TABLE 5. 

 Trematodea Score Series 



Abhreviations: N, Nemata, R, Rotatoria; G, Gastrotricha; 

 E, Echinodera; Ac, Acanthocephala; No, Nematomorpha; 



score series, the groups are arranged in order of score, 

 and breaks in the score series are indicated by transverse 

 lines. It is very similar to the modified grade curve 

 often used in small college classes. Groups necessarily 

 show reciprocal scores but the position in the series 

 is regarded as indicating degree of similarity. 



The remarkable homogeneity of the Platyhelmintha is 

 emphasized by the minimum score of 80 (with 96 as base 

 score) scoring two groups on the basis of the third 

 group (Turbellarea, Trematodea, Cestodea). In all three 

 instances the position of these groups in the score series 

 is 1, 2, 3. The Nemerta, included as a class in the 

 Platyhelmintha by the Pearse Classification (1936) have 

 fourth high score in two series Turbellarea and Trema- 

 todea) with a score of 74, and fifth high score in the 

 third series (Cestoda) with a score of 54. The Nemerta 

 also shows reciprocally close similarity to these groups 

 since in their own score series the Turbellarea, Trema- 

 todea, and Cestodea are placed 2, 3, 4. Only in the 

 annelid score series are the Nemerta disassociated from 

 the other three and this may be due to either real or 

 superficial similarity because of circulatory system and 

 body cavity. The Acanthocephala are associated with 

 the Cestodea and Nemerta in five score series. They 

 are placed fourth in the Cestodea series and fifth in 

 the Turbellarea, Trematodea, and Nemerta series. In 

 their own series they place the Cestodea second and 

 Nemerta third. Considering the breaks in the various 

 series, the (Series Parenchymata would appear to contain 

 three phyla, namely, Platyhelmintha, Nemerta, and 

 Acanthocephala; the first of these would contain three 

 classes Turbellai'ea, Trematodea, and Cestodea. Of the 

 latter classes, the Turbellarea show the greatest similarity 

 to the Nemerta while the Cestodea show the greatest 

 similarity to the Acanthocephala. 



The Gastrotricha, Echinodera, Rotatoria and Nemata 

 also seem to show reciprocal relationships but not as 

 close as those of the classes of the Platyhelmintha. Thus 

 the Rotatoria (90 base score) provide a basis for scoring 

 Gastrotricha, 64; Echinodera, 63; and Nemata, 57. The 

 Echinodera (90 base score) provides scores of Gastro- 

 tricha, 63; Rotatoria, 63; and Nemata, 56. The Gastro- 

 tricha (84 base score) provides scores of Rotatoria, 64; 

 Echinodera, 62; Nemata, 45; and Turbellarea, 45. And 

 the Nemata (96 base score with Rotatoria and Echinodera 



Ta, Tardigrada; Ar, Arthropoda; An, Annelida; Tu, 

 Turbellarea; Tr, Trematodea; Ce, Cestodea; Ne, Nemerta. 



at 6 point disadvantage and Gastrotricha at 12 point disad- 

 vantage tt) provides the scores Rotatoria, 57; Echinodera, 

 56; Tardigrada, 52; and Gastrotricha, 45. The Tardi- 

 grada appear in the table as fifth group in the Rotatoria 

 score series, third in the Annelida series, sixth in the 

 Echinodera series and second group in the Arthropoda 

 series (the latter position is reciprocal). It would ap- 

 pear, therefore, that the Tardigrada more correctly 

 belong to the Arthropoda. 



The Arthropoda (base score 96) might be said to lay 

 claim to only two close relatives, the Tardigrada and 

 Annelida; the Annelida (base score 90) by the same 

 token, claim distant kinship with the Nemerta with 44 

 (see discussion above); the Arthropoda, 48; Tardigrada, 

 44; and Nematomorpha and Acanthocephala, 34. The 

 Tardigrada (base score 96) show similarity to Arthro- 

 poda, 61; Nemata, 52; Annelida, 44; Rotatoria, 43; 

 Echinodera, 42; Gastrotricha, 39; Nematomorpha, 34. 

 The Nematomorpha (No) score series (base score 96) 

 provides us with the odd series Nemata and Rotatoria, 

 42; Acanthocephala and Echinodera, 41; Gastrotricha, 

 3a; Turbellarea, 36; Annelida and Tardigrada, 34; Nem- 

 erta and Trematodea, 32; Cestodea, 29; and Arthropoda, 

 16. 'ihis is practically a uniform series with no obvious 

 break. 



According to Schepotieff's (1908) illustrations (Fig. 

 145 U) the proboscis of the larva of Gordius is triradiate 

 with one ray directed dorsad instead of ventrad as in 

 nenias. If this is true, the non-radiate symmetry of the 

 adult esophagus may be considered secondary degeneracy 

 due to parasitism such as happens in the development 

 of mermithids (p. 92). The inverted triradiate sym- 

 metry also occurs in one group of gastrotrichs. The 

 echinoderid non-radiate esophagus may be interpreted as 

 a modification of the triradiate, which it resembles more 

 closely than that of the turbellarean. May (1919) found 

 that the larval stylets of gordiids and adjoining cuticle 

 are lost at the time the parasite leaves its host; whether 

 or not this should be interpreted as a molt seems ques- 



IfBy disadvantage we mean that due to lack of information 

 tliere is no statement in one or more brackets in table 4 and 

 the forms are given zero as though the information indicated 

 total dissimilarity, wliich it does not. 



201 



