Sphaerodromia kendalli (Alcock & Anderson, 1894)

Guinot, Danièle & Quenette, Gwenaël, 2005, The spermatheca in podotreme crabs (Crustacea, Decapoda, Brachyura, Podotremata) and its phylogenetic implications, Zoosystema 27 (2), pp. 267-342 : 298-301

Sphaerodromia kendalli (Alcock & Anderson, 1894)

Ovigerous female 36.4 × 36.2 mm, Philippines, MUSORSTOM 3, CP 143 (MNHN-B 22543).

The axial skeleton, with two transverse bridges similarly to that of S. lamellata , was not completely dissected, but it was possible to partially examine the endosternite 7/8. Spermathecal apertures are concealed. Despite that suture 7/8 is slightly longer than in S. lamellata , a tube does not exist, however.

CONCLUSIONS FOR THE DROMIACEA

In all the Dromiacea that were examined, the spermatheca consisted of a bulb, which is formed by infoldings of the phragma 7/8, and a sort of pocket, herein called “chamber”, which corresponds to delamination of the two laminae of the endosternite 7/8, one belonging to the segment 7, the other to the segment 8. Another structure may be present along a part of the suture 7/8: an internal, closed tube, completely calcified, hollow and, in very most cases, perforated at its extremity, namely the spermathecal aperture. This tube is the forward prolongation of the chamber and continues well beyond it, sometimes along a great length of the suture 7/8 (in [ Dromia ] dormia, the tube is as long as the suture 7/8 of about 50 mm length). The tube, which is “doubtless formed by infoldings of sternites 7 and 8 along their sutural margins” ( Gordon 1950: 248), is the result of the fusion, on a short space, of the two laminae of the phragma 7/8. Its lumen forms a channel leading to the spermathecal aperture, which is generally terminal. Thus, the spermathecal tube corresponds to an entirely modified and elaborate structure: it is the result of a specialization. It is found only in the females. In dromiine males, the suture 7/8 is short, and the endosternite 7/8 is only a thin double septum, consisting of two coalescent sheets, not modified and without any prolongation. Gordon (1950: 245) observed that, in a small female Dromia “ already the anterior third of the suture 7/8 is wider and more conspicuous than it ever is in the male”. For Hartnoll (1979: 82) “the dromiid structure has been elaborated by the development of spermathecal canals along the line of suture 7/8 to link the openings with the spermathecae”.

Considering the material available in the MNHN collections that was used to prepare the skeletons, the Dromiacea exhibit two main patterns concerning the spermathecal tube: 1) the tube is absent and the chamber communicates directly with the exterior through a spermathecal aperture: Dynomenidae ( Fig. 4 ) and Sphaerodromiinae ( Fig. 17 ); or 2) a more or less long tube is present and leads to an external aperture: Homolodromiidae ( Fig. 3 ), Dromiinae ( Figs 1 ; 2 ; 6-11 ; 13-15 ), Hypoconchinae ( Fig. 16 ), and the enigmatic genus Frodromia ( Fig. 12 ).

The visible but short tube is present even in the pattern with short sutures 7/8 ( Homolodromiidae ). Gordon’s (1950: 250, fig. 1) hypothesis about Dicranodromia baffini , a suture 7/8 of the dromiid type and “in all probability” a very short “channel leading to the spermathecal pit”, is thus verified.

The Homolodromiidae , which shows a unique combination of plesiomorphic morphological characters (pediform mxp3, abdominal pleurae, exopod present on G2, uropods showing as ventral lobes, elongated coxae of P5, skeletal connections by interfingering), exhibits the same spermathecal tube pattern as in the Dromiinae , in contrast to the Sphaerodromiinae (at least in the only ovigerous dissected female, Sphaerodromia lamellata ). If we consider the tube a more advanced condition, it corroborates the basal place of the Sphaerodromiinae within the Dromiidae , as previously pointed out ( Guinot & Tavares 2003). The presence of a (short but well visible) tube in the Hypoconchinae supports the placement of this subfamily in the Dromiidae . The specialized Hypoconcha is perhaps not as primitive as indicated until now.

