HOMOLODROMIIDAE Alcock, 1900

Guinot, Danièle & Quenette, Gwenaël, 2005, The spermatheca in podotreme crabs (Crustacea, Decapoda, Brachyura, Podotremata) and its phylogenetic implications, Zoosystema 27 (2), pp. 267-342 : 278-280

Family HOMOLODROMIIDAE Alcock, 1900

The family Homolodromiidae , considered to be monophyletic, consists of only two genera, Homolodromia A. Milne-Edwards, 1880 , and Dicranodromia A. Milne-Edwards, 1880 , with some 20 extant species, relatively rare but distributed in major oceans ( Guinot 1993a, 1995: figs 39-41), including New Zealand waters ( Dawson 2002). Numerous ancestral homolodromiids constitute the closely related, exclusively fossil family Prosopidae , known from the Early Jurassic (including Eoprosopon klugi Förster, 1986 ) but that disappeared at the early Palaeocene ( Müller et al. 2000). The genus Homolodromia is known since the Upper Cretaceous of New Zealand (Feldmann 1993; Feldmann & McLay 1993).

Scholtz & Richter (1995) supported the primitive status of the Homolodromiidae but went so far as regarding homolodromiids as the sistergroup of all other Brachyura . They have since, however, returned homolodromiids to the Dromiacea (Scholtz & Richter, oral statement in the 2nd European Crustacean Conference, Liège 1996). The extant homolodromiid representatives show a great number of plesiomorphic characters that supports the contention that the family probably contains the most primitive members of the Podotremata .

The male abdomen, which completely fills the sterno-abdominal depression, maintains vestigial pleopods and markedly extended abdominal pleurae. The thoracic sternum has its sternites distinctly layered, with exclusively lateral but visible sutures. Sutures 7/8 are more or less situated laterally along the species and are sometimes very convergent, as in Dicranodromia foersteri Guinot, 1993 (Guinot 1995: fig. 17d). They end either far back on the plate behind level of P3 coxae ( Homolodromia kai ; H. robertsi Garth, 1973 ; Dicranodromia karubar Guinot, 1993 ) or approximately at the level of the P3 coxae ( H. bouvieri Doflein, 1904 , see Fig. 27A; D . aff. foersteri Guinot, 1993; D. nagaii Guinot, 1995 ; D. felderi ), or extend slightly beyond (notably D. spinosa Martin, 1994 ) (Guinot 1995: 182, figs 6, 10C, 12C, 14b, 16C, 17d, 28b, 32c, d, 33, 37b-g). The spermathecal apertures are generally tiny, rounded or slightly ovate, and diversely (along the species) accompanied by a sternal tubercle or a thickening ( Gordon 1950: fig. 1; Guinot 1995: 182). In a recently examined female of D. spinulata Guinot, 1995 from Fiji Islands (MNHN-B 28901), however, the terminal spermathecal apertures are each replaced by a long slit (about half the length of the suture 7/8) because of the two sheets of endosternites 7/8 that do not join in their subterminal parts.

It should be noted that Homolodromia species show relatively distinct patterns of the sutures 7/8. Sutures 7/8 are regularly curved to converge medially and their apertures are located, in the middle of a ring, posteriorly to the gonopores on the P3 coxae (as in H. kai ; see Guinot 1995: fig. 10C; and Fig. 3A ). Or they are oblique and open behind the females gonopores (as in H. robertsi Garth, 1973 ; see Guinot 1995: fig. 6), or they run along the margins of the sternum, being almost vertical, and open each on the summit of a strong tubercle at the level of the P3 gonopores (as in H. bouvieri ; see Fig. 27A ). Further investigations are needed to clarify the systematics of the genus Homolodromia .

In the family Homolodromiidae , the tip of a male second gonopod was found broken-off in the spermathecal apertures (on one side or on both sides) of some females (Guinot 1995: 178, 182, fig. 6), an indication that the long G2 enters the spermatheca and can be used for an internal insemination (see discussion below). In other species (for example in an ovigerous female of Dicranodromia foersteri , MNHN-B 24866) a small amount of brownish sperm protrudes from the two apertures.

In the homolodromiid axial skeleton ( Fig. 3B, D ), the connections still occur by interfingering, i.e. by simple digitations, a condition encountered in the Nephropidae ( Drach 1959, 1971; Guinot 1979a; Secretan 1998; Secretan-Rey 2002) and in most Decapoda . Endosternites are not grouped in a single mass but join each other transversally metamere by metamere. All parts are regularly layered. A large intertagmal phragma (which links the tagma/thorax to the tagma/abdomen) extends toward the last endosternite and joins it.

A carrying behaviour of members of the family, similar to that of the Dromiinae and Sphaerodromiinae , is now documented, always with a sponge, in Dicranodromia doederleini Ortmann, 1892 ( Ikeda 1998) , in D. felderi Martin, 1990 ( Martin & Zimmerman 2001) and in Homolodromia kai Guinot, 1993 ( Ho & Ng 1999).

Figures

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.

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.