Platydromia Brocchi, 1877

Guinot, Danièle & Tavares, Marcos, 2003, A new subfamilial arrangement for the Dromiidae de Haan, 1833, with diagnoses and descriptions of new genera and species (Crustacea, Decapoda, Brachyura), Zoosystema 25 (1), pp. 43-129 : 86-91

Genus Platydromia Brocchi, 1877

( Figs 15 ; 16 )

Platydromia Brocchi, 1877: 53 , 54. (Non Platydromia Fulton & Grant, 1902a: 57 , replacement name: Epipedodromia André, 1932: 180 footnote, see McLay 1993: 124, 224, table 8, type species: Platydromia thomsoni Fulton & Grant, 1902 by monotypy).

Dromien – Vélain 1878: 67, 73.

Platydromia – André 1932: 178, 179.

Dromidia – Stimpson 1858 pro parte: 225; 1907: 170. — Henderson 1888: 12. — Bouvier 1896 pro parte: 21 (54). — McLay 1993 pro parte: 121, 183, 224, 225. (Non Dromidia Stimpson, 1858 sensu nobis, type species: Dromia hirsutissima Lamarck, 1818 by original designation).

Cryptodromiopsis – Barnard 1947 pro parte: 369; 1950: 329. (Non Cryptodromiopsis Borradaile, 1903 sensu nobis, type species: C. tridens Borradaile, 1903 by monotypy).

? Parasphaerodromia Spiridonov, 1992: 69 .

Pseudodromia – Macpherson 1988: 61. (Non Pseudodromia Stimpson, 1858 ).

TYPE SPECIES. — Dromidia spongiosa Stimpson, 1858 which is a senior synonym of Platydromia depressa Brocchi, 1877 , type species of Platydromia Brocchi, 1877 by monotypy. Gender: feminine.

Several specimens of Platydromia depressa Brocchi, 1877 , from Saint-Paul Island (M. de l’Isle coll., 600- 1876) ( MNHN-B 8739 ), may be considered syntypes. A lectotype, a male 9 × 10 mm, is selected herein ( MNHN-B 27934 ) ; the remaining specimens are paralectotypes. Other specimens from the same expedition (see Vélain 1878) are labeled “ Saint-Paul Island, Vélain coll., 178-1875” ( MNHN-B 12724 ) .

SPECIES INCLUDED. — Dromidia spongiosa Stimpson, 1858 .

Whether other species of Dromidia or Cryptodromiopsis should be transferred to Platydromia requires further investigation. For example, the status of C. lepidota Barnard, 1947 , based on an immature specimen and assigned to Dromidia by McLay (1993: 183-185), is uncertain.

DISTRIBUTION. — South Africa and south western Indian Ocean.

DESCRIPTION

Carapace wider than long, convex; dorsal surface with not well-defined regions; branchial groove weakly marked. Anterolateral margin long, strongly convex, entire, only undulated, with only blunt knob behind level of branchial groove; posterolateral margins very short, markedly convergent posteriorly. Front narrow, with rostrum in lower plane and deflexed, and two low pseudorostral lobes; only a slight supraorbital tooth, no suborbital and exorbital teeth. Antenna: urinal article noticeably developed, with anterior part of beak rounded, wider and shorter than posterior ones; basal article very short, with exopod thick; internal angle acutely produced. Mxp3 with coxae not closely approximated.

Thoracic sternites 1 and 2 narrrow and hardly visible; sternite 3 largely visible dorsally, at level not much lower than sternite 4. Thoracic sternite 4 broad, deeply medially hollowed in males, with lateral borders convex and anterior margin medially concave in both sexes ( Figs 15A ; 16 ). In males, thoracic sternites 7 and 8 perpendicular in relation to preceding ones; in females, sternites 5- 8 perpendicular in relation to sternite 4. Female sternal sutures 7/8 very long, with apertures of spermathecae ending together on slight prominence between chelipeds ( Fig. 16 ). When male abdomen is applied against ventral surface, sternites 1-2 partly discernible, sternite 3 and anterior part of sternite 4 remaining visible, and no episternites exposed.

