Pseudechiniscus novaezeelandiae ( Richters, 1908 )

Tumanov, DV, 2020, Analysis of non-morphometric morphological characters used in the taxonomy of the genus Pseudechiniscus (Tardigrada: Echiniscidae), Zoological Journal of the Linnean Society 188, pp. 753-775 : 768-770

Pseudechiniscus novaezeelandiae ( Richters, 1908) s.l.

The problematic status of this species is recognized ( Fontoura et al., 2010; Kaczmarek et al., 2015). Currently it includes several forms with an unclear status described from different zoogeographic regions and attributed to P. novaezeelandiae s.l. by different authors ( Ramazzotti & Maucci, 1983; Degma et al., 2009 –18).

Pseudechiniscus novaezeelandiae s.s. was described by Richters (1908) from the North Island, New Zealand. The description is short, but clear, and is accompanied by a photograph of a specimen in toto and a drawing of the pseudosegmental plate ( Richters, 1908). To note, Richters did not mention any lateral papillae in the species description. On the contrary, he stated that ‘ Ausser den üblichen Borsten neben der Sinnespapille an der Schnauze und dem Borstenpaar vor II keine Anhänge ’ [‘Apart from the usual bristles next to the sensory papilla on the snout and the bristle pair before II no attachments’] ( Richters, 1908: 205). It seems unlikely that Richters could have missed these structures considering that several years earlier he described lateral papillae in P. conifer ( Richters, 1904a, b).

Two years later, Murray (1910) attributed to this species specimens found in New Zealand, Australia and Hawaii. He tried to emend Richters’ diagnosis, but his additions were mainly based on the Australian material and he presented drawings of the Australian and Hawaiian specimens only. Murray (1910) noted lateral papillae in P. novaezeelandiae , but commented that these structures were not seen in the New Zealand material. He also reported a spine on legs I, which had not been mentioned in Richters’ description. The dorsal plate pattern in his drawings is different from that described by Richters (1908). At that time, a high variability of species with a world-wide distribution was a dominant concept in the tardigrade taxonomy, while nowadays such differences are considered as species-specific ( Faurby et al., 2011; Guidetti et al., 2016, 2019; Stec et al., 2018). Later, Richters (1911) reported a single specimen of P. novae-zeelandiae (sic!) from South America ( Colombia), but did not provide any detailed description or drawing noting only ‘ Von Murray auf Hawai beobachtet ’ [‘Seen by Murray on Hawaii’] ( Richters, 1911: 276). We may assume that this specimen was similar to Murray’s material from Hawaii but Murray’s specimens, given their morphological distinctiveness, would currently be attributed to a different species than P. novaezeelandiae (see above).

Marcus also adhered to the idea of a great intraspecific variability in tardigrades in his influential monographs ( Marcus, 1929, 1936). His diagnosis for P. novaezeelandiae was based on Murray’s description and drawings, and so the presence of lateral papillae was accepted as typical of the species. Marcus (1936) synonymized P. marinae BartoŠ, 1934, a species described from a very distant zoogeographic region (Europe, Moravia), with P. novaezeelandiae , accepting it as P. novaezeelandiae forma marinae . According to the description of BartoŠ, P. marinae is characterized by the presence of lateral papillae and a spine on legs I, and an extremely developed relief on the caudal plate and lateral teeth of the pseudosegmental plate, which is a unique feature within Pseudechiniscus .

Marcus’s monograph was the basis of the tardigrade taxonomy for a long time. His diagnoses were accepted mostly uncritically and so Murray’s description of the Australian specimens was treated as representing the species described by Richters from New Zealand. The situation became more complicated when Iharos (1963) published the descriptions of two new forms of P. novaezeelandiae , forma aspinosa and forma laterospina, from Argentina. Both these new forms have no lateral papillae and no spines, only blunt lobes on the pseudosegmental plate. Iharos included Murray’s drawing of P. novaezeelandiae designating it as ‘forma typica ’. He also presented a drawing of a form, named in the legend as ‘f. dorsospinosa Richt.’ ( Iharos, 1963; Fig. 2B), without giving any diagnosis or description. This name probably refers to the form described by Richters. The source of the depicted specimen is unclear, but in comments to table 1 ( Iharos, 1963: 295), Iharos stated that P. novaezeelandiae was represented in his material by three forms and that the typical form was absent. So, it may be assumed that specimens attributed to P. f. dorsospinosa were also found in the material from Argentina except the two new forms described in the paper. The drawing by Iharos is different from the description of Richters: there are no spines, but lobes are present on the pseudosegmental plate, and the shape of the third median plate is different and could not belong to the species described by Richters.

Horning et al. (1978) reported specimens of P. novaezeelandiae from New Zealand that corresponded perfectly to the description of Richters. A reinvestigation of this material ( Pilato et al., 2005) revealed striations between the dots of the cuticular sculpture, but other characters, such as the absence of lateral papillae or spines on legs I, matched the original description.

Jørgensen et al. (2011) sequenced COI, 18S rRNA and 28S rRNA markers from specimens from Chile and attributed these specimens to P. novaezelandiae (sic!). However, the presence of this species in South America is doubtful (see above) and most published findings of P. novaezeelandiae in this region are poorly documented ( Heinis, 1914; du Bois-Reymond Marcus, 1944; Séméria, 1993; Garitano-Zavala, 1995; Jerez Jaimes & Narváez Parra, 2001; Nickel et al., 2001). The only record of a South American Pseudechiniscus similar to the original description is found in the publication of Grigarick et al. (1983) and derives from Venezuela. The authors compared their material with New Zealand specimens and reported that, in general, they were similar, but also noted the presence of the basal spurs on the inner claws, which are absent in P. novaezeelandiae ( Horning et al., 1978; Pilato et al., 2005). It is likely that they compared their Venezuelan material with New Zealand specimens representing a yet undescribed species of the genus Pseudechiniscus . This assumption is supported by the presence of the specimen from New Zealand exhibiting basal spurs on the claws and attributed to P. novaezeelandiae in the collection of Maucci (slide 6859). This means that the sequences published by Jørgensen et al. (2011) cannot be attributed to P. novaezeelandiae until this material is reinvestigated and its identity to the original description is confirmed. Specimens of Pseudechiniscus found in Australia by Sandra Claxton and attributed to P. novaezeelandiae also have some differences compared to the original description (S. Claxton, pers. comm.).

Summarizing, only New Zealand specimens conforming to the original description by Richters (1908) with corrections by Pilato et al. (2005) should be considered as nominal P. novaezeelandiae . The presence of this species in other regions should be confirmed by new findings or a reinvestigation of the material in collections. Specimens described by Murray (1910) from Australia and Hawaii should be considered as belonging to a new, yet undescribed species. The taxa described as P. novaezeelandiae forma aspinosa Iharos, 1963, P. novaezeelandiae forma laterospina Iharos, 1963 and P. novaezeelandiae forma dorsospinosa Iharos, 1963 are, in my opinion, yet undescribed species of the genus Pseudechiniscus and should be considered as nomina dubia until the investigation of the type material of these forms is performed. Pseudechiniscus novaezeelandiae forma marinae BartoŠ, 1934 should be re-evaluated as a bona species Pseudechiniscus marinae BartoŠ, 1934.