Austrotheres holothuriensis ( Baker, 1907 ), 2018

Ahyong, Shane T., 2018, Revision of Ostracotheres H. Milne Edwards, 1853 (Crustacea: Brachyura: Pinnotheridae), Raffles Bulletin of Zoology 66, pp. 538-571 : 550-553

Austrotheres holothuriensis ( Baker, 1907)

( Figs. 5 , 7 )

Pinnoteres holothuriensis Baker, 1907: 177 , 178, pl. 23: fig 3 (type locality: Gulf St. Vincent, South Australia).

Pinnoteres obesa . — Fulton & Grant, 1906: 18 (Not P. obesa Dana, 1852 ).

Pinnotheres obesus . — Schmitt et al., 1973: 60. — Davie, 2002: 433–434. (Not P. obesa Dana, 1852 ).

Ostracotheres (?) (‘ Pinnotheres ’) holothuriensis . — Tesch, 1918: 287 (list).

Pinnotheres holothuriensis . — Tesch, 1918: 262. — Hale, 1927a: 173, 174, fig. 175. — Silas & Alagarswarmi, 1967: 1192, 1200. — Schmitt et al., 1973: 6, 14, 49–50. — Davie, 2002: 433.

Ostracotheres holothuriensis . — Takeda & Konishi, 1989: 1222. — Berggren, 1999: 187. — Ahyong & Brown, 2003: 11–12. — Ng et al., 2008: 250.

Type material. Lectotype: SAM C1389 , female (cl 8.3 mm, cw. 7.2 mm; dry), Gulf St. Vincent, 12 fathoms [22 m], in holothurians, coll. J.C. Verco. Paralectotypes: SAM C12652, 1 male (cl 6.2 mm, cw 6.5 mm; dry), Gulf St. Vincent, 12 fathoms [22 m], in holothurians, coll. J.C. Verco ; SAM C1388 , 1 male (cl 4.3 mm, cw 4.3 mm), 1 juvenile male (cl 3.6 mm, cw 3.5 mm), 1 female (cl 5.3 mm, cw 4.9 mm), 1 juvenile female (cl 3.1 mm, cw 3.6 mm), Gulf St. Vincent, 5 fathoms [9 m], in ascidians, coll. J.C. Verco.

Other material examined (all Australia). VICTORIA: AM G5724 , 1 male (cl 5.5 mm, cw 5.2 mm), Shoreham, Victoria, dredged, coll. F. Grant, 1900 ; NMV J58309 , 1 female (cl 5.4 mm, cw 5.2 mm), Popes Eye, Port Phillip Bay , 38°17′S, 144°41′E, 6–10 m, from algal sample, coll. J. Watson, 22 March 2008 ; NMV J10682 , 1 ovigerous female (cl 11.6 mm, cw 11.4 mm), eastern Bass Strait , S of Waratah Bay, 39°10′S, 145°59.8′E, 69 m, polyzoa bottom, HMAS Kimbla, K 7/73-65, 26 November 1973 .

TASMANIA: AM P4047 , 1 female (cl 13.6 mm, cw 12.6 mm), E of Schouten Island , 73–92 m, coll. C. Harrison , 1910; NMV J10739 , 1 male (cl 3.3 mm, cw 3.0 mm), Little Squally Cove, Deal Island, Bass Strait , 39°29′S, 147°21′E, 20 m, 3 May 1974 ; NMV J10740 , 1 juvenile male (cl 2.4 mm, cw 2.2 mm), Little Squally Cove, Deal Island, Bass Strait , 39°29′S, 147°21′E, 20 m, 3 May 1974 .

SOUTH AUSTRALIA: NMV J10684 , 1 female (cl 9.2, cw 8.4 mm), Point Sinclair , 32°06′S, 132°59′E, coll. D.C. Pearsons, 26 June 1973; NMV J10737 , 2 females (cl 8.1 mm, cw 7.3 mm; cl 7.1 mm, cw 6.6 mm), Point Sinclair, 32°06′S, 132°59′E, coll. D.C. Pearsons, 10 May 1973; SAM C1506 , 1 male (cl 4.1 mm, cw 4.3 mm), 1 female (cl 10.3 mm, cw 9.4 mm) , South Australia.

