Karumballichirus sp.
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publication ID |
https://doi.org/10.4202/app.01112.2023 |
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persistent identifier |
https://treatment.plazi.org/id/774EBE08-DC15-FF8C-812F-FE6024F3FE91 |
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treatment provided by |
Felipe |
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scientific name |
Karumballichirus sp. |
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Fig. 7 View Fig .
Material.—MSNM i28030 (collective number), one entire right major cheliped dactylus and two fingertips of left major cheliped dactyli. It was collected in the surrounding of the village of Berivotra, ca. 50 km S of the city of Mahajanga, NW Madagascar where the Berivotra Formation of the late Maastrichtian age crops out ( Rogers et al. 2000). Brief overview of the accompanying fauna (including other decapods) was presented by Garassino and Pasini (2003).
Description.—Major cheliped dactylus long and slender, approximately seven times longer than tall. Upper margin proximally adorned with tubercles and with five complex pores accommodating tufts of setae during life. Lateral surfaces tuberculated proximally and adorned with complex setal pores; outer lateral surface with two distinct rows of tubercles positioned in the upper half and five large elongated setal pores perpendicular to the dactylus-longitudinal axis; inner lateral surface with tubercles arranged in less-distinct rows and adorned with setal pores with oval outline. Occlusal margin armed with a number of teeth; complex molariform protuberance positioned proximally with four blunt teeth and followed by a gap, two peg-like blunt teeth of unequal length, another gap and a saw-like series of 10+ teeth ending with a sharp curved fingertip.
Remarks.—The studied material is fragmentary, no propodus is preserved. Identification based on isolated dactyli of decapod crustaceans may prove difficult; in the present case, however, we argue for assignment to ghost shrimps, and the genus Karumballichirus in particular, based on the following characters:
(i) arrangement of setal pores; ghost shrimps often have large setal pores on the dactylus of the major cheliped, especially on the upper margin and outer lateral surface. In representatives of Karumballichirus (e.g., Dworschak 2008: figs. 4b, 5k), Lepidophthalmus (e.g., Felder and Manning 1997: figs. 1b, 3a, 4d, f) and Callianopsis Saint Laurent, 1973 ( Schweitzer Hopkins and Feldmann 1997: fig. 4A, B), to name a few examples, they are elongated and oriented perpendicularly to the longitudinal axis of the dactylus. This character is also present in many ghost shrimp fossils (e.g., Schweitzer Hopkins and Feldmann 1997: fig. 7D; Hyžný and Klompmaker 2015: fig. 4D; Hyžný et al. 2016a: figs. 5, 6D). Moreover, dactyli from Madagascar show rather complex setal pores which, during life, accommodated tufts of setae, a condition which is common in extant ghost shrimps (e.g., Felder and Manning 1997; Dworschak 2008, 2011a, b). Similar setal pores can be found in some hermit crabs ( Komai and Rahayu 2014; Fraaije et al. 2015; Hyžný et al. 2016b), their chelae, however, have a completely different general morphology, usually having robust, suboval propodi with short fingers ( McLaughlin 2003);
(ii) curvature of the dactylus; ghost shrimps have major cheliped dactyli curved inward in a specific manner; the proximal portion is relatively straight whereas curvature is present in the distal portion close to the tip ( Klompmaker et al. 2016a: figs. 14R, 14T, 15C–D);
(iii) dentition; decapod crustaceans are highly variable in the shape of chelipeds and development of their dentition ( Schäfer 1954; Glaessner 1969). Often, dentition is regular along the occlusal margin of the fingers. Many ghost shrimps have highly irregular “tooth formulae”, often with large blunt molariform teeth positioned proximally and many near-equal teeth positioned close to the tip (e.g., Pillai 1954; Sakai 1969; Hyžný 2012; Hyžný and Hudáčková 2012; Hyžný and Muñiz 2012). Additionally, a strongly hooked dactylus is rather typical for ghost shrimps (e.g., Sakai 1969; Manning and Felder 1991; Hyžný and Hudáčková 2012), whereas it is fairly uncommon among brachyurans (see some representative figures in Ng et al. 2008 and in Poore and Ahyong 2023). The dentition of the studied dactyli from Madagascar is similar to several fossil and extant ghost shrimps (see discussion below).
The material from Madagascar exhibits a strong resem- blance to ghost shrimps of the genus Karumballichirus (as discussed above). Although it most probably belongs to a species yet unknown to science, the material is simply not sufficient to justify the erection of a new taxon. In ghost shrimps, intraspecific variation and sexual dimorphism is commonly expressed in the morphology of the major pereiopod 1 dactylus (as discussed in detail by Hyžný and Klompmaker 2015). Therefore, assignment of the dactyli from Madagascar to the species level must await the discov- ery of more complete material.
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