Portaratrum Guerrero-Kommritz, 2003

Bird, Graham J., 2014, Tanaidacea (Crustacea: Peracarida) of the North-east Atlantic: the genera Leptognathioides and Portaratrum of the ‘ Atlantic Margin’, Journal of Natural History 48 (29 - 30), pp. 1771-1815 : 1786-1788

Genus Portaratrum Guerrero-Kommritz, 2003

Portaratrum: Guerrero-Kommritz (2003) ; Guerrero-Kommritz and Brandt (2005): 294 (familial status regarded as incertae cedis)

Diagnosis (see Guerrero-Kommritz 2003, incorporating genus description)

Additions/modifications: pleonite-5 sternite with ventrally-directed spur. Pleotelson subpentagonal, narrower at join with pleon. Mandible molar spines in coronal or subcoronal array. Maxilliped endite with distolateral lobe and distomedial rounded tubercle. Cheliped coxal sclerite massive, posterior to basis, not fused ventromedially, separated by medial sclerite; basis with small free posterior lobe; palm superior and inferior margins sub-parallel, with two inferior setae. Pereopods 1–3 with coxa (bearing seta). Pereopods 4–6 with coxa indistinct/fused (and naked); carpus with three bayonet spines and one seta. Pleopod rami narrow, without proximal setae. Preparatory male similar to female but antennule broader than female, four-articled.

Composition

Portaratrum afer Guerrero-Kommritz, 2003 ; Portaratrum holdichi n. sp.; P. fascinatus Guerrero-Kommritz, 2003

This genus may also include Leptognathia zezinae Kudinova-Pasternak, 1973 , but this requires confirmation; the taxon should retain its generic name until this is done (see below).

Remarks

Although Guerrero-Kommritz (op. cit.) originally placed Portaratrum within the Colletteidae , in his later phylogeny ( Guerrero-Kommritz and Brandt 2005) it was revealed as a sister taxon to the Agathotanaidae Lang , rather than as a nominal colletteid (represented by Collettea Lang 1974 in that analysis); it was therefore regarded, though not formally designated, as incertae sedis. This is not unexpected as the cheliped-cephalothorax articulation is close to that of agathotanaids and the pleotelson is subpentagonal (narrower at junction with the pleon – a character consistent among the agathotanaids as well as several other genera of indefinite classification). Although Guerrero-Kommritz reported the cheliped as being ‘fused’ with the cephalothorax this is unlikely as he figured a basis-cephalothorax suture as well as a free posterior lobe in both species – the same configuration as seen in the new species described below. While this does approach the agathotanaid condition where the basis completely lacks a free lobe, the (coxal) sclerites in Portaratrum are separated by a sternal sclerite, and these are confluent or fused in agathotanaids ( Bird and Holdich 1988, Figure 2 ; 1989a, Figure 1 ; Bird 2010, Figure 4a ). A similar configuration occurs in Leptognathioides and the two genera are very similar in many respects of mouthpart, cheliped, pereopod, pleopod, and uropod morphology.

The pattern of occurrence of pereopodal coxae was used as a phylogenetic ‘character’ by Larsen and Wilson 2002, although proof of these structures, particularly for pereopods 4–6, is often extremely difficult with light-microscopy. Lack of a coxa on these last three pairs was one diagnostic for the family Colletteidae (although not unique), but in the original description ( Guerrero-Kommritz 2003: 282) coxae were stated to be absent from all six pairs. This is most unlikely to be the case as, in the new species described below, pereopods 1–3 exhibit a typical annular coxa that bears an anterior seta while that of pereopods 4–6 is indistinct (seemingly fused with the pereon) and lacking setae.

In many other respects, the morphology of Portaratrum does fit with the diagnosis for the Colletteidae given by Larsen (2005, p. 147–148) but the family appears to be excessively heterogeneous and the phylogenetic analysis given by Guerrero- Kommritz and Brandt (2005) only included this genus and the type, Collettea . Almost at the same time as that analysis, eighteen genera (including Portaratrum ) were known in the family and usefully keyed by Błażewicz-Paszkowycz (2005). At best, Portaratrum might be considered ‘colletteoid’.

Males of P. holdichi n. sp. are the first to be recorded for this genus, described below, but it is unclear if they are truly ‘preparatory’ or terminal, or whether dimorphic natatory males exist at all for this taxon.

The two previously described abyssal species are from widely separated ocean regions, P. afer from the Angola Basin and P. fascinatus from the eastern tropical Pacific, south of the Galapagos Islands. I have recently recorded an undescribed species at bathyal depths off the eastern margin of North Island, New Zealand. This might imply that the genus is present over a wide intervening area, and a broader depth range, especially if L. zezinae from the Gulf of Alaska is shown to belong in the genus. This last taxon is close to P. holdichi n. sp. (see below) in habitus, mandible, maxilliped, cheliped, and pleopod morphology, but new material is required to confirm if it has, or has not, a pleonal spur.

Figures

Figure 1. Leptognathioides polita. Female (BIOICE Stn 2673): (A) Maxilliped; (B) maxilla. Preparatory male (BIOICE Stn 2673): (C) habitus; (D) pleopod (all setae plumose); (E) uropod, lateral. Scale bar: 2 mm for (C), 0.25 mm for (A, B, D, E).

Figure 2. Leptognathioides biarticulata n. sp. Holotype non-ovigerous female: (A) habitus; (B–C) cephalothorax-cheliped, lateral and ventral respectively; (D) pleon, lateral (pleopods omitted); (E) pleotelson. Paratype non-ovigerous female (IINH 27879): (F) antennule; (G) antenna. Scale bars: i: 1 mm for (A), 0.5 mm for (D, E); ii: 0.5 mm for (B, C); iii: 0.25 mm for (F, G).

Figure 4. Leptognathioides biarticulata n. sp. Paratype non-ovigerous female (IINH 27879): (A–F) Pereopods 1–6 respectively. Scale bar: 0.25 mm.