WESTERN AUSTRALIA: WAM C23501, 1 ovigerous female (cl 11.8 mm, cw 10.4 mm), Port Jackson Cove, Fitzgerald River National Park , 34°31.064′S, 119°15.911′E , 9

m, inside Herdmania momus , large boulders, mostly covered in brown algae, stn F38, coll. M. Berggren, 20 March 1997; WAM C23495, 1 ovigerous female (cl 9.7 mm, cw 9.1 mm), 1 spent female (cl 11.6 mm, cw 11.0 mm), Stream Beach, CALM Fitzgerald Reserve, 34°29.69′S, 119°17.01′E, 12 m, inside Herdmania momus with Notopontonia platycheles , granite reef, stn F12, coll. M. Berggren, 13 March 1997; WAM C23500, 1 male (cl 4.4 mm, cw 4.0 mm), 1 ovigerous female (cl 13.6 mm, cw 13.0 mm), NW side Horatio Island, CALM Fitzgerald Reserve, 34°30.365′S, 119°17.283′E, 18 m, inside Herdmania momus , granite reef, brown algae, under large boulder covered with sponges & a few tunicates, stn F37, coll. M. Berggren, 20 March 1997; WAM C23499, 1 male (cl 6.4 mm, cw 6.0 mm), James Cove, CALM Fitzgerald Reserve, 34°22.394′S, 119°26.835′E, 9 m, inside Herdmania momus , limestone reef covered in brown algae, stn F32, coll. M. Berggren, 18 March 1997; WAM C23493, 1 ovigerous female (cl 11.0 mm, cw 9.9 mm), Peppermint Beach South, CALM Fitzgerald Reserve, 34°24.028′S, 119°28.704′E, 12 m, granite reef, inside Herdmania momus with Notopontonia platycheles , stn F12, coll. M. Berggren, 11 March 1997; WAM C23494, 1 male (cl 7.8 mm, cw 7.6 mm), 1 ovigerous female (cl 11.0 mm, cw 10.5 mm), 1 juvenile female (cl 3.8 mm, cw 3.6 mm), Peppermint Beach South, CALM Fitzgerald Reserve, 34°24.028′S, 119°28.704′E, 12 m, granite boulders covered in algae, 9–12 m, inside Herdmania momus together with shrimps, stn F10, coll. M. Berggren, 10 March 1997; WAM C23498, 1 ovigerous female (cl 9.0 mm, cw 8.3 mm), Whalebone Point, CALM Fitzgerald Reserve, 34°21.891′S, 119°31.597′E, 12 m, inside Herdmania momus , granite reef, some boulders, dense brown algae cover, stn F28, coll. M. Berggren, 18 March 1997; WAM C23497, 1 male (cl 7.3 mm, cw 7.0 mm), 1 ovigerous female (cl 14.8 mm, cw 13.6 mm), 1 female (cl 10.5 mm, cw 10.3 mm), Doubtful Islands (middle), 34°22.335′S, 119°36.241′E, 18 m, inside Herdmania momus with Notopontonia platycheles , rocky reef, dense cover of brown algae on free surfaces, stn F26, coll. M. Berggren, 17 March 1997; WAM C23496, 1 male (cl 9.2 mm, cw 8.8 mm), 1 ovigerous female (cl 11.5 mm, cw 10.3 mm), Red Island Point, CALM Fitzgerald Reserve, 34°01.617′S, 119°46.889′E, 12 m, inside Herdmania momus with Notopontonia platycheles , granite reef, high ridge on moderate slope, boulders, brown algae cover, stn F23, coll. M. Berggren, 16 March 1997; WAM C17302, 1 male (cl 5.5 mm, cw 5.4 mm), between Rottnest Island and Fremantle, triangle dredge, RV Flinders stn 11, coll. M. Clark, 27 June 1975; WAM C23502, 1 female (cl 10.0 mm, cw 9.2 mm; with rhizocephalan externa), N of Wedge Rock, outside Hospital Bay, Bernier Island, Shark Bay, 24°47.60′S, 113°10.26′E, 8–9 m, inside Herdmania momus with shrimp, stn SB214, coll M. Berggren, 17 April 1997.

