Tenupedunculus Schultz, 1982 sensu stricto

Song, Ji-Hun, Bruce, Niel L. & Min, Gi-Sik, 2018, The first records of Stenobermuda Schultz, 1982 and Tenupedunculus Schultz, 1979 from Australia, with description of two new species from the Great Barrier Reef (Isopoda, Asellota, Stenetriidae), ZooKeys 733, pp. 1-24 : 2-5

Genus Tenupedunculus Schultz, 1982 sensu stricto

Tenupedunculus Schultz, 1982: 77.- Serov and Wilson 1995: 77.

Type species.

Tenupedunculus elongatus Schultz, 1982; by original designation and monotypy.

Species included.

Tenupedunculus elongatus (type species), south-eastern Argentine Basin, 4696 m; T. virginale (Schultz, 1982), Scotia Sea, Antarctica, 567 m; T. pulchrum (Schultz, 1982), southern Argentina, 1911 m; T. serrulatus sp. n., Great Barrier Reef, Australia, 25 m.

Species here excluded from Tenupedunculus s. str., are regarded as Stenetriidae incertae sedis: Tenupedunculus acutum ( Vanhöffen, 1914); T. beddardi (Kussakin, 1967); T. dentimanum (Kussakin, 1967); T. drakensis (Schultz, 1982); T. inflectofrons (Schultz, 1982); T. serraticaudum (Kussakin & Vasina, 1984); T. smirnovi (Vasina, 1982); and T. haswelli (Beddard, 1886).

Diagnosis

(male). Cephalon frontal margin antennal spines small; lateral spines moderate, acute, slightly longer than antennal spines or sub-equal length. Pseudorostrum quadrate to trapezoid, wider than long. Eyes small, round. Male pereopod 1 ischium–carpus superodistal margin produced with acute process, inferodistal margins not produced; propodus moderate, length 1.2-1.5 times maximum width, 1.9-2.1 times carpus length, propodal palm transversely truncate or distally inflected; dactylus length similar to propodus distal width. Male pleopod 2 appendix masculina bluntly rounded apically, without apical setae.

Description

(male).Body dorsal surface smooth or sparsely setose, widest at pereonites 6 and 7; pereonite 1 length greater than 0.9 times pereonite 2 length; pereonites 2-4 lateral margins convex, anteriorly acute. Pleotelson length subequal to width; lateral margins or finely serrate, sub-parallel, posterolateral spines prominent, margin posterior to spines rounded with weak or no apical lobe; dorsal surface smooth, or sparsely setose. Cephalon lateral margins smooth or finely serrate. Antennae length equal or longer than total body length, article 1 lateral spine absent. Pereopod 1 basis superior margin with irregularly spaced setae along length; propodal palm with teeth along palm margin; dactylus length subequal to propodal palm length. Pleopod 1 protopod rectangular, lateral margin setae present; rami lateral margins evenly convex. Pleopod 2 protopod longer than wide, distal apex blunt, transversely truncate; appendix masculina lateral margin groove absent. Pleopod 5 distal apex with 3-5 plumose setae.

Remarks.

The genus Tenupedunculus Schultz, 1982 was established as a monotypic genus based on a single male specimen lacking legs. Serov and Wilson (1995), who included eleven species in the genus, doubted the unity (= monophyly) of Tenupedunculus without referring to specific characters. Our overview of the species included in Tenupedunculus recognizes that many species are inadequately described, some lacking details of any pereopods or of the male pereopods and some lacking description of the male pleopods 1 and 2. There are two significant characters that differ between the species formerly placed in Tenupedunculus that we consider to be of generic significance, namely eye shape and pseudorostrum shape. Those species with large reniform eyes (or traces thereof) and an elongate pseudorostrum are here all excluded from Tenupedunculus Schultz, 1982 sensu stricto.

The characters that serve best to identify the genus Tenupedunculus are: small round eyes; anterior margin of head with only lateral spines prominent; pseudorostrum wider than long, quadrate or trapezoid; inferodistal margin of ischium–carpus in male pereopod 1 without process, and superodistal margin of ischium–carpus usually produced and acute (strongly produced as a process in T. serrulatus sp. n.). The principle differentiating and diagnostic characters for Tenupedunculus sensu stricto are presented in Table 1.

