Mastigotragus, a new generic name for Mastigoteuthis pyrodes Young, 1972 (Cephalopoda: Mastigoteuthidae)

A recent paper on the phylogenetic relationships of species within the cephalopod family Mastigoteuthidae meant great progress in stabilizing the classification of the family. The authors, however, left the generic placement of Mastigoteuthis pyrodes unresolved. This problem is corrected here by placing this species in a new monotypic genus, Mastigotragus, based on unique structures of the photophores and the funnel/mantle locking apparatus.


Introduction
The squid family Mastigoteuthidae contains oceanic, mostly bathypelagic, species that are soft bodied and easily damaged in trawls.The inaccessibility of species and their fragile nature are in large degree responsible for problems in the classifi cation of this family.Little consistency has existed between classifi cations, even with the same senior author (e.g., Salcedo-Vargas &Okutani 1994 andSalcedo-Vargas 1997).In a revision of the family on the Tree of Life website, Vecchione et al. (2004, with subsequent modifi cations up to 2014) suggested, because of the uncertainties in classifi cation, "… that modifying the classifi cation is premature and should wait until our knowledge has increased to the point where a full phylogenetic study can be made.We recognize, therefore, only the single genus Mastigoteuthis."Vecchione et al. (2004Vecchione et al. ( -2014) ) then placed species (excluding species of doubtful validity and those known only from paralarvae; see below) into the following six species groups: Mastigoteuthis agassizii group (three-species group), M. cordiformis (one-species group), M. glaukopis group (threespecies group), M. hjorti (one-species group), M. magna group (two-species group) and M. pyrodes (one-species group).The excluded species from the Vecchione et al. species groups are: Mastigoteuthis latipinna (Sasaki, 1916), M. islini MacDonald & Clench, 1934, M. inermis Rancurel, 1972, M. okutani (Salcedo-Vargas, 1997) and Chiroteuthoides hastula Berry, 1920.
The phylogenetic study that was called for by Vecchione et al. (2004Vecchione et al. ( -2014) ) to establish a proper classifi cation for the Mastigoteuthidae has now been published by Braid et al. (2014).Those authors analyzed three mitochondrial genes from 29 mastigoteuthid squids in eight species and re-examined morphological characters.Their results agreed with the species groups established by Vecchione et al. (2004Vecchione et al. ( -2014) ) and enabled them to establish a formal generic classifi cation for the family that utilized generic and subgeneric names previously present in the literature.The following table compares these two classifi cation systems: Braid et al. (2014) left one problem unresolved.They stated, " Unfortunately, no specimens of this species [Mastigoteuthis pyrodes] were examined or available for genetic analysis, and therefore, its generic placement remains unclear."In this paper we examine the generic affi nities of Mastigoteuthis pyrodes Young, 1972 and place it in a new genus.

Materials and methods
We examined all of the specimens of Mastigoteuthis pyrodes at the U.S. National Museum of Natural History (USNM) and at the Santa Barbara Museum of Natural History (SBMNH).Included were the following type specimens: SBMNH 34983, holotype, ♂, ML 110 mm, and USNM 727462, 3 paratypes (2 ♂♂, ML 85 and 94 mm; 1 sex indet., ML 77 mm).

