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Description of Male.
Length 4 mm.; depth ⅓ mm.; width ¾ mm. Rostrum reaching no further than ¼ along 1st segment of antenna 1 peduncle.
Antennae. First: Reaching to about end of 4th segment of antenna 2 peduncle, length 1 ½ mm. Peduncle expanded somewhat proximally, then slightly narrowing; greatest width ⅖ length, median row of about 3 stout spines proximally, 1 spine distally; inner margin has stout spine proximally, setae on margins and surface; 2nd segment ⅔ length 1st and narrower, setae on margins and surface; 3rd ⅖ length 2nd, narrower, 1 or 2 setae. Flagellum of 6 segments, all except very small end one longer than wide, each with single long flaccid sensory seta distally. Second: Peduncle, gland-cone has 3 stout spines; 3rd segment stout, as wide as long, inferodistal angle has setae and single stout spine; 4th segment twice length 3rd, width ½ length; inferodistal angle has stout tooth-like process, a smaller one just above; 1 or two small stout spines proximally on inferior surface; several tufts of setae on margins and surface; 5th segment ¾ length 4th, width ⅓ length; setae singly and in groups on margins and surface. Flagellum of 3 segments; as in female.
Uropods. As in female but a little less spinose.
Localities. Lyttelton Harbour, New Zealand (Chilton Collection); on wharf structures, Portobello Marine Biological Station, Otago Harbour, 20/6/53 and 2/8/53, coll. D. E. Hurley.
Hypotypes. Slides C.43, male; C.44, female (Chilton Collection).
Distribution. Plymouth and “Wembury, England; “off mouth of Tagus,” Portugal; New Zealand.
Remarks. The species was first described by Crawford (1937) from Plymouth and Wembury in England. He had also a single female specimen from “off the mouth of Tagus,” Portugal (Copenhagen Museum, Dana Station, 4155, 12.6.1930).
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Its abundance at Plymouth, he remarks, “is the more surprising since it is not present in the rich collection of Corophium made from the same dredging grounds in 1895–1911. It seems possible, therefore, that it is not indigenous at Plymouth … I cannot guess at its original locality.” Zoological records for 1950 and 1951 list references to this species from the Laguna di Venezia, Italy, in two papers by Soika (1947, 1949) which I have not seen.
C. sextonae is possibly an immigrant from New Zealand: The fact that the New Zealand Corophium fauna has not been worked since Chilton's 1921 paper would explain why it has not been reported before or since. It is present in his material There is an established, well-documented precedent for such marine invasion from this country in the case of the barnacle, Elminius modestus Darwin (cf. Bishop, 1947). Species of Corophium appear very tolerant of changes in salinity; and, as Crawford states, “species which build tubes on sessile objects are clearly likely to be carried by shipping … C. acherusicum has been collected off a ship's bottom at Sheerness.”
Sexton and Reid (1951: 29), discussing another tube-dwelling amphipod, Jassa falcata, indicate how this dispersal may take place: “It is well known that the species-habit is to attach itself to any floating object, such as buoys moored around the coast, for instance, and the bottoms of any ships anchored in harbour. On reacting such positions the animals immediately begin constructing their ‘nests’ amongst the algal growth on the ship and these, soon collecting the mud and sand held in suspension by the water, afford fresh foothold for more algae and hydroids, and the dense shelter thus provided enables the Jassa colonies to increase in immense numbers. It can be seen how in the different ports of call, groups of the animals would swim away and establish fresh colonies.”
Dr. C. R. Shoemaker has kindly pointed out to me that, if this species is named in honour of Mrs. E. W. Sexton, the name C. sextoni should be emended to C. sextonae.
Corophium acutum Chevreux, 1908. (Figs. 22–34.)
Corophium acutum Chevreux, Chevreux, 1908: 75, fig. 6.
Crawford, 1937: 624–625.
Shoemaker, 1947: 59, fig. 9 a-m.
(non) Corophium crassicorne Bruz. Chilton, 1921: 229–233, fig. 5.
(non) Corophium contractum Stimpson. Thomson, 1880: 220, pl. 8, fig. 9.
Thomson, 1880a: 6.
Thomson & Chilton, 1886: 142.