.83’E to 34°02.50’S, 123°19.65’E, 58– 57 m, 11-10-2007: male 72.0 × 62.8 mm ; WAM C40544, Ningaloo Marine Park, off Mandu Sanctuary , 87.9– 81.2 m, 22°9’26”S, 113°48’02”E, 22°10’07”S, 113°48’19”E, 22-04-2006: female 6.8 × 6.9 mm ; WAM C40672, Ningaloo Marine Park, off Osprey Sanctuary , 58– 57 m, 22°15’41”S, 113°49’04”E to 22°14’48”S, 113°48’29”E, 23-04-2006: male 10.1 × 10.0 mm ; WAM C43229, Mandu Creek , 50.8 m, 22°3’40”S, 113°51’53”E to 22°3’40”S, 113°51’52”E, 4-08-2008: male 10.6 × 10.8 mm (sponge cap) ; WAM C43837, Montgomery Island, Kimberleys , intertidal, 16°01.226”S, 124°0900.72”E, 23-10-2009: 2 females 2.8 × 3.1 mm, 3.5 × 3.8 mm ; WAM C43838, Montgomery Island, Kimberleys , hand collected, 15°58’00.877”S, 124°16’00.836”E, 22-10-2009: male 3.7 × 3.9 mm ; WAM C6517 (metal tag shows “65-50”), trawled in the Great Australian Bight by Inspector of Fisheries , 7-06-1950: male 91.3 × 74.9 mm (large dried specimen used for description) .

Description (based on male, WAM C6517). Entire body and pereopods covered by short, sparse bristly tomentum, somewhat denser on chelipeds and P2–3.

Carapace smooth after removal of tomentum, tumid, rising steeply behind rostrum and frontal margins, then sloping gradually down to posterior margin; overall shape changing during ontogeny from approximately as wide as long to much wider than long, ratio ~1.22 (see Remarks below); rostrum tridentate, strongly deflexed, all 3 teeth similar short, sub-acute, median tooth on lower level; similar teeth on supra-orbital margin and at postorbital corner; sub-orbital margin separated by narrow fissure from supra-orbital margin and bearing small tooth visible dorsally; anterolateral margin with 5 similar evenly-spaced teeth beginning at level of sub-orbital tooth, curving posteriorly towards widest point of carapace; deeply marked branchial notch just behind widest point of carapace, bluntly rounded posterolateral tooth directed upwards, followed by strongly convergent margin to posterior carapace border; branchial groove deeply marked and connecting with deep cardiac grooves, encompassing area marked by pair of depressions and short ridges; short, shallow frontal groove extending posteriorly from median rostral tooth and pair of shallow depressions, separated by 2 small tubercles, behind first 2 anterolateral teeth.

Third maxillipeds operculate, crista dentata armed with 9 or 10 strong corneous spines.

Male chelipeds massive, merus trigonal, margins dentate; carpus surface smooth except for shallow groove on outer surface, inner distal margin with stout subacute tooth with 2 similar teeth on distal margin above propodal joint. Inner dorsal margin of propodus with 3 large sub-equal teeth, outer face smooth to finely granulate. Cheliped fingers stout, slightly down-curved, occlusal margins armed with 9 or 10 well developed, white, sub-acute teeth that interlock when closed leaving small basal gape. Occlusal teeth on right cheliped fingers larger than those on left: teeth on pollex gradually becoming smaller proximally, dactyl teeth of similar size except for proximal 3, being more widely spaced and stronger. Occlusal armature forming “crusher” teeth, but similar on both right and left cheliped ( Fig 4 ).

P2–3 shorter than chelipeds, margins smooth, dactyli ending in brown, sharp, curved, corneous tips and inner margins armed with 5 stout spines, decreasing in size proximally. P4 much shorter than P2–3, used for carrying camouflage over carapace, sub-chelate with strongly curved dactylus opposed by 2 large spines on propodal margin with 2 further spines on outer propodal margin at base of dactyl. P5 missing.

Male abdomen with 6 free segments and telson, surface smooth, strong, sculptured median ridge on last segments 2–6. Lateral margins of segment 6 deeply indented to accommodate well developed tubercles on coxae of first walking legs providing abdominal locking mechanism. Telson triangular, posterior margin evenly rounded. Uropod plates at articulation between telson and segment 6, not visible dorsally.

Remarks. Various incomplete descriptions of A. octodentata have been published (Haswell 1882; Baker 1907; Rathbun 1923a; Hale 1925, 1927). These accounts are not all in agreement so we present a more detailed description based on the largest specimen available to us (WAM C6517, male, 91.3 × 74.9 mm). The morphology of A. octodentata changes as it grows larger. Juveniles have a carapace width/length ratio of around 0.9, reaching 1.0 at maturity and around 1.2 in the largest crabs (compare Figs 5 and 7 herein). During growth, the lateral margin of the carapace becomes more convex, as a result of carapace widening and the number of teeth increases from 3 to 5. The front (orbital-rostral area) becomes proportionally smaller and teeth (including the post-orbital tooth) become more prominent (see Hale 1925: text figs. 1–5; Fig. 5 ). This species has large eggs (1.9 mm diam.) that give rise to juvenile crabs, brooded by the female.

Distribution. Australian endemic: New South Wales, South Australia, Victoria and Western Australia; intertidal to 209 m ( Farrelly & Ahyong 2019).

Figures

FIGURE 4. Austrodromidia octodentata (Haswell, 1882), male 10.6 × 10.8 mm (WAM C43229) carrying sponge cap: A, frontal view; B, ventral view.

FIGURE 5. Austrodromidia octodentata (Haswell, 1882): ontogenetic changes in carapace shape during growth. Letters mark reference points: A, lateral rostral tooth; B, supraorbital tooth; C, post orbital tooth; D, last anterolateral tooth; E, posterolateral tooth. (After Hale 1925: text-figs. 1–5).

FIGURE 6. Austrodromidia octodentata (Haswell, 1882): A, dorsal view ovigerous female beneath Pecten medius Lamarck, 1819 shell; B, ventral view of ovigerous female in Pecten medius shell; C, ventral view of a female brooding 530 juvenile crabs, which was carrying a large piece of sponge. (A–B, after Hale 1925: pl. 40A; C, after Hale 1925: pl. 39).

FIGURE 7. Austrodromidia octodentata (Haswell, 1882), dried male, 91.3 × 74.9 mm (WAM C65-1950): A, dorsal view; B, frontal view; C, ventral.