Magnoteuthis microlucens: Description continued

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Figure. ventrolateral view of Mg. microlucens, paratype, swimming in an aquarium after being sucked into a cold, sea-water pipe from about 925 m depth. The white spot in front of the eye is the stub of a tentacle; both tentacles were lost during capture. Photograph by Michael Darden.

1. Arms
   1. Largest arm suckers tend to be located mid-arm but pattern highly variable. More information on relative sucker sizes can be found here.
      
      

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      Figure. Arm sucker arrangement in Mg. microlucens. Left - Oral view of selected arm suckers, paratype, 140 mm ML (estmate). All suckers maintain relative sizes. White numbers indicate sucker number counted from arm base. Sucker measurements can be found below. Photographs by R. Young.  Right - Oral-oblique view of the arms and suckers of the live squid, paratype, 135 mm ML, showing mid-arm suckers on arm II that are much larger than those found mid-arm on arm IV. Color has been altered slightly to improve contrast. Photographed in an aquarium by Jan War .
      

2. Tentacles
   1. Club length more than 80% of tentacle length.
      
   2. Club suckers numerous, extremely small (ca. 0.05 mm); suckers lack enlarged lateral pegs on their outer rings and have smooth inner rings.
      
   3. Base of club long, tapers gradually.
   

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   Figure. Oral view of the base of the tentacular club of Mg. microlucens, 77 mm ML. Top - Photograph of club base stained with methylene blue stain. Bottom - Artistic interpretation of the same club. Sucker-bearing portion of club in green. Illustration by R. Young.

   4. Protective membranes present but very low (height comparable to that of individual suckers); trabeculae cannot be detected.
      
      

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      Figure. Side view of the mid-region of the tentacular club of Mg. microlucens showing club protective membrane with an enlarged insert on the right. Photograph modified from Young, et al. (2008).

   5. Tentacular stalk not completely surrounded by club even at tip.
      
      

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      Figure. Aboral view near the tip of the tentacular club of Mg. microlucens showing bare aboral surface of the club tip. Photograph by R. Young.

3. Head
   
   1. Olfactory organ a short broad papilla with reduced head.
   

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   Figure. Side view of the olfactory organ of Mg. microlucens. Photograph by R. Young.

4. Funnel
   1. Funnel pocket between bridles absent.
      
      

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      Figure. Ventral view of funnel groove of Mg. microlucens, holotype, 79 mm ML, preserved. Photograph modified from Young, et al. (2008).

5. Fins
   
   1. Fin length approximately equal to fin width.
      
      
6. Tubercules
   1. Skin tubercules absent.
      
      
7. Pigmentation 
   
   1. Arms with dense chromatophores aborally, epithelial pigmentation orally (?).
   2. Head, funnel, mantle and fins with dense chromatophores.
   3. Most pigment beyond oral region in chromatophores.
      
      
8. Measurements (from Young, et al., 2008)

   Specimen	Holotype NMNH 1111879	Paratype NMNH 11118800	Paratype SBMNH 422886 Teuthis 23	Paratype SBMNH 422887 HM 1996	Paratype SBMNH 422888 HM Hawaii	Paratype SBMNH 422889 Keahole Pt.	Paratype SBMNH 422890 HM Hawaii
   Sex	Immature female	Unknown	Unknown	Immature female	Unknown- head only	Immature female	Mature male
   Mantle length	79	37	77	138	ND	135	215
   Tail length	14	8.5	ND	ND	ND	ND	ND
   Mantle width	21	9	ND	ND	ND	25	ND
   Fin length	54	22	54	ND	ND	90	ND
   Fin width	57	25	68	ND	ND	115	ND
   Head width	22	9	ND	ND	ND	ND	ND
   Head length	16*	10	ND	ND	ND	34	ND
   Eye diameter	16**	ND	ND	ND	ND	ND	ND
   Arm I, length	34	11	44+	87	90+	105	125
   Arm II, length	49	17	56	105+	139	126	145
   Arm III, length	36	10	43	94	111	105	137
   Arm IV, length	79	35	92	110+	174	174	ND
   Tentacle length	ND	46	158	ND	ND	ND	ND
   Club length	ND	30	130 ?	ND	ND	ND	ND

   Measurements in mm. ND = no data.
   *Measured laterally from olfactory organ to tentacle.
   **Calculated from lens diameter (= 6 mm).
   
   
9. Sucker diameter measurements from a single squid (see above)
   

   Sucker number	2	3		13	14	15		25	26	27		34	35		43	45		50
   Arm I	1.9				2.1			2.0					1.8			1.3
   Arm II		2.2				2.4				3.3		3.1			2.5			1.9
   Arm III	1.9			2.0					2.2				1.9			1.5
   Arm IV	1.9				2.0				1.8				1.6			1.3

   Measurements in mm. Photographs of these suckers appear above on this page.

Comments

Not only are the photophores small (ca. 1/3 the diameter of the large integumental photophores of Mastigoteuthis spp. , but they are very difficult to recognize as photophores. The photophores lack the readily visible white reflectors seen in the Mastigoteuthis spp.; the whitish "lens" that distinguishes them as photophores are often not seen at all. Their position immediately beneath the chromatophore layer is their most apparent characteristic. In the photograph below the chromatophore layer was lost from portions of the skin shown on either side of an intact chromatophore layer. Most of the dark structures (arrows) are photophores. Where the covering of chromatophores is intact, the photophores become difficult to detect.

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Figure. Ventral view of head skin of Mg. microlucens, 138 mm ML, showing regions with and without outer chromatophore layer intact. Photograph by R. Young.

References

Young, R. E., A. Lindgren and M. Vecchione. 2008. Mastigoteuthis microlucens, a new species of the squid family Mastigoteuthidae (Mollusca: Cephalopoda). Proc. Biol. Soc. Wash. 121(2): 276-282.