Description. Female: Carapace ( Fig. 7A, R ) subcircular to longitudinally subovate, slightly longer than wide in adults, slightly wider than long to slightly longer than wide in juveniles, lateral margins rounded to slightly flattened, longitudinally vaulted, profile rounded to sinuous in lateral view; front slightly produced, subtruncate, broadly rounded, medially straight or weakly emarginated; anterolateral margins defined; dorsal surface smooth, without tubercles, regions not indicated; epigastric ridge blunt.

Epistome ( Fig. 7S ) with broad triangular interantennular septum; median buccal margin with obtuse median point. Antennular sinus larger than orbit; antennules folded slightly obliquely. Antenna short, free antennal articles not extending dorsally beyond eye; antennal articles 1 and 2 fused to epistome. Eyes filling orbit, cornea pigmented.

Maxilliped 3 ( Fig. 7B ) margins and surface with short setae; ischiomerus length about 1.8 × width; inner, proximal twothirds concave, distomesial angle obtusely rounded; distal margin produced slightly beyond palp articulation; outer margin strongly convex. Carpus half propodus length. Propodus spatulate, length about twice width, distally widened, apex blunt, rounded. Exopod margins convex.

Cheliped (pereopod 1) ( Fig. 7C ) outer surface largely glabrous. Dactylus and pollex relatively straight, crossing distally, without gape, with row of short setae. Dactylus as long as dorsal margin of propodus palm, occlusal margin with 2 small teeth. Pollex occlusal margin irregular, crenulate, with low blunt tooth at midlength; inner ventral margin setose; inner surface of palm with short scattered setae. Propodus palm dorsal margin length 1.3–1.5 × height; ventral margin distinctly weakly concave at base of pollex. Carpus mesial margin with brush of setae, unarmed; merus unarmed, stout, shorter than propodus.

Walking legs (pereopods 2–5) similar ( Fig. 7D–G ); relative lengths: pereopod 2≈pereopod 3>pereopod 4>pereopod 5; smooth, sparsely setose; pereopod 2 propodus with row of short flexor marginal setae; pereopod 3–4 propodus with row of long natatory setae near extensor margin, extending onto dorsal surface of carpus, each article with row of natatory setae on flexor margin, with short row of distal flexor marginal setae; pereopod 5 propodus flexor margin and distal meral flexor margin setose. Meri unarmed, length 3.7–4.0 × height (pereopods 2–4), about 3.0 × height (pereopod 5). Propodi unarmed, 2.5–3.2 × height. Dactyli similar, stout, strongly curved, falcate, evenly tapering, apices spiniform, corneous; flexor margin sparsely setose proximally; pereopod 2–4 dactyli 0.7 × propodus length; pereopod 5 dactylus 0.9 × propodus length.

Egg diameter 0.3–0.4 mm (in preservative).

Male: Similar to female but smaller maximum size ( Fig. 7H–Q ). Cheliped ( Fig. 7J ) palm dorsal margin length 1.2–1.3 × height. Abdomen narrow ( Fig. 7N ), distally tapering, widest at somite 3; somite 6 weakly trapezoid, slightly wider than long, about as along as telson; telson slightly wider than long, apex rounded to subtruncate. G1 with long setae along central one-third of lateral and mesial margins, small tuft of short setae on step proximal to gently sinuous, glabrous, finely tapering, lanceolate tip ( Fig. 7O, P ). G2 short, simple, about one-fourth G1 length; exopod absent ( Fig. 7Q ).

Hosts. Holothurians and the ascidians, Herdmania grandis ( Heller, 1878) and H. momus Savigny, 1816 (Pyuridae) . As is the case with the ascidian host of A. pregenzeri , host records of A. holothuriensis as H. momus may referable to the similar species, H. grandis , given that the latter apparently does not occur in southern Australia ( Kott, 2002). In Western Australia, A. holothuriensis was frequently observed sharing the branchial chamber of its ascidian host with the caridean shrimp, Notopontonia platycheles Bruce, 1991 (Palaemonidae) ; the crabs lived close to the inhalant siphon whereas the shrimps lived among the folds within the branchial chamber ( Berggren, 1999). Crabs were often found in male-female pairs, singly or in some cases with three crabs (male, two females) in the same ascidian.

Remarks. Austrotheres holothuriensis occurs only in southern Australia, ranging from Western Australia to Victoria and Tasmania. Previous records of A. holothuriensis from eastern Australia ( Pregenzer, 1988) are based on A. pregenzeri new species. Features distinguishing A. holothuriensis from A. pregenzeri are discussed under the account of the latter.

