Heteroptychus, Baba, 2018

Baba, Keiji, 2018, Chirostylidae of the Western and Central Pacific: Uroptychus and a new genus (Crustacea: Decapoda: Anomura), Tropical Deep-Sea Benthos (Mémoires du Muséum national d'Histoire naturelle 212), pp. 1-612 : 570-572

HETEROPTYCHUS n. gen.

ETYMOLOGY„ From the Greek heteros (different), plus the last syllables of Uroptychus (ptychos = plate). The gender is masculine.

Type species. Uroptychus scambus Benedict, 1902 .

DIAGNOSIS„ Carapace dorsal surface smooth and glabrous, lateral margin with anterolateral spine only, rarely with 1 or 2 processes along branchial region. Rostrum narrowly or broadly triangular. Pterygostomian flap very low on posterior half, height of posterior half 0.1-0.3 × that of anterior half. Sternal plastron different in sexes, posterior margin in females strongly excavated, with median parts of sternites 5-7 absorbed into sternite 4 (left and right parts of sternites 5-7 discontinuous, interrupted by loss of median parts). Antennal scale articulated or fused with article 2, not reaching distal end of article 4, articles 4 and 5 unarmed. P1 ischium with anterior dorsal process lobe-like or spiniform, posterior process usually lobe-like (rarely obsolescent). P4 very short, especially carpus 0.3-0.5 × length of P3 carpus. Distal two articles of P2-4 with long prehensile margins thickly fringed with setae, dactyli with slender spines perpendicular to flexor margin. G1 and G2 present.

REMARKS„ The new genus is established on the basis of the following characters: the female sternal plastron is strongly excavated on the posterior margin, with sternites 5-7 medially discontinuous; the pterygostomian flap is very low in the posterior half (the posterior height at most 0.3 times the anterior height, but usually slightly lower in the majority of Uroptychus species); and the P4 carpus is very short, at most half as long as the P3 carpus, whereas it is subequal to, slightly shorter or rarely longer in Uroptychus . In addition, it is noteworthy that the antenna is inclined laterally or posteriorly in most of preserved specimens.

The present proposal of the new genus is supported by molecular data that showed that Uroptychus is not monophyletic ( Roterman et al. 2013; Bracken-Grissom et al. 2013). Apparently U. scambus resides in a clade separate from other species of Uroptychus species, although the specific identity of U. scambus reported by these papers remains to be confirmed.

The unique shape of the sternal plastron, different in sexes in Uroptychus scambus , was first mentioned by Baba et al. (2009). This is also applicable to U. brevis Benedict, 1902 from the western Atlantic Ocean, the features confirmed by examination of the type material (holotype, ovigerous female, poc 5.2 mm, USNM 20566) of that species. Heteroptychus scambus is definitely a deep-sea species and has been believed to show a wide distribution from the western Indian Ocean to the western Pacific. However, molecular analyses (L. Corbari, personal comm.) suggest that there are some cryptic species, so that an attempt was made to detect morphological differences. Accordingly, slight differences that had been regarded as individual variations were validated as discriminating characters: the presence or absence of articulation between the antennal scale and article 2 and in the carapace shape, especially the rostrum and anterolateral spine. These characters delineate nine species including six new species, but no clear differences are found on other characters in all the material examined. However, there exist unstable characters in H. claudeae n. sp., i.e. the presence or absence of the lateral orbital spine, and the presence or absence of median processes of the anterior margin of sternite 3. In addition, color differences are found in morphologically identical specimens from Taiwan ( Baba et al. 2009). It is not unlikely that this species may contain cryptic species, for which extensive studies are required.

Two classical names pose a problem for establishing this new genus because of the brief species descriptions: U. scambus Benedict, 1902 and U. glyphodactylus MacGilchrist, 1905 . Examination of the holotype of Uroptychus scambus from Japan now in the collection of the Smithsonian Institution has elaborated on its systematic status. However, the type material of U. glyphodactylus from the Andaman Sea now housed in the collection of the Zoological Survey of India could not have been examined, despite repeated queries to the director of the institution. Some of the morphological features of this species that were not described in MacGilchrist (1905) are interpreted from the illustrations given by Alcock & MacGilchrist (1905: pl. 70, fig. 4, pl. 71, figs 1, 1a, 1b, 1c, 1d) albeit not in sufficient detail: the antennal scale in the figure appears to be articulated with article 2. As shown in the key to species provided below, these two species key out in the same couplet. Given that these species are known from disjunct localities, it is not unlikely that they are different. However, they are treated as synonymous for the time being. Uroptychus edwardi Kensley, 1981 from off the east coast of South Africa was synonymized with U. scambus (see Baba, 1988), but it is validated in this paper, on the basis of differences in the rostrum and anterolateral spine of the carapace (see below under the remarks of H. colini n. sp.).

The genus now contains nine species, including six new species: eight from the Indo-West Pacific and one from the western Atlantic. Females of three species have not been collected ( H. apophysis n. sp., H. colini n. sp. and H. lemaitrei n. sp.).

KEY TO SPECIES

1. Antennal scale articulated with antennal article 2 ..................................................................................................... 2

– Antennal scale fused with antennal article 2 ................................................................................................................ 7

2. Branchial margin with 2 processes ............................................................................................... H. apophysis n. sp.

– Branchial margin smooth .................................................................................................................................................. 3

3. Anterolateral spine of carapace slightly overreaching apex of rostrum ............................. H. anouchkae n. sp.

– Anterolateral spine of carapace not overreaching apex of rostrum ........................................................................ 4

4. Rostrum not reaching apex of eye..................................................................................................................................... .................................................................. H. scambus ( Benedict, 1902) (= H. glyphodactylus (MacGilchrist, 1905))

– Rostrum overreaching eye ................................................................................................................................................ 5

5. Rostrum broad triangular, distally blunt ........................................................................................... H. paulae n. sp.

– Rostrum narrow triangular or distally spiciform ........................................................................................................ 6

6. Rostrum narrow triangular. Sternite 3 with pair of median processes ......................................... H. colini n. sp.

– Rostrum spiciform. Sternite 3 with median notch, with no median processes .... H. edwardi ( Kensley, 1981) 7. Rostrum and anterolateral spines distally blunt. P1 ischium with posterior dorsal lobe obsolescent ............. ............................................................................. H. brevis ( Benedict, 1902) [Western Atlantic; holotype examined]

– Rostrum and anterolateral spines sharply pointed. P1 ischium with posterior dorsal lobe overhanging basis ........................................................................................................................................................................................... 8

8. Carapace lateral margin smooth. Rostrum narrow, more or less depressed distally ........... H. claudeae n. sp.

– Carapace lateral margin with small protuberance at anterior end of branchial margin. Rostrum spiniform. ..................................................................................................................................................................... H. lemaitrei n. sp.