Porcellidium ovatum, Haller, 1879

Harris, Vernon A., 2014, Porcellidiidae of Australia (Harpacticoida, Copepoda). I. A Reassessment of the European Species of Porcellidium, Records of the Australian Museum 66 (2), pp. 63-110 : 106

The “ ovatum ” problem

Porcellidium ovatum Haller, 1879 and P. scutatum Claus, 1889 have caused problems even to this day because of Haller’s poor description. Lang (1948) and Wells (2007) consider them synonymous, but Bodin 1997 does not list either (presumably because he considers both synonymous with Claus’ Porcellidium tenuicauda ). The illustration Haller (1880) gives of Porcellidium ovatum Haller, 1879 shows a remarkable resemblance to Porcelloides tenuicaudus . It is not clear whY Haller (1879) regarded his animal as a separate species, but the body proportions of Claus’ (1860) original drawing appear distorted and not obviously egg-shaped. This, together with the apparent difference in shape of the caudal rami, maY have led Haller (1879) to regard them as different species. The caudal rami on most preserved specimens of Porcelloides tenuicaudus are depressed and appear short in dorsal view, just as Haller (1880) shows in his illustration, but when dissected and laid flat the rami are elongate as shown by Claus (1860).

Monard (1935) states Porcellidium ovatum is identical to Porcellidium tenuicauda , but gives no evidence for this. There are, however, good reasons for accepting his opinion. Both Claus (1863) and Haller (1879) record a length of 1.3 mm. This is unusually large for members of the Porcellidiidae and is only exceeded by two other species: Dilatatiocauda bipartita ( Kim & Kim, 1997) , 1.45 mm and Murramia magna Harris, 1994 , 1.38 mm. Haller (1880) describes his animal as “egg-shaped” in outline (hence the trivial name ovatum ), but Porcelloides tenuicaudus is also “egg-shaped” or ovoid, although this is not obvious from Claus’ (1860) drawing (the “egg shape” is more obvious when the animal conglobates).

Most members of the Porcellidiidae are coloured or have a colour pattern, due to the colour of the chitinous exoskeleton and/or pigment localized immediately under the cuticular exoskeleton, but Porcelloides tenuicaudus shows a marked departure from this arrangement. Specimens from Scotland contained a large number of dark orange or brown oil droplets in the haemocoel that gave the animals an orange or reddish-brown colouration (these are lost in spirit preserved specimens). In his description of Porcellidium ovatum, Haller (1880) states that the animals are coloured due to the presence of red and yellow fat globules in the body that glitter through the colourless cuticle. It should be noted that Porcelloides scutatus , the only other egg-shaped European species, does not have oil droplets and its dorsal red patch is due to sub-cuticular pigment. However, bY far the most compelling reason for regarding Porcellidium ovatum synonymous with Porcelloides tenuicaudus is the presence of two reniform spermatophores on the female’s P5 limbs shown in Haller’s (1880) illustration. Claus (1860) and Bartsch (1987) both show two reniform spermatophores in their illustrations of Porcellidium tenuicauda . This is in contrast to the rest of the Porcellidiidae where only one spermatophore is deposited on a female and this only stays attached for a matter of hours.

Lang (1948) treats Porcellidium scutatum Claus, 1889 and Porcellidium acuticaudatum Thompson & Scott, 1903 as synonyms for P. ovatum Haller, 1879 , thus, anYone using Lang’s key will misidentify Porcelloides scutatus as Porcellidium ovatum . Three other species have been misidentified through Lang’s keY. Geddes (1968) referred animals from Barbados to P. ovatum , but they do not show any of the characteristics of Porcelloides tenuicaudus and probably belong to Acutiramus . Holmes & O’Connor (1990) referred specimens in the NMI of Porcelloides scutatus collected from Loch HYne bY D. Minchin (JulY 1982) to Porcellidium ovatum . Animals from Oshoro BaY, Hokkaido, Japan ( Kito 1977) and Guandong Province, China (Zhang & Li 1976) both referred to as P. ovatum are unlikely to belong to that species. The porcellidiid fauna of Japan is reasonably well known but the genus Porcelloides has not been recorded from that region. It is probable that the animals from Hokkaido and Guandong are a species of Kensakia because the caudal rami of Porcelloides and Kensakia are superficiallY similar. AnYone using Lang’s (1948) keY for identification would misidentifY species of Kensakia as P. ovatum . Porcellidium acuticaudatum almost certainly belongs to Kensakia .

Haller (1879) described another species, Porcellidium parvulum , also from Messina, which he illustrated the following Year, Haller (1880). One of his animals appears to be a stage III or IV female copepodid (it does not have typical stage V P5 limbs and is only 0.55 mm). The other animal is a male but its antennules are not transformed and therefore it is not an adult. With a body length of 0.71 mm, it is likely to be a stage IV or possibly stage V male copepodid. The large size of these juveniles suggests they belong to Porcelloides tenuicaudus , but their identity cannot be established with certaintY from Haller’s (1880) description.