365
Interestingly it has been suggested that Branchiura is closely related to (or nested
within?) Cycloida, a group of still enigmatic, exclusively fossil crustaceans
(Fig. 10.9c, d; Dzik 2008; see also Schram et al. 1997; Schweigert et al. 2009). Yet,
Cycloida itself is highly problematic to understand, in fact we cannot even be sure
whether all of these are crustaceans at all. The group included forms that have in the
meantime been interpreted as larval forms either of meiuran decapod crustaceans or
mantis shrimps (Hyžný et al. 2016). Other forms have been functionally compared
to crabs (see Dzik 2008). These possess a rounded shield in dorsal view, that is distantly resembling the shield of branchiurans. A further aspect in common is that
both groups have been supposed to represent an ingroup of Maxillopoda, yet neither
branchiurans nor cycloidans are known to show the developmental patterns characterising Maxillopoda. Although it has been indicated that cycloidans could be parasitic (Müller 1955), there are no real indications (of whatever type) that would
support such an interpretation (see also discussion in Schram et al. 1997).
10.7 Pentastomida
10.7.1 General Aspects
Pentastomida (tongue worms) is a group of exclusively parasitic forms living in the
respiratory tracts of tetrapods (e.g., Böckeler 2005). Pentastomidans possess two
pairs of prominent appendages; together with the mouth this makes five attachment
structures in the modern forms, hence the latinised name, “five mouths”. Unlike
Fig. 10.8 Fossil barnacles as epibionts on decapod crustaceans. Both specimens from NHM
London, UK. (a) Specimen 43617, long side of stone ca. 55 mm. (b) Specimen I3754, long side of
stone ca. 80 mm. In case of very few barnacles as in a, little or no negative effect for the carrying
animal is expected. In cases of a heavy infestation, the carrying animal will be negatively affected,
while the barnacles are benefitting; here barnacles may be considered as facultative parasites
10 Evolutionary History of Crustaceans as Parasites
Interestingly it has been suggested that Branchiura is closely related to (or nested
within?) Cycloida, a group of still enigmatic, exclusively fossil crustaceans
(Fig. 10.9c, d; Dzik 2008; see also Schram et al. 1997; Schweigert et al. 2009). Yet,
Cycloida itself is highly problematic to understand, in fact we cannot even be sure
whether all of these are crustaceans at all. The group included forms that have in the
meantime been interpreted as larval forms either of meiuran decapod crustaceans or
mantis shrimps (Hyžný et al. 2016). Other forms have been functionally compared
to crabs (see Dzik 2008). These possess a rounded shield in dorsal view, that is distantly resembling the shield of branchiurans. A further aspect in common is that
both groups have been supposed to represent an ingroup of Maxillopoda, yet neither
branchiurans nor cycloidans are known to show the developmental patterns characterising Maxillopoda. Although it has been indicated that cycloidans could be parasitic (Müller 1955), there are no real indications (of whatever type) that would
support such an interpretation (see also discussion in Schram et al. 1997).
10.7 Pentastomida
10.7.1 General Aspects
Pentastomida (tongue worms) is a group of exclusively parasitic forms living in the
respiratory tracts of tetrapods (e.g., Böckeler 2005). Pentastomidans possess two
pairs of prominent appendages; together with the mouth this makes five attachment
structures in the modern forms, hence the latinised name, “five mouths”. Unlike
Fig. 10.8 Fossil barnacles as epibionts on decapod crustaceans. Both specimens from NHM
London, UK. (a) Specimen 43617, long side of stone ca. 55 mm. (b) Specimen I3754, long side of
stone ca. 80 mm. In case of very few barnacles as in a, little or no negative effect for the carrying
animal is expected. In cases of a heavy infestation, the carrying animal will be negatively affected,
while the barnacles are benefitting; here barnacles may be considered as facultative parasites
10 Evolutionary History of Crustaceans as Parasites