Male abdomen very broad, with distinct pleural parts, not covering whole sterno-abdominal depression, and with all segments free; telson broadly triangular, ending in sharp tip ( Fig. 15B, C ); telson of females without acute tip. Segment 6 with external borders parallel. In males, vestigial pleopods present on segments 3-5 (Pl5 as small lobes and Pl4 and Pl3 as short papillae, difficult to see, Fig. 15C ). Uropods as ventral plates, not visible dorsally, oriented forward instead laterally; uropods not involved in holding of abdomen. No efficient holding of abdomen: at the more least, a very low prominence on coxa of P2 just in contact with external margin of abdominal segment 6 which is not modified. Female gonopore on P3 coxa relatively large.

Chelipeds without epipod. P1, P2 and P3 very short and stout, not knobbed nor nodose; propodus of P2 and P3 without distal spine; inner margin of dactylus armed with spines. P4 and P5 reduced, P5 being slightly longer and more slen- der. Propodus of P4 and P5 short and with only one distal spine opposing dactylus which is short and ends in horny spine.

Male P5 coxa with mobile penial tube ( Fig. 15A ).

Carrying behaviour

Compound ascidians.

REMARKS

Dromidia spongiosa differs substantially from D. hirsutissima , type species of Dromidia (see above), so that it is necessary to separate it in a different genus. For D. spongiosa we rehabilitate the genus Platydromia Brocchi, 1877 , its type species P. depressa being a junior synonym of Dromidia spongiosa ( McLay 1993: 121, 183).

The species described as Dromidia spongiosa by Stimpson has been known under five specific names and placed in at least six genera ( McLay 1993: 183). In the present study D. spongiosa is excluded from Dromidia , its original ( Stimpson 1858) and last genus ( McLay 1993: 183,184), as well as from Cryptodromiopsis where it was placed by Barnard (1947, 1950). It is now Platydromia spongiosa ( Stimpson, 1858) n. comb.

We agree with McLay (1993: 184) who placed Pseudodromia inermis Macpherson, 1988 (p. 61, figs 6, 7) in the synonymy of his Dromidia spongiosa . McLay also synonymised with D. spongiosa Parasphaerodromia subglobosa Spiridonov, 1992 (p. 70, fig. 2a-d), from the South Indian Ocean, indicated with reduced uropods (see below).

Platydromia spongiosa n. comb. differs from Dromidia sensu nobis ( Fig. 5 ) in particular by having the frontal, orbital and anterolateral margins without teeth, a thick, sponge-like tomentum, and no spine on P2 coxa. Other characters which distinguish Platydromia from Dromidia sensu nobis are: 1) front lobate (tridentate in Dromidia ); 2) sternite 3 visible (not visible dorsally in Dromidia ); 3) male sternite 4 relatively wide, with convex lateral margins and medially cleft anterior margin (with oblique lateral margins and rounded tip in Dromidia ); 4) male abdomen that leaves uncovered sternite 3 and part of sternite 4 ( Figs 15A ; 16 ) (covering whole abdominal depression with exception of extreme anterior part of sternite 4 in Dromidia , Fig. 5A, B ); 5) uropods showing as small, totally concealed, ventral plates ( Fig. 15B, C ) (oblique and intercalary ventral plates, almost entirely concealed in Dromidia , Fig. 5B, C ); and 6) no efficient abdominal holding (efficient holding by strong coxal spine on P 2 in Dromidia , Fig. 5B ).

Platydromia is easily distinguishable from Cryptodromiopsis sensu nobis ( Fig. 4 ) by a number of characters, chiefly: 1) round shape of carapace, longer than wide (distinctly wider than long in Cryptodromiopsis ); 2) uropods showing as totally concealed ventral plates (salient dorsal plates in Cryptodromiopsis ); 3) male telson ending in acute tip (triangular tip in Cryptodromiopsis ); 4) male segment 6 broad (narrower in Cryptodromiopsis ); 5) male sternite 4 broad, deeply hollowed medially (narrower, not hollowed medially in Cryptodromiopsis ); and 6) an inconspicuous low prominence on P2 coxa (a serrated prominence, and uropods not involved in Cryptodromiopsis ).

Platydromia and Lamarckdromia n. gen. (type species: Dromia globosa ), both with ventral and concealed uropods, differ from each other by several features of the carapace and pereopods, and specially by: 1) sternite 3 largely visible in Platydromia (only a small part visible in male Lamarckdromia n. gen., Fig. 10A, D ); 2) sternite 4 wide, with convex lateral margins in both sexes (triangular in Lamarckdromia n. gen., Fig. 10A, D ); 3) male telson ending in acute tip (rounded at tip in Lamarckdromia n. gen., Fig. 10B, C ); and 4) apertures of spermathecae ending together on slight prominence between chelipeds (ending together on central prominence between P 2 in Lamarckdromia n. gen., Fig. 10A ).

