Tuerkayana latens Ng and Hsi-Te Shih 2023, n. sp.

Tuerkayana latens n. sp.

(Figs. 3, 4, 7C, D, 8F, 9D, 10D, H, 11D, H, L) urn:lsid:zoobank.org:act: 238242FD-2DD3-4AAD-901E-0362737978D4

Cardisoma rotundum – Türkay 1974a: 234, figs. 1, 14 (part); Poupin 1994: 54, pl. 6g; Poupin 1996: 66.

Discoplax rotunda – Poupin 2010: 42 (part); Poupin and Juncker 2010: 56 (part); PKL Ng and Shih 2015: 382. (not Thelphusa rotunda Quoy & Gaimard, 1824).

Material examined: Holotype: male (52.8 × 42.7 mm) (MNHN-IU-2011-5594), Niau Atoll, Tuamotu, French Polynesia, coll. J. F. Butaud, 2006. Others: Pitcairn Islands – 1 dried carapace (right side broken off) (75.2 × 56.7 mm) (UF 5457), North Beach, Henderson Island, coll. S. Waldren, 1 January 1997.

Diagnosis: Frontal region covered with small granules; epigastric, epibranchial and anterior part of mesobranchial regions with scattered low granules and low striae, surface appears relatively smoother; mesogastric, metagastric regions smooth; posterior part of meso-, metabranchial regions with few oblique striae and granules; epigastric regions prominent, margin relatively sharp; postorbital cristae strong, separated from epigastric by shallow concavity; external orbital tooth broadly triangular, margin confluent with anterolateral margin, separated by small cleft (Figs. 3A, B, 7D). Merus of third maxilliped subovate, as long as wide (Fig. 7C). Surfaces of adult chelae with low granules on margins, punctate to rugose (Fig. 9D). Ambulatory legs short; ratios of maximum length to maximum width of third and fourth ambulatory meri 2.5, 2.4, respectively; surfaces covered with striae, appears rugose; dorsal margin of merus rugose, uneven; lateral margins of propodus, dactylus lined with strong, stiff spines or setae (Figs. 3A, 10D, H). Male pleon relatively broad; somite 6 wider than long, lateral margins strongly convex (Figs. 8G). Adult G1 almost straight, when viewed from ventral perspective; distal part curved at angle of about 45° from vertical; distal part of outer margin forming gentle shelf–like structure; base of the distal part not obviously tapering, with outer margin gently curving to meet truncate tip in dorsomesial view, in ventral view, outer margin almost straight, with flange wide, distinctly developed (Fig. 11D, G, L).

© 2023 Academia Sinica, Taiwan

© 2023 Academia Sinica, Taiwan

Colour: Not known.

Distribution: Tuamotu Islands and Pitcairn Islands (Fig. 13).

Etymology: The species name is from the Latin word “latens”, for hidden and concealed; alluding to how the taxon has eluded formal discovery until now.

Remarks: Tuerkayana latens n. sp. is morphologically close to T. rotundum. While there is good series of specimens of T. rotundum from a wide geographical range, unfortunately, we have only been able to study only one intact specimen of T. latens which limits our comparisons. That being said, the carapace of T. latens is still distinct in that the orbital and anterolateral regions are all distinctly smoother (Fig. 3A, B). In T. rotundum, these regions are almost always densely covered granules and rugae, giving the surface a very rough appearance (Fig. 4A, B, D, E). There are a few specimens which have fewer granules in these areas and the carapaces appear smoother (Fig. 5C, F), but these are still rougher than what is observed in T. latens. A more subtle difference is that the gastric regions in T. latens are more swollen with the surface more convex in frontal and lateral views (Figs. 3C, 7D); in T. rotundum, the gastric regions are only gently convex and relatively less swollen (Figs. 6, 7B). In addition, the merus of the third maxilliped of T. latens is proportionately wider than adult specimens of T. rotundum examined (Fig. 7C versus Fig. 7A). The male pleon shapes vary too substantially for this character to be used; in T. rotundum, somite 6 in particular, varies from having gently convex lateral margins (Fig. 8A, C) to strongly convex ones (Fig. 8B, D, E). The G1s of the two species, while superficially similar, differ in one major aspect. In T. rotundum, the distal part of the G1 gently curves towards the corneous tip, and in dorsomesial view, the basal part tapers gradually to the truncate tip, the outer margin appearing gently concave in ventral view and only forming a narrow triangular flange (Fig. 11A–C, E–G, I–K). In T. latens, however, the distal part of the G1 does not taper much, with the outer margin gently curving to meet the truncate tip in dorsomesial view, and in ventral view, the outer margin is almost straight with the flange wider and distinctly more developed (Fig. 11D, G, L). None of the male specimens of T. rotundum examined has a G1 that resembles that of T. latens.

© 2023 Academia Sinica, Taiwan

The records of “ Cardisoma rotundum ” or “ Discoplax rotunda ” from Marquesas and Tuamotu by Poupin (1994, 1996, 2010) should all be referred to Tuerkayana latens. Poupin (1994: 54, pl. 6g) recorded one large female (64.5 × 50.0 mm) from Hatiheu Bay, Nuku Hiva, in the Marquesas but his specimen could not be located in MNHN at the time of the study. His figure of the carapace (Poupin 1994: pl. 6g), however, clearly shows the orbital and anterolateral regions being distinctly smoother than T. rotundum, and is the same as that for the holotype male of T. latens. Poupin’s (1994: fig. 50) drawing of the carapace was from De Man (1902: 548, as Cardisoma frontalis); that specimen was from the Loyalty Islands, so it is actually T. rotundum s. str.; it agrees in all aspects of the carapace features.

© 2023 Academia Sinica, Taiwan

The only specimen from the Pitcairn Islands is a partially damaged dried carapace so it is hard to be certain it is T. latens. On the basis of the relatively smooth dorsal carapace surface and the somewhat more convex gastric regions (Fig. 4), it agrees with the holotype male and is therefore referred to this species.