The type series of A. holothuriensis was collected from both ascidians and holothurians, of which the specimens from the latter host are larger ( Baker, 1907). Whether host type affects crab size remains to be determined, although A. pregenzeri from eastern Australia, hosted by similar ascidians, attains a similar maximum size to A. holothuriensis . The largest female type specimen (cl 8.3 mm, cw. 7.2 mm; SAM C1389; Fig. 7A–G ) is herein selected as the lectotype to fix the identity of the species.

A number of specimens of A. holothuriensis were collected outside the host, corroborating Baker’s (1907: 178) observation that the “crab is able to swim, and probably does not spend all its time within the host”. It is unusual for the range of hosts occupied by pinnotherid species to span phyla. Whereas O. tridacnae was thought to infect both molluscs ( Tridacna sp. ) and ascidians, the single record from the latter host ( Adensamer, 1897) is based on a misidentification (see Remarks for O. tridacnae and O. cynthiae ). Austrotheres holothuriensis , however, is confirmed from both holothurians and ascidians. Known obligate holothurian associates are conspicuously tomentose: Alain Manning, 1998 , Buergeres Ng & Manning, 1998 , Holotheres Ng & Manning, 1998 , Holothuriophilus Nauck, 1880 , and Trichobezoares Ng, 2018 . That these taxa are probably not all closely related suggests that the dense setation might be adaptive for holothurian occupation. Austrotheres holothuriensis , however, has setose pereopod margins typical of other pinnotherids, but is otherwise largely glabrous. Notably, most records of A. holothuriensis are from ascidians or outside of the host. Austrotheres holothuriensis has only once been recorded from holothurians ( Baker, 1907) and the lack of subsequent holothurian records may be an observational artefact given that ascidians are more routinely dissected for taxonomic identification than holothurians. Alternatively, A. holothuriensis may be only a facultative holothurian associate, accounting for both the low relative frequency of host records and differences in body setation compared to known obligate holothurian commensals. The American Opisthopus transversus Rathbun, 1893 , a temporary associate of holothurians, also lacks the body tomentum ( Campos & Manning, 2000).

Males mature by cl 3.3–3.6 mm. The cl 2.4 mm male (NMV J10740 ) is a juvenile: pleopods 3–5 are absent but the G1 is incompletely developed; by cl 3.3 mm (NMV J10739 ), the gonopods are fully developed. Juvenile females to about cl 5.4 mm have a narrow, male form abdomen. The smallest ovigerous female A. holothuriensis examined is comparatively large (cl 9.0 mm, WAM C23498), but as in A. pregenzeri , female A. holothuriensis appear to be mature by about cl 6 mm judging from abdominal and pleopodal development. The northermost specimen of A. holothuriensis (WAM C23502, Shark Bay) and one reported from Edithburgh, South Australia ( Hale, 1927a), has a rhizocephalan parasite.

Distribution. Southern and western Australia, from Tasmania and Port Phillip Bay, Victoria, to Shark Bay, Western Australia; 6– 92 m.

Figures

Fig. 5. Distribution of species of Austrotheres new genus. (■) A. holothuriensis (Baker, 1907) new combination; (●) A. pregenzeri new species.

Fig. 7. Austrotheres holothuriensis (Baker, 1907) new combination. A–G, female lectotype, cl 8.3 mm, cw 7.2 mm, Gulf St. Vincent, SAM C1389; H–N, male paralectotype, cl 6.2 mm, cw 6.5 mm, Gulf St. Vincent, SAM C1389; O–Q, male, cl 5.5 mm, cw 5.2 mm, Shoreham, AM G5724; R–S, female, cl 13.6 mm, cw 12.6 mm, Tasmania, AM P4047. A, H, carapace, dorsal view; B, I, left maxilliped 3; C, J, right cheliped, anterior view; D, right pereopod 2; E, K, right pereopod 3; F, L, right pereopod 4; G, M, right pereopod 5; N, male abdomen; O, right G1, sternal view; P, right G1 tip, mesial view; Q, right G2, sternal view; R, carapace, right lateral view; S, cephalothorax, anterior view. A, C–H, J–M = 2.0 mm; B, I, N = 1.0 mm; O–Q = 0.5; R = 2.8 mm; S = 1.4 mm.