Distribution.

All species of the genus, with the exception of the new species, are from the Antarctic and the sub-Antarctic region-off Argentina, Patagonian Shelf and also Scotia Sea (all Atlantic sector); at depths 500 to 4696 metres. Tenupedunculus serrulatus sp. n., from the southern Great Barrier Reef, is the first record of the genus from beyond the Southern Ocean and from depths less than 500 metres.

Remarks on the species excluded from Tenupedunculus .

The species listed here are retained in Tenupedunculus Schultz, 1982, but excluded from the genus sensu stricto as they either lack the diagnostic characters of Tenupedunculus or possess unique characters that also preclude their inclusion in other stenetriid genera. The here termed ' dentimanum group’ of species, particularly when considered in conjunction with their shared characters, potentially warrants a new genus.

' dentimanum group’

All species share the following characters: cephalon antennal spines small, lateral spines large. Pseudorostrum anteriorly round to acute, as long as or longer than wide. Eyes large, reniform. Male pereopod 1 ischium and merus superodistal margins weakly to strongly forming an acute process, inferodistal margins not produced. Male pleopod 2 appendix masculina excavate, apically rounded, with apical setae.

Tenupedunculus beddardi (Kussakin, 1967). Southern Argentina; 680 m; similar to T. dentimanum with the following characters common to the group: pseudorostrum approximately as long as wide, lateral spines large, eyes reniform and male pereopod 1 carpus with distinct acute superodistal process. The pseudorostrum uniquely converges to a narrowly rounded apex. The appendix masculina is acute (not excavate), differing significantly from that of others in this group, but on balance the species otherwise agrees well with and is best placed within the ' dentimanum group’ at present.

Tenupedunculus dentimanum (Kussakin, 1967). Southern Argentina; 680 m; pseudorostrum as long as posterior width, anteriorly broadly rounded.

Tenupedunculus inflectofrons (Schultz, 1982). Scotia Sea, Antarctica; 588 m; pseudorostrum rounded; male pereopod 1 not known; appendix masculina with terminal process.

Tenupedunculus smirnovi (Vasina, 1982). Patagonian Shelf; 500 m. Female only; seems to have reniform eyes, pseudorostrum stepped, acute; female pereopod 1 with ischium and merus with acute superodistal margin but not carpus; pleotelson with distinct caudomedial lobe.

Ungrouped species.

Tenupedunculus acutum ( Vanhöffen, 1914). Gauss Station, Davis Sea; 3397 m; pseudorostrum longer than wide, anteriorly rounded with median point; moderate lateral spines on cephalon; eyes moderate in size (more than six ommatidia) round (eye shape is not entirely clear in the original figures); appendix masculina blunt (excavate), with apical setae; male pereopod 1 ischium and merus with acute processes but carpus without process. Eye size and shape precludes inclusion of T. acutum in the ' dentimanum group’.

Tenupedunculus haswelli (Beddard, 1886). Rio del la Plata; 1097 m; eyes reniform; male pereopod 1 with superodistal process on carpus (i.e. pereopod 1 similar to Tenupedunculus serrulatus sp. n.); not evident if there is a rostrum or pseudorostrum; eyes reniform; appendix masculina not known.

Tenupedunculus drakensis (Schultz, 1982). Tierra del Fuego, Argentina; 548 m; pseudorostrum rounded to acute; weak lateral spines on cephalon; reniform eyes; appendix masculina not known; male pereopod 1 not known. Originally placed in Protallocoxa Schultz, 1978 this species was later transferred to Tenupedunculus by Serov and Wilson (1995).

Tenupedunculus serraticaudum (Kussakin & Vasina, 1984). South Atlantic; 500 m; pseudorostrum anteriorly round to acute; large lateral spines on cephalon; reniform eyes; appendix masculina blunt (excavate) with apical setae; male pereopod 1 carpus with superodistal process.

Key to the species of Tenupedunculus sensu stricto