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Arquivos de Zoologia

Melanoides luberculatus, M. modulus, Cerithidea costata)', 2- present and posteri-or (pleurocerids) (Cl= 33, Rl= 42, not additive).

70. Connection of ml with cartilages: 0= absent; 1= present (Aylacostoma tenuilabris, Melanoides luberculatus, Bittium varium, Batillaria minima, Cerithidea costata) (CI= 20, RI= 0).

71. M8: 0= absent; 1= short and broad (Turritella

hookeri, M. modulus, Campanile symbolicum, Serpulorbis decussatus); 2— narrow and long (pleurocerids, Batillaria minima) (CI= 50, RI= 83, additive).

72. M8: 0= absent; 1= connected to outer

membranę around odontophore (Turritella hookeri, M. modulus, Campanile symbolicum, Serpulorbis decussatus)', 2= free from any membranę (pleurocerids, Batillaria minima) (Cl= 50; RI= 83, additive).

The m8 is a single muscle that connects the radular nucleus with the odontophore in some cerithioideans. When present, it may have two forms: short and broad or long and narrow. Nothing similar to m8 was found in the outgroups.

73. M10: 0~ origin in m4; 1= origin in m5 (all

cerithioideans except pleurocerids and M. modulus) (Cl= 50, RI= 88).

74. M10 very thick, forming a single błock: 0=

absent; 1= present (Turritella hookeri, Serpulorbis decussatus) (Cl= 100, Rl= 100).

75. Ml 1: 0= origin in m4; 1= free from m4 (all

cerithioideans) (CI= 100, Rl= 100).

76. M11 a: 0= absent, 1=present (Doryssa ipupiara,

D. atra, Supplanaxis nucleus) (Cl= 33, RI- 0).

77. M11: 0= part of m4; 1 = attached to subradular

membranę (all cerithioideans) (CI= 100, Rl=

100).

The complex m7-ml 1 is another peculiarity ofthe cerithioidean odontophore. Typically, the ml 1 is that pair of smali muscles inserted in the inner

surface of the subradular membranę and originating i in the buccal region. The pair m7 originates from j mil and the adjacent region of the subradular membranę and inserts in the radular sac. However, thcre is great variation among the species cxamined. Somctimes differentiation of m7 and m 11 is difficult, mainly in thosecases where no insertion in the buccal region exists. Examination of the outgroups show the m7-m 11 complex originated from the median-dorsal margin of m4, inserting directly in the radular sac. Apparently, in cerithioideans, the m7-ml! complex separated from m4, situating nearer median linę, attached only in subradular membranę (and not in m4). In several cerithioideans, the m7-mll complex developed muscular connections with the buccal muscles, the anterior region of the cartilages, and other adjacent areas. Variation occurs within species of single gcnera (c.g., Aylacostoma), and while this character may be of great value for species comparisons, it is of less value in analyzing higher level relationship. In the examined pleurocerids, th connection with the mouth is posterior, almost i the transition of the snout with foot. Several annex muscles of the m7-ml 1 complex weTe detected, they are also of poor value at higher systematie levels.

78. Length of m 12: 0= smali; 1 = long (Aylacostoma

exoplicata, A. ci) (CI= 100, RI= 100).

79. M12: 0= absent; 1= present (all cerithioideans)

(Cl= 50, Rl= 66).

A distinctive character of cerithioideans is the presence of the pair of muscles m 12, which apparently may have the function of complementing the action of the horizontal muscle. The ml2 pair is present in all examined cerithioideans, including Campanile symbolicum, and absent in other examined groups. A somewhat similar pair of muscle are found in viviparids and ampullariids, but disposed morę longitudinal.

80. M15 (annex of m 10): 0= absent; 1 = as part of

buccal walls (Doryssa spp); 2= free from buccal walls (Melanoides luberculatus) (CI= 100, Rl= 100, not additive).

81. M16:0= absent; 1- present (pleurocerids) (CI=

100, RI= 100).