Typtonomenaeus, Marin, Ivan & Chan, Tin-Yam, 2013

Marin, Ivan & Chan, Tin-Yam, 2013, Typtonomenaeus formosanus gen. et sp. nov., a new sponge-associated pontoniine shrimp (Crustacea: Decapoda: Palaemonidae: Pontoniinae) from northern Taiwan, Zootaxa 3664 (1), pp. 45-56 : 46-47

Typtonomenaeus gen. nov.

Type species. Typtonomenaeus formosanus gen. et sp. nov., by present designation.

Included species. Presently monotypic, including a single species— Typtonomenaeus formosanus gen. et sp. nov.

Etymology. The genus is named to reflect its morphological similarity to two other sponge-associated pontoniine genera, both Typton Costa, 1844 and Periclimenaeu s Borradaile, 1915. Gender masculine.

Diagnosis. Medium-sized pontoniine shrimp with swollen, smooth, subcylindrical body. Carapace smooth, with antennal tooth, without hepatic or supraorbital teeth; rostrum well developed, reaching to distal margin of basal segment of antennular peduncle, sharply pointed distally, armed with teeth dorsally, ventrally unarmed. Abdominal somites unarmed, with tergites non-carinate; three last somites small, with feebly developed rounded pleurae, distoventral margins of the sixth somite with posterolateral process. Telson broad, strongly tapering distally, with 2 pairs of small dorsal spines, with straight posterior margin armed with 3 pairs of distal spines. Eyes well developed, with pigmented, rounded cornea; eyestalk swollen, cylindrical, without specific features. Antenna with scaphocerite substantially reduced, not reaching carpocerite, with small but well marked distolateral tooth. Mandible well developed, without palp. Maxillula with bilobed palp, with well developed lacinia. Maxilla with simple, tapering palp, with stout, well developed endites and well developed scaphognathite. Maxillipeds I and II normal, with well developed epipods and exopods. Maxilliped III normal, with rounded epipod and small arthrobranch. Pereiopod I relatively slender, without specific features. Pereiopods II unequal in size and slightly dissimilar in shape; minor pereiopod II generally similar in morphology but smaller in size; major pereiopod II with inner margin of ischium and merus armed with a double row of small sharp tubercles; carpus widening distally, hood-like distally excavate, distal margin not overlapping proximal part of propodus; palm convexive dorsally, proximal part subcylindrical in cross-section, not tapering, finely tuberculate distodorsally, distodorsal margin truncate, forming rectangular distodorsal angle; fixed finger (pollex) triangular, tapering distally and slightly curved, with well marked deep dorsal depression open proximally; movable finger with ventral margin forming a well marked plunger, distoventral angle armed with convex nail-like apex. Pereiopods III–V generally similar, smooth; dactylus biunguiculate, with ventral margin serrated, main unguis smooth, curved and sharp; accessory unguis triangular, sharp, about twice shorter than main unguis; segments of pereiopod V covered with simple setae; ventral margin of propodus unarmed. Pleopods normal; pleopod II of males with appendix masculina bearing 4 long simple setae laterally and a single long apical setae. Uropods not exceeding telson; lateral margin of uropodal exopod straight, with sharply produced distolateral angle and small curved distolateral spine; diaeresis simple.

Differential diagnosis. Presently, 22 pontoniine genera are known as sponge-associated. They are Anisomenaeus Bruce, 2010 , Apopontonia Bruce, 1976 , Climeniperaeus Bruce, 1995 , Epipontonia Bruce, 1977 , Exopontonia Bruce, 1988 , Hamiger Borradaile, 1916 , Holthuisaeus Anker & De Grave, 2010 , Isopericlimenaeus Marin, 2012, Nippopontonia Bruce & Bauer, 1997, Onycocaridella Bruce, 1981 , Onycocaridites Bruce, 1987 , Onycocaris Nobili, 1904 , Orthopontonia Bruce, 1982 , Onycomenes Bruce, 2009 , Paraclimenaeus Bruce, 1988 , Periclimenaeus Borradaile, 1915 , Periclimenoides Bruce, 1990 , Plesiomenaeus Bruce, 2009 , Poripontonia Fransen, 2003 , Thaumastocaris Kemp, 1922 , Typton Costa, 1844 and Typtonychus Bruce, 1996 (see Bruce & Bauer, 1997; Bruce, 2009b; Anker & De Grave, 2010; key in Bruce, 2010a; De Grave & Fransen, 2011; Marin, 2007, 2012). Probably, the monotypic genus Typtonoides Bruce, 2010 is also sponge-associated but its host is still unrecorded (Bruce, 2010b).

