Mclaydromia, Guinot & Tavares, 2003

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 : 78-80

Genus Mclaydromia n. gen.

( Figs 12 ; 13 )

? Dromidiopsis – Lewinsohn 1984 pro parte: 102.

Dromidiopsis – McLay 1993 pro parte: 135, 138; 2001a pro parte: 79, 80. (Non Dromidiopsis Borradaile, 1900 sensu nobis).

TYPE SPECIES. — Mclaydromia colini n. gen., n. sp., by present designation.

SPECIES INCLUDED. — Mclaydromia colini n. gen., n. sp.; Dromidiopsis dubia Lewinsohn, 1984 .

ETYMOLOGY. — We dedicate the new genus Mclaydromia n. gen. to our colleague Colin L. McLay (University of Canterbury, Christchurch, New Zealand), for greatly improving our view of the Dromiidae . Gender: feminine.

DISTRIBUTION. — New Caledonia and Madagascar.

DESCRIPTION

Carapace distinctly longer than wide, convex. Dorsal surface with regions poorly defined; branchial groove defined and posteriorly marked by blunt tooth. Anterolateral margin of carapace not joining exorbital angle and armed with two or three teeth. Posterolateral margin slightly shorter than anterolateral margin and with blunt tooth just behind branchial groove. Front ( Fig. 13 ) wide, obscurely tridentate: rostrum very small, directed downwards, and not visible dorsally; two pseudorostral teeth, more or less developed, sometimes eave-like. Supraorbital and suborbital teeth not well marked; exorbital angle not produced.Antenna: urinal article broader than long, with anterior part of beak small and downcurved; basal article with well-developed exopod; internal corner about as long as exopod; antennal article 4 long and fitted in between. Mxp3: coxae closely approximated.

Thoracic sternite 3 partly visible at lower plane (sternites 1-2 not exposed); sternite 4 narrow, with subparallel margins, anterior margin truncated ( Fig. 12 ). Female sternal sutures 7/8 long, apertures of spermathecae placed apart, each on a tubercle, between coxae of P2 ( Fig. 12B ). When male abdomen folded against cephalothorax, sternite 3 (partly) and large part of sternite 4 remaining visible; a minute part of episternite 4 exposed; episternite 5 not visible.

Male abdomen not completely covering sternoabdominal depression. All abdominal segments free in males and females. Male abdominal segment 6 abruptly constricted, edge markedly thickened. Telson rather long, with enlarged base and rounded anterior margin. No vestigial pleopods in males. Uropods showing as strongly salient dorsal plates in males, that are obliquely oriented. Uropods markedly involved in abdominal holding. Abdominal holding provided by curved, serrate, strong flange on P2 coxa, which is in close contact with uropod and fits into excavation on lateral edge of abdominal segment 6; additionally, on coxa of P1, few tiny tubercles placed closely together, or one more distinctly marked tubercle, without contact with telson.

Chelipeds with an epipod. In both sexes cutting edges of fixed finger and dactylus of two chelipeds armed halfway with strong molariform tooth (may be bifid), which is directed backwards and followed by the usual interlocking distal teeth. P2 and P3 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 longer than P4; propodus of P4 and P5 very short, subequal in size. Subcheliform apparatus formed by one small distal spine opposing short and curved dactylus; an outer propodal spine may be present on P5.

Male P5 coxa with mobile penial tube.

Male G2 with a needle-like flagellum, long but completely included in sterno-abdominal depression.

Carrying behaviour

Sponges ( McLay 1993: 139, under Dromidiopsis dubia ).

REMARKS

In assigning with doubt his new species D. dubia to Dromidiopsis, Lewinsohn (1984: 102 , 104, fig. 2b, c) stressed its peculiar features, particularly the fingers and dactyli of chelipeds. The presence of a molariform tooth on two cutting edges in Mclaydromia n. gen. appears unique amongst the Dromiidae (which is sometimes present in the Dynomenidae ) and may indicate a specialized feeding habit ( McLay 1993: 139). A proximal tooth may be present along the cutting edge of dactylus in a few dromiid genera (as in Epigodromia McLay, 1993 ), but the condition of Mclaydromia n. gen., with two molariform teeth halfway on prehensile margin of fixed finger and dactylus, is exceptional.

Mclaydromia n. gen. can be readily distinguished from Dromidiopsis sensu nobis ( Fig. 6 ) as follows: 1) abdominal segments free (abdominal segments 5 and 6 fused together in Dromidiopsis ); 2) propodus of P4 and P5 subequal in size (dissimilar, much longer on P5, in Dromidiopsis ); 3) when extended forward, P5 barely overreaching last lateral tooth of carapace (much long, reaching about outer orbital angle in Dromidiopsis ); 4) female sutures 7/8 wide apart, oblique, getting progressively close to each other as they run forward over thoracic sternites (getting much closed to each other at level of P3 and subparallel in Dromidiopsis ); 5) apertures of spermathecae at level of P2 and placed wide apart from each other, on tubercles (at level of P1 or just behind and lying close together, on central prominence, in Dromidiopsis ); and 6) male uropods showing as dorsal plates that are obliquely oriented (vertically oriented in Dromidiopsis ).

The following characters readily distinguish Mclaydromia n. gen. from Cryptodromiopsis sensu nobis ( Fig. 4 ), which also has obliquely oriented dorsal uropods: 1) male segment 6 with external borders deeply hollowed and thickened (subparallel on anterior half in Cryptodromiopsis ); 2) apertures of spermathecae apart, each on a tubercle, at level of P2 (ending together on slight tubercle between chelipeds in Cryptodromiopsis ); and 3) P2 and P3 not knobbed (knobbed in Cryptodromiopsis ).