Results
We strongly support most of the conclusions reached by Braid et al. (2014).Our examination of Mastigoteuthis pyrodes indicates that this species does not belong in Mastigoteuthis or in any of the other genera defi ned by Braid et al. (2014)."M." pyrodes presently remains in Mastigoteuthis by default.On superfi cial examination one could easily conclude that "M." pyrodes does, indeed, belong in Mastigoteuthis.In fi n length, fi n shape and tentacle structure "M." pyrodes is most similar to members of Mastigoteuthis.The most compelling feature for placing "M." pyrodes in Mastigoteuthis (and the feature that excludes this species from all other genera in the family) is the unique presence of readily visible integumental photophores on the mantle, head and ventral arms in these taxa.A closer comparison of the integument of "M." pyrodes and the type species of Mastigoteuthis, however, shows that they are very different.
The photophores of Mastigoteuthis agassizii Verrill, 1881, the type species of the genus, appear to lie in pockets (Fig. 1).The appearance of a pocket is due to the presence of transparent, vacuole-like cells that surround the photocytes and their covering chromatophores.A photophore of "M." pyrodes appears very different from that of M. agassizii under the dissecting microscope.It is seen as a slight bulge in the skin, not a pocket (i.e., without obvious vacuole-like cells), and is backed by a white refl ector and covered by a dark chromatophore (Fig. 2B).Other features of the skin are also important.Mastigoteuthis agassizii has relatively few, scattered chromatophores in the epidermis and each is surrounded by a white ring (the thick edge of a disc that seems to extend beneath the chromatophore); this leaves most of the pigment of the skin in the dermis and not in chromatophore organs of the epidermis (Fig. 2A).In contrast, "M." pyrodes lacks these ringed chromatophores but has more numerous and densely arranged, typical chromatophores which provide most of the skin pigmentation, even though light pigmentation is present in the underlying dermis.Mastigoteuthis agassizii also has numerous small, spherical, white structures in the skin whose histology and function are unknown.These structures are lacking in "M." pyrodes.

Comparison of classifi cations
These large differences in the structure of the integument, by themselves, are enough to conclude that "M." pyrodes is not a Mastigoteuthis."M." pyrodes, however, also differs from species of Mastigoteuthis in the distribution of the photophores: both taxa have photophores on the ventral surfaces of the mantle, head and ventral arms, but only in "M." pyrodes are photophores also present on the ventral sides of the fi ns and the dorsal surfaces of the head and mantle.Moreover, the eyelid photophore in "M." pyrodes is much larger than its integumental photophores, while in Mastigoteuthis species the eyelid and integumental photophores are approximately the same size.One other major difference in these taxa is important in the derivation of the new generic name: the funnel component of the funnel/mantle locking apparatus.In "M." pyrodes this structure has a large tragus but is without an antitragus and without a posterior undercut shelf; these latter two features are always present in Mastigoteuthis species, although weakly expressed in some.
Because of these large morphological differences between "M." pyrodes and true species of Mastigoteuthis, we place "Mastigoteuthis" pyrodes as the sole species in a new genus, Mastigotragus.

Diagnosis
A mastigoteuthid with (1) numerous small, but easily observed integumental photophores on the ventral surface of arms IV, on the dorsal and ventral surfaces of the head, mantle and fi ns, and with a relatively large photophore on each eyelid; (2) a broad funnel component of the funnel/mantle locking apparatus, with strong tragus, but without antitragus or undercut posterior margin; (3) comparatively large club suckers (about 0.3 mm in diameter).

Etymology
Here "mastigo" refers to the name of the family and "tragus" refers to the prominent tragus of the funnel locking apparatus.Mastigo is Latin for "whip" which refers to the form of the tentacle; "tragus" is a Latin word derived from the Greek trágos, indicating an appearance similar to the tragus of the human ear.

Discussion
No additional histological information is available on the structure of the integument of these taxa, but the position of Mastigotragus pyrodes as a separate genus is well supported by morphology.We hope that, before long, fresh specimens will be captured that will enable determination of the genetic relationships of this taxon within the family.The species is known only from the eastern North Pacifi c, mostly off Southern Calfornia.Additional information and illustrations of the diagnostic features of Mastigotragus pyrodes are presented on the species page of the Tree of Life website (Vecchione et al. 2004(Vecchione et al. -2014)).

Fig. 2 .
Fig. 2. Photomicrographs of the slightly damaged integument of the head (modifi ed from Vecchione et al. 2004-2014). A. Mastigoteuthis agassizii.B. "Mastigoteuthis" pyrodes [= Mastigotragus pyrodes].-Large, white arrows indicate photophores; only two photophores are visible in A but seven are visible in B. Small, white arrows indicate two of the many "white spherical structures."Black arrows indicate ringed chromatophores in A and typical chromatophores in B.