The new genus most closely resembles following Indo-West Pacific sponge-associated genera such as Anisomenaeus , Epipontonia , Exopontonia , Periclimenaeus , Periclimenoides , Plesiomenaeus and Typton having 1) dorsally armed rostrum; 2) normal, non-densely setose, maxilliped III (in contrast to Typtonychus ); 3) fingers of pereiopod II with structures resembling a plunger on movable fingers (dactyli) of both pereiopod II or the presence of an opposing fossa on the fixed finger of minor pereiopod I; 4) biunguiculate dactylus of pereiopod III; and 5) entire lateral margin of uropodal exopod (except some species of the genus Periclimenaeus (see Ďuriš et al, 2009)). Some of these genera show feeble development of some of above-mentioned features, especially the development of rostrum and the presence of well developed plunger on dactyli of both pereiopod II. Nevertheless, the new genus can be clearly distinguished from all of them by the following combinations of morphological features.

From the genus Anisomenaeus the new genus can be clearly separated by different shape of fingers of pereiopod I (subspatulate vs. simple in Anisomenaeus ) and different structure of fingers of pereiopods II, especially the presence of a well developed fossa on fixed finger (pollex) of minor pereiopod II (vs. simple fingers in Anisomenaeus ; see Bruce, 1978: fig. 3).

From the genus Exopontonia it can be clearly separated by well developed endites of maxilla (vs. complete reduction in Exopontonia ), the absence of a cutting lamina on movable finger of pereiopod I (see Bruce, 1988: fig. 5) and different shape of fingers of minor pereiopod II (see Bruce, 1988: fig. 4).

From the genus Typton the new genus can be separated by well developed rostrum, the presence of a developed distolateral tooth on scaphocerite of antenna (mostly reduced in Typton spp.) and the presence of a plunger on dactylus and well marked fossa on fixed fingers (pollex) of pereiopod II.

From the genera Epipontonia , Periclimenoides and Plesiomenaeus it clearly differs in the presence of a plunger on dactylus and a corresponding fossa on the opposable fixed finger of either pereiopod II. Furthermore, it is distinguished from Epipontonia by biunguiculate dactyli of ambulatory legs (simple in Epipontonia ).

The new genus mostly resemble representatives of the genus Periclimenaeus but clearly differs from all known species by antennula and antenna reduced in size (resembling the same in Typton but always well developed in Periclimenaeus ) and the presence of a broad carina on ventral margin of dactylus resembling “a plunger” with a well marked opposing depression (“fossa”) on the fixed finger (pollex) of minor pereiopod II ( Fig. 5 h, i). In conclusion, such structures of fingers of minor pereiopod II has not been previously reported among pontoniine shrimps and is unique within the subfamily Pontoniinae . Also the convex nail-like apices on dactyli of pereiopod II are of unique shape among pontoniine shrimps. However, some species of the genus Periclimenaeus possess the same structure of pereiopods II (for example, Periclimenaeus bidentatus Bruce, 1970 (Bruce, 1970) and Periclimenaeus djiboutensis (see Bruce, 1978: 258, fig. 29D)) but the type species of the genus, Periclimenaeus robustus Borradaile, 1915 , has different structure and generic status of the referred species should be verified. The main difference from the genus Periclimenaeus in the structure of appendix masculina. Male pleopod II has the appendix masculina mostly reduced in most of species presently belonging to the genus Periclimenaeus , while in the new genus it is well developed, elongate, with large apical and lateral setae.

Figures

FIGURE 5. Typtonomenaeus formosanus gen. et sp. nov., holotype, non-ovigerous female: a, b — major pereiopod II, general view; c – e — same, distal part of propodus and dactylus, different views; f — minor pereiopod II, general dorsal view; g – i — same, distal part of propodus and dactylus, different views.