The carapace and legs of Platydromi a spongiosa are completely covered with “a dense and firm envelope of pubescence, sponge-like in appearance”, “distinctly marked with shallow pits or depressions” ( Stimpson 1907: 171, as Dromidia spongiosa ), or with “a very short close and thick pile” ( Barnard 1950: 330, as Cryptodromiopsis spongiosa ). By comparison, the carapace and legs of Dromidia hirsutissima are “covered with short stiff pile, and long dense fibrous and shaggy brown or yellow hairs” ( Barnard 1950: 320), hence the name of hirsutissima given by Lamarck and the common name of “shaggy sponge crab” ( Barnard 1950). The same common name was given to Cryptodromiopsis plumosa Lewinsohn, 1984 by Hoover (1998: 266, fig. n. n.; see below under Stebbingdromia plumosa n. comb.). In Lamarckdromia globosa n. comb. the whole body and legs are covered by a dense shaggy coat of hairs, and the deflexed front portion of carapace is concealed by transverse fringe of longer setae, giving it a characteristic appearance.

The soft and areolated tomentum of Platydromia spongiosa n. comb. somewhat resembles that of “ Dromia ” wilsoni ( Fulton & Grant, 1902b: 61, as Cryptodromia wilsoni ). The two species may be confused but differ by: 1) shape of carapace, rounded and not toothed laterally in P. spongiosa n. comb. (distinctly wider and armed laterally in D. wilsoni ); 2) uropods, only ventral in P. spongiosa n. comb. (very salient dorsal plates in D. wilsoni ). We agree with McLay in that the generic status of “ Dromia ” wilsoni needs a re-appreciation (see McLay 1991: 470, figs 7, 8, as Petalomera wilsoni ; 2001a: 84, as Dromia wilsoni ; Ng et al. 2000: 160, fig. 2b, as D. wilsoni ; McLay et al. 2001: 742, table 1, as D. wilsoni ). “ Dromia ” wilsoni differs from other Dromia species by several morphological features (in particular the abdominal holding with a coaptation by engagement between P2 coxae and the modified edges of abdominal segment 6, and no involvement of uropods, see Bouchard 2000) and larval development (see McLay et al. 2001). Its worldwide geographical distribution includes all the three major oceans; it is found as deep as 520 m.

Genus Pseudodromia Stimpson, 1858 Pseudodromia Stimpson, 1858: 226 . — Henderson 1888: 15. — Alcock 1900 pro parte: 149. — Stebbing 1900: 23. — Stimpson 1907: 177. — Barnard 1950 pro parte: 315. — Gordon 1950 pro parte: 209. — Kensley 1977 pro parte: 183; 1978: 257; 1980 pro parte:25. — McLay 1993: 125, 175, table 4. — McLay et al. 2001: 741, table 3. — Guinot 1995: 186. — Guinot & Bouchard 1998: 626, table 3. — Stewart et al. 2001: 136. TYPE SPECIES. — Pseudodromia latens Stimpson, 1858 by original designation ( Stimpson 1858: 226). Gender: feminine. SPECIES INCLUDED. — Pseudodromia latens Stimpson, 1858 ; Dromia rotunda MacLeay, 1838 (see Ng & Ahyong 2001); Pseudodromia trepidus Kensley, 1978 . Pseudodromia cacuminis Kensley, 1980 , from the South Atlantic (Vema Seamount), does not belong to Pseudodromia ( McLay 1993: 176) . DISTRIBUTION. — South Africa.

DESCRIPTION

Carapace more or less longer than wide, extremely narrow anteriorly, convex; dorsal surface smooth, without defined regions; cervical groove not present, branchial groove strongly marked. Anterolateral margin very long, usually without tooth; posterolateral margin short. Front very narrow, tridentate, with rostrum markedly deflexed and hardly or not visible dorsally at all, may be elongated ( P. trepidus ) and with two pseudorostral teeth; supraorbital tooth marked or not; suborbital and exorbital teeth absent. Antenna: urinal article with anterior part of beak much shorter than posterior one and with broad tip; basal article with exopod enlarged and internal angle not elongated. Mxp3 with coxae closely approximated.

