Like a Child's Bad Drawing...

Well, I've survived another round of finals, on with the blogging!


Unexpectedly, fishes in the deepest parts of the oceans (Hadal zone) have rather conservative bauplans (like Abyssobrotula) and only in the bathy- and abyssalpelagic species do the truly bizarre forms exist. I'm guessing that while such divergent forms are efficient at capturing prey/food particles, they can only be practical up to a certain point. Recently I discussed a denizen from the Zone of Bizarre Fishes, the stoplight loosejaw, which had odd characters such as a mouth with no floor that could somehow capture copepods and modified chlorophyll (from the copepods) that was used to detect red light emitted in order to see prey (like...copepods). Even with these peculiar features, the stoplight loosejaw is still recognizably a dragonfish, albeit a rather extreme one.

The genus Lasiognathus ("Wolftrap anglers") is a member of the order Lophiiformes (anglerfish) and the suborder Ceratioidei (Deep sea anglers), although this is rather hard to recognize at first. I was wondering if the artists who drew these species screwed up horribly - until I saw a photograph:

L. amphirhamphus from Pietsch 2005, used with permission.

Lasiognathus is recognizable as a lophiiform due to the presence of a modified first dorsal fin or illicium and bioluminescent "bait" or an esca at the end. The lack of pelvic fins unites this with other ceratioids and the characteristic dwarfed males have yet to be found (which would hint at them being small of course). Along with the sister taxa Thaumatichthys* (in the family Thaumatichthyidae) Lasiognathus has denticles on the esca and a bizarre premaxillary that can flip down to form a venus flytrap-like cage. The features of the esca have established 5 species of Lasiognathus (Pietsch 2005) known from only 27 adult female specimens (Pietsch 2005a).

*Pietsch and Orr 2007 mention some possible morphological and preliminary genetic evidence that may suggest otherwise. Support for maintaining the family is still convincing. Also, if you have access check out the Lasiognathus skeleton on page 14.

While the esca is key to differentiating species, the genus is still riddled with apomorphies. Thaumatichthys shares the massive overbite and premaxillary cage - but it has an esca in the roof of its mouth (how does a fin ray wind up there?) and looks broadly different. The head is extremely long (>60% standard length) and narrow (Pietsch 2005); the pterygiophore is 85% of the SL and can slide back and forth in a deep cranial trough, forming a tentacle when retracted(!); the illicium supported by the pterygiophore is 50% of the SL (Bertelsen and Pietsch 1996); illustrations of the flipped-down premaxillaries can be found here and here.

Unfortunately, that about wraps it up for Lasiognathus. Anatomically it seems pretty well known (particularly the esca), but there still are a great deal of unanswered questions for this taxa. Several of the species co-exist and I can't help but wonder if the different esca shape can attract different prey items. And who knows what genetic tests will do to the species count (some specimens lacked the critical esca) and the monophyly of Thaumatichthyidae. With only 27 specimens known, there undoubtedly is a great deal more to learn about this bizarre taxa.


I guess this was some sort of bloated picture-of-the-day post. I have no idea what to do next, but fortunately I have a lot of time to do it.

References:

Bertelsen, E. and Pietsch, Theodore W. 1996. Revision of the Ceratioid Anglerfish Genus Lasiognathus (Lophiiformes: Thaumatichthyidae). Copeia, Vol. 1996, No. 2, pp. 401-409

Pietsch, Theodore W. and Orr, James Wilder. 2007. Phylogenetic Relationships of Deep-sea Anglerfishes of the Suborder Ceratioidei (Teleostei: Lophiiformes) Based on Morphology. Copeia, Vol. 2007, No. 1, pp. 1-34.

Pietsch, Theodore W. 2005. New Species of the Ceratioid Anglerfish Genus Lasiognathus Regan
(Lophiiformes: Thaumatichthyidae) from the Eastern North Atlantic off Madeira. Copeia, 2005(1), pp. 77–81

Pietsch, Theodore W. 2005a. Thaumatichthyidae. Wolftrap Seadevils. Version 06 November 2005 (under construction). http://tolweb.org/Thaumatichthyidae/22007/2005.11.06 in The Tree of Life Web Project, http://tolweb.org/

Pietsch, Theodore W. and Kenaley, Christopher P. 2007. Ceratioidei. Seadevils, Devilfishes, Deep-sea Anglerfishes. Version 02 October 2007 (under construction). http://tolweb.org/Ceratioidei/22000/2007.10.02 in The Tree of Life Web Project, http://tolweb.org/