The absence of a spermathecal tube in the Dynomenidae is of particular interest. The Dynomenidae shares several characters with the Dromiidae (dorsal uropods, skeletal junctions occuring by fusion), but it shows a peculiar mix of characters. Plesiomorphic are notably the presence of vestigial pleopods on the somites 3-5 as (generally) biramous vestiges, and elongated male coxae of P5. Apomorphic are a widened thoracic sternum and innovation in some genera ( Dynomene , Hirsutodynomene ) of a sternal differentiation on the thoracic somite 5 (corresponding to P2) for the holding (although not efficient, see Guinot & Bouchard 1998) of the abdomen.

To examine phylogenetic relationships between Homolodromiidae , Dromiidae and the Dynomenidae , spermatological characters (exemplified by Homolodromia kai , Sphaerodromia lamellata , and Metadynomene tanensis , respectively) were used. They strongly endorse monophyly of the Dromioidea , but without a clear recognition of the three families (Guinot et al. 1998).

In addition to features of the carapace during the course of this investigation, the Homolodromiidae , Dynomenidae and the Sphaerodromiinae share the following features, considered plesiomorphic: 1) male pleopodal formula complete or nearly complete (vestigial pleopods on abdominal somites 3-5, biramous in the Sphaerodromiinae and most Dynomenidae , uniramous in the Homolodromiidae ) (the Hypoconchinae maintains various vestiges of these pleopods, while most Dromiinae lack male Pl3-Pl5; see Guinot & Tavares 2003: table 1); 2) exopod present on G2 (in the Sphaerodromiinae , present only in the genus Sphaerodromia , probably absent in Eodromia ); G2 exopod absent in the Dromiinae and Hypoconchinae ; and 3) a totally modified male P5 coxa, which assumes the shape of a hard and elongated extension, resulting in a dimorphic male P5 coxa (the Dromiinae and the Hypoconchinae share a never dimorphic P5 coxa, bearing in males a long movable, “articulated”, sclerotized tube, the penial tube; see Guinot & Tavares 2003: 115, fig. 28).

The enigmatic genus Frodromia combines dromiine and sphaerodromiine characters, and its status remains uncertain ( Guinot & Tavares 2003: 110). Its sphaerodromiine features include short female sternal sutures 7/8 and spermathecal apertures lying close to the female gonopores on the P3 coxae. The present study permits to add two dromiine features to Frodromia : the presence of a spermathecal tube and skeleton with only one transverse bridge. The most important features which still conflict with the inclusion of Frodromia in the Dromiinae are the elongated male P5 coxa and the absence of a mobile penial tube.

All the Dromiacea, either basal ( Homolodromiidae , Dynomenidae , Spharodromiinae) or more advanced ( Dromiinae , Hypoconchinae ), share a similar spermathecal aperture, that is generally a small orifice. For the moment, only five cases differ from the typical condition.

1) In the Homolodromiidae , only one species, Dicranodromia spinulata Guinot, 1995 , shows suture 7/8 occupied by a long subterminal slit, while other homolodromiids have rounded or ovate terminal apertures.

2) The dromiine genus Sternodromia ( Fig. 15 ) shows very tiny terminal apertures but they are replaced (or complemented) by subterminal slits, long ( S. spinirostris ) or shorter ( S. monodi ), the bottom of the tube being partly exposed and opened along its subterminal part so that the underlying spermathecal channel is connected with the exterior (Guinot unpubl. data).

3) The dromiine species [ Dromia ] dormia (a species that belongs to a different genus [Guinot unpubl. data]) is devoid of the usual circular terminal spermathecal aperture ( Figs 8A ; 9 ). Each suture 7/8 opens in a partly decalcified and unperforated pit; at its extremity, the thick spermathecal tube is no longer closed, and the bottom of the phragma 7/8 itself is opened and becomes exposed at the sternal surface to form an ovate pit, which is the spermathecal aperture.