Thoracic sternite 3 not visible dorsally. Thoracic sternite 4 very narrow, deeply hollowed medially in males, with lateral borders convex and anterior margin pointed and deflexed. In females, thoracic sternites 7 and 8 very tilted in relation to preceding ones. Female sternal sutures 7/8 long, with apertures of spermathecae ending together on prominence between P2. When male abdomen applied against ventral surface, anterior part of sternite 4 remaining visible and no episternites exposed. Sterno-coxal depressions absent.

Male abdomen completely covering sternoabdominal depression and with all segments free; male telson relatively long, ending in sharp tip; telson of females without acute tip. Segment 6 becoming more or less narrow posteriorly. No vestigial pleopods present on segments 3-5 in males. Uropods as relatively small but distinct ventral plates, not visible dorsally ( P. latens , P. trepidus ) or hardly visible ( P. rotunda ). Absence of any efficient holding of abdomen.

Chelipeds without epipod. P1, P2 and P3 not knobbed nor nodose; propodus of P2 and P3 without distal spine; inner margin of dactylus with spines, longer distally. P4 reduced, P5 distinctly longer than P4 and being about of same size than P2. Propodus of P4 and P5 without spines opposing dactylus; outer propodal spines absent; presence of lateral propodal spines, one on P4 and two on P5; P5 dactylus straight.

Male P5 coxa with mobile and very long penial tube.

Carrying behaviour

Compound ascidians.

REMARKS

Pseudodromia is distinguished by having uropods that show as ventral plates, sometimes partly visible dorsally. This is the major difference from Ascidiophilus , since there are no vestigial pleopods in the males of both genera (Guinot 1995: 186). Pseudodromia differs from Austrodromidia sensu nobis ( Figs 1 ; 2 ) as follows: 1) sternite 3 not visible dorsally (visible dorsally, clearly or slightly in Austrodromidia ); 2) sternite 4 very narrow and hollowed medially in males (truncate at tip and not hollowed in Austrodromidia ); 3) no episternites visible when male abdomen flexed (episternites 4 and 5 visible in Austrodromidia ); 4) male telson ending in acute tip (bluntly triangular or rounded in Austrodromidia ); 5) male segment 6 with external borders may be slightly concave (deeply hollowed laterally in Austrodromidia ); 6) female sternal sutures 7/8 ending together at level of P2 (apart in Austrodromidia ); and 7) absence of an abdominal holding (abdominal holding by prominence on P2 coxa in Austrodromidia ).

In Pseudodromia (as well in Ascidiophilus ) the absence of an abdominal holding system seems to be related to the complete protection by a host, the body being almost entirely enclosed by an ascidian ( Guinot & Bouchard 1998).

Using DNA sequence data, Stewart et al. (2001: 136) questioned the monophyly of Pseudodromia but confirmed the specific status of two close species, P. rotunda and P. latens .

Figures

FIG. 15. — Platydromia spongiosa (Stimpson, 1858) n. comb.; A, B, Saint-Paul Island, Brocchi det. Platydromia depressa Brocchi, 1877, Vélain coll., 178-1875, 11 × 14 mm (MNHN-B 12724); A, thoracic sternum, two front views, note sternite 4 medially hollowed; B, dorsal view of abdomen; C, Amsterdam Island, Ams-A4, 11.II.1971, Beurois coll., 13 × 16 mm (MNHN-B 12728), ventral view of abdomen, note uropods not visible dorsally and oriented forward, and the vestigial pleopods showing only as papillae on segments 3-4. Abbreviations: a2-a6, abdominal segments 2-6; cx1-cx5, coxae of P1-P5; e4, e5, episternites 4, 5; mxp3, external maxilliped; pt, penial tube; t, telson; u, uropod; v3-v5, vestigial pleopods 3-5; 1-2, sternites 1-2; 3-8, sternites 3-8; 4/5-7/8, thoracic sternal sutures 4/5-7/8. Dotted line indicates difference in level. Scale bars: 1 mm.

FIG. 16.— Platydromia spongiosa (Stimpson,1858) n.comb.,Saint- Paul Island, Vélain coll., 178-1875, Brocchi det. Platydromia depressa Brocchi,1877, 12 × 16 mm (MNHN-B 12724),thoracic sternum, two front views,and spermathecae.Abbreviations:cx1- cx5,coxae of P1-P5;e4, e5, episternites4,5;gy, episternalgynglyme receiving sternal articular condyle of the pereopod;mxp3, external maxilliped; o, female gonopore; s, aperture of spermatheca; 1-2, sternites 1-2;3-8, sternites 3-8;4/5-7/8, thoracic sternal sutures 4/5-7/8.Dotted line indicates difference in level.Scale bar:2 mm.

