Lamarckdromia beagle Mclay & Hosie 2022, sp. nov.

Lamarckdromia beagle sp. nov.

(Figs. 25–27)

Type material. Holotype: WAM C15512, male 40.5 × 39.0 mm. Mistaken Island, Albany,?depth, 34°58’00”S, 117°58’00”E, 14-12-1983, coll. D. Jones & W. Humphries. Paratypes: WAM C43596, female 44.0 × 45.5 mm, Hopetoun, low tide among rocks, coll. L. Wignell, February 1969; WAM C51681, male 31 × 27 mm carrying small brown sponge, locality details unknown; WAM C13503, male 27.1 × 25.5 mm, NE side of Cape Naturaliste, under boulder at low tide, 26-12-1958, coll. L.M. March & B.R. Wilson; WAM C1653, male 26.3 × 24.5 mm, Nornalup Inlet, 35°00’25”S 116°43’39”E, 12-1925, coll. P.J. Hampshire.

Etymology. The specific name commemorates the importance of the ship HMS “Beagle” that first carried Charles Darwin to Albany, Australia in 1836 during its second voyage (1831–1836) and surveyed and mapped many coastal areas around Australia during the third voyage (1837–1843), captained by Commander John Clements Wickham. Used as a noun in apposition.

Description. Carapace about as long as wide, convex, smooth beneath dense cover of long tangled setae, which also covers all limbs and the abdomen. Front weakly vaulted, weak median groove separates pair of low rounded epigastric swellings; branchial grooves evident, lateral cardiac grooves strongly marked with pair of small pits medially. Rostrum tridentate, lateral teeth short, blunt, triangular; similar median tooth strongly deflexed, scarcely visible dorsally when carapace is horizontal. Lateral tooth continuing as supraorbital margin interrupted by small blunt tooth above eyestalk; external orbital corner projecting, evenly rounded and separated by narrow fissure from infraorbital margin, bearing small blunt tooth beneath cornea of eye, visible dorsally. Broad flattened area lateral to orbit, weakly concave, with shorter setae; oral area arranged as most anterior part of face on which longer setae accentuate mouth-frame, pterygostomial surface and orbital margins, making eyes appear deeply sunken. Viewed anteriorly, elongate narrow sunken strip above the eyes and 2 small sunken patches amongst the setae lateral to the orbits. Anterolateral carapace margin obtuse, sinuous, sloping gradually down to weakly concave sub-hepatic area; lower sub-hepatic margin forming convex diagonal edge armed with 3 faint, evenly-spaced convexities; edge connecting epistome to blunt shoulder-like corner, marking widest part of carapace. Carapace margin posterior to widest point convex, interrupted by notch marking branchial groove. Posterior carapace margin weakly concave.

Chelipeds fitting closely against inferior carapace surface; both fingers white, curved, gaping widely when closed, hollowed out internally, tips spoon-like, occlusal margins with 7 or 8 teeth, decreasing in size proximally, only distal 3 teeth interlocking. Distal inner edge of carpus without tubercle; inner superior border of propodus with 3 or 4 small rounded proximal tubercles. Cheliped coxae with epipod.

P2–3 shorter than cheliped, dactylus curved, well developed, inner margins armed with 4 short spines decreasing in size proximally. P4–5 reduced, last pair shortest, P4 dactyl strongly curved, opposed by well-developed propodal spine; P5 dactyl similar but with 2 to 5 spines at base of dactyl on outer propodal margin, arranged in comb-like row, decreasing in size anteriorly when limb is in normal sub-dorsal position.

Abdomen of 6 free segments and telson, uropods reduced to small plates hidden ventrally beneath joint between segment 6 and telson. Male abdominal holding mechanism consisting of well-developed tubercles on P2 coxae, which can be rotated into position at joint between segments 5 and 6, when abdomen is folded. Male without pleopods 3–5. Gonopods stout setose-tipped G1 and long needle-like G2, extending well beyond tip of G1 when engaged. G2 without exopod. Mobile penial tube extending from male P5 coxa, inserted into base of G1 endopod.

Female thoracic sternal sutures 7/8 deeply incised into sternum, strongly convergent, ending together on raised sternal area between chelipeds. Tips of sutures 7/8 encased in hardened dark brown secretion (sperm plaque). Posterior margin of female sternite 8 concave, medially depressed to form anvil-shaped pit, separating sternal sutures. Vestigial first pleopods fitting into channels on sternite margins and terminating in anvil pits.

Male thoracic sternite 8 with evenly concave posterior margin, not depressed.

Remarks. A comparison of morphological characters that separate the three species of Lamarckdromia is given in Table 2. The main differences between the two Australian species are: long shaggy tomentum and tangled mass of setae on the carapace and chelipeds in L. beagle sp. nov. (most of carapace has short even tomentum except for conspicuous post-frontal fringe of longer erect setae across whole width of carapace in L. excavata); median rostral tooth strongly deflexed and scarcely visible dorsally (versus median rostral tooth prominent); post-frontal area of carapace weakly vaulted (versus post-frontal area strongly vaulted, cliff-like; sub-hepatic area weakly concave, ventral margin obtuse, maze-like patches on hepatic area with very short setae (versus strongly excavated, ventral area forms a shelf, almost whole area uniformly covered in short setae); inner superior border of cheliped propodus has 3 or 4 small rounded proximal tubercles (versus inner superior border of cheliped propodus armed with 6 or 7 prominent evenly spaced sub-acute tubercles).

The chief difference between the two Australian species and L. globosa is that neither has a strong sub-acute tooth on the anterolateral carapace margin, but they do have a similar row of small tubercles along the inner superior border of the cheliped propodus (see De Man’s 1887: pl. 18 fig. 1) illustration of L. globosa reproduced in Fig. 24b).

Distribution. Western Australia; shallow subtidal.