4) In Lauridromia the two sheets of the phragma 7/8 are not completely joined subdistally, but it does not prevent the presence of a terminal aperture; sperm may penetrate in the space between the two separated sheets ( Fig. 13 ).

5) I n t h e g e n u s C r y p t o d r o m i a S t i m p s o n, 1858 sensu lato, the two phragmae of the endosternite 7/8 do not join, being sometimes significantly opened in their half distal part. In C. tuberculata Stimpson, 1858 ( Fig. 27B ), the margins of the suture 7/8 are distinctly raised, there is a wide, long slit, and the rounded aperture is located on the summit of a strong tubercle.

In the Dromiacea, due to the shortness or the lengthening of sutures 7/8, the spermathecal apertures are situated either just below or slightly behind the female gonopores on the P3 coxae ( Homolodromiidae pro parte, Dynomenidae ) or approximately opposite the P3 coxae ( Sphaerodromiinae , Stebbingdromia and Frodromia ). Or they extend slightly beyond and are not very far from the female gonopores ( Homolodromiidae pro parte, Hypoconchinae ) or extend far forward in leaving a great gap between the spermathecal apertures and the female gonopores and also the storage chambers (most Dromiinae ).

Figures

FIG. 4. — A, B, Metadynomene tanensis (Yokoya, 1933), female 20.5 × 21.9 mm, New Caledonia (MNHN-B 26576); C, D, Dynomene pilumnoides Alcock, 1900, female 12.4 × 14.5 mm, Madagascar (MNHN-B 6913); A, C, thoracic sternum; B, D, axial skeleton, with connections by fusion. Abbreviations: a, spermathecal aperture at extremity of sternal suture 7/8; br, transverse bridge; cx3, P3 coxae; g, female gonopore; i.p., intertagmal phragma; 1-3, sternites 1-3; 4-8, sternites 4-8; 7/8, thoracic sternal suture 7/8. Scale bars: 5 mm.

FIG. 17. — Sphaerodromia lamellata Crosnier, 1994, ovigerous female 36.4 × 36.2 mm, New Caledonia, Norfolk Ridge (MNHN- B 28389). See Guinot & Tavares (2003: fig. 21C as S. ducoussoi McLay, 1991) for the peculiar location of the spermathecae; A, axial skeleton, with connections by fusion; B, detailed view of posterior part. Abbreviations: br1, anterior transverse bridge; br2, posterior transverse bridge; cx3, P3 coxae; i.p., intertagmal phragma. Scale bar: A, 1 cm.

FIG. 3. — Homolodromia kai Guinot, 1993, female 12.4 × 8.3 mm, Indonesia, Kai Islands (MNHN-B 22704); A, thoracic sternum; B, axial skeleton, with spermathecal bulb visible but short spermathecal tube not discernible; C, detail of A, left posterior part; D, detail of B, left posterior part. Abbreviations: a, spermathecal aperture at extremity of sternal suture 7/8; b, bulb; i, connections by interfingering; i.p., intertagmal phragma; 4-8, sternites 4-8; 7/8, thoracic sternal suture 7/8. Scale bars: A, B, 4 mm; C, D, 2 mm.

FIG. 1. — Modified thoracic sternum and long sutures 7/8 of the female of an unidentified dromiid (probably Lauridromia sp.) (Dromiidae, Dromiinae) (MNHN) (see Tavares 1994: fig. 37C, D); A, external view, with spermathecal aperture at level of P1; B, internal view, most of interosternites 4/5-7/8 removed, showing internally closed tube. Abbreviations: a, aperture of the spermatheca at extremity of sternal suture 7/8; a.c., arthrodial cavity of P3; i4/5-i7/8, interosternites 4/5-7/8; s, location of the spermathecal pocket or chamber; t, spermathecal tube; 4-8, sternites 4-8; 6/7, 7/8, thoracic sternal sutures 6/7, 7/8. (Courtesy of S. Secretan and M. Tavares).