FIG. 5. — Dromidia hirsutissima (Lamarck, 1818), “Cap de Bonne-Espérance”, 26.6 × 31 mm, lectotype (MNHN-B 22034); A, thoracic sternum, two front views; B, C, abdomen, dorsal and ventral views; note uropods showing as ventral plates, hardly visible dorsally. Abbreviations: a5, a6, abdominal segments 5, 6; cx1-cx5, coxae of P1-P5; e4, e5, episternites 4, 5; pr, spiniform holding prominence; pt, penial tube; v4, v5, elongated vestigial pleopods 4 and 5 (pleopods present also on segment 3); t, telson; u, uropod; 4-6, sternites 4-6; 5/6-7/8, thoracic sternal sutures 5/6-7/8. Dotted line indicates difference in level. Scale bars: 2 mm.

FIG. 4. — Cryptodromiopsis tridens Borradaile, 1903, Polynesia, Moorea, 1979, C. Bouchon coll., 6.2 × 7.5 mm (MNHN-B 22579); thoracic sternum with (A) and without (B) abdomen. Abbreviations:a6, abdominal segment 6; cx1-cx5, coxae of P1-P5; e4, e5, episternites 4, 5; mxp3, external maxilliped; pr, holding prominence; pt, penial tube; t, telson; u, uropod; 1-3, sternites 1-3; 4-8, sternites 4-8; 6/7-7/8, thoracic sternal sutures 6/7-7/8. Scale bar: 1 mm.

FIG. 10. — Lamarckdromia globosa (Lamarck, 1818) n. comb., New South Wales, Port Jackson, det. Dromidia excavata Stimpson, McLay redet. Dromidiopsis globosa (MNHN-B 22041); A, 25 × 25 mm, thoracic sternum and spermathecae; B-D, 24 × 25 mm, extremity of abdomen in dorsal view, abdomen in ventral view, and thoracic sternum without abdomen. Abbreviations: a3, a6, abdominal segments 3, 6; cx1-cx5, coxae of P1-P5; e4, e5, episternites 4, 5; mxp3, external maxilliped; o, female gonopore; pr, holding prominence; pt, penial tube; s, aperture of spermatheca; t, telson; u, uropod; 1-2, sternites 1-2; 3-8, sternites 3-8; 4/5-7/8, thoracic sternal sutures 4/5-7/8. Dotted line indicates difference in level. Scale bars: 2.5 mm.

FIG. 1. — Austrodromidia australis (Rathbun, 1923), New South Wales, off Eden, Goonambee, 1922, 29.5 × 33 mm (AM P5777); A, thoracic sternum, two front views; B, abdomen, dorsal view; C, abdomen, ventral view; note uropods showing as very narrow ventral plates. Abbreviations: a6, abdominal segment 6; cx1-cx5, coxae of P1-P5; e4, e5, épisternites 4, 5; mxp3, external maxilliped; pr, holding prominence; pt, penial tube; t, telson; u, uropod; 1-2, sternites 1-2; 3-8, sternites 3-8; 4/5-7/8, thoracic sternal sutures 4/5-7/8. Dotted line indicates difference in level. Scale bar: 5 mm.

FIG. 2. — Austrodromidia octodentata (Haswell, 1882), South Australia, Kangaroo Island, Endeavour, Rathbun det. Cryptodromia octodentata; A, B, 39 × 42 mm (AM E. 801); A, thoracic sternum, two front views; B, abdomen, ventral view; note uropods reduced to nearly obsolete buds; C, 44 × 46 mm (AM P. P2311), thoracic sternum and apertures of spermathecae, covered with spermatic plug. Abbreviations: a6, abdominal segment 6; cx1-cx5, coxae of P1-P5; e4, e5, episternites 4, 5; mxp3, external maxilliped; o, female gonopore; pr, holding prominence; pt, penial tube; sp, spermatic plug; t, telson; u, uropod; 1-2, sternites 1-2; 3-8, sternites 3-8; 4/5-7/8, thoracic sternal sutures 4/5-7/8. Dotted line indicates difference in level. Scale bars: 5 mm.