Sepia adults and Pleurobrachia at Southend-on-Sea

May 18-20 2009
During the end of a long period of relatively cool and windy weather, coincident with relatively low high tides (neap), the strandlines of dead crabs, brown and recently grown green algae still lacked jellyfish (studied Shoebury to Leigh on 19th May). They did show an only slightly bird-peck-marked cuttlebone of 179 mm length, 68.3 mm width and 20.1 thickness, deposited by the morning tide of the 19th, with the posterior end pointing 102° E. of true north on the Westcliff strandline with that trend. A hundred m or so to the west, a corpse of a female cuttlefish was aligned with the posterior end pointing towards 94° E. of N. between two strandlines spaced about 0.6 m apart and trending 104°E. of N. Both specimens were dorsal-up, and the corpse had evidently arrived earlier during the two tides of similar, slightly higher height on May 18. When removed the shell had slightly large dimensions of 191 mm by 69.6 mm by 22.2 mm thickness. Both the thickness and the length of the last septum measured in the median plane are a good guide to the maturity and races of these adults Sepia officinalis L. and the last septa were respectively 66 mm and 72.5 mm long. It is possible that the smaller one was the male of a pair that had recently mated in the Zostera beds of Canvey Island, but the female still contained numerous 6 mm diameter oocytes in a 40 mm diameter posterior-dorsal ovary. The jaws had dimensions of 25.5 mm by 24.0 mm width and 10.5 mm by 32.3 mm. The two tentacles were largely gone and the arms contracted and or similarly degraded, producing stranded body dimensions of about 210 by 88 by 60 mm, which sank with the shell insitu and the head jack-knifed after 3.0 hours in seawater

A water sample taken after the morning tide of May 20 at Chalkwell, was of interest in containing a sea gooseberry Pleurobrachia pileus (O.F. Mueller) which was still alive in the tank on the 21st and attempting to feed from the poor animal food supply in the water sample, with the mouth at the waterline and the two tentacles with spreading lassoe cells


Stranding of Cuttlebones

Two more adult Sepia officinalis L. shells were stranded by the afternoon tide on June 8, 2009 within 8 km of strandline from Leigh to Thorpe Bay, probably after local spawning. The posterior end of one shell with dimensions of 181 by 71.4 by 21.4 mm (septum 78 mm long) was pointing 179° E. of N., 0.3 m from the edge of the wet sand trending 94° E of N. The second shell, also from Southchurch, had dimensions of 164 by 64.9 by 19.4 mm (septum 72 mm long) and had a posterior end directed towards 121° E. of N., 0.6 from the limit of wet sand trending 99° and deposited by Force 3 winds blowing from 79° producing breaking waves roughly parallel to the wind flow. Both shells were dorsal-up with bird puncture marks ventrally. The successive orientations of the posterior end of the smaller cuttlebone were recorded as it was moved about 50 m westwards by the rising high tide before developing this higher final orientation partly covered by sand and gravel. The first three strandings were dorsal-up and defined a clockwise rotation of the posterior end 40, 20 and then 170° E. of N. at different sites in the sand slope of the swash zone. When in the waves the long axis was parallel to the wind and wave crests, but it flipped over into a ventral-up orientation from this more orthogonal orientation and then repeated another clockwise rotation defined by four ventral-up strandings around 60°, 130°, 160° and 200° E. of N. It then flipped back when out in the breaking waves and showed dorsal-up strandings of about 50°, 140° and 50° E. of N. on the sand slope, followed by 49°, 69° and then 121° on the gravel berm. Wet sand was initially 0.3 m beyond the 121° position and later spread to 0.6 m without moving it.

The 18 mm long radula of the stranded sepia showed a total of about 60 transverse rows of translucent chitinous teeth (‘’i.e.’’ not black like the parrot-like jaws around it, or yellowish brown like the chitinous hood and margins of the cuttlebone). The taxonomically stable feature of the radula is the seven longitudinal rows of sharp teeth and additional flat marginal plates, which in Sepia all lack the jagged denticulation of each tooth seen in most octopus, squid and ammonites. The width of the seven rows is 3 to 4 mm on the concave basal membrane and consist of a central radial tooth, flanked by three rows termed lateral one two and three of increasing lateral height.