Colossendeis megalonyx Hoek, 1881

Lucena, Ruda Amorim & Lindsey Christoffersen, Martin, 2022, Pycnogonida (Arthropoda) from Museu de Ciencias Naturais, Rio Grande do Sul, Brazil, Zoosystematics and Evolution 98 (2), pp. 305-312 : 305

Colossendeis megalonyx Hoek, 1881

Fig. 3

Colossendeis frigida Hodgson, 1902: 63.

Colossendeis rugosa Hodgson, 1907: 64, pl. IX, fig. 3, pl. X, figs 5, 6.

Colossendeis orcadense - Hodgson 1908: 184.

Colossendeis scoresbii Gordon, 1932: 18-21, figs 5c, 6b, c, 7a, b.

Material examined.

(FZB.Pyc-002) 1 female, South Atlantic , July 8, 1964; (FZB.Pyc-004) 5 females, off Mar del Plata , Argentina (38°22'S, 55°37'W), May 1961, col. L.R. Pontes; (FZB.Pyc-005) 1 female, Uruguay, Mar1961 .

Distribution.

Circumpolar. Antarctic, Western South America and up to Buenos Aires (Argentina), South Africa, Madagascar, New Zealand, Eastern South America ( Child 1995a; Munilla and Soler-Membrives 2009; Scarabino et al. 2019). This is the first record for Uruguayan waters.

Depth.

7 to 4900 m in depth.

Remarks.

Colossendeis megalonyx is a very variable species ( Fry and Hedgpeth 1969; Child 1998b) and may represent a group of cryptic species. Only the long proboscis, palp article 8 shorter than articles 9 and 10 and a tarsus longer than the propodus remain stable amongst all examined specimens ( Child 1995a). Variable characters are the shape and size of the ocular tubercle (elevated or short, conical or rounded), the occurrence of eyes (similar in size or larger anteriorly, well pigmented, white or even absent), the size of the proboscis (equal to, or longer than the trunk) and the size of the legs (either the femur or the tibia represent the longest article) ( Child 1995a, 1998b; Cano-Sanchez and López-González 2007).

Molecular studies confirm that a complex of species exists under the name C. megalonyx . Five species and another seven cryptic species were indicated ( Krabbe et al. 2010; Dietz et al. 2015; Dömel et al. 2020). These papers suggest the use of the name C. megalonyx for specimens from South America and the Subantarctic Region, the type locality ( Krabbe et al. 2010; Dietz et al. 2015, 2019). Although morphology was not used for the delimitation of these species, subspecies were previously proposed by Fry and Hedgpeth (1969). This indicates that morphology can be used successfully for the delimitation of species ( Cano-Sanchez and López-González 2007).

Specimens analysed thus should belong to C. megalonyx , as they were collected in Uruguay (the northernmost record for the species, a full two degrees of latitude north of the record provided by Child (1995a)). Further, they conform to the description of Hoek (1881). Yet, variations in the shape of the ocular tubercle were observed, in some specimens this structure being conical and in others, rounded. All specimens had a proboscis 1.5 times as long as the trunk, on average, the same proportion observed by Stock (1963) for individuals identified as C. orcadensis . Although molecular analyses are an important new source of evidence, their results need to be correlated with detailed morphological analyses, in order to corroborate or refute the recent results with the older morphological work available in literature.

Pallenopsidae Fry, 1978

Pallenopsis Wilson, 1881

Figures

Figure 3. Colossendeis megalonyx (FZB. Pyc- 002), female. A. Dorsal view; B. Distal articles of palp; C. Distal articles of oviger; D. Tarsus and propodus.