BATHYPELAGIC SQUID BATHYTEUTHIS 55 



The nuchal component of the mantle-nnchal locking apparatus is 

 long and naiTO\Y with three longitudinal grooves: a narrow, shallow, 

 median groove and two broader, deeper, lateral grooves. The median 

 groove complements the low, thin, median ridge of the mantle com- 

 ponent of the locking apparatus. The lateral grooves receive the rolled 

 edges of the rhachis of the gladius that partially make up and provide 

 support for the mantle component. 



The head narrows considerably anterior to the eyes where it forms 

 the base of the brachial crown. A single, small, simple photophore is 

 embedded in the chromatophore layer of the subcutaneous tissue at 

 the base of each of the dorsal three pairs of arms. Photophores are 

 characterized by a darkly pigmented ring that is generally broadest 

 posteriorly and a central mass that is much more lightly pigmented. 

 Photophores in the holotype are embedded and not easily seen, but the 

 photophores in the juvenile and larval specimens contrast more with 

 the background pigmentation, are slightly raised, and are more readily 

 seen. 



The arms are long, slender and drawn out into attenuate tips (pi. 11). 

 All arms are of nearly equal length in the holotoype, so the arm for- 

 mula for adults is 4 = 3 = 2= 1. 



A moderately deep web joins the bases of the four pairs of arms. 

 The depth of the web decreases from the dorsal to the ventral pairs, 

 and no web occurs between the fourth arms. 



Low aboral swimming keels occur on the dorsal three pairs of arms, 

 with those of the third arms the best developed. The web between the 

 third and fourth arms extends distally along the fourth arms as the 

 lateral membrane or "tentacular sheath." 



Protective membranes occur on all arms. They are particularly well 

 developed at the basal portion of the arms where they are thick, fleshy, 

 and ruffle-like (pi. 11a). The thickened ruffles diminish quickly distal 

 to the bases of the arms, and the protective membranes extend distally 

 as low, even keels. Protective membranes on the fourth arms are con- 

 siderably less developed than on the dorsal three pairs. No distinct or 

 separate trabeculae support the protective membranes. 



The oral surfaces of the arms are covered with extremely numerous 

 small to minute suckers (pi. 11a). The proximal suckers are quite 

 small, and widely spaced; they originate in a single row, then soon 

 increase in size and split off into two widely separated rows. About one- 

 third of the way out the arms, the suckers become smaller and more 

 closely packed and the rows become irregularly arranged so that occa- 

 sionally 3-4 suckers occur across the oral surface of the arms. On the 

 distal one-third to one- fourth of the arms, the suckers grade smaller, 

 become very closely packed, and are exceedingly numerous. On the 



