Heteroaxianassa heardi, (Anker, 2011)

Anker, Arthur, 2020, Strianassa lerayi gen. et sp. nov., a new laomediid mud-shrimp from the eastern Pacific, with new records of Axianassa ngochoae Anker, 2010 and Heteroaxianassa heardi (Anker, 2011) in the western Pacific (Malacostraca: Decapoda: Gebiidea), Zootaxa 4820 (3), pp. 523-539 : 534-536

Heteroxianassa heardi ( Anker, 2011)

( Fig. 9 )

Axianassa heardi Anker 2011: 14 , figs. 9–14.

Heteroaxianassa heardi — Sakai 2016: 597.

Material examined. 1 male (cl 4.3 mm), MNHN-IU-2013-1466, Papua New Guinea, Madang lagoon, Panab Island , sta. PR203, 05°10.3′S– 145°48.5′E, sandy slope, depth: 1–5 m, scuba diving, suction pump, in burrow, leg. A. Anker, 7 December 2012 [fcn PZD-600C] .

Remarks. The relatively young but complete male specimen from Madang ( Fig. 9 ) represents the first record of H. heardi from Papua New Guinea. The species was previously known only from the holotype from Lizard Island, Great Barrier Reef, Australia, and Moorea Island, Society Islands, French Polynesia ( Anker 2011). The relatively broad and not anteriorly produced rostrum, the transverse suture of the uropodal exopod with a row of numerous small teeth and the unarmed distolateral margin of the uropodal exopod are the most obvious features that separate H. heardi from its only congener, H. japonica Komai, 2014 , presently known only from Japan ( Komai 2014).

The present author tentatively follows Komai & Fujita (2019), who recognised the validity of the genus Heteroaxianassa . Sakai (2016) separated Heteroaxianassa from Axianassa based on two differences, the marginally dentate rostrum and the presence of a dentate transverse suture on the uropodal exopod. Both Anker (2011) and Komai (2014), describing A. heardi and A. japonica , respectively, were well aware of these differences, but preferred not to establish a new genus awaiting a more comprehensive revision of the axianassid (now laomediid) genera. Anker & Pachelle (2016) stated: “The exact position of A. heardi and A. japonica , as well as S. [ Saintlaurentiella ] heterocheir, can only be clarified through a more comprehensive molecular analysis and complementarily, a rigorous cladistic analysis of morphological characters of all or most taxa currently assigned to the Laomediidae and Axianassidae … However, we feel that splitting Axianassa and describing a new genus for A. heardi and A. japonica based only on two characters, one of them being rather insignificant (dentate rostral margin) on a broader phylogenetic scale is not really necessary.” However, the same year, Sakai (2016), clearly in yet another act of his typical “nomenclatural mihilism” ( Dubois 2008; Evenhuis 2008), quickly claimed the genus Heteroaxianassa , using the previous authors’ hard descriptive work and without even examining material of the two component species.

The two characters used by Sakai (2016) to separate Heteroaxianassa from Axianassa are the same characters discussed by Anker (2011), Komai (2011) and Anker & Pachelle (2016), i.e. the marginally dentate rostrum and the presence of a transverse suture (diaeresis) on the uropodal exopod. These two characters need to be reassessed taking into the account all genera currently placed in the Laomediidae . In most species of Laomedia , the rostrum is dentate, i.e. the lateral margins of the rostrum are furnished with small, widely spaced teeth (e.g. Sakai 1962: pl. V, fig. 4; Ngoc-Ho 1997: fig. 1A). However, in one species, more precisely L. paucispinosa Ngoc-Ho, 1997, the rostral margins are largely smooth, except for one minute apical tooth ( Ngoc-Ho 1997: figs. 2C, 4C). Thus, the marginal dentition of the rostrum may be intragenerically variable within the family, as in the case of Laomedia (with most of the marginal teeth on the rostrum apparently secondarily lost in L. paucispinosa ). Furthermore, in Axianassa arenaria Kensley & Heard, 1990 , the rostrum also bears a minute apical tooth, described as “papilla” by Kensley & Heard (1990: fig. 5B). Consequently, the use of this character in the separation between the laomediid genera is at least questionable, as already pointed out by Anker & Pachelle (2016). Importantly, Strianassa gen. nov. is different from Laomedia and Heteroaxianassa by the presence of both marginal and dorsal dentition on the rostrum, this configuration being unique within the family. On the other hand, the presence or absence of a transverse suture (diaeresis) on the uropodal exopod may represent a more reliable character for the generic diagnoses in the Laomediidae . In Laomedia , Jaxea and Naushonia both uropodal rami have a well-developed, complete, i.e. extending from the mesial to the lateral margin of the ramus, transverse suture, typically armed with small teeth (e.g. Selbie 1914; Hgoc-Ho 1997; Anker 2014; Komai & Anker 2015). In Saintlaurentiella and Heteroaxianssa, only the exopod has a complete transverse suture armed with more or less widely spaced teeth; however, in H. japonica , the endopod also has an incomplete and unarmed suture running from the lateral tooth to about mid-width of the ramus (LeLoeuff & Intès 1974; Anker 2011; Komai 2014). Finally, in Axianassa and Strianassa gen. nov., the uropodal rami are lacking a transverse suture; however, in S. lerayi sp. nov., the exopod bears a row of transversally aligned teeth adjacent to its posterior margin ( Kensley & Heard 1990; Anker & Pachelle 2016; present study).

Based on the present morphological evidence, the two western Pacific species currently placed in Heteroaxianassa , viz. H. heardi and H. japonica , undoubtedly represent a small clade within the Laomediidae . In the two most likely phylogenetic scenarios, this clade either forms a sister clade to the remaining species of Axianassa or is embedded within Axianassa . Only in the first case, a generic status for this clade, i.e. Heteroaxianassa , is perhaps justifiable, defined mainly by the presence of a complete transverse suture on the uropodal exopod as the only intergenerically valid differentiating character. The description of Strianassa gen. nov. makes the phylogeny of the Laomediidae even more intriguing as the new genus shows clear affinities to both Axianassa and Heteroaxianassa , while also exhibiting several, possibly plesiomorphic features.

Figures

FIGURE 9. Heteroaxianassa heardi (Anker, 2011), male (cl 4.3 mm), MNHN-IU-2013-1466, from Madang, Papua New Guinea: A—living individual, dorsal view; B—same, lateral view. Photographs by the author.