FIG. 2. — The three main internal parts of a typical dromiacean spermatheca, after the removal of the skeleton, median view, Dromia marmorea Forest, 1974 (Dromiidae, Dromiinae), female 57 × 72 mm, Azores (MNHN-B 21900). Abbreviations: a, communication with exterior by spermathecal aperture; b, bulb; c, chamber; t, spermathecal tube. Scale bar: 0.5 cm.

FIG. 6. — Details of the spermatheca of Dromia marmorea Forest, 1974 (Dromiidae, Dromiinae), female 57 × 72 mm, Azores (MNHN- B 21900); A, posterior part of axial skeleton in median view to show spermatheca in situ; B, details of foldings at level of the spermathecal bulb; C, lateral view, skeletal parts removed; D, vertical view of spermathecal chamber, cut to show sperm inside. Abbreviations: a, communication of the spermatheca with exterior; b, bulb; c, chamber, uneven surface of inner wall; e5, episternite 5; en 6/7, endopleurite 6/7; is 6/7, interosternite 6/7; t, spermathecal tube. Scale bars: A, C, 1 cm.

FIG. 7.— Dromia personata (Linnaeus,1758),female 64.2 × 77.1 mm, France (MNHN-B 21971); A, axial skeleton, dorsoventral view, spermathecae in situ, bulb and chamber visible; B, posterior part enlarged, tube discernible on the bottom. Abbreviations: b, bulb; br, transverse bridge; c, spermathecal chamber; i.p., intertagmal phragma; t, spermathecal tube; 8, sternite 8. (See Secretan 1998: fig. 11). Scale bar: A, 1 cm.

FIG. 8. — [Dromia] dormia (Linnaeus, 1763), female 107 mm carapace length, New Caledonia (MNHN-B 26439); A, thoracic sternum; B, detailed part view of spermatheca, skeletal parts removed. Abbreviations: b, bulb; b.t., basal thickening; c1, soft part of spermathecal chamber; c2, rigid part of spermathecal chamber; cx3, P3 coxa; e4, e5, episternites 4, 5; g, female gonopore; p, pit; r, ridge between the two pits; 4-8, sternites 4-8; 4/5-7/8, thoracic sternal sutures 4/5 to 7/8. Scale bar: A, 1 cm.

FIG. 9. — [Dromia] dormia (Linnaeus, 1763), female 88 × 105.8 mm, New Caledonia (MNHN-B 26438); A, anterior part of thoracic sternum (see Fig. 8A), showing terminal part of sutures 7/8 forming two pits; B, detailed view of pits; C, schematic section at level of the pits. Abbreviations: cx1, P1 coxa; e4, episternite 4; l, weakly calcified lateral parts of the pits; p, pit; r, ridge between the two pits; t, location of spermathecal tube; 4, sternite 4; 7/8, thoracic sternal suture 7/8. Scale bars: 5 mm.

FIG. 10. — [Dromia] wilsoni (Fulton & Grant, 1902), female 35 × 47.8 mm, Marquesas Islands (MNHN-B 26480); A, thoracic sternum; B, axial skeleton, dorsoventral view, spermathecae not visible. Abbreviations:a, spermathecal aperture; br, transverse bridge; cx3, P3 coxa; e4, e5, episternites 4, 5; g, female gonopore; i.p., intertagmal phragma; 4, sternite 4; 7/8, thoracic sternal sutures 7/8. Scale bars: 1 cm.

FIG. 11. — A, Takedromia cristatipes (Sakai, 1969), ovigerous female 19.8 × 21.6 mm, New Caledonia (MNHN-B 26420), axial skeleton; B, Epigodromia areolata (Ihle, 1913), female 12.2 × 13.3 mm, New Caledonia (MNHN-B 26336), thoracic sternum. Abbreviations: a, spermathecal aperture; br, transverse bridge;cx3, P3 coxa; e4, e5, episternites 4, 5; g, female gonopore; i.p., intertagmal phragma; s, spermathecal chamber; 4, 8, sternites 4, 8; 7/8, thoracic sternal suture 7/8. Scale bars: A, 4 mm; B, 1 mm.