Mclaydromia n. gen. is very close to Hemisphaerodromia on account of similarities on the frontal and orbital regions and of subcheliform nature of the P4 and P5. Additionally, they share a sternite 4 that is anteriorly truncated and with subparallel lateral borders; male abdominal segment 6 broad, and with external borders deeply hollowed and thickened to receive coxal prominence of P2; dorsal uropods salient, that are obliquely oriented and completely involved in abdominal holding ( Guinot & Bouchard 1998: fig. 3C, D, H. monodus ); apertures of spermathecae apart, at about the level of P2 (see Fig. 7B for H. monodus , and Fig. 12B for M. colini n. gen., n. sp.). The following characters distinguish the two genera: 1) thoracic sternite 3 not exposed in Hemisphaerodromia (partly visible at lower plane in Mclaydromia n. gen., sternites 1-2 not exposed, however); 2) apertures of spermathecae located at level of episternites 5 in Hemisphaerodromia (apertures forward, between P2, in Mclaydromia n. gen.); and 3) fingers of chelipeds normally toothed along prehensile margin in Hemisphaerodromia (molariform teeth on fixed finger and dactylus in Mclaydromia n. gen.).

The following characters readily distinguish Mclaydromia n. gen. from Lewindromia n. gen. ( Fig. 11 ), with vertically oriented dorsal uropods: 1) sternite 4 with anterior margin truncated (acutely produced in Lewindromia n. gen.); 2) male abdominal segment 6 abruptly constrict- ed (with external borders sinuous, oblique, in Lewindromia n. gen.); 3) male telson not longer than wide and rounded at tip (very long and pointed in Lewindromia n. gen.); and 4) propodus of P4 and P5 not much different in size, a distal spine opposing the curved dactylus, and an outer propodal spine may be present on P5 (P5 much longer than P4 and, when extended forward, reaching about mid-length of anterior margin of carapace, a propodal distal spine opposing the dactylus which is not strongly curved, and two outer propodal spines in Lewindromia n. gen.).

Figures

FIG. 12. — Mclaydromia colini n. gen., n. sp.; A, LAGON, stn 111, 25 m, 10.4 × 9.1 mm, paratype (MNHN-B 26282), thoracic sternum with abdomen; B, LAGON, stn 569, 62 m, ovigerous 9.4 × 8.6 mm, paratype (MNHN-B 26289), thoracic sternum and spermathecae. Abbreviations: a6, abdominal segment 6; cx1-cx4, coxae of P1-P4; e4, episternite 4 (very small); mxp3, external maxilliped (coxae separated for clarity); o, female gonopore; pr, holding prominence; s, aperture of spermatheca; t, telson; u, uropod; 1-2 sternites 1-2 (normally not exposed); 3, sternite 3; 4-8, sternites 4-8; 4/5-7/8, thoracic sternal sutures 4/5-7/8. Dotted line indicates difference in level. Scale bars: 2.5 mm.

FIG. 13. — Mclaydromia colini n. gen., n. sp., LAGON, stn 111, 25 m, 10.4 × 9.1 mm, paratype (MNHN-B 26282), views of frontal border of carapace; A, dorsal view; B, anterodorsal view. Scale bar: 2.5 mm.

FIG. 6. — A, Dromidiopsis tridentata Borradaile, 1903, New Caledonia, LAGON, stn DW 554, ovigerous 12.7 × 12 mm (MNHN-B 22550), thoracic sternum and spermathecae; B, D. australiensis (Haswell, 1882), Australia, Queensland, Cape Bedford, D. J. G. Griffin det., 15.4 × 14 mm (AM P16598), thoracic sternum with abdomen. Abbreviations: a5, a6, abdominal segments 5, 6; cx1- cx5, coxae of P1-P5; e4, episternite 4; mxp3, external maxilliped; o, female gonopore; pr, holding prominence; s, aperture of spermatheca; t, telson (setae covering sternite 4 not shown); u, uropod; 4-8, sternites 4-8; 4/5-7/8, thoracic sternal sutures 4/5-7/8. 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. 7. — A, Epipedodromia thomsoni (Fulton & Grant,1902),Australia,Victoria, Port Phillip, 9 × 11 mm (BM 1884-39), thoracic sternum and spermathecae; B, Hemisphaerodromia monodus (Stebbing, 1918), Madagascar, Fort-Dauphin,Decary coll., det.H. abellana Barnard, 1954, 16 × 18 mm (MNHN-B 12725), thoracic sternum and spermathecae.Abbreviations: cx1-cx5, coxae of P1-P5; e4, e5, episternites 4, 5; mxp3, external maxilliped; o, female gonopore; r, medial ridge; s, aperture of spermatheca; 1-3, sternites 1-3; 4-8, sternites 4-8; 4/5-7/8, thoracic sternal sutures 4/5-7/8. Dotted line indicates difference in level.Scale bars: 2.5 mm.

FIG. 11. — Lewindromia unidentata (Rüppell, 1830) n. comb.; A, B, Obock, Lewinsohn det. Dromidia unidentata, about 30 mm width (MNHN B-6930), thoracic sternum, two front views, without abdomen and with abdomen; C, Red Sea, Aden and Obock, Nobili det. D. unidentata, 24 × 24 mm (MNHN-B 6940), thoracic sternum and spermathecae. Abbreviations: a6, abdominal segment 6; cx1-cx5, coxae of P1-P5; e4, e5, episternites 4, 5 (in fact, episternite 4 not so visible when abdomen folded); mxp3, external maxilliped; o, female gonopore; pr, holding prominence: blunt prominence on P1, carina on P2; s, aperture of spermatheca; t, telson; u, uropod; 4-8, sternites 4-8; 4/5-7/8, thoracic sternal sutures 4/5-7/8. Dotted line indicates difference in level. Scale bars: 2.5 mm.