FIG. 13. — Lauridromia intermedia (Laurie, 1906), female 37.3 × 35.4 mm, New Caledonia (MNHN-B 26441); A, thoracic sternum; B, C, two views of the tubercle bearing spermathecal aperture (notice that the two sheets of the phragma 7/8 are not completely joined in their terminal parts). Abbreviations: a, spermathecal aperture; cx1-cx3, cx5, P1, P2, P3, P5 coxae; g, female gonopore; o.p., opened part of the phragma 7/8; s.p., sperm plug; t, tubercle; 4-8, sternites 4-8; 5/6-7/8, thoracic sternal sutures 5/6 to 7/8. Scale bars: A, C, 2.5 mm; B, 5 mm.

FIG. 14. — Lauridromia dehaani (Rathbun, 1923), female 52 mm length, Madagascar (MNHN-B 6868), spermatheca in lateral view, skeletal parts removed. Abbreviations: a, location of the spermathecal aperture on sternum; b, bulb; b.t., basal thickening; c, spermathecal chamber; s8, internal surface of sternite 8; t, spermathecal tube. Scale bar: 1 mm.

FIG. 15. — Sternodromia spinirostris (Miers, 1881); A, female 40 × 41 mm, Gulf of Guinea (MNHN-B 22052), thoracic sternum showing sperm plug around slits of the spermathecae; B, female 34 × 37.2 mm, Gulf of Guinea (MNHN), detailed view of anterior sternal plate. Abbreviations: a, spermathecal aperture; cx1, cx5, P1, P5 coxae; e5, episternite 5; g, female gonopore; sl, slit; s.p., sperm plug; t, tubercle; 4-8, sternites 4-8; 5/6-7/8, thoracic sternal sutures 5/6 to 7/8. Scale bar: A, 2.5 mm.

FIG. 16. — Hypoconcha panamensis Smith, 1869, female approximately 30 mm width, Mexico, Cabo San Miguel (MNHN-B 20865); A, thoracic sternum; B, detail of posterior part; C, axial skeleton, not dissected so that spermathecae are not visible. Abbreviations: a, spermathecal aperture; br, transverse bridge; c, crest surrounding spermathecal aperture; cx1, cx3, P1, P3 coxae; e4, e5, episternites 4, 5; g, female gonopore; i.p., intertagmal phragma; m, membranous zone separating the flat anterior sternal part from tilted last sternites; 4, 8, sternites 4, 8; 7/8, thoracic sternal suture 7/8. Scale bars: A, C, 4 mm.

FIG. 12. — Frodromia? atypica (Sakai, 1936), ovigerous female 10.6 × 9.9 mm, New Caledonia, McLay det. (MNHN-B 26360); A, thoracic sternum; B, thoracic axial skeleton, with endopleurites cut away at left to expose spermatheca. Abbreviations: a, spermathecal aperture at extremity of sternal suture 7/8; b, bulb; bo, flat bottom of the sterno-abdominal depression; br, transverse bridge; cx1, cx3, P1, P5 coxae; e4, e5, episternites 4, 5; g, female gonopore; i.p., intertagmal phragma; sr, spur on P3 coxa; s8, internal surface of sternite 8; tb, tubular process on P3 coxa; 4, 8, sternites 4, 8; 7/8, thoracic sternal suture 7/8. Scale bars: 1 mm.

FIG. 27. — A, Homolodromia bouvieri Doflein, 1904 (Homolodromiidae), ovigerous female 33 × 26 mm, Madagascar (MNHN- B 28940), thoracic sternum (sternites 1-3 not drawn); B, Cryptodromia tuberculata Stimpson, 1858 (Dromiidae), ovigerous female 9 × 10 mm (with large eggs), New Caledonia, Karembé, McLay det. (MNHN-B 26387), spermathecal apertures as long opened slits. Abbreviations: a, spermathecal aperture; cx1-cx5, P1-P5 coxae; e4, e5, episternites 4, 5; g, female gonopore; sl, slit; t, tubercule; 4-8, sternites 4-8; 6/7, 7/8, thoracic sternal sutures 6/7, 7/8. Scale bar: A, 5 mm